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Post subject: Grounding and potential electrocution!!
Posted: Tue Apr 29, 2008 2:22 pm
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Joined: Sat Jan 26, 2008 2:23 pm
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Hi guys!

As an electrician/electronics tech who has worked with the innards of amps and power distribution inside buildings, the likelihood of receiving a fatal or nonfatal shock through your grounded guitar is very remote. Typically, if there's a short circuit in an amp it'll either blow fuses, trip breakers, or simply not work. As equipment ages, heat and wear and tear can degrade wire insulation. Most dangerous situations arise due to that and excessive moisture, rain, spilled drinks, etc., inside the equipment. Avoid using electrical equipment when wet. Playing in a downpour is not a good idea. All bets are off if your amp gets full of water!

However, each one of us can be the path to ground for a separate piece of faulty equipment. In this case an RCD (British) or GFCI (U.S.) won't protect you if it's not used on the faulty device (amp, PA, Lamp, etc.) These work by measuring the difference of the current going into the hot wire and whats coming out through the neutral. If it sees a difference above its set point, it trips. As in the case of our friend Tony474 on the TDPRI forum, he would be taking a dirt nap now because the lamp was not RCD protected and would have continued to conduct current through his body had he not gotten loose, breaking the circuit. From the GFCI circuit diagram I've just seen, only the hot and neutral wires get disconnected when a trip occurs. The ground does not, so Tony474 was VERY lucky.

Here's his story from the 70s:

"A long time ago, at a rehearsal in someone's house, I reached up with my right hand to turn on a lamp that had a brass bulb-holder... one of the wires inside must have come loose, because the holder was live. I was holding my guitar neck with the left hand, in contact with the strings. My amp wasn't even switched on but the guitar strings were earthed (grounded) via the lead (cord) through the chassis of the amp. I got a huge 240-volt shock right across my chest from arm to arm and if I hadn't collapsed and broken my hold on the lampholder I wouldn't be around to tell the tale. Nasty and unbelievably scary. As it is I still have a scar on my thumb where the flesh burned and bubbled up.

These days, unless everything is plugged via an RCD I just won't play. I'd sooner lose the gig than my life."

Remember, fuses and circuit breakers are designed to protect the equipment and facility wiring, not humans. RCDs and GFCIs are designed to protect humans, but they only work on the equipment plugged into them.

A good rule of thumb is to avoid touching anything while grounded. If you have a voltmeter you can touch one lead to the strings or ground on your guitar and the other to the mic, etc. to check for harmful voltages (>50vac, according to the US NEC). Might also try it on the DC setting as well to see if the tube B+ voltage is present from a tube amp.

You can use a portable Ground Fault Circuit Interrupter like we use at work to plug in our corded power tools. http://www.watergarden.org/s.nl/it.A...artner=froogle

Keep in mind that these only work on the devices plugged into them, not on a faulty lamp you might touch while holding onto your strings!

I've never tried one of these on an amp, I assume they would work. These use similar circuitry as the ones in your bathroom and are designed to protect you from electric shock. They also do a good job protecting equipment, because they work lots faster than a fuse or circuit breaker.

One rule of thumb; If you plug one into the outlet, then plug in your equipment and it trips, reset it. If it trips again, you may have to call in a pro to figure out if something's bad wrong. Be sure to test/reset it before each use to make certain it works.

If anyone has tried to use one of these for protecting themselves and their gear, let me know how it worked out.


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