> Date: Thu, 14 Nov 1996 09:24:00 -0500 > Subject: Electric Guitars and Electrocution > I saw the page you have on the Web about Musicians and > injuries... > > Have you ever heard of or have some information on Electric > Guitarists getting electrocuted during a show in which they > were plugged into a PA system which was either reverse grounded > or not grounded in respect to thier guitar / amplifier setup? > > I seem to remember reading something about it somewhere, like, > if you have a Les Paul or something you're more safe because > they don't ground the bridge to the player or something like > that. > > Do you have any information to clear this up? As an electronics technician, and a guitarist who spent plenty time on the high school prom/homecoming circuit, I can tell you that there's a very real problem with grounding. Ideally all sound equipment chassis/signal grounds should be the same, and should go to the third prong on the power, but often one encounters only two-wire power and then the problems arise. I've been "lit up" many times when touching my guitar and a mike when the grounding situation was wrong. A Les Paul _may_ (don't know for sure) be safer if the the bridge or tailpiece doesn't go to signal ground, because then you're not likely to be touching your amp's ground unless you contact the pickup shields (which are always grounded.) That's still not SAFE, in my view. Now, what usually happens is you touch a mike and ZAP, you bounce back, you lose track of the lyrics for a second, but then things are OK, no harm done. But this _is_ dangerous. Even in high school, we quickly developed a protocol: we bought an AC voltmeter, and after setting up our stage & plugging everything in we'd MEASURE for voltage between the mikes and instruments. Many amps have ground reversing switches, and we'd fool with these until we were all safe from zapping. The earlier practice was just to touch the mike & axe and see if it gave a shock; this gets old REAL FAST. If an amp has no grounding switch, then reversing the plug in the power outlet (in 2-prong situations) can do the same thing, BUT THE IDEAL IS FOR EVERYTHING TO HAVE 3 PRONGS PLUGGED INTO REAL 3-PIN GROUNDING OUTLETS. Again, I don't remember hearing of people getting killed, but it could happen. Voltmeters are cheap at Radio Shack. Get one! Date: Wed, 7 Oct 1998 10:23:48 -0500 (CDT) Subject: (fwd) Re: Anyone get shocked playing live? Newsgroups: alt.guitar,alt.guitar.amps,alt.guitar.effects,rec.music.makers.guitar,uk.music.guitar,rec.music.makers.guitar.acoustic Subject: Re: Anyone get shocked playing live? >Date: Mon, 5 Oct 1998 00:18:27 -0700 >Last night I played a gig and 3 songs in, my lips touched the mic and I got >a bad shock! It kinda of knocked my head back. Scared the shit out of >me!!! I don't know what caused it? Brand new shure beta58 and cord and my >amp has a 3 prong plug. The bar manager suggested it might just have been >static seeing as the stage is carpeted and was moving my feet a lot with >running shoes. S'pose that's possible. >Anyone have any idea why this would happen? You're lucky it knocked your head back; some guys stick and die. In 1980, just as I was finishing a customising book, which dealt mainly with electric guitar wiring, I came across a trick which reduces the voltage to the strings up the string earth in the event of an electrical difference between amps. Cut the string earth, and run it through a parallel .001mF capacitor with a 500 volt rating and 220k ohm resistor. We checked this out in the electronics dept. of the place I then worked and found it reduced the voltage of a (UK) 240 volt current passed through it to 40 volts, plus or minus depending on your body's resistance. It's not the whole cure though - it's really no more than a backstop. Radio is better, but it screws up the tone. A couple of years (? - can't find the files) after that I picked up a story about a young Scottish musician, one Donald Leckie, who was killed on stage (there've been quite a few deaths over here from this kind of problem) and followed it up for a UK music magazine. The inquest found that he had been on stage with his band when his bass player found his amp wasn't working properly. Without turning his amp off, the bass player handed his bass to our now dead young man, who took it with his left hand. He had his own guitar on, steadied by his right. At this point, the loose ground wire in the a.c. plug of the bass amp touched the live terminal, and current flowed from the bass amp to the properly grounded guitar amp straight across Donald's chest, killing him instantly. His mum, bless her, raised a sufficient fuss about it that it came to a lot of peoples' notice, and she hopes that the story might stop a few other needless young deaths from the same kind of accident. That's why I'm using his name here. During the research, I found that there had been a change to the Electricity At Work regulations here which extended them to cover people who were working *outside* factories. I got a copy of them from the Health and Safety Executive, and rang up my local Musicians' Union branch sec., and asked him if he'd heard of them. He hadn't. I read him the opening paragraphs of the regs. and asked him if he thought they applied to musicians working at gigs using electrical equipment. Quite clearly they did, and he agreed. The HSE at that point had only advised the miners' union and the transport and general union. Natch, he followed up and got a copy, and I assume the HSE spread it about a bit more widely. The basis of the regs. as they apply to us in the UK is that anyone working with equipment which uses mains (or heavier supplies-three phase etc..) to which equipment they handle is connected have a legal duty to see that the dangerous or lethal voltages in the power equipment do not reach the peripheral equipment (instruments) where low voltage small currents are in use (like the a.c. signal generated by a pick-up, for example). The area of responsibility is the area under the control of the people using the peripheral equipment; effectively from the mains socket to the mike and guitar, in the case of musicians. The best way we have of ensuring that unsafe levels of electricity don't reach the peripheral stuff, after checking the supply to them is safe, regular maintenance of plugs, power strips and so on, is to use an earth leakage circuit breaker. An ELCB is a device that trips and cuts power when, in this case, it detects a leak of less than 30 milli-amps in 30 milli-seconds. That 30/30 is reckoned to be a safe level. So there is actually a legal requirement on UK musicians to use these things - not in so many words, but as a part of taking all reasonable precautions to ensure that lethal or dangerous levels of electricity are avoided at the handled parts of the gear. If some idiot punter gets up to sing and gets a belt off the mike, the band is liable to prosecution for the said idiot punter's bit of involuntary electrical therapy. The band members are also liable to prosecution for an accident to one of their members due to their negligence. How it is in the USA I don't know - President Reagan cut the funding for your equivalent of our HSE to the point where it's pretty much ineffective, and I am old and scared enough to throw a wobbler about iffy gear anywhere I work. However, the technical bottom line for survival is the same - you run all your gear, after you've checked that every piece of a.c. sucking gear is grounded, from one ECLB, and if you get an unexpected problem, the whole lot goes off, and should stay off until you've traced the fault. If you have ground loops causing hum between different pieces of linked gear, you break the ground loop by lifting the shield on the signal side, *not* by lifting the ground on the power supply. I did my story for my mag.,and we covered the new HSE regs., and I hassled the editor of another mag. to do one (under their name so people wouldn't think it was just me being neurotic). They did a great job, gave away a bunch of free ELCBs and publicised the company that made them and how to get them. Sadly, it seems it takes regular tragedies to maintain regular awareness, and it's been a while since these stories, so I'll cross-post this to uk.music.guitar and rec.music.makers.guitar.acoustic (acoustic amps - an oxymoron but alive and sparking) - you might want to delete one or other if you're responding to something else in the thread. Oh, sure the voltage in the US is lower, but the electricians' adage is "It's the volts that jolts, but the mills (milliamps) that kills" Play safe eh? Date: Wed, 7 Oct 1998 10:24:00 -0500 (CDT) Subject: (fwd) Re: Anyone get shocked playing live? Subject: Re: Anyone get shocked playing live? Adrian Legg wrote: [some of Mr. Legg's good post snipped] > > The best way we have of ensuring that unsafe > levels of electricity don't reach the peripheral > stuff, after checking the supply to them is > safe, regular maintenance of plugs, power strips > and so on, is to use an earth leakage circuit > breaker. An ELCB is a device that trips and cuts > power when, in this case, it detects a leak of > less than 30 milli-amps in 30 milli-seconds. > That 30/30 is reckoned to be a safe level. > So there is actually a legal requirement on UK > musicians to use these things - not in so many > words, but as a part of taking all reasonable > precautions to ensure that lethal or dangerous > levels of electricity are avoided at the handled > parts of the gear. We have GFI or GFCI devices here in the US. Ground Fault Interrupter or Ground Fault Circuit Interrupter. Does the same thing. I install the in-wall type of these things, ones you would normally find in a domestic bathroom, into a junction box with a hefty, long, cord, and fasten the j-box to the inside, bottom or side, of a combo amp (wherever there is room). I plug the amp into the GFCI box and everything is probably a bit safer. The whole thing costs less than $20. Many years ago, I saw a singer, holding a mic in one hand, get stuck to a water fountain that she was operating with her free hand. She couldn't let go until someone had the presence of mind to pull the wall plug from the PA. Amazingly she was only severely shaken. -- Newsgroups: rec.music.makers.guitar.acoustic Subject: Re: Anyone get shocked playing live? I haven't seen one in a while, but y'all who perform a lot might look for one of those small screwdrivers that have a neon light (NOT an incandescent one!!!) inside the handle - you touch your finger to a metal ring on the end of the handle, and place the blade against the metal surface in question. If said surface is at about 65 VAC or higher, the neon light will glow. They have a 1 megohm (or higher) resistor in series so you won't get a shock and it'll let you detect a really nasty situation fairly quickly. Note that 24 VAC (or less!) at 60Hz can still be dangerous if your skin resistance gets low enough (like from sweaty hands). FWIW, I've measured my hand to hand resistance at as low as 200 ohms when I've been sweating profusely. At that resistance, a mere 12 VAC would be enough to drive 60 ma through the body! On the one occasion I was polygraphed, the poor guy giving me the test thought the galvanometer was broken because he couldn't get a good skin resistance reading; small wonder -- I was sweating like a pig at the time! Newsgroups: alt.guitar,alt.guitar.amps,rec.music.makers.guitar,uk.music.guitar,rec.music.makers.guitar.acoustic Subject: Re: Anyone get shocked playing live? >Safety should always be of paramount concern, and Adrian Legg's >excellent advice should be very helpful. > >Regarding electrical safety, what causes the "tingle" you sometimes >get from a mic on your lips when they brush against it? > The "tingle" is the your body's reaction to electrical current flowing. At higher levels, this current flow is called "electrocution". The fundamental cause of the current flow through you is a difference in electrical potential (voltage) between the "grounded" case of the microphone and whatever else you happen to be in contact with -- typically the "grounded" strings of an electric guitar. >What I'd like to know is, is it a sign that something potentially >harmful is present? > It could be. If the potential (voltage) of your "grounded" electric guitar strings is actually something significantly above earth ground there is a problem with your amplifier or the electical system to which it is connected. If the case of the microphone is not at ground potential, there's REALLY something wrong. It's not too unusual for a "vintage" tube amp to be floating a bit above ground -- this is not really a good thing, nor necessary, but it is a consequence of older design practice. You may be familiar with the two position "ground" switch on these old amps. This switch connects the chassis of the amp (where your guitar strings are "grounded") to either of the two main AC power leads (one of which is neutral) through a small capacitor. Things may have been done differently during the '60's in the UK, but this is the way it was done on black-face Fenders and similar amps. When the switch is in the right position and the capacitor is healthy, this works fine. If the cap short circuits (a typical failure mode) and the switch is in the wrong position, you have a lethal situation. Mr. Legg's recommendation to use an ELCB (or GFCI as we call them in the US) is excellent advice and an absolute MUST if you're using older equipment that has not been modified with a safer arrangement. >What could cause this at the PA end, or within the venue's electrical >system, and which is it more likely to be? > Even if you're using modern properly grounded equipment and the house is properly wired, it's still possible to get a shock if the PA is powered from a circuit that is "distant" electrically from the stage power. You can eliminate this as a possibility (and usually fix some ground loop problems) by running power for the mixing console from the stage. When I did this sort of thing for a living, we would carry a power distribution system along with all the rest of the PA gear because you could never trust the house power. Another possiblity is that the safety ground wire on the PA or stage outlets is miswired. If such a miswiring exists, the outlet will work fine, but the protection afforded by the safety wire won't be there when you need it. An inexpensive "wiring verifier" can detect this sort of problem. >I suppose that it's pretty obvious that I'm not well-versed in >electrical theory, so a simple explanation would be greatly >appreciated! > but it's to your credit that you're concerned _before_ someone gets hurt. Apologies for the long winded response. To sum up: 1. Power everything from a single source if possible. If not, make sure the sources are as close to the same ground potential as possible. 2. Check the wiring with a verifier plug or neon test light. 3. Seriously consider the installation of a fault current interrupting device (GFCI). 4. Have older equipment checked by a qualified technician before use. Newsgroups: alt.guitar,alt.guitar.amps,alt.guitar.effects,rec.music.makers.guitar,uk.music.guitar,rec.music.makers.guitar.acoustic Subject: Re: Anyone get shocked playing live? : Oh, sure the voltage in the US is lower, but the : electricians' adage is "It's the volts that : jolts, but the mills (milliamps) that kills" : Play safe eh? : Very true indeed. As an electrical engineering student, I was required to take a class in electrical safety prior to the EE lab courses. The professor who taught the course was a specialist in electrical safety, and the effects of electricity on the human body. He was a consultant to the state of Alabama regarding the botched electrocution (execution) a number of years ago. Anyway, it only takes 60 mA flowing through your diaphragm to stop your breathing. As the current gets higher, your heart can begin fibrilation; higher current can de-fibrilate it. Frequency can also change the effects of a shock. Obviously, extremely high voltage just destroys tissue. gets to kill people, mostly due to paralyzing the diaphragm. CPR is pretty effective since the diaphragm will regain itself given a few minutes to recover. Your body is a very non-linear resistor. At low current levels, you'll measure a few Meg ohms from hand to had, but at higher current levels it can fall below 1 K ohm. Since I=V/R, 120/1000 gives 120 mA, more than enough to shut off breathing if it goes the wrong way. To sustain the minimum dangerous current level of .06A, only 120/.06=2,000 ohms resistance could let it happen. So remember house current is lethal, and many victims can be saved if CPR is administered. Newsgroups: alt.guitar,alt.guitar.amps,alt.guitar.effects,rec.music.makers.guitar,uk.music.guitar,rec.music.makers.guitar.acoustic Subject: Re: Anyone get shocked playing live? wrote: Ref the shocks when playing live post. I play bass with a band, and we always take along a board I made up which has loads of strip sockets fed from a elcb ( current trip ). This protects the whole band from shocks. ( As I am also an electronics engineer, I know this stuff). I would advise all folks to equip themselves with this sort of set up. Even buy a plug in type, and put it in your gig bag. When you get to the venue, plug the elcb into the wall socket, and run your amp from that, and all other stuff like effects pedals etc. Hope that was useful Subject: (fwd) Re: Anyone get shocked playing live? I wish that Ground Fault Interrupters had been available back when I was on the high-school-prom/homecoming circuit, because playing in all sorts of aging school gymnasiums with dubious wiring, this was a constant problem. Early on we determined that quickly touching the guitar and mike to see if there was a "buzz" was a very uncomfortable way to determine if we had all our various amplifier/PA ground swapping switches set correctly to avoid shocks: somebody nipped over to Radio Shack and got a cheapo AC voltmeter, and regardless of whether we thought the grounds *OUGHT* to be safe, we *measured* between mikes and instruments and fiddled about until everything was RIGHT. The suggestion of running from a single power source, through a GFI is an excellent one. If this is not completely possible because you're drawing a ton of current and need to run from more than one circuit (very possible if you carry your own lights), try to keep all the audio and amps on the same, GFI-protected circuit, and fob off the power hogs like lighting onto a different circuit. Newsgroups: alt.guitar,alt.guitar.amps,alt.guitar.effects,rec.music.makers.guitar,uk.music.guitar,rec.music.makers.guitar.acoustic Subject: Re: Anyone get shocked playing live? >I see you're in the UK, look up >your local Health andSafety Executive office. >The town hall may be able to help you find them >if you can't find them in the phone book. Or you can goto http://www.open.gov.uk/hse/pubns/indg231.htm There you will find addresses and a pamphlet which will explain quite a bit( but not all) about electrical safety and accident prevention. Thanks Adrian for a really excellent article. Newsgroups: alt.guitar,alt.guitar.amps,rec.music.makers.guitar,uk.music.guitar,rec.music.makers.guitar.acoustic Subject: Re: Anyone get shocked playing live? Date: Wed, 7 Oct 1998 14:31:27 -0500 >Ok, whilst we're on the subject, I'll throw out another stupid >question: I have a VOM that I carry with me on every gig. What >would be the proper procedure for checking between mic & instrument, >or between mic & person? There are no stupid questions, only stupid answers, and I hope this isn't one of them! Ideally, everything exposed to a human being should be at earth ground potential, so the ideal way to measure would be to connect one lead to a known good earth ground and the other to everything that might conceivably be "hot" -- strings, mikes, amp racks, lighting trusses, etc. with a known good high impedance AC voltmeter. The difficulty with this is finding a "known good" ground -- to be absolutely sure, you'd need to drive an eight foot copper plated steel ground rod into moist earth to get one. Finding the time during a hectic stage setup can be a problem too. So, you start making compromises. An effective procedure would be to use the chassis of a modern guitar amp with a three wire plug which has been plugged into an outlet that you've already verified as your ground reference. Use one of the verifier plugs mentioned earlier in this thread for that, or you can check it with your meter if you can find a water pipe or a bit of metallic conduit nearby that you have a reasonable assurance is at ground. If you measure anything more than 15 volts AC between the amp chassis and anything else with an inexpensive analog meter, stop and correct the problem. I choose 15 VAC as the safety limit because your body resistance can be as low as 1k (as Bob Alman described, particularly on a hot, sweaty night) and some electrical safety texts use 20 milliamps as the value for the onset of defibrillation. If your cheapo meter is reading 30% low, you're still safe if the reading is 15 VAC.