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G4 Mac Power supply really loud

Message #1 - Posted 2007/06/11 - LongJohn

We have a G4 Powermac but it's really noisey; I think it's the PSU.

Are the PSU's the same as PC PSU as I have a spare one of those?

Thanks

Message #2 - Posted 2007/06/12 - Rowland McDonnell

LongJohn wrote:

We have a G4 Powermac but it's really noisey; I think it's the PSU.

Umm. Best to find out exactly what's wrong first. Could be a software issue. The fans are variable speed and can run flat out if there's a hiccup in the software that controls them, and also if they need to because it's hot in there.

However, the tower G4s are famously noisy, some of them.

Are the PSU's the same as PC PSU as I have a spare one of those?

Not the same at all: totally different.

Erm.

See if you can isolate the fault properly. Could be that someone has a spare of what you need. Well, I possibly have, but I'm not up to offering to do anything for anyone at the moment (if it weren't for that and the model's right, I'd offer you a PSU for postage).

Rowland.

Remove the animal for email address: rowland.mcdonnell@dog.physics.org Sorry - the spam got to me
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Message #3 - Posted 2007/06/12 - LongJohn

"Rowland McDonnell" <real-address-in-sig@flur.bltigibbet> wrote in message news:1hzkldb.1ud0wl9ud31ckN%real-address-in-sig@flur.bltigibbet...

LongJohn wrote:

We have a G4 Powermac but it's really noisey; I think it's the PSU.

Umm. Best to find out exactly what's wrong first. Could be a software issue.

Software issue? What software? The firmware?
The OS is OSX 10.3.9

The fans are variable speed and can run flat out if there's a

hiccup in the software that controls them, and also if they need to because it's hot in there.

However, the tower G4s are famously noisy, some of them.

Are the PSU's the same as PC PSU as I have a spare one of those?

Not the same at all: totally different.

Erm.

See if you can isolate the fault properly.

Sounds loudest when I put my ear to the PSU. Don't think it's the hard disk. What else could it be?

It's very dust around the PSU, would vacuuming it out help?

Could be that someone has a

spare of what you need. Well, I possibly have, but I'm not up to offering to do anything for anyone at the moment (if it weren't for that and the model's right, I'd offer you a PSU for postage).

That would have been grand

Rowland.

Thanks Rowland

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Message #4 - Posted 2007/06/12 - Debbie Wilson

LongJohn wrote:

We have a G4 Powermac but it's really noisey; I think it's the PSU.

Are the PSU's the same as PC PSU as I have a spare one of those?

There was an issue with G4 (Mirrored Drive Doors) PSU noisiness - I have a G4 dual 867 which sounded like a vacuum cleaner before I replaced the PSU - and Apple had a replacement program for them, but this seems to have ended in 2003. https://depot.info.apple.com/generic/index.html

The replacement PSU they supplied was quieter, but it's still noisier than any other Mac I've owned.

I'm afraid I don't know if the PSU is the same as the PC version, but you could try searching/asking in the Apple discussion forums, e.g. here:

<http://discussions.apple.com/thread.jspa?messageID=2976890&#2976890>

HTH
Deb.

http://www.scientific-art.com

"He looked a fierce and quarrelsome cat, but claw he never would; He only bit the ones he loved, because they tasted good." S. Greenfield

Message #5 - Posted 2007/06/12 - Rowland McDonnell

LongJohn wrote:

Rowland McDonnell wrote:

LongJohn wrote:

We have a G4 Powermac but it's really noisey; I think it's the PSU.

Umm. Best to find out exactly what's wrong first. Could be a software issue.

Software issue? What software? The firmware?
The OS is OSX 10.3.9

Could be something getting confused due to something buggy and/or corrupted.

The fans are variable speed and can run flat out if there's a hiccup in the software that controls them, and also if they need to because it's hot in there.

However, the tower G4s are famously noisy, some of them.

Are the PSU's the same as PC PSU as I have a spare one of those?

Not the same at all: totally different.

Erm.

See if you can isolate the fault properly.

Sounds loudest when I put my ear to the PSU. Don't think it's the hard disk. What else could it be?

Could be a dying PSU :-) Dunno about `else' - but if you're fairly sure, you're fairly sure.

It's very dust around the PSU, would vacuuming it out help?

Oh yes lots! My old 2G4 ran a lot quieter if I took the trouble to clean out the dust every few weeks. Lots of dust all over the place needed removing.

Do the deed with the Mac *plugged in to the mains*.

Yes, that's right - but make sure that the power is turned off at the wall socket too.

That way, you keep the machine earthed.

Caution: do not let any of the fans get themselves spun round by the vacuuming process. Slow rotation by hand is okay, but an electric motor being driven mechanically tends to behave as a generator, doesn't it? Right.

Could be that someone has a
spare of what you need. Well, I possibly have, but I'm not up to offering to do anything for anyone at the moment (if it weren't for that and the model's right, I'd offer you a PSU for postage).

That would have been grand

[snip]

If the PSU packs up, don't throw the machine away. Ask me.

Rowland.

Remove the animal for email address: rowland.mcdonnell@dog.physics.org Sorry - the spam got to me
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Message #6 - Posted 2007/06/12 - Rowland McDonnell

Debbie Wilson wrote:

LongJohn wrote:

We have a G4 Powermac but it's really noisey; I think it's the PSU.

Are the PSU's the same as PC PSU as I have a spare one of those?

There was an issue with G4 (Mirrored Drive Doors) PSU noisiness - I have a G4 dual 867 which sounded like a vacuum cleaner before I replaced the PSU

And main fan, surely?

FWIW, I had the same - but memory says it was a 1.25Ghz 2G4.

- and Apple had a replacement program for them, but this seems to have ended in 2003. https://depot.info.apple.com/generic/index.html

The replacement PSU they supplied was quieter, but it's still noisier than any other Mac I've owned.

[snip]

It was quieter - just about - at low running speeds. But at higher running speeds, I'm not sure the noise was any less annoying. The replacement kit kicked out higher frequency sound which was more annoying to my ears when running fast.

Rowland.

Remove the animal for email address: rowland.mcdonnell@dog.physics.org Sorry - the spam got to me
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Message #7 - Posted 2007/06/13 - Debbie Wilson

Rowland McDonnell wrote:

And main fan, surely?

Ummm - can't remember, TBH. All that was sent by Apple under this replacement scheme was the large metal power supply box thing (technical term :-) ) which does have a small fan in it, IIRC. But without opening up my Mac I can't be sure if that's also the main fan, or if that's separate. I have a feeling that's elsewhere inside.

Deb.

http://www.scientific-art.com

"He looked a fierce and quarrelsome cat, but claw he never would; He only bit the ones he loved, because they tasted good." S. Greenfield

Message #8 - Posted 2007/06/13 - J. J. Lodder

Rowland McDonnell wrote:

LongJohn wrote:

It's very dust around the PSU, would vacuuming it out help?

Oh yes lots! My old 2G4 ran a lot quieter if I took the trouble to clean out the dust every few weeks. Lots of dust all over the place needed removing.

Do the deed with the Mac *plugged in to the mains*.

Yes, that's right - but make sure that the power is turned off at the wall socket too.

How very British.

That way, you keep the machine earthed.

Caution: do not let any of the fans get themselves spun round by the vacuuming process. Slow rotation by hand is okay, but an electric motor being driven mechanically tends to behave as a generator, doesn't it? Right.

You are exaggerating greatly.
(as in the case of the excessively dangerous high voltage
in the Mac Plus)
Can you cite any example at all of a PSU being blown up
by vacuuming the fan?

Jan

Message #9 - Posted 2007/06/13 - LongJohn

"Rowland McDonnell" <real-address-in-sig@flur.bltigibbet> wrote in message news:1hzm7yg.f548o3q8epesN%real-address-in-sig@flur.bltigibbet...

LongJohn wrote:

Rowland McDonnell wrote:

LongJohn wrote:

We have a G4 Powermac but it's really noisey; I think it's the PSU.

Umm. Best to find out exactly what's wrong first. Could be a software issue.

Software issue? What software? The firmware?
The OS is OSX 10.3.9

Could be something getting confused due to something buggy and/or corrupted.

The fans are variable speed and can run flat out if there's a hiccup in the software that controls them, and also if they need to because it's hot in there.

However, the tower G4s are famously noisy, some of them.

Are the PSU's the same as PC PSU as I have a spare one of those?

Not the same at all: totally different.

Erm.

See if you can isolate the fault properly.

Sounds loudest when I put my ear to the PSU. Don't think it's the hard disk.
What else could it be?

Could be a dying PSU :-) Dunno about `else' - but if you're fairly sure, you're fairly sure.

It's very dust around the PSU, would vacuuming it out help?

Oh yes lots! My old 2G4 ran a lot quieter if I took the trouble to clean out the dust every few weeks. Lots of dust all over the place needed removing.

Do the deed with the Mac *plugged in to the mains*.

Yes, that's right - but make sure that the power is turned off at the wall socket too.

That way, you keep the machine earthed.

Caution: do not let any of the fans get themselves spun round by the vacuuming process. Slow rotation by hand is okay, but an electric motor being driven mechanically tends to behave as a generator, doesn't it? Right.

Could be that someone has a
spare of what you need. Well, I possibly have, but I'm not up to offering to do anything for anyone at the moment (if it weren't for that
and the model's right, I'd offer you a PSU for postage).

That would have been grand

[snip]

If the PSU packs up, don't throw the machine away. Ask me.

Rowland.

--
Remove the animal for email address: rowland.mcdonnell@dog.physics.org Sorry - the spam got to me
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Thanks for all the help everyone.

Am I really OK to vacuum the inside of my mac? This seems like a dodgy thing to do.

Message #10 - Posted 2007/06/13 - Sara Kirk

Previously, LongJohn wrote:

Am I really OK to vacuum the inside of my mac? This seems like a dodgy thing to do.

Oh heavens yes! I've been doing that for years with no ill effects.

Sara

The teeth are free at last! Fly free, young teethies!

Message #11 - Posted 2007/06/13 - Paul Russell

LongJohn wrote:

"Rowland McDonnell" <real-address-in-sig@flur.bltigibbet> wrote in message news:1hzm7yg.f548o3q8epesN%real-address-in-sig@flur.bltigibbet...

LongJohn wrote:

Rowland McDonnell wrote:

LongJohn wrote:

We have a G4 Powermac but it's really noisey; I think it's the PSU.

Umm. Best to find out exactly what's wrong first. Could be a software issue.

Software issue? What software? The firmware?
The OS is OSX 10.3.9

Could be something getting confused due to something buggy and/or corrupted.

The fans are variable speed and can run flat out if there's a hiccup in the software that controls them, and also if they need to because it's hot in there.

However, the tower G4s are famously noisy, some of them.

Are the PSU's the same as PC PSU as I have a spare one of those?

Not the same at all: totally different.

Erm.

See if you can isolate the fault properly.

Sounds loudest when I put my ear to the PSU. Don't think it's the hard disk.
What else could it be?

Could be a dying PSU :-) Dunno about `else' - but if you're fairly sure, you're fairly sure.

It's very dust around the PSU, would vacuuming it out help?

Oh yes lots! My old 2G4 ran a lot quieter if I took the trouble to clean out the dust every few weeks. Lots of dust all over the place needed removing.

Do the deed with the Mac *plugged in to the mains*.

Yes, that's right - but make sure that the power is turned off at the wall socket too.

That way, you keep the machine earthed.

Caution: do not let any of the fans get themselves spun round by the vacuuming process. Slow rotation by hand is okay, but an electric motor being driven mechanically tends to behave as a generator, doesn't it? Right.

Could be that someone has a
spare of what you need. Well, I possibly have, but I'm not up to offering to do anything for anyone at the moment (if it weren't for that
and the model's right, I'd offer you a PSU for postage).

That would have been grand

[snip]

If the PSU packs up, don't throw the machine away. Ask me.

Rowland.

--
Remove the animal for email address: rowland.mcdonnell@dog.physics.org Sorry - the spam got to me
http://www.mag-uk.org http://www.bmf.co.uk UK biker? Join MAG and the BMF and stop the Eurocrats banning biking

Thanks for all the help everyone.

Am I really OK to vacuum the inside of my mac? This seems like a dodgy thing to do.

I've heard stories about vacuums generating static, but I've never had any problems myself.

Paul

Message #12 - Posted 2007/06/13 - LongJohn

"Paul Russell" <prussell@sonic.net> wrote in message news:5dabhcF33pcf2U1@mid.individual.net...

LongJohn wrote:

"Rowland McDonnell" <real-address-in-sig@flur.bltigibbet> wrote in message news:1hzm7yg.f548o3q8epesN%real-address-in-sig@flur.bltigibbet...

LongJohn wrote:

Rowland McDonnell wrote:

LongJohn wrote:

We have a G4 Powermac but it's really noisey; I think it's the PSU.

Umm. Best to find out exactly what's wrong first. Could be a software
issue.

Software issue? What software? The firmware?
The OS is OSX 10.3.9

Could be something getting confused due to something buggy and/or corrupted.

The fans are variable speed and can run flat out if there's a hiccup in the software that controls them, and also if they need to because it's hot in there.

However, the tower G4s are famously noisy, some of them.

Are the PSU's the same as PC PSU as I have a spare one of those?

Not the same at all: totally different.

Erm.

See if you can isolate the fault properly.

Sounds loudest when I put my ear to the PSU. Don't think it's the hard disk.
What else could it be?

Could be a dying PSU :-) Dunno about `else' - but if you're fairly sure, you're fairly sure.

It's very dust around the PSU, would vacuuming it out help?

Oh yes lots! My old 2G4 ran a lot quieter if I took the trouble to clean out the dust every few weeks. Lots of dust all over the place needed removing.

Do the deed with the Mac *plugged in to the mains*.

Yes, that's right - but make sure that the power is turned off at the wall socket too.

That way, you keep the machine earthed.

Caution: do not let any of the fans get themselves spun round by the vacuuming process. Slow rotation by hand is okay, but an electric motor being driven mechanically tends to behave as a generator, doesn't it? Right.

Could be that someone has a
spare of what you need. Well, I possibly have, but I'm not up to offering to do anything for anyone at the moment (if it weren't for that
and the model's right, I'd offer you a PSU for postage).

That would have been grand

[snip]

If the PSU packs up, don't throw the machine away. Ask me.

Rowland.

--
Remove the animal for email address: rowland.mcdonnell@dog.physics.org Sorry - the spam got to me
http://www.mag-uk.org http://www.bmf.co.uk UK biker? Join MAG and the BMF and stop the Eurocrats banning biking

Thanks for all the help everyone.

Am I really OK to vacuum the inside of my mac? This seems like a dodgy thing to do.

I've heard stories about vacuums generating static, but I've never had any problems myself.

Paul

Yes. Static rings a bell

Message #13 - Posted 2007/06/13 - J. J. Lodder

Sara Kirk wrote:

Previously, LongJohn wrote:

Am I really OK to vacuum the inside of my mac? This seems like a dodgy thing to do.

Oh heavens yes! I've been doing that for years with no ill effects.

Mere vacuuming isn't enough.
The dirt collects on the leading edge of the fan blades,
and has te be rubbed or blown off
to restore the clean aerodynamic shape.

Jan

Message #14 - Posted 2007/06/14 - Rowland McDonnell

J. J. Lodder wrote:

Rowland McDonnell wrote:

LongJohn wrote:

It's very dust around the PSU, would vacuuming it out help?

Oh yes lots! My old 2G4 ran a lot quieter if I took the trouble to clean out the dust every few weeks. Lots of dust all over the place needed removing.

Do the deed with the Mac *plugged in to the mains*.

Yes, that's right - but make sure that the power is turned off at the wall socket too.

How very British.

Eh? It's just sense, surely? I don't see anything nationally-specific about `just doing the sensible thing'.

And even if it *is* very British - well, we're generally superior to everyone else, so it's bound to be the right thing to do.

<cough> (sorry, couldn't help myself)

That way, you keep the machine earthed.

Caution: do not let any of the fans get themselves spun round by the vacuuming process. Slow rotation by hand is okay, but an electric motor being driven mechanically tends to behave as a generator, doesn't it? Right.

You are exaggerating greatly.
(as in the case of the excessively dangerous high voltage
in the Mac Plus)

What I did in that case was pass on the warnings from the Apple Service Source CD which explained how to discharge the CRT's potentially fatal charge. It was Apple which made the initial claim of the danger of the charge that you might be facing - Apple's advice was `Always discharge using this procedure.'

So I think it's pretty clear I wasn't exaggerating at all. Of course, if you want to risk it and assume that you'll not get zapped or blow up some internal circuitry (another specific risk mentioned by Apple and the compact Mac service book I have), you go ahead. You might well get lucky. Personally, I'd rather heed the warnings given by the people who really know about this sort of stuff.

Can you cite any example at all of a PSU being blown up by vacuuming the fan?

The positioning of the PSU fans and the vacuum cleaner tools available to me are such that it was impossible to vacuum the PSU fans effectively without first removing the PSU. What I could do involved shoving the bristles of the brush tool into the fans at an oblique angle; they couldn't spin.

I have had trouble from letting one internal fan spin quickly when vacuuming inside my old 2G4 - it behaved very strangely afterwards. It wouldn't start up at first, and just beeped continuously. Unplugged from the mains, plugged back in again, booted into single user mode, all was okay.

Rowland.

Remove the animal for email address: rowland.mcdonnell@dog.physics.org Sorry - the spam got to me
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Message #15 - Posted 2007/06/14 - Rowland McDonnell

J. J. Lodder wrote:

[snip]

Mere vacuuming isn't enough.
The dirt collects on the leading edge of the fan blades,
and has te be rubbed or blown off
to restore the clean aerodynamic shape.

Vacuuming with a brush tool achieves that rather well with most of the fans in my old 2G4; the PSU fans didn't seem to pick up much dust, FWIW.

Only the graphics card fan needed close attention, and it was that fan bearing which finally packed up and somehow managed to take a CPU down with the graphics card death.

Rowland.

Remove the animal for email address: rowland.mcdonnell@dog.physics.org Sorry - the spam got to me
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Message #16 - Posted 2007/06/14 - Rowland McDonnell

LongJohn wrote:

Paul Russell wrote:

LongJohn wrote:

[snip]

Am I really OK to vacuum the inside of my mac? This seems like a dodgy thing to do.

I've heard stories about vacuums generating static, but I've never had any problems myself.

Paul

Yes. Static rings a bell

It's a risk. What you want to do is keep the Mac plugged in to the mains but switched off at the wall too - that way, it'll be earthed (important!) and completely electrically `off' (pretty much - let's not talk about the neutral line, eh?).

Don't vacuum close to open PCI slots or any other electrical terminals - they're the bits that are in a position to suffer from static (although USB and Firewire ports are pretty damned robust when it comes to electrical abuse; don't worry overmuch about them). Just vacuum the dusty bits around the fans and HDDs and whatnot, clean out the grills, and carefully clean the CPU heatsinks.

The only time I've ever had any trouble was when I let a fan spin quickly in the draught from the vacuum cleaner. Slow turning of a fan isn't a problem, but it seems that letting it spin quickly is a different matter: my 2G4 wouldn't start up after that until I'd powered down and powered up again. Gawd knows... And yes it *was* switched off at the mains when I was cleaning it that time.

Rowland.

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Message #17 - Posted 2007/06/14 - Rowland McDonnell

Debbie Wilson wrote:

Rowland McDonnell wrote:

And main fan, surely?

Ummm - can't remember, TBH. All that was sent by Apple under this replacement scheme was the large metal power supply box thing (technical term :-) ) which does have a small fan in it, IIRC. But without opening up my Mac I can't be sure if that's also the main fan, or if that's separate. I have a feeling that's elsewhere inside.

Oh right - sounds like a different arrangement to what I thought. Y'see, I though you had the same noisy G4 I had, which also had the noisy bits replaced for free by Apple. We got a replacement PSU with two small fans inside it, and a single replacement main fan - quite a big one.

Doing the swap was maddening - Apple's instructions were wrong, and neglected to mention *that* screw... Found it eventually.

Rowland.

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Message #18 - Posted 2007/06/14 - J. J. Lodder

Rowland McDonnell wrote:

J. J. Lodder wrote:

Rowland McDonnell wrote:

LongJohn wrote:

It's very dust around the PSU, would vacuuming it out help?

Oh yes lots! My old 2G4 ran a lot quieter if I took the trouble to clean out the dust every few weeks. Lots of dust all over the place needed removing.

Do the deed with the Mac *plugged in to the mains*.

Yes, that's right - but make sure that the power is turned off at the wall socket too.

How very British.

Eh? It's just sense, surely?

Are you sure that Apple recommends it?

I don't see anything nationally-specific about `just doing the sensible thing'.

Britain is unique in having choosen
a potentially unsafe home wiring system,
with the corresponding need for switches and fuses in plugs. It may save a few pennies worth of copper.

And even if it *is* very British - well, we're generally superior to everyone else, so it's bound to be the right thing to do.

<cough> (sorry, couldn't help myself)

Of course, of course.
However, what Apple recommends for normal parts of the world is: Shut down the machine.
Touch a metal part of it, with the power cord still connected. Then disconnect the power cord and start working.

That's what I would do in Britain too.
After all, switches may fail, and it is possible
that only the neutral is broken,
leaving a source of live power somewhere in the machine.
So, my rule:
never work on a machine connected to the mains
unless you really have to.

That way, you keep the machine earthed.

Caution: do not let any of the fans get themselves spun round by the vacuuming process. Slow rotation by hand is okay, but an electric motor being driven mechanically tends to behave as a generator, doesn't it? Right.

You are exaggerating greatly.
(as in the case of the excessively dangerous high voltage
in the Mac Plus)

What I did in that case was pass on the warnings from the Apple Service Source CD which explained how to discharge the CRT's potentially fatal charge. It was Apple which made the initial claim of the danger of the charge that you might be facing - Apple's advice was `Always discharge using this procedure.'

Apple is US-based, and needs to cover itself legally.
If it wasn't too big they would tell you not to eat it.

So I think it's pretty clear I wasn't exaggerating at all. Of course, if you want to risk it and assume that you'll not get zapped or blow up some internal circuitry (another specific risk mentioned by Apple and the compact Mac service book I have), you go ahead. You might well get lucky. Personally, I'd rather heed the warnings given by the people who really know about this sort of stuff.

That doesn't mean there is any real danger involved in practice.

Can you cite any example at all of a PSU being blown up by vacuuming the fan?

The positioning of the PSU fans and the vacuum cleaner tools available to me are such that it was impossible to vacuum the PSU fans effectively without first removing the PSU. What I could do involved shoving the bristles of the brush tool into the fans at an oblique angle; they couldn't spin.

I have had trouble from letting one internal fan spin quickly when vacuuming inside my old 2G4 - it behaved very strangely afterwards. It wouldn't start up at first, and just beeped continuously. Unplugged from the mains, plugged back in again, booted into single user mode, all was okay.

Impossible to say what happened. You did other things too. My guess would be a case of post hoc, ergo propter hoc.
Or as you say elsewhere: Gawd knows...

You didn't try to reproduce, I assume?

Jan

Message #19 - Posted 2007/06/14 - J. J. Lodder

Rowland McDonnell wrote:

LongJohn wrote:

Paul Russell wrote:

LongJohn wrote:

[snip]

Am I really OK to vacuum the inside of my mac? This seems like a dodgy thing to do.

I've heard stories about vacuums generating static, but I've never had any problems myself.

Paul

Yes. Static rings a bell

It's a risk.

Another imaginary one, under the circumstances.
If you were pouring hundreds of tons of grain
you might have to worry about an industrial dust explosion.

What you want to do is keep the Mac plugged in to the mains but switched off at the wall too - that way, it'll be earthed (important!) and completely electrically `off' (pretty much - let's not talk about the neutral line, eh?).

Don't vacuum close to open PCI slots or any other electrical terminals - they're the bits that are in a position to suffer from static (although USB and Firewire ports are pretty damned robust when it comes to electrical abuse; don't worry overmuch about them). Just vacuum the dusty bits around the fans and HDDs and whatnot, clean out the grills, and carefully clean the CPU heatsinks.

More nonsense. Charging up the machine is no problem.
Only charging up parts differently might cause problems. Your vacuum cleaner won't be doing that.

Best,

Jan

Message #20 - Posted 2007/06/14 - Tim Streater

Previously, J. J. Lodder wrote:

[snip]

Britain is unique in having choosen
a potentially unsafe home wiring system,
with the corresponding need for switches and fuses in plugs. It may save a few pennies worth of copper.

[snip]

It is noticeable that other countries don't have switches in their sockets. Personally I find it useful - means we can switch off e.g. the whole TV setup (otherwise lots of boxes on standby) each night without having to unplug anything. *Much* more convenient.

But I would be interested in your characterisation of it as "potentially unsafe" - could you explain a bit (or a lot :-)

I feel the Yanks have the unsafe one, with their cheese-paring 110 volts and so four times the heating effect anywhere there is a poor connection in the circuit.

Message #21 - Posted 2007/06/14 - Peter Ceresole

Tim Streater wrote:

I feel the Yanks have the unsafe one, with their cheese-paring 110 volts and so four times the heating effect anywhere there is a poor connection in the circuit.

Indeed. But 110V AC is *human* safe, whereas 230V is smack in the most lethal range.

There has to be a trade-off; I wonder how many fatal house fires are started by the doubled current values in the Yank system, as against the extra deaths by electrocution in the European system?

Peter

Message #22 - Posted 2007/06/14 - Tim Streater

Previously, Peter Ceresole wrote:

Tim Streater wrote:

I feel the Yanks have the unsafe one, with their cheese-paring 110 volts and so four times the heating effect anywhere there is a poor connection in the circuit.

Indeed. But 110V AC is *human* safe, whereas 230V is smack in the most lethal range.

There has to be a trade-off; I wonder how many fatal house fires are started by the doubled current values in the Yank system, as against the extra deaths by electrocution in the European system?

Yes, this is a good question. Having lived there I found that there is a variety of plugs - 2-pin, 2-pin polarised, three pin - and corresponding sockets. So you can't plug a 2-pin polarised in a 2-pin socket (one blade is a bit bigger that the other). Houses also have 240 anyway to run the washing machine etc - and a variety of plugs for that, too. You can't buy a regular 3-pin plug to wire yourself - the ones you can wire are ugly as sin and look industrial.

The pins on any 3-pin plug are bendy - and the whole plug can easily be kicked out of the socket by accident, especially if its on the end of an extension socket strip, the cable is almost as fat as your finger.

The worst thing I saw was a sort of 2-pin socket strip - but the pin-holes were each about 15cm long. So you could pplu in as many 2-pin plugs as there was physically room for. When I examined this item, it was quite hot.

Double the current means four times the heating effect, don't forget.

Message #23 - Posted 2007/06/14 - Rowland McDonnell

Peter Ceresole wrote:

Tim Streater wrote:

I feel the Yanks have the unsafe one, with their cheese-paring 110 volts and so four times the heating effect anywhere there is a poor connection in the circuit.

Indeed. But 110V AC is *human* safe, whereas 230V is smack in the most lethal range.

Actually, 110V DC which is where the Yanks started[1] isn't at all human safe. And 110V AC and 10A (or whatever they can get) is plenty enough to start a fire. And in any case, 110V AC can kill a person - if said person is frail or unlucky.

There has to be a trade-off; I wonder how many fatal house fires are started by the doubled current values in the Yank system, as against the extra deaths by electrocution in the European system?

But how many such `extra deaths' are there? We, for example, do tend to have proper earthing, unlike in the USA. I wouldn't be surprised if that bumps up their death by electrocution rate.

Rowland.

[1] That total wanker rip-off lying evil bastard Thomas Edison gave 'em that shite setup.

I'm sorry? You think I should be more polite about the inventor of the electric chair, possibly the cruellest form of legalised murder used by any nation today? The man who shamelessly stole his employees inventions? Etc?

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Message #24 - Posted 2007/06/14 - Rowland McDonnell

J. J. Lodder wrote:

Rowland McDonnell wrote:

J. J. Lodder wrote:

Rowland McDonnell wrote:

LongJohn wrote:

It's very dust around the PSU, would vacuuming it out help?

Oh yes lots! My old 2G4 ran a lot quieter if I took the trouble to clean out the dust every few weeks. Lots of dust all over the place needed removing.

Do the deed with the Mac *plugged in to the mains*.

Yes, that's right - but make sure that the power is turned off at the wall socket too.

How very British.

Eh? It's just sense, surely?

Are you sure that Apple recommends it?

I haven't the faintest idea what Apple recommends in this sort of situation.

I don't see anything nationally-specific about `just doing the sensible thing'.

Britain is unique in having choosen
a potentially unsafe home wiring system,
with the corresponding need for switches and fuses in plugs. It may save a few pennies worth of copper.

Eh? Britain is unique in having one of the very safest domestic wiring schemes in existence - for example, unlike everyone else in Europe, we have adequate fusing and earthing and (as far as I can tell) by far the safest mains plugs.

On the continent, you don't have adequate fusing and there are places in the supply chain where you lot can have fires and we can't - because we've got more fuses in the way. You are mistaken if you think that we've got those extra fuses because our wiring is so much more dangerous than yours: it's safer, because you lot are missing fuses that are needed.

Everyone else has much more dangerous domestic mains supply arrangements than Britain - aside from the point that you can hurt yourself a lot more easily on a British mains plug if it's left lying around on the floor to be trodden on.

I've no idea where you think the copper's being saved.

And even if it *is* very British - well, we're generally superior to everyone else, so it's bound to be the right thing to do.

<cough> (sorry, couldn't help myself)

Of course, of course.
However, what Apple recommends for normal parts of the world is: Shut down the machine.
Touch a metal part of it, with the power cord still connected. Then disconnect the power cord and start working.

Yes, I know. So what? I've been ignoring the rules for a long time.

That's what I would do in Britain too.
After all, switches may fail, and it is possible
that only the neutral is broken,

Not with any normal switch, it's not. Single pole - live switching only is normal.

leaving a source of live power somewhere in the machine. So, my rule:
never work on a machine connected to the mains
unless you really have to.

One can of course run a test, am I not right?

FWIW, I assume that there's live mains inside anything that's still plugged in, and act with appropriate caution. I've even been known to behave as if there were live mains when I *knew* it was all `off'. This has probably saved my life on occasion when it wasn't all `off' due to wiring faults and other such irregularities.

That way, you keep the machine earthed.

Caution: do not let any of the fans get themselves spun round by the vacuuming process. Slow rotation by hand is okay, but an electric motor being driven mechanically tends to behave as a generator, doesn't it? Right.

You are exaggerating greatly.
(as in the case of the excessively dangerous high voltage
in the Mac Plus)

What I did in that case was pass on the warnings from the Apple Service Source CD which explained how to discharge the CRT's potentially fatal charge. It was Apple which made the initial claim of the danger of the charge that you might be facing - Apple's advice was `Always discharge using this procedure.'

Apple is US-based, and needs to cover itself legally.
If it wasn't too big they would tell you not to eat it.

This is advice to the technicians. The advice includes a very dodgy scheme for making a very dodgy discharge tool that I'm not sure I'd trust - it's not `all cleared by the lawyers' to that extent, you know.

So I think it's pretty clear I wasn't exaggerating at all. Of course, if you want to risk it and assume that you'll not get zapped or blow up some internal circuitry (another specific risk mentioned by Apple and the compact Mac service book I have), you go ahead. You might well get lucky. Personally, I'd rather heed the warnings given by the people who really know about this sort of stuff.

That doesn't mean there is any real danger involved in practice.

Nor does it mean that there is no danger in practice.

Can you cite any example at all of a PSU being blown up by vacuuming the fan?

The positioning of the PSU fans and the vacuum cleaner tools available to me are such that it was impossible to vacuum the PSU fans effectively without first removing the PSU. What I could do involved shoving the bristles of the brush tool into the fans at an oblique angle; they couldn't spin.

I have had trouble from letting one internal fan spin quickly when vacuuming inside my old 2G4 - it behaved very strangely afterwards. It wouldn't start up at first, and just beeped continuously. Unplugged from the mains, plugged back in again, booted into single user mode, all was okay.

Impossible to say what happened. You did other things too. My guess would be a case of post hoc, ergo propter hoc.
Or as you say elsewhere: Gawd knows...

My guess is that it was the fan - I've cleaned the inside of that machine scores of times, only met that behaviour once, and that was the time I let the fan spin quickly. It seemed like a pretty obvious link to me.

You didn't try to reproduce, I assume?

Of course not.

Rowland.

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Message #25 - Posted 2007/06/14 - Rowland McDonnell

J. J. Lodder wrote:

Rowland McDonnell wrote:

LongJohn wrote:

Paul Russell wrote:

LongJohn wrote:

[snip]

Am I really OK to vacuum the inside of my mac? This seems like a dodgy thing to do.

I've heard stories about vacuums generating static, but I've never had any problems myself.

Paul

Yes. Static rings a bell

It's a risk.

Another imaginary one, under the circumstances.
If you were pouring hundreds of tons of grain
you might have to worry about an industrial dust explosion.

Oh, get out. I've blown up static sensitive electronics more times than you've had hot dinners, at a guess.

I'm telling you, it's a real risk.

What you want to do is keep the Mac plugged in to the mains but switched off at the wall too - that way, it'll be earthed (important!) and completely electrically `off' (pretty much - let's not talk about the neutral line, eh?).

Don't vacuum close to open PCI slots or any other electrical terminals - they're the bits that are in a position to suffer from static (although USB and Firewire ports are pretty damned robust when it comes to electrical abuse; don't worry overmuch about them). Just vacuum the dusty bits around the fans and HDDs and whatnot, clean out the grills, and carefully clean the CPU heatsinks.

More nonsense. Charging up the machine is no problem.
Only charging up parts differently might cause problems. Your vacuum cleaner won't be doing that.

More nonsense.

There's no point in trying to explain, but you are entirely wrong in your assumptions.

Rowland.

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Message #26 - Posted 2007/06/14 - D.M. Procida

Rowland McDonnell wrote:

[1] That total wanker rip-off lying evil bastard Thomas Edison gave 'em that shite setup.

<http://www-static.cc.gatech.edu/~jimmyd/laurie-anderson/lyrics/UnitedSt ates.txt> and search for "electricity".

Daniele

Message #27 - Posted 2007/06/14 - J. J. Lodder

Tim Streater wrote:

Previously, Peter Ceresole wrote:

Tim Streater wrote:

I feel the Yanks have the unsafe one, with their cheese-paring 110 volts and so four times the heating effect anywhere there is a poor connection in the circuit.

Indeed. But 110V AC is *human* safe, whereas 230V is smack in the most lethal range.

There has to be a trade-off; I wonder how many fatal house fires are started by the doubled current values in the Yank system, as against the extra deaths by electrocution in the European system?

Yes, this is a good question. Having lived there I found that there is a variety of plugs - 2-pin, 2-pin polarised, three pin - and corresponding sockets. So you can't plug a 2-pin polarised in a 2-pin socket (one blade is a bit bigger that the other). Houses also have 240 anyway to run the washing machine etc - and a variety of plugs for that, too.

But it is immediately obvious that they can't be civilized, for (due to their puny 110 V supply) they lack electric kettles. They have centre-tapped 220 V, 2*110 Volt
and call that (incorrectly of course) two-phase.

Jan

Message #28 - Posted 2007/06/14 - J. J. Lodder

Tim Streater wrote:

Previously, J. J. Lodder wrote:

[snip]

Britain is unique in having choosen
a potentially unsafe home wiring system,
with the corresponding need for switches and fuses in plugs. It may save a few pennies worth of copper.

[snip]

It is noticeable that other countries don't have switches in their sockets.

If you really need to you can install switched plugs.

Personally I find it useful - means we can switch off e.g. the whole TV setup (otherwise lots of boxes on standby) each night without having to unplug anything. *Much* more convenient.

You can use switched blocks for that.

But I would be interested in your characterisation of it as "potentially unsafe" - could you explain a bit (or a lot :-)

It's the ring which is potentially dangerous, when broken.

I feel the Yanks have the unsafe one, with their cheese-paring 110 volts and so four times the heating effect anywhere there is a poor connection in the circuit.

Indeed, the European 230 Volt system is probably much safer. (but good statistics are hard to find)

Many more people are killed in electricity related fires than by electric shock.

Best,

Jan

Message #29 - Posted 2007/06/14 - Tim Streater

Previously, J. J. Lodder wrote:

Tim Streater wrote:

Previously, Peter Ceresole wrote:

Tim Streater wrote:

I feel the Yanks have the unsafe one, with their cheese-paring 110 volts and so four times the heating effect anywhere there is a poor connection in the circuit.

Indeed. But 110V AC is *human* safe, whereas 230V is smack in the most lethal range.

There has to be a trade-off; I wonder how many fatal house fires are started by the doubled current values in the Yank system, as against the extra deaths by electrocution in the European system?

Yes, this is a good question. Having lived there I found that there is a variety of plugs - 2-pin, 2-pin polarised, three pin - and corresponding sockets. So you can't plug a 2-pin polarised in a 2-pin socket (one blade is a bit bigger that the other). Houses also have 240 anyway to run the washing machine etc - and a variety of plugs for that, too.

But it is immediately obvious that they can't be civilized, for (due to their puny 110 V supply) they lack electric kettles.

Not completely. I was able to buy one while living there (a Russell-Hobbs). But electric turn-themselves-off kettles are not normally part of their national psyche.

Message #30 - Posted 2007/06/14 - J. J. Lodder

Tim Streater wrote:

Previously, J. J. Lodder wrote:

Tim Streater wrote:

Previously, Peter Ceresole wrote:

Tim Streater wrote:

I feel the Yanks have the unsafe one, with their cheese-paring 110 volts and so four times the heating effect anywhere there is a poor connection in the circuit.

Indeed. But 110V AC is *human* safe, whereas 230V is smack in the most lethal range.

There has to be a trade-off; I wonder how many fatal house fires are started by the doubled current values in the Yank system, as against the extra deaths by electrocution in the European system?

Yes, this is a good question. Having lived there I found that there is a variety of plugs - 2-pin, 2-pin polarised, three pin - and corresponding sockets. So you can't plug a 2-pin polarised in a 2-pin socket (one blade is a bit bigger that the other). Houses also have 240 anyway to run the washing machine etc - and a variety of plugs for that, too.

But it is immediately obvious that they can't be civilized, for (due to their puny 110 V supply) they lack electric kettles.

Not completely. I was able to buy one while living there (a Russell-Hobbs).

But it's so sloow.

But electric turn-themselves-off kettles are not normally part of their national psyche.

Indeed, no tea,

Jan

Message #31 - Posted 2007/06/14 - J. J. Lodder

Rowland McDonnell wrote:

J. J. Lodder wrote:

Rowland McDonnell wrote:

LongJohn wrote:

Paul Russell wrote:

LongJohn wrote:

[snip]

Am I really OK to vacuum the inside of my mac? This seems like a dodgy thing to do.

I've heard stories about vacuums generating static, but I've never had any problems myself.

Paul

Yes. Static rings a bell

It's a risk.

Another imaginary one, under the circumstances.
If you were pouring hundreds of tons of grain
you might have to worry about an industrial dust explosion.

Oh, get out. I've blown up static sensitive electronics more times than you've had hot dinners, at a guess.

That does not inspire confidence in your abilities,

Jan

Message #32 - Posted 2007/06/15 - Rowland McDonnell

J. J. Lodder wrote:

Tim Streater wrote:

[snip]

But electric turn-themselves-off kettles are not normally part of their national psyche.

Indeed, no tea,

They drink tea all right, just *bad* tea made with off-the-boil water.

I visited Dallas once...

Rowland.

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Message #33 - Posted 2007/06/15 - Rowland McDonnell

Peter Ceresole wrote:

Tim Streater wrote:

I feel the Yanks have the unsafe one, with their cheese-paring 110 volts and so four times the heating effect anywhere there is a poor connection in the circuit.

Indeed. But 110V AC is *human* safe, whereas 230V is smack in the most lethal range.

No it's not. Not at all - 240V rms is `as high a voltage as you can get away with because anything much higher is when it gets really dodgy'.

I've got away with 240V rms mains in my mouth. Don't ask - it was very embarrassing, but I got away with it.

Really, European mains voltage is *okay*, just about. Potentially fatal for sure, but so's 110 V AC and the old 110V DC US system was *horribly* dangerous.

Anything above 30V, and you need to start to think about proper electrical safety, although you've got to be *really* unlucky to get killed by `under 100V, ish'.

I've had about 60V AC rms applied to me via a salt water bath across both hands (also an embarrassing mistake so don't ask). That hurt (oh god it hurt), but didn't seem to bother my heart.

There has to be a trade-off; I wonder how many fatal house fires are started by the doubled current values in the Yank system, as against the extra deaths by electrocution in the European system?

You want to start out by asking about the effect of the form and implementation of the wiring standards in each region - that's a lot more significant.

If you've got decent wiring regs and they're adhered to, you won't get fires due to dodgy wiring.

Rowland.

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Message #34 - Posted 2007/06/15 - Rowland McDonnell

J. J. Lodder wrote:

Rowland McDonnell wrote:

J. J. Lodder wrote:

Rowland McDonnell wrote:

LongJohn wrote:

Paul Russell wrote:

LongJohn wrote:

[snip]

Am I really OK to vacuum the inside of my mac? This seems like a dodgy thing to do.

I've heard stories about vacuums generating static, but I've never had any problems myself.

Paul

Yes. Static rings a bell

It's a risk.

Another imaginary one, under the circumstances.
If you were pouring hundreds of tons of grain
you might have to worry about an industrial dust explosion.

Oh, get out. I've blown up static sensitive electronics more times than you've had hot dinners, at a guess.

That does not inspire confidence in your abilities,

<chuckle> I don't suppose it does - but I've blown up static sensitive electonics by just looking at the bloody stuff as far as I can tell.

My experiences fiddling around with CMOS components means that I've never blown up a completed circuit of any sort. I learnt, but you know what? I just blew stuff up, and I wasn't the only one who was baffled at the frequency with which it happened.

Rowland.

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Message #35 - Posted 2007/06/15 - Peter Ceresole

Rowland McDonnell wrote:

Really, European mains voltage is *okay*, just about. Potentially fatal for sure, but so's 110 V AC and the old 110V DC US system was *horribly* dangerous.

Electrical safety officers I've talked to disagree with you. 110V AC is pretty safe, 230V is bloody dangerous. The conducting path goes through the body. Much above that, the conducting path is via the outside of the body, and danger falls off again. Then the main risk is burns at the contact points. At Imperial College we were given an electrical safety lecture by a safety officer from the CEGB, who was on sick leave because he'd reached up to a 1500V bus which should have been isolated, but was actually live. He woke up with the palms of his hands and the soles of his feet severely burnt, but his heart was okay. He said that was entirely down to the high voltage on the bus, and that at 230V he'd have been dead.

Peter

Message #36 - Posted 2007/06/15 - Rowland McDonnell

Peter Ceresole wrote:

Rowland McDonnell wrote:

Really, European mains voltage is *okay*, just about. Potentially fatal for sure, but so's 110 V AC and the old 110V DC US system was *horribly* dangerous.

Electrical safety officers I've talked to disagree with you.

Electrical safety officers I've talked to disagree with that opinion /very/ strongly in some cases.

110V AC is
pretty safe, 230V is bloody dangerous.

110V AV and 240V AC are both dangerous, and both are survivable - much more than 440V three phase, for example. If you think that 110V AC is a *lot* safer than 230V AC, you're daft. Both can kill and both do kill; both are also survivable.

I've survived 240V rms AC in my mouth without damage. How? Hair-trigger reflexes, and it must have been a fairly high resistance connection via the saliva.

What kills is current across the heart - the voltage isn't important. Bear that in mind and you'll understand a lot better.

The conducting path goes through
the body.

Yes, that's right.

Much above that, the conducting path is via the outside of the body, and danger falls off again.

Not true. High frequency pushes the juice onto the skin, not high voltage. 5kV is a /lot/ more dangerous than 240V.

I've had electrical safety officers tell me about that misconception that you are repeating and emphasise that it's a common misconception that has resulting in lots of people ending up dead. I've also had 'em give me the talk on safe handling of HT power supplies and whatnot.

Then the main risk is burns at the
contact points.

Yeah, well, the electrical safety officers (my dad's one of them) have pointed out to me that 440V three phase is one of the scariest supply sources you'll meet. *That* is the seriously lethal one you want to watch out for.

And you know, if the conduction path was down the outside as you claim, you'd not just have contact burns, would you? No, you'd also have burn tracks on the skin - you'll find that in cases of high frequencies (lightning strikes, for example), but not AC electrical supply burns unless - well, I dunno, what about the 400 Hz supply they use on subs and whatnot?

Anyway, that should be enough to convince you that this `high voltage down the outside' idea is bullshit. High /frequency/ goes down the outside, yes - hence lightning survivability.

< At Imperial College we were given an electrical safety lecture by a safety officer from the CEGB, who was on sick leave because he'd reached up to a 1500V bus which should have been isolated, but was actually live. He woke up with the palms of his hands and the soles of his feet severely burnt, but his heart was okay.

So what? You've got to be unlucky for a shock to stop your heart, really. Your body seems quite good at keeping itself running.

That's why the electric chair is such an evil way of killing people - it kills not by stopping the heart, but by cooking the victim slowly and hideously painfully.

He said that was
entirely down to the high voltage on the bus, and that at 230V he'd have been dead.

He was talking total bollocks - and back then, it was 240V, right?

Rowland.

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Message #37 - Posted 2007/06/16 - Peter Ceresole

Rowland McDonnell wrote:

Anyway, that should be enough to convince you that this `high voltage down the outside' idea is bullshit. High /frequency/ goes down the outside, yes - hence lightning survivability.

You don't convince me at all. And the wrongness of your reasoning is absolutely clear from your statement that "And you know, if the conduction path was down the outside as you claim, you'd not just have contact burns, would you? No, you'd also have burn tracks on the skin". Of course you do- at the contact points, where the current density is highest. Elsewhere the current is flowing over the whole skin surface and the density is much lower.

I'll go with the CEGB safety officer.

Peter

Message #38 - Posted 2007/06/16 - Rowland McDonnell

Peter Ceresole wrote:

Rowland McDonnell wrote:

Anyway, that should be enough to convince you that this `high voltage down the outside' idea is bullshit. High /frequency/ goes down the outside, yes - hence lightning survivability.

You don't convince me at all.

Look it up! Don't take my word for it or your lack of understanding - look it up!

And the wrongness of your reasoning is absolutely clear from your statement that "And you know, if the conduction path was down the outside as you claim, you'd not just have contact burns, would you? No, you'd also have burn tracks on the skin". Of course you do- at the contact points, where the current density is highest. Elsewhere the current is flowing over the whole skin surface and the density is much lower.

You look at those who survive lightning - I've seen *them* with burn tracks running down the outside.

I'll go with the CEGB safety officer.

<shrug> I'll go with the electrical safety people who taught me.

Rowland.

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Message #39 - Posted 2007/06/16 - Mark Ingle

LongJohn wrote:

We have a G4 Powermac but it's really noisey; I think it's the PSU.

Are the PSU's the same as PC PSU as I have a spare one of those?

Thanks

If you have a dual processor mirror drive door G4, it most likely has the original noisy fans.

I had one of these and I bought replacement fans from here:

http://www.pcsilent.de/en_pd_smartCooler_fan_set_for_Apple_PowerMac_G4_q uieten_Apple_Power_Macintosh_G4_quiet_powermac_LFS1130_307.html

Seeing as this model G4 is very old now and not worth much, it may not be worth paying for the replacement fans which cost me 40 odd pounds at the time, but they did work very well.

Previously I did look on eBay for replacement power supply/fan, but these were going for silly prices at the time.

And here are the instructions on how to replace the fans:

http://www.xlr8yourmac.com/systems/g4_mirrored_drive_doors/noise_reducti on/g4_ddr_noise_reduction.html

Message #40 - Posted 2007/06/17 - Phil Taylor

Previously, Rowland McDonnell wrote:

Peter Ceresole wrote:

I'll go with the CEGB safety officer.

<shrug> I'll go with the electrical safety people who taught me.

Rowland.

FWIW, I'm with Roland here. It's a silly argument though.

The points to remember are:

Anything over about 60V can kill you under some circumstances.

It's current which kills, so contact area and the internal resistance of the source matter, and by virtue of Ohm's law higher voltages are more dangerous.

The most dangerous shock is one where the current flows from hand to hand. If you work with high voltage you develop a reflex which prevents you from touching two metal surfaces simultaneously with your left and right hands. (And you always wear rubber-soled shoes.)

Phil Taylor

Message #41 - Posted 2007/06/17 - Rowland McDonnell

Phil Taylor wrote:

Previously, Rowland McDonnell wrote:

Peter Ceresole wrote:

I'll go with the CEGB safety officer.

<shrug> I'll go with the electrical safety people who taught me.

Rowland.

FWIW, I'm with Roland here. It's a silly argument though.

Not terribly - one should get these things straight. There is no mechanism that I've ever heard of that'll push current down the outside of a body with higher voltage (unless we're talking about something involving insulated charged bodies or similar trickery).

There is a mechanism that'll push high frequency down the outside of a body.

The points to remember are:

Anything over about 60V can kill you under some circumstances.

That's `very roughly 60V' and actually rather less than that can kill - if you apply it across the heart.

Skin resistance counts for a lot - my dad claims that his dry skin has kept him safe when he shouldn't have been.

It's current which kills, so contact area and the internal resistance of the source matter, and by virtue of Ohm's law higher voltages are more dangerous.

Skin resistance is very, very variable - that matters, too, and it's more significant that source impedance most of the time (but note that HT PSUs are often equipped with a high impedance output to give you a bit of protection). Hot and sweaty? You're in trouble.

The most dangerous shock is one where the current flows from hand to hand. If you work with high voltage you develop a reflex which prevents you from touching two metal surfaces simultaneously with your left and right hands. (And you always wear rubber-soled shoes.)

Umm. You don't have to work with particularly high voltages to develop the reflex. Just mains has been enough to scare that way of working into me. Oh yeah, and anything that feels like electrical tingling makes me jump - and whatever was tingling gets jerked away very fast. I'm pretty sure that reflex has spared me some damage.

Rowland.

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