Are Little Shocks OK?
First of all, ANY shock on a stage or in your home is dangerous. There’s really no such thing as a little shock being OK. If anyone in your band feels a shock when touching guitar stings or a microphone, the they’re playing a game of electrical Russian Roulette which rarely ends well. You need to find and fix the electrical problem causing this right now, before somebody gets seriously hurt or killed. In the USA alone there are 1,000 deaths per year from electrocution, and 4,000 more injured seriously enough to require hospitalization. And many of those electrocutions started as a “little shock” that became deadly.
First, let’s define the word “electrocution”. It actually means death by electricity. So if you’re reading this now, you were NOT electrocuted by your guitar last night. You could have been seriously shocked or even knocked unconscious, but to qualify as being electrocuted you have to be dead. The press uses this word way too loosely and I’m correcting them all the time.
To see something REALLY interesting, here’s a video where I created a hot-mic condition ON PURPOSE. http://livesoundadvice.com/noshockzone/live-sound-byte-hot-chassis-testing/ Yes, I regularly do these type of experiments to find better ways to measure dangerous electrical conditions and learn how to fix them.
It only takes about 20 mA of electrical current (20/1000 of an amp) to cause your hands to clamp down and not be able to let go of an energized wire or microphone. And 30 mA of current (30/1000 of an amp) for a few seconds can cause your heart to go into fibrillation. So just 30 volts AC with 30 mA of current can kill you if your hands and feet are wet. That’s only about 1 watt, less than the power of a small nightlight bulb.
Any amplifier chassis or microphone with a significant voltage above earth potential (2 or 3 volts max) is proof that you’ve lost your gear’s safety ground connection. Now, by itself an open ground connection won’t cause a a guitar amp or PA system to develop a hot-chassis voltage condition, but nearly all sound gear has some line leakage current to the chassis-ground. And that leakage is additive between all the pieces of gear plugged into your sound system. This normal high-impedance/low-current leakage will show up as a hot-chassis voltage of varying degrees, typically around 1/2 of the line potential (60 volts). The really dangerous thing is that sometimes these “little” 60-volt shocks can be caused by high-impedance leakage currents that aren’t particularly dangerous. And that’s when you feel a “little” shock. However, that same “little” shock can quickly become low-impedance/high-current leakage in a heartbeat, and that will almost certainly kill you if you touch the your guitar and mic with wet hands and lips. It’s just a matter of degree, and you never know what that degree is. So any feeling of shocks from your guitar or microphone is a warning to figure out the source or the problem immediately.
If you do have a proper electrical safety ground back to the service panel, then it should be impossible to develop more than 1 or 2 volts on your amplifier chassis or microphone. It will harmlessly drain away the small currents from normal high-impedance gear leakage, as well as trip the circuit breaker form huge currents that result from abnormal low-impedance leakage, such as a wire with insulation worn through hanging on a chassis.
So if you measure more than 2 volts between the earth and the chassis of your amplifier there’s a serious problem with your safety ground. This is usually as simple as a broken or loose ground contact on your extension cord or spider, but can also be due to a problem in your main power distro or wall power outlet. Old bars are especially dangerous since they can be ungrounded for years without you knowing it, and the first time you plug an guitar into a broken outlet there can be a deadly hot-chassis condition. And certainly any worn house outlets can have corrosion or loose contacts, and that can cause a hot-chassis condition.
There’s one other really dangerous mis-wiring condition that I’ve seen at dozens of garages and concert stages around the country. It’s something I call an RPBG (Reverse Polarity Bootleg Ground). This can happen when a DIY guy or old electrician tries to add a grounded outlet to a pre 1970’s non-grounded electrical system by simply putting a jumper wire between the ground and neutral screws on the back of the outlet. This is called a Bootleg Ground since it’s not accepted as code. While not immediately dangerous, if the black and white wires are accidentally reversed on a Bootleg Grounded outlet, then the hot wire is sitting at zero volts and the ground and neutral wires are at 120 volts. Note this is not the same thing as a simple “Reversed Polarity” outlet where the Hot and Neutral Wires are reversed, but the Ground Wire is connected properly. That condition alone will NOT cause a hot chassis condition if all other wiring is done correctly.
However, note that you can’t find an RPBG condition using a 3-light outlet tester and a voltmeter measuring between H-N, H-G and G-N will report the outlet as safe, when in fact it will electrify anything you plug into it that has a ground plug. And there’s no surge or voltage protector product on the market that will detect or disconnect your RV from a RPBG outlet. They will report that everything is fine with an RPBG outlet, when in fact your entire RV and connected tow vehicle has been hot-skin electrified to 120-volts. The simplest way to detect this dangerous condition is by using a Non Contact Voltage Tester as I demonstrate in the video above.
Read my complete article about RPBG outlets is at http://livesoundadvice.com/noshockzone/noshockzone-rpbg-dangers/
The bottom line is NEVER accept feeling a shock from any microphone or guitar. A shock is a warning that the next time somebody touches your instrument they could very well die from electrocution. I think it’s socially irresponsible to expose your band memebers to this potentially deadly situation, so get it repaired immediately. If you’re not 100% sure that you can measure and work around live electricity safely, then please contact an electrical technician immediately. The life you save could be your own, or that of a friend or family member.