Electric Shock - Clarification

[networkn]

Hi There!

Whilst photographing my Crack Amp (Whilst stupidly it was plugged into the power but turned off at the Crack Amp Switch), I have myself a nice 240 Volt Kick in the chest.

I am not sure what I touched, it's a bit of a blur, I am trying to work out what I would have had to have touched for the situation to occur. I'd like to think that I would have only touched the plate (the thing the components are attached to) with both hands, but if that's the case, then I think I have done something wrong with assembly as I don't think that would be normal.

I am not saying categorically that I did only touch both hands to the plate, just that is my (very) fuzzy recollection.

Assuming I am wrong, with the crack amp plugged into the mains, but the switch OFF and 1 hand was I am 99% sure on the plate, what would I have needed to have touched to get a shock?

thanks.

[kgoss]

I don't have a Crack amp but on my SEX amp the IEC has electricity if the amp is plugged in. The power switch just keeps it from reaching the amp circuit but the IEC is always hot. If that is the case for the Crack I bet you touched the IEC terminals by mistake.  That is unless a wiring mistake caused the shock.

[Doc B.]

Yes, if the amp was wired correctly you must have touched a terminal on the IEC power inlet on the underside at the rear corner. But we don't have enough information to determine that, and you really should Very Carefully redo your resistance measurements and if they pass, your voltage measurements. If you measure high voltage on the chassis relative to ground you have a problem that must be corrected before you use the amp. Test this simply by clipping the black meter lead to the E terminal on the IEC socket and clipping the red lead to the chassis plate and measuring resistance. Do use clip leads to make the test hands free. The reading should be very close to 0 ohms. Then switch your meter to read DC volts, extremely carefully turn the amp on and check the reading, which again should be close to 0. Then switch the meter to AC volts and look once again for a very low reading.

If you see high voltage, shut the amp off and figure out what is miswired before using it.

[networkn]

I'll check it out tonight or tomorrow night depending on how I feel. It was a mighty unpleasant surprise I can tell you.

Is there a plastic cover I could use to cover the particularly dangerous parts of the IEC to minimize the risk of accidental touching?

[Doc B.]

That parts you shouldn't touch are on the underside of the chassis panel. If you were shocked by the top of the panel, do not use the amp until it is repaired. If you were shocked by touching live terminals under the chassis panel when the amp was plugged in I would suggest A) not lifting the panel when the amp is plugged in to power B) securing the chassis panel to the wood base with adhesive, and C) covering the bottom of the wood base with a piece of perforated plastic.

We point out that these kits are not complete in terms of encapsulation in the first pages of the assembly manuals. If you wish to do all that you can to make them foolproof I would also suggest putting a cage over the hot tubes.

[networkn]

That parts you shouldn't touch are on the underside of the chassis panel. If you were shocked by the top of the panel, do not use the amp until it is repaired. If you were shocked by touching live terminals under the chassis panel when the amp was plugged in I would suggest A) not lifting the panel when the amp is plugged in to power B) securing the chassis panel to the wood base with adhesive, and C) covering the bottom of the wood base with a piece of perforated plastic.

We point out that these kits are not complete in terms of encapsulation in the first pages of the assembly manuals. If you wish to do all that you can to make them foolproof I would also suggest putting a cage over the hot tubes.

Hi.

I do understand the risks in general, I am not blaming anyone or suggesting that the unit is unsafe.  I am trying to understand what I did. I don't believe I got a shock from the base alone. Kids usually understand "hot" without too much trouble.

I'll do the tests. As I mentioned, I feel pretty stupid, I am not sure why I thought it would be ok to lift the unit whilst it was plugged in, but I guess I didn't expect to be touching any part near where I could be shocked.

I am simply looking at practical ways to protect against accidents going forward.

[Doc B.]

Sorry if I may seem a little overbearing, please understand that it is simply because we have a very heavy obligation to make it clear that a person can get a shock when constructing or working on the underchassis components of any kit we make that uses high voltage, and that we have published guidelines that will help to avoid this in the manuals.

It's difficult to offer much more than speculation of what might resolve the issue without knowing exactly what you touched, so I'm trying to be thorough. We have all unthinkingly grabbed a plugged in chassis here at work and inadvertently touched the terminals on the IEC and sworn like sailors. So I would suggest that as the most likely scenario to have happened, which is simply solved by not picking up an amp if it is plugged in.

But since it is not clear if that is what happened it is important to understand whether or not the chassis might in fact be live due to a miswire. Because if the chassis is live it must be fixed before it is used again. Once you have completed the tests I suggested to determine this and you are assured that the chassis is properly grounded to the safety ground and the Earth pin of the IEC socket you should only need to cover the bottom and maybe fasten the top to the base to keep the amp safe if being handled while plugged in. If you do a bottom cover be sure that it has ventilation holes, as some parts under the chassis get pretty hot.

[networkn]

Sorry if I may seem a little overbearing, please understand that it is simply because we have a very heavy obligation to make it clear that a person can get a shock when constructing or working on the underchassis components of any kit we make that uses high voltage, and that we have published guidelines that will help to avoid this in the manuals.

It's difficult to offer much more than speculation of what might resolve the issue without knowing exactly what you touched, so I'm trying to be thorough. We have all unthinkingly grabbed a plugged in chassis here at work and inadvertently touched the terminals on the IEC and sworn like sailors. So I would suggest that as the most likely scenario to have happened, which is simply solved by not picking up an amp if it is plugged in.

But since it is not clear if that is what happened it is important to understand whether or not the chassis might in fact be live due to a miswire. Because if the chassis is live it must be fixed before it is used again. Once you have completed the tests I suggested to determine this and you are assured that the chassis is properly grounded to the safety ground and the Earth pin of the IEC socket you should only need to cover the bottom and maybe fasten the top to the base to keep the amp safe if being handled while plugged in. If you do a bottom cover be sure that it has ventilation holes, as some parts under the chassis get pretty hot.

Thanks. I do understand it must be your worst nightmare to hear when someone has had a shock.

I am unsure if tonight I'll have time to do any testing, it may yet be Friday night before I get a chance.

Rest assured, despite my accident, I have been otherwise incredibly cautious and this has reminded me that taking even small shortcuts can be a serious problem. I made my wife stand in the room when I did the resistance and voltage checks so if something went wrong she could act.

[JamieMcC]

I had a bad electric 240V mains shock when I was 10 years old and doing any voltage checks scares the cr#p out of me and to be honest I am thankful for it.

[networkn]

I had a bad electric 240V mains shock when I was 10 years old and doing any voltage checks scares the cr#p out of me and to be honest I am thankful for it.

Same actually.

[networkn]

Yes, if the amp was wired correctly you must have touched a terminal on the IEC power inlet on the underside at the rear corner. But we don't have enough information to determine that, and you really should Very Carefully redo your resistance measurements and if they pass, your voltage measurements. If you measure high voltage on the chassis relative to ground you have a problem that must be corrected before you use the amp. Test this simply by clipping the black meter lead to the E terminal on the IEC socket and clipping the red lead to the chassis plate and measuring resistance. Do use clip leads to make the test hands free. The reading should be very close to 0 ohms. Then switch your meter to read DC volts, extremely carefully turn the amp on and check the reading, which again should be close to 0. Then switch the meter to AC volts and look once again for a very low reading.

If you see high voltage, shut the amp off and figure out what is miswired before using it.

Hi There!

I completed this and got zero for all tests. Amp is now working, though with an annoying buzz being addressed in another thread.

One of the photos I took shows me nearly touching the IEC so I imagine when it started to twist, I made contact and when I touched the base, zap. Answers that question.