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Well, yeah, again, electric shocks from mics !!

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Re: Well, yeah, again, electric shocks from mics !!

Postby Gary_W » Tue Jun 19, 2012 12:20 pm

Thanks again, Hugh :)

With regard to RCD's, it's all very well protecting my equipment (and I'll ensure I do so) but this still won't protect me from a dodgy mixer (for example) that has been brought and set up by someone else will it? As my guitar is well grounded, if my RCD detects current to earth it'll trip out MY RCD. As the offending live part is the microphone here which is coming from a mixer I'm not better off as that will keep going and passing me the juice!!

It's one of those situations where it's a very necessary conversation for a guitar player / bassist as you have both hands on a perfect earth connection. As such, you are at the mercy of other folks equipment / venue wiring more than most band members. You are in the position of being worse off if your kit IS perfectly grounded if someone else's is not!

I think I need a chat....
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Re: Well, yeah, again, electric shocks from mics !!

Postby Sheriton » Tue Jun 19, 2012 1:07 pm

Gary_W wrote:As my guitar is well grounded, if my RCD detects current to earth it'll trip out MY RCD.

Note quite. Your RCD will only trip if it detects an imbalance between the live and neutral currents flowing through your own kit; it doesn't measure current flowing through the earth connection. So it won't trip if you're getting zapped by someone else's faulty kit. On the plus side, that does give you an indication of where the stray current is coming from - if your RCD hasn't tripped, it's probably not coming from your mains supply.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Hugh Robjohns » Tue Jun 19, 2012 2:36 pm

You're right -- if the PA system is live and grounding via your system your RCD won't help because it won't interrupt the ground -- but it might still trip if it senses an imbalance of current on the supply.

If you have any doubts about the PA system, look for the PAT stickers -- ask to see the PAT records. Check if they are running their gear through RCDs... and if in doubt, be careful not to touch anything metallic!

And if you do detect anything that you're not happy about, make sure you get those responsible for the kit to investigate properly.

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Re: Well, yeah, again, electric shocks from mics !!

Postby Gary_W » Wed Jun 20, 2012 6:33 am

Thank you both - eBay socket tester is in the post and I will be multimetering the rest of the bands extension leads. Also going to take my DMV to the next venue so as, if anything daft DOES happen I can get a bit more buy-in from everyone..... If it says there is voltage it then makes it a lot more believable vs folks thinking I'm wearing nylon ;)
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Re: Well, yeah, again, electric shocks from mics !!

Postby Jorge » Wed Jun 20, 2012 7:45 am

I don't know how common this is, either in the US or UK, but the subject of Reverse Polarity Bootleg Ground wiring in venues has been discussed on another forum. RPBG is one possible explanation for electric shocks from mics, and could potentially lead to fatal shocks.

I know nothing about electrical wiring in the UK, but for US 120 v three conductor circuits, a Bootleg Ground is when, if no true ground is available, the outlet neutral is connected to the outlet ground. This in itself is not usually a problem. Occasionally, however, on top of the Bootleg Ground miswiring, the building neutral is mistakenly switched with the building hot (Reverse Polarity). When what is thought to be the building hot and neutral leads are then connected to the outlet hot and neutral leads, respectively, what actually occurs is that the building hot is connected to the outlet neutral and the outlet ground (RPBG). This, unlike simple Reverse Polarity, or a simple Bootleg Ground, can cause the case and ground of devices (eg, mixer chassis, mic, guitar strings) to be at live potential. Not a problem until a person touches both that and an actual ground. Then (and this would happen commonly) the person will get a shock, potentially at high voltage.
The problem is that your simple outlet ground tester will find most faults but completely misses the RPBG configuration. You need in addition a noncontact tester that will identify a hot wire without actual metal to metal contact or access to a true ground. Here is a video that explains a simple procedure to find RPBG wiring. A noncontact tester could also find a high voltage (>90 volts) hot chassis, guitar strings, mic cable or mic.

http://www.youtube.com/watch?v=iLk-6pvSlWg&feature=plcp
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Re: Well, yeah, again, electric shocks from mics !!

Postby Hugh Robjohns » Wed Jun 20, 2012 8:39 am

Jorge wrote:I don't know how common this is, either in the US or UK, but the subject of Reverse Polarity Bootleg Ground wiring in venues has been discussed on another forum.

It's a very scary bodge, but thankfully not likely to happen in the UK. I have heard of similar situations in other countries though!

The reason it is so prevalent in the US is because a lot of buildings are fed with what is, in effect, a balanced 230V mains feed with a centre neutral. Some sockets are then run from one side and centre neutral (giving the 115V supply), while other sockets are run from the other side and neutral. Devices that require a lot of power -- like washing machines and so on -- are often powered from the 240V supply directly.

The centre neutral is normally bonded to earth at some point to make the 115V supplies 'unbalanced' in the conventional way, and hence some electricians have been known to indulge in the lazy practice of using the neutral as a makeshift earth rather than run a proper earth cable to the mains sockets.

However, if things then get confused elsewhere in the building it is possible for the live and neutral wiring to end up being reversed, potentially resulting in equipment cases becoming live relative to a genuine earth (like the water pipes and CH radiators!).

In the UK, because we only have a 240V supply in domestic buildings, and because the IEE wiring regulations are so strict, we can't suffer the RPBG syndrome you describe for the US. It could potentially happen in buildings with 3-phase supplies, but again, the wiring regulations are so strict that it just won't happen.

The problem is that your simple outlet ground tester will find most faults but completely misses the RPBG configuration. You need in addition a noncontact tester that will identify a hot wire without actual metal to metal contact or access to a true ground.

Yes... it would be a bit of a worry! For all it's faults, there are many good things about living in the UK! ;)

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Re: Well, yeah, again, electric shocks from mics !!

Postby Dave Gate » Wed Jun 20, 2012 9:32 am

Many years ago, before the UK switched to the European standard for three phase colour coding (green for Earth, blue for neutral and brown/black/grey for the three lives) I was working on a show in what had been a reasonably famous venue (no names) where the three phase mains had to be tailed in by an electrician. Who attached the blue live phase cable to the neutral, and the black neutral cable to the live phase that should have had the blue cable.

Oh that was fun when the power went on
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Re: Well, yeah, again, electric shocks from mics !!

Postby Jorge » Wed Jun 20, 2012 2:17 pm

Thank you Hugh for that crystal clear explanation. Yes there are some downsides to the anti-regulatory ideology and/or poor enforcement of regulations that have become so prevalent in the US. The good news is no one I know has ever been electrocuted by an RPBG wiring configuration or anything else. Just to be safe, however, I have just ordered a noncontact tester and will add that to my wall outlet testing routine in the venues we play.
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Re: Well, yeah, again, electric shocks from mics !!

Postby seablade » Wed Jun 20, 2012 2:19 pm

Dave Gate wrote:Many years ago, before the UK switched to the European standard for three phase colour coding (green for Earth, blue for neutral and brown/black/grey for the three lives) I was working on a show in what had been a reasonably famous venue (no names) where the three phase mains had to be tailed in by an electrician. Who attached the blue live phase cable to the neutral, and the black neutral cable to the live phase that should have had the blue cable.

Oh that was fun when the power went on

Remind me never to touch UK/EU power. In the US the standard is Green = Ground, White = Neutral, and Red, Blue, Black for the three phases. Would be way to confusing.

I can't think of any place I have ever run across with hot swapped to ground and neutral on the hot for the record, scary thoughts there that that can even exist.

Hugh is correct on the basic wiring for most houses in the US (Commercial buildings tend to have true 3-phase though). But even in houses a fairly standard coloring is used, where there is not usually differentiation between phases, but rather the hot is usually black with neutral white and green ground. For 220v in the US Red and Black are usually hot and White is still Neutral with Green for Ground.

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Re: Well, yeah, again, electric shocks from mics !!

Postby Dave Gate » Wed Jun 20, 2012 3:24 pm

It used to be very confusing here, which is where the offending electrician went wrong. Three phase mains had Earth = green, Neutral = black, Red/Blue/Yellow = 3 x live; but single phase had Earth = green & yellow, Neutral = blue, Live = brown.

This is one area where we can wholeheartedly thank the EU for imposing a standardisation . . .
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Re: Well, yeah, again, electric shocks from mics !!

Postby Hugh Robjohns » Thu Jun 21, 2012 9:21 am

Three phase power isn't something I get to play with these days, but when I did it was red, blue, and yellow and I think if I was presented with brown, black, gey cables today I'd be scratching my head with them!

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Re: Well, yeah, again, electric shocks from mics !!

Postby Dave Gate » Thu Jun 21, 2012 9:47 am

I was there at the changeover, and had to get my venue's old Red/Blue/Yellow Camlock outlets and cables converted to Brown/Black/Grey Powerloks. But the new colours make more sense, as the earth, neutral and first live phase are in line with what you'd find in a single phase UK mains plug.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Hugh Robjohns » Thu Jun 21, 2012 11:08 am

I agree it makes sense in the wider construct -- but red, blue and yellow, all being bright colours, shouted 'live' to me. Brown black and grey are all pretty earthly colours....

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Re: Well, yeah, again, electric shocks from mics !!

Postby Dave Gate » Thu Jun 21, 2012 11:13 am

That sounds like the old UK wiring system (before my time!) where red was live and black was neutral (can't remember what earth was). You still find that in domestic wiring behind the sockets and switches, with the earth usually being an unshielded core (which most sensible people slip a green and yellow sheath over!). If you've ever changed a socket or a lightswitch you'll know what I mean.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Raphbass » Wed Jul 11, 2012 10:58 am

On a gig last Saturday, the guitarist plugged into a different socket to the rest of us - there was what felt like a good 100+ voltsAC between his strings and his mic that was going into the PA. When he first mentioned it I thought he meant the common little static "zap" you sometimes get - I didn't realize till I myself touched his strings and the mic at the same time that it was a serious buzz - I remember from messing about with transformers as a kid what 120V AC feels like, this was similar.

I got him to plug into a plugboard on the same wall socket as the rest of us and the problem was solved. Not sure whether I should have informed the venue that there was an issue between two earths in different sockets in the same room - or is this normal?

I assume that for example if they plug in two brass standard lamps or similar, one on each wall socket, that the guy holding both would be getting a good dose of current and if the two lamps came into contact there would be a shower of sparks between them.

I've always assumed that earth is earth is earth - I don't quite get how two earths can be so many volts apart, unless something's gone terribly wrong with the building's wiring. This is a posh modern hotel by the way, not a crumbling third-world establishment (and I've seen a few!).
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Re: Well, yeah, again, electric shocks from mics !!

Postby Raphbass » Wed Jul 11, 2012 11:08 am

PS - re colours - yes, brown seems to me the most earthly of all colours, how that got to be "live" totally beats me. And given that a common symptom of colour blindness is to confuse green and brown it seems mental to have the two close together in a mains plug. What was wrong with red for live?
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Re: Well, yeah, again, electric shocks from mics !!

Postby seablade » Wed Jul 11, 2012 11:18 am

Raphbass wrote:On a gig last Saturday, the guitarist plugged into a different socket to the rest of us - there was what felt like a good 100+ voltsAC between his strings and his mic that was going into the PA. When he first mentioned it I thought he meant the common little static "zap" you sometimes get - I didn't realize till I myself touched his strings and the mic at the same time that it was a serious buzz - I remember from messing about with transformers as a kid what 120V AC feels like, this was similar.

If it was a true shock from incorrect grounding that indicates two things. First that the socket ground was a much higher impedance than it should be(Bad connection) or missing(No connection). And that there was likely a fault inside of the guitar amp that needs to be checked out.


I got him to plug into a plugboard on the same wall socket as the rest of us and the problem was solved. Not sure whether I should have informed the venue that there was an issue between two earths in different sockets in the same room - or is this normal?

Yes they need to be informed.


I assume that for example if they plug in two brass standard lamps or similar, one on each wall socket, that the guy holding both would be getting a good dose of current and if the two lamps came into contact there would be a shower of sparks between them.

Not unless there was some VERY bad wiring in the venue, or there is a fault in the lamp attached to the socket with the bad ground.

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Re: Well, yeah, again, electric shocks from mics !!

Postby Dave Gate » Wed Jul 11, 2012 12:08 pm

Raphbass wrote:PS - re colours - yes, brown seems to me the most earthly of all colours, how that got to be "live" totally beats me. And given that a common symptom of colour blindness is to confuse green and brown it seems mental to have the two close together in a mains plug. What was wrong with red for live?

For domestic use it's supposed to be green and yellow striped. So, for colour-blind people you have a dark colour, a light colour and stripes. Not sure how effective it is, though.
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Re: Well, yeah, again, electric shocks from mics !!

Postby dmills » Wed Jul 11, 2012 10:30 pm

Red/Green/Black was replaced for flexible cables many years ago precisely because of the problem of red/green colour blindness (Back when appliances commonly came without plugs), a red/green reverse in the plug would leave the case live, and this was in the days before RCDs!

This left us with the interestingly odd situation in that single phase flexible cables were brown/blue/green-yellow, three phase flexible cables were usually brown/black/grey with a blue neutral and the usual striped earth (EU standard).
Fixed installation wiring however was usually red/black/green-yellow for single phase or red/blue/green-yellow/black(neutral) for three phase (Note that blue means different things depending on whether the wiring is a flex(Neutral) or installation(Phase)). Note also that a single phase circuit fed from any phase was usually red/black.....

Anyway all this got harmonised across Europe with the new scheme being brown/blue for single phase circuits, black/brown/grey + blue neutral for three phase, this is the same for both fixed install wiring and flexible circuits. It caused some few problems (and a very few expensive mistakes) when first introduced, but the fact that in a modern install blue has only one possible meaning (neutral) is on aggregate a net win.

The only striped wire in common use for mains voltage is the green/yellow one that is only ever used for earth connections and is two colours precisely so that no matter what colour vision problems you have it is obvious.

That concludes a short history of UK wiring.

Regards, Dan.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Raphbass » Mon Jul 16, 2012 5:28 pm

seablade wrote:
Raphbass wrote:On a gig last Saturday, the guitarist plugged into a different socket to the rest of us - there was what felt like a good 100+ voltsAC between his strings and his mic that was going into the PA. When he first mentioned it I thought he meant the common little static "zap" you sometimes get - I didn't realize till I myself touched his strings and the mic at the same time that it was a serious buzz - I remember from messing about with transformers as a kid what 120V AC feels like, this was similar.


If it was a true shock from incorrect grounding that indicates two things. First that the socket ground was a much higher impedance than it should be(Bad connection) or missing(No connection). And that there was likely a fault inside of the guitar amp that needs to be checked out.


I got him to plug into a plugboard on the same wall socket as the rest of us and the problem was solved. Not sure whether I should have informed the venue that there was an issue between two earths in different sockets in the same room - or is this normal?


Yes they need to be informed.


I assume that for example if they plug in two brass standard lamps or similar, one on each wall socket, that the guy holding both would be getting a good dose of current and if the two lamps came into contact there would be a shower of sparks between them.


Not unless there was some VERY bad wiring in the venue, or there is a fault in the lamp attached to the socket with the bad ground.

Seablade


Well yes there was a comedy moment as I looked at his 20yr-old Fender amp and he sort of took umbrage and said with a dry hint of confrontation "never had a problem before", and he then looked just as implicatingly (if that's a word!) at my mixer which is less than a year old, and PAT tested fairly recently... and there we stood for a few seconds in a stalemate. [Cue soundtrack to "the Good the Bad and the Ugly"]

In retrospect, I feel pretty pathetic that it didn't occur to me to get out the mains tester I have in my kit.

If there's a fault in the mains of one of the circuits, couldn't it render the earth live even without a fault in the gear? Haven't thought it through (and unlikely to bother!) but it seems it can't be a simple reversal of live and neutral as the amp was working fine, and the rogue voltage was a lot less than mains (about half I reckon).

Anyway I've emailed the venue to suggest they should check what's going on in their mains sockets.
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