How much/what electrical danger performing on a covered stage during rain?

Does anyone use 1:1 120v isolation transformers?

Doesn't folks plug EVERYTHING into a GFI? If the GFI is tripping, You Have a Problem -- fix it.

Clearly what's needed is fiber-connected mikes, both vocal and instrument...

Reply to
David Lesher
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The metal screen on an SM58 or SM57 is grounded. The guys that touch the mic with the guitar strings all learned that if your lips hit the mic grill, the whap that hits you in the face is like a big blue ball of lightning, followed by little fireflys floating around for a few more minutes while you get your senses back. It pretty much ruins the whole set for me. What causes it is the stage backline is plugged into a breaker box running off phase A, the lights are on phase B, and the sound is on phase C, and they are all drawing different currents, so the neutral is floating about 20V above ground because of the unbalanced load. I can test a 9V battery by licking it, but 20V is like a mule kick.

Reply to
BobG

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Shows that the push to elimanate DC was still on in 2005. I think it is still on going. The Steam pipe that exploded over the summer was a Con Ed supply for building uses. I have not heard of any efort to eliminat that service.

Reply to
Stephen B.

"BobG"

** That sounds like copping the full 120 AC on the lips.

** WTF has the neutral voltage got to do with it ?

Must be a VERY badly wired AC supply system for the safety ground on any circuit to be more than 1 volt compared from the ground on any other.

Needs to be condemned.

....... Phil

Reply to
Phil Allison

Sometimes the person is in contact with another current source and is killed by touching a grounded microphoe or instrument, so somone can die if the sysytem is properly installed. A GFI won't detect the current flow to earth from a different source.

There was a recent news story of a pastor dying while baptising someone. A lot of plumbing is now all PVC, so a bad heating element that is shorthed to its casing won't trip the breaker, or blow a fuse. The skin of a water heater is grounded, but the tank may not be.

The man was waist deep (or more) in the water when he picked up the grounded microphone, and couldn't let go.

Reply to
Michael A. Terrell

simply not true what causes it is a ground fault in the backline gear(99%) of the time and the other % would be other fauklt conditiopns there is nothing inherently unsafe in useing 3 phase power george

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Reply to
<tbmoas58

what i find more than I care ton is some yahoo removes the 2 slot edisons and replaces them with the grouded version , only there is no ground connected on the back

every outlet get tested before it gets used George

Reply to
<tbmoas58

like what? your cell phone? here in the USA wireless micsare in turmoil because the government is selling the bandwidth it exists on george

Reply to
<tbmoas58

In the uk the regulator (Ofcom) is preserving a chunk of UHF spectrum from the digital switchover for wireless mics.

d
Reply to
Don Pearce

Idiot. Live performers use wireless hooks EVERY DAY.

Reply to
ChairmanOfTheBored

you are so out of the loop no more debate can be had tell me about the last time you set up 35 wireless mics for a show I have

oh and while you at it can you name the protocol that will/is replaceing uhf /vhf as a transmission mode? put up or shut up jerk

Reply to
<tbmoas58

Please note the word "EVERYTHING" above. Not some of the amps, one of the mixers... everything on stage running from one GFI or another... [Except the drummer, of course, who's likely running on crank, but at least he's not a current source...]

Reply to
David Lesher

What do you think about Audio Technica's SpectraPulse?

Reply to
Romeo Rondeau

What causes it is the stage backline is plugged into

I have not seen a show hooked up this way with a single 3 phase hook up we put the sound INCLUDING stage and back line on 1 leg and lights on the other two bigger venues have several 3 phase disconnects generall sound will take the smaller(200 amp or so) and lights will take the larger(4-600 amps) but still the backline is IME always on the same leg(s) as the sound george

Reply to
<tbmoas58

"Michael A. Terrell" wrote in message news: snipped-for-privacy@earthlink.net...

That is why I said earlier to touch the mic with the back of your hand before grabbing or kissing it.

peace dawg

Reply to
Deputy Dumbya Dawg

Sometimes, but the NEC in the US limits what you can do as far as breaking safety grounds, when isolation transformers are in use. Normally folks use isolation transformers only as low-pass filters, really.

NEC says you have to use GFIs on most circuits outside, but not everyone does. Personally, although GFIs are prone to falsing in high RFI environments, I think they have saved more lives than they are given credit for.

Yes, but now you need to get power to the mike, as well, since the fibre can't carry it. There are plenty of systems with fibre links between the stage box and the console; you can see one at the National Gallery of Art in their sculpture garden system. Plenty of isolation, and you can run the skinny little fibre into an existing power conduit rather than having to pull a big snake. Of course you now have to set the console trims on the stage box which can be a pain without a big stage crew.

--scott

Reply to
Scott Dorsey

This is a sign you got a BIG problem, not just with an unbalanced load, but with poor neutral-ground bonding.

This is when it's time to walk offstage and cut your losses.

--scott

Reply to
Scott Dorsey

Right. The GFI dectects only an imbalance in neutral and hot currents on the device it's protecting.

This means that EVERYTHING on the stage area needs to be on a GFI, and that includes backline. If an amp is popping the GFI, you need to fix it.

Now, I know that outdoor festivals it's very common to defeat GFIs in order to deal with backline equipment that has ground fault issues. I don't have a real problem with this, IF the power system grounds are good enough and the crew is watching out.

Note that he was electrocuted by a circuit which BY LAW needs to be on a GFI, and has been for more than a decade now.

See, in a perfect world, there are no electrical leakage issues. But the ground is there to protect you when things go wrong. And the GFI is there to protect you when the ground goes wrong. It's a belt-and-suspenders thing.

Maybe you'll never need the ground to be there. Probably you'll never need the GFI. But if you SHOULD need it, you'll be really glad you have it.

--scott

Reply to
Scott Dorsey

In a perfect world, all exposed metal should be tied to a non current-carrying grounding buss. Then the neutral can float wherever it wants.

I've worked on a few old time guitar amps. IIRC, some Fender amps included a 'hum' switch that coupled the amp chassis to one side or the other of the line. I forget the value of the cap., but if anyone recalls, it would be interesting to see what sort of currents might pass from the hot side of the line, through the cap., a human body (Mick Jagger's tongue?), and another similar cap. in a second amp to the neutral side.

Perhaps this is why all the British bands came over to the USA. 110V is more survivable than 220V. ;-)

Reply to
Paul Hovnanian P.E.

Starting in the 60's I've enjoyed playing guitar and singing in various garage bands. Nothing serious, loads of fun and we even made a bit of money at it. I know this situation well: playing guitar with the fingers of your left (fretting) hand wrapped around the neck and strings and leaning into the mike to belt out the chorus...Suddenly your lips brush against the metal wind screen of the mike and you feel the jolt which hasn't killed you but now tells you that this is going to be one of those "electrical evenings" with one more thing to worry about other than harmonies, lyrics and timing!

Over the decades, I've noticed this phenomenon becoming much less frequent and today it's virtually a non-issue. This of course is due to the fact that nowadays everything is grounded. Even vintage gear can be made safe such that no performer or tech should be in the position of becoming the return path for two conductors that are at significantly different potentials.

But what was the cause of this event? It was actually fairly common. Every musician who played amplified instrument in the 60's and 70's experienced it and very few of the amplifiers involved were actually faulty.

I refer you to the schematic of a Fender Bassman model AA864

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This model is an example of the type of amplifier used in the 60's for everything from bass to organ to guitar and yes, vocals. It was common practice (although not ideal) to run all instruments and mikes off 2 to 4 instrument amplifiers all of which had non-grounded and non- polarized power plugs. Even when you graduated to a real PA system the amplifier's design looked basically the same. Note the primary (mains) circuit of the power supply. No earth ground, no polarization for the plug or accessory socket.

Note the .047mfd 600 vdc cap attached to the "ground switch". This allowed you to switch the chassis ground through the capacitor to either the hot or neutral side of the mains. Other amplifiers lacked the switch but still had a cap of similar value hard wired to one side of the mains. In practice, you flipped the switch or unplugged and reversed the "polarity" of the the power cord to the position which gave you the least hum. It is ironic that the "least hum" position was sometimes the one where the cap was connected to the hot side. For this reason or simply because the band couldn't care less about a bit of hum during the quiet passages their was a good chance that one or more chassis ground was actually connected through a cap to the hot side.

Now the reactance of a .047 ufd capacitor at 60 Hz is 56.4 Kohm. If shunted across 117 vac the resulting "leakage current" is 2.074 ma definitely enough to feel as a shock but probably not enough to kill you unless you had other medical issues. In fact it would not trip most GFCIs. Unless you had very sweaty hands and very moist lips, the actual current flowing from one "hot" amp through your body to another "cold" amp would be considerably less especially when the second series connected cap is taken into account. This is probably why most of the aforementioned musicians of the 60's are still alive though perhaps a bit impaired.

So what was the problem? Well consider what the consumer-grade capacitors of that area were made of. Was it mylar or polypropylene or polystyrene? Did Jimi Hendrix use a capo onstage? Well the typical cap of that value and voltage rating was a paper/foil/wax device. If you've ever taken one of these apart (which is easily done), you'll appreciate how low-tech they were and how flimsy was the paper barrier which could short reducing the reactance to ZERO. If you were unlucky enough to be standing on wet ground or lying in a bathtub or brushed up against a genuinely grounded PA system you could be in for a really bad day!

Fortunately what I've described above was a rare event but I sure am happy to use properly grounded gear so that I can concentrate on harmonies, lyrics and timing!

David

Reply to
PopMed

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