electric shock

[Audiopile]

 

on to checking out amps etc.

 

I'm curious what the methodology was concerning "The venue power outlet/socket was ok tested."

 

I ask, because in my experience, the common problems with venue outlets are:

 

1) The outlet is physically damaged or severely worn. Oftentimes venue outlets are "the cheapest available at a local hardware store", and that's when they were new. Commodity grade outlets typically aren't cycled (plugged into and unplugged from) all that often... I'd suspect stage outlets could easily see thousands of times the cycles of the average household outlet. And oftentimes "band gear" male cord ends are tweaked, which can tweak the contacts inside the outlet. And stage outlets are likely much more susceptible to physical abuse. And oftentimes stage outlets are passing fairly high current... and that stage outlet might be a 15A rated outlet on a 20A circuit. Point is: Stage outlets can be "pretty sloppy" and unreliable but still "test ok".

 

2) Mis-wired. It's very common for outlets to have the neutral and load conductors swapped... seemingly especially so if the venue has a handyman who's changed/replaced outlets. I believe the reason for this is that commonly the neutral conductor's insulation is white and the load's conductor is black... many equate white with "positive" and black with "negative", and equate the "neutral" as "ground"... and equate that with "negative"... so they attach the black/load conductor to the neutral lug of the outlet, and connect the white/neutral conductor to what they consider to be the "positive"/ load lug of the outlet. This type of mis-wiring can easily be tested for and identified with a multi-meter or cheap outlet tester.

 

3) Intentionally falsely wired with the ground bonded to the neutral at the outlet (bootlegged). This is common where ungrounded outlets were replaced with grounded outlets. Be suspicious of this condition in older buildings where the outlets were built into a wall or similar and/or the wiring is likely not in conduit.... because: If there wasn't a ground conductor installed with the circuit originally, pulling a ground to the outlet may be very difficult (expensive) when the outlet was changed out from ungrounded to grounded. This condition is difficult to test for... a cheap outlet tester will be useless in identifying this condition.

 

4) Dysfunctional ground circuit due to carrying the ground on the conduit and one or many of the conduit joints are compromised.

 

5) Intermittent connections: This condition can be common especially where aluminum wiring was used and the lugs in the breaker box or outlets haven't been retightened for awhile or never retightened.

 

6) Two circuits sharing a neutral, and one of those circuits is heavily loaded... or intermittently loaded heavily.

 

My experience over the decades is that it's common for stage outlets to be "pretty iffy" or worse, and it's pretty rare that they are "a-ok, fine". 100% of the time when I've brought it to the attention of venue management that I've identified an outlet (or many outlets) as "bad"... they say: "Bands play here all the time and they never have a problem." I can sight stage outlets that I personally know have been bad messed up for over 40 years and absolutely nothing has ever been done about it... and yes: bands play in those venues "all the time" and plug into those bad outlets "all the time"... and have problems "all the time"... and I guess that's just the way it is... to the point where I absolutely don't "plug in" and my band mates don't plug in until I've personally tested the outlets and the outlets check-out as unquestionably good. And it's common that I have to string a couple hundred feet of AC extension cable to hit two good circuit outlets in a venue.

 

And: I have purchased brand new extension cords and IEC320 power cords that were mis-wired. It's not all that common that I find a mis-wired factory built extension cable or power cord, but because it "can happen", I test every new cable I get before I put it into service.

[mkfs9]

I did actually retest the cables at home before getting rid,and they still showed faulty.

[WRGKMC]

The problem usually occurs when you have the PA and Guitar amps on different outlets.

The length of the ground back to the Breaker panel can have different lengths of wire in the walls of the building.

This in turn makes the ground resistance back to the box different for each outlet.

The result is you have a difference in potential between one ground vs the other and therefore you can have

current flow from one ground to the other.

 

If you're doing sound, and the outlet situation looks lame, beat up or otherwise, You should carry a Volt Ohm Meter.

They can be bought for less than $10. Once everything is plugged up you can simply check the AC voltage between

the shield of the guitar cords and the shield of the mic XLR cable. If you have a voltage you have a ground loop you have to fix.

If it reads less than a Volt you are in good shape.

 

You can do this between outlets too if they are close enough for your leads to reach.

If there's no voltage between outlet grounds and there is between the mic and guitar cable sleeves,

then you have an issue with the head or PA mixer chassis and outlet grounds that need to be addressed.

[agedhorse]

If there is a difference of more than a few volts between grounds, it means there is a defect in the ground. Ground loops are entirely different and do not apply to anything being discussed. They just confuse the subject at hand. Receiving a shock has absolutely nothing to do with the guitar amp being on a different outlet from the PA. In the touring world we don't have this problem even though we may have 50 or more circuits in a system, but we also don't often have miswired circuits. Is the op talking about 120 or 240v power?

[Craig Vecchione]

If there is a difference of more than a few volts between grounds' date=' it means there is a defect in the ground. Ground loops are entirely different and do not apply to anything being discussed. They just confuse the subject at hand. Receiving a shock has absolutely nothing to do with the guitar amp being on a different outlet from the PA. In the touring world we don't have this problem even though we may have 50 or more circuits in a system, but we also don't often have miswired circuits. [b']Is the op talking about 120 or 240v power?[/b]

 

I'm glad you asked. I just checked his profile, and he's likely talking about 250v 50hz. He's in the UK.

 

There's a slight difference in wiring practice in the UK (vs. the US) in that it's common to use a "ring" circuit design, where current carrying and grounding conductors encircle a room. There is automatically a ground loop due to the wiring redundancy. Kinda proves that mains ground loops don't have to automatically result in noisy audio gear.

[Craig Vecchione]

I should add and emphasize that the higher voltage of UK mains greatly increases the danger imposed by shocks.

 

And for mkfs9, where I mentioned GFCI's (ground fault circuit interrupter) previously, refer to RCD's (residual current devices) in the UK.

[mkfs9]

Yes we are uk based. The two guitarist were on the same Dual wall outlet/socket. Bass player need to get power to his position,hence the need to extend cables. Other guitarist was in affected.. And yes the ring main is a common wiring method and can cause hums ect sometimes but not often at all.

[RoadRanger]

I should add and emphasize that the higher voltage of UK mains greatly increases the danger imposed by shocks.

Even our 240v circuits are only 120v to ground on either leg - theirs is a full 240v to ground .

 

[Iamthesky]

I absolutely don't "plug in" and my band mates don't plug in until I've personally tested the outlets and the outlets check-out as unquestionably good.

This is something that's always concerned me but I don't know how to test it.

 

What procedure/tools do you use to perform these checks?

 

[agedhorse]

At 240 volts, leakage current is automaticaklly doubled regardless of anything else that may be happening. This makes fault thresholds 1/2 that of the 120 volt market.

[Audiopile]

This is something that's always concerned me but I don't know how to test it.

 

What procedure/tools do you use to perform these checks?

The cheap plug-in testers are a heck of a lot better than nothing:

 

http://www.ebay.com/itm/New-Electric...item3cd748bb4d

 

They're cheap, small, lightweight, quick and easy to use, and will ferret out most messed up outlet situations.

 

Beyond that: I suggest to use your eyes and common sense: Don't plug into an outlet who's guts are hanging out of it's mouth, or you need to gaff tape your male cord end into the outlet to keep it from falling out.

 

Testing for bootlegged grounds is a little trickier. I use a multimeter with outlet probes and load one side of a duplux outlet with a 1K par can, then measure the voltage difference of the neutral and ground... there should be some difference... if there isn't, then it's almost assured the ground is bootlegged. Again: use your eyes and common sense... if there's 4 stage outlets built into a wall and much of the rest of the place looks like it should be equipped with tail fins... and 1 or more of the 4 outlets are two hole outlets, but the others are 3 hole outlets... be thinking: "I ain't buying it Scooter."

[mikekars]

Mike Sokol over on PSW has some really clear write ups on "Reverse Polarity Bootleg Ground" and how to test for that condition with an inexpensive non-contact probe. He has some well done youtube videos on the subject as well. Search up RPBG and Mike Sokol and you should get on the path.

[Craig Vecchione]

Mike Sokol over on PSW has some really clear write ups on "Reverse Polarity Bootleg Ground" and how to test for that condition with an inexpensive non-contact probe. He has some well done youtube videos on the subject as well. Search up RPBG and Mike Sokol and you should get on the path.

 

Just want to add a general safety comment on non-contact testers. Just as Ronald Reagan stated that the US should "trust but verify" the USSR (should apply today too!), never trust a non-contact testing device for any work that could risk life/safety. Basically that means any work that involves possible contact with live conductors, or work that verifies the final condition of a system. While non-contact devices have come a long way, they're still called "idiot sticks" in the trade. Always verify a circuit's condition with a contact device (that's also been verified as working immediately before the test) before touching anything or putting your work back into service.

[wesg]

Excellent thread! It's always nice to learn about possible electrical gotchas and best practices when walking into a hole-in-the-wall bar.

 

My big concerns always revolve around mixing "house" and generator power on temporary stages. I need house power for my organ, unless there is a real generator tech on site who can promize me a rock-steady 60Hz signal for the synchronous motor controlling the tone generator. I worry greatly about plugging equipment into two grounds inadvertently when setup like this, because I don't trust that the grounds are bonded together...meaning, I believe, that equipment could be the bonding point between two wildly different grounds. My solution is to mike the Leslie and only run the organ and Leslie from "House" power. I have been able to avoid singing on gigs like that, but may have to someday. This scares the hell out of me. What if my lips touch the mic ball (generator) while my hand touches the organ chassis (house).

 

Is this one of those situations where the organ chassis is better NOT earthed? (they were not earthed when they left the factory in the 60s)

 

Wes

[RoadRanger]

What if my lips touch the mic ball (generator) while my hand touches the organ chassis (house).

What if your foot touches the grounded metal staging? Either the grounding is right or it's wrong - guess you have to trust the power guys or learn how to meter it yourself.

[wesg]

Great, now you've given me something else to worry about.

 

FWIW - no, when I'm doing a benefit and the stage is a trailer and the sound company is a small local outfit with no staff electrician -- I don't really want to trust that the grounds are bonded correctly.

 

If the grounds are unbonded, will I be able to measure a potential difference between them? I know in ham radio land years ago it was possible to have hundreds of volts between grounds when they weren't bonded correctly. I'd rather not be the guy connecting them.

 

Wes

[Audiopile]

This scares the hell out of me. What if my lips touch the mic ball (generator) while my hand touches the organ chassis (house).

 

Is this one of those situations where the organ chassis is better NOT earthed? (they were not earthed when they left the factory in the 60s)

 

Wes

Wes: In my opinion it's really tough to make recommendations about this sort of stuff on an open forum.

 

I could suggest that wood and bakelite are fairly good insulators, and I could suggest that I'd find it doubtful that anyone would be mucking around with the chassis of a Hammond B3 while singing vocals, and I could suggest to source a Nord C2D or similar when running on a genset, and I could suggest to buy a decent multimeter and meter the voltage difference of the mic ball and anything you might touch when playing your keyboard rig... and I could suggest some other stuff... but I won't.

[agedhorse]

IIRC, in the B3, the chassis of the amp is bonded to the metal on the keyboard frame. This may present a problem if the chasis is not grounded and there is excessive leakage.

[Audiopile]

 

IIRC' date=' in the B3, the chassis of the amp is bonded to the metal on the keyboard frame. This may present a problem if the chasis is not grounded and there is excessive leakage.[/quote']

 

I could suggest: As I recall, the metal parts exposed to the B3 operator are the slidebar "sticks" and the Leslie speed control lever (that is factory equipped with a bakelite knob)... and the frame under the rubber coated volume pedal.

 

But I won't.

 

What do you think Andy?

[agedhorse]

I recall the Leslie backing box, the select switching backing box, the frame under the keys (all painted black IIRC). I also may be micing some of this up with C's and M's, I worked on all of them back in the day.

[Audiopile]

I recall the Leslie backing box' date=' the select switching backing box, the frame under the keys (all painted black IIRC). I also may be micing some of this up with C's and M's, I worked on all of them back in the day.[/quote']

As I recall, the Leslie select switch is a bakelite hunk with a metal prong sticking out with a bakelite knob.

[Audiopile]

 

I recall the Leslie backing box' date=' the select switching backing box, the frame under the keys (all painted black IIRC). I also may be micing some of this up with C's and M's, I worked on all of them back in the day.[/quote']

 

As I recall: The C's had the same guts as the B's. The C's were the cabinet version (or church version) where-as the B's were the spinit version. There were CV's and BV's as predecessors to the "B3's and C3's"... the 3's had the percussion thing happening... otherwise the guts of a BV or CV were identical to a B3 or C3.

[Craig Vecchione]

 

Great, now you've given me something else to worry about.

 

FWIW - no, when I'm doing a benefit and the stage is a trailer and the sound company is a small local outfit with no staff electrician -- I don't really want to trust that the grounds are bonded correctly.

 

If the grounds are unbonded, will I be able to measure a potential difference between them? I know in ham radio land years ago it was possible to have hundreds of volts between grounds when they weren't bonded correctly. I'd rather not be the guy connecting them.

 

Wes

 

Wes,the two general theories are that either *everything* is bonded and then grounded, or *everything* is bonded but not grounded. But as it's nearly impossible for an outdoor stage setup to be isolated from ground, the former is the way to go. If you want to check your setup at an event, a volt meter with long enough leads and clamp ends will allow you to check for voltage differences between conductive items, and between those items and whatever the ground pin out receptacles is attached to.

 

Using GFCI's will protect you from many, but not all, wiring and device faults. GFCI's do not need a grounded system in order to operate, and in fact are recommended for ungrounded home wiring. But a GFCI will protect faults that leak to someplace other than the neutral. A GFCI will NOT protect you from a direct phase to neutral shock. As this is fairly uncommon, GFCI's are still the preferred method of protection and are code-required for all outdoor circuits. You can purchase ready-made extension cords with GFCI built in.

[RoadRanger]

I'm pretty sure a GFCI on the house power to the B3/Leslie will not protect against the particular fault the OP is worried about - the generator's (and thereby PA mics') ground being "hot" relative to the B3/Leslie's ground.

[WRGKMC]

There is a mod guitarists can use to help prevent shocks.

Most guitars have the ground connection inside their guitars

hard wired to the strings so the human body acts as a ground to help shield the electronics inside

when the strings are touched.

 

One method of reducing the risk of shock is to insert a .1uf capacitor in series with the ground connection to the strings.

Since a cap in essence disconnects the strings from the ground there's no possibility of having high current flow through it.

The cap will still dampen the CA noise but since a cap is a voltage device there's not enough current there to hurt you.

 

This would only apply to the strings of course. The guitar cable, metal knobs, metal pickup covers may still be grounded,

but you'd be less likely to be touching those when you walk up to a mic and zap your lips.

 

One other note. Its not the voltage that kills its the sustained current that does.

A person can walk across a carpet and pick up 20,000 of static electricity and get a good zap when they discharge touching something grounded.

It doesn't kill them because there is very little current involved nor is the current sustained like it is from an AC source.

 

You also need a path of least resistance (a conductive path) For example, The hot side of an AC lead through your body to ground, standing barefoot in water

will kill you. Wearing tennis shoes standing on a rubber mat may not even give you a tickle because the path to ground is removed.

 

The path usually has to be across the heart as well. One arm to another, one arm to one foot can stop a heart. If you were insulated from

earth ground and placed the hot and cold leads from AC across a hand, only the hand gets zapped (in ideal conditions) Of course this could

damage the nerves of fry the hand but the current isn't passing across the heart itself so there's less chance on the heart being stopped.

 

Of course no shocks are pleasant. I been a tech for nearly 50 years and by rights I should glow in the dark with all the zaps I've had

in my career. The most sever was when I was 3 years old. My father had given me some keys to play with as a kid and I attempted to

try them out in an AC socket and got my butt kicked. Guess I had a fascination and respect for it ever since and its why I took it on

as a perfession.