Rehearsal room/stage electrical safety gear

[Beedster]

There's a current thread re some small shocks a singer is getting from a mic and it prompted me to think a bit more about safety. Although I think I'm careful around this stuff, I'm probably not as careful as I could/should be - especially looking at the state of sockets and cables in some venues - so I'm keen to know what devices folks use to reduce the chances of electricity going where we don't want it? 

[Franticsmurf]

If I don't know the venue, if I'm playing outside or if anything looks dodgy I use an RCD circuit breaker on my main power block. I went wireless years ago to give me some isolation from my backline. In my current band we have two working electricians, so they are always on the case regarding venue electrics.

[dudewheresmybass]

Part of the reason why I'm totally wireless. 

I've played enough venues with dodgy electrics to protect myself.

These days - fortunately - there seem to be less iffy venues (at least around the south east)

But I always carry an RCD as well JIC

[Burns-bass]

We always take plug testers to gigs after a dodgy connection.

 

Cost £15 or so and easy to stick in the gig box. 
 

https://www.screwfix.com/c/tools/socket-testers/cat7910008

[ossyrocks]

11 minutes ago, Burns-bass said:

We always take plug testers to gigs after a dodgy connection.

 

Cost £15 or so and easy to stick in the gig box. 
 

https://www.screwfix.com/c/tools/socket-testers/cat7910008

There's a socket tester in that link for £5.00. Is that the kind of thing you mean, if so, I'll get one?

 

[Burns-bass]

33 minutes ago, ossyrocks said:

There's a socket tester in that link for £5.00. Is that the kind of thing you mean, if so, I'll get one?

 

 

Yes, that's what I have. It provides a check of each plug and tells you if it's correctly wired and grounded or not. 

 

I'm no electrician (and the guys who put in the cabling also have an RCD) but I do it every venue I go to now to ensure me and my equipment will be OK.

 

One of the singers in my band got a shock one gig and we ended it early as we had no faith in the safety of the venue. After that, I didn't want to take any risks.

 

 

[casapete]

Think I’ve mentioned this before but when a venue asks to see any PAT certificates for your gear,

then you also have the right to see their up to date EIC (Electrical Installation Certificate).

If it’s a temporary event then the organiser should have evidence of the electrical supply 

completed to BS7909 standards. 

[42Hz]

Aren't residual current breakers required for any legal installation ?

(General question)

Do they exist as simple carry along / plugin devices ?

[godathunder]

15 minutes ago, 42Hz said:

Aren't residual current breakers required for any legal installation ?

(General question)

Do they exist as simple carry along / plugin devices ?

Yes, and cars arent allowed to run you over on a zebra crossing but it's still wise to look left and right before you cross.............. (less snarkily, yes, theyve been required for over 20 years but you'll still encounter the odd legacy system out there so its a good idea to carry your own. Be prepared and all that dib dib dib)

 

Yes, 13a plug in rcds exist - they cost about the same as a couple of pints

https://www.screwfix.com/p/masterplug-13a-fused-plug-in-active-rcd-plug/44855

[Huge Hands]

In my experience as a former sound engineer, these shocks are caused by potential differences in the earths between your mixer and your PA, backline amps etc.   If it is a small system, and everything is plugged into the same socket, it is usually fine.

 

The problem comes when you have your on-stage gear plugged into one socket/ring main, and your mixer out front in another and they don't have a fully shared resistance free common earth.  Any potential difference then takes the fastest route to earth via you and your mouth when you get close enough to the mic, especially if you're holding a guitar.

 

The best way is to take a marked up XLR cable for the mic with the ground (pin 1) disconnected at one end. This will act as a ground lift (like the switch on a DI box) and should stop the belts in the mouth.   Obviously this may cause the mic feed to be noisier in certain venues as you've removed the ground, but that could be the better of the two evils. 

 

I remember doing this about 25 years ago with the band Nine Below Zero at the venue I worked at.  The venue was desperate to open but the lead singer was still soundchecking, strumming his guitar and getting shocks.  I got one of the crew to open up his XLR, cut the connection to pin one, tape it up and put it back together in front of him.   He stood there and watched in disbelief thinking we were idiots.

 

He put the lead back together just as the venue manager decided to close the curtains and let everyone in.   As the crowd ran in to get their positions, the lead singer strummed behind the curtains with just the monitors on (that were still loud in the venue) and went "Hey mate - either that was lucky guess or you're a f***ing genius!" 

 

We kept that lead but hardly ever had complaints that would mean we needed to use it again - I assume it may have been something to do with his amp, perhaps earthing him faster through the mic, rather than the other way round.

Edited Friday at 08:11 by Huge Hands

[TimR]

4 hours ago, Huge Hands said:

In my experience as a former sound engineer, these shocks are caused by potential differences in the earths between your mixer and your PA, backline amps etc.   If it is a small system, and everything is plugged into the same socket, it is usually fine.

 

The shocks I've recieved are where someone has removed an earth to prevent a ground loop hum. 

 

Eg. Guitar amp (hand)  to Microphone (mouth) where the Pa Earth has been removed to prevent hum from Keys. 

 

 

Edited Friday at 12:39 by TimR

[Huge Hands]

Hi Tim,

 

The point of what I suggested is that you isolate the ground to the mic itself.    I assume in the example you quoted, someone has lifted the ground elsewhere, so the mic is still connected to the PA ground via the cable shield, and therefore any potential in the PA earth plane is earthed through your mouth and guitar/amp.  I think this is more likely than it travelling from your guitar earth to the PA earth if you're saying the ground was removed? 

 

If you remove the shield from the mic, the casing of the mic should not be connected to earth and therefore stop you getting belts. 

 

Maybe I have misunderstood what you meant.

[TimR]

8 hours ago, Huge Hands said:

I assume it may have been something to do with his amp, perhaps earthing him faster through the mic, rather than the other way round.

 

Or a compelte lack of earth. 

 

If a venue has different ring voltages on the earth, that's not good and implies a problem with the ring earth somewhere. The earths in a building should be common. 

 

 

[Huge Hands]

Hi TIm,

 

Agreed.   I think you're arguing the same points as me, but probably in a more succinct way.

 

The problem with potential differences between ground planes on different sockets in a room is usually that they are not commonly earthed, or the connection for one is not as good as the other or is not there at all.

 

In my example you quoted, I assumed it was his amp/guitar setup as we had a multitude of guitarists using the same setup in that venue without issue.   We kept the doctored cable marked up on a peg in our office, but don't think we ever used it again (probably until he came back the next year).

[TimR]

Ok. I wondered how you'd tested it. 

 

All earths should be common. The 'Martindale' testers upthread would show missing/bad earths on sockets. More reason for performers to have their PAT certificates up to date. 

 

Edited yesterday at 14:18 by TimR

[LawrenceH]

I am temporarily popping out of my posting retirement to say, the solution to an untraced fault causing electric shocks via the mic is NEVER to remove more earth connections. This is a potentially (geddit) lethal scenario.

 

If you have any doubts at all about a venue's electrics or your gear, at least plug in through a decent RCD. For god's sake don't try and work around it by removing earths!

 

By the way, a local RCD on your gear is safer than relying on an RCBO back at the distribution board, because RCD effectiveness is influenced by length of a cable run.

[Crusoe]

26 minutes ago, LawrenceH said:

I am temporarily popping out of my posting retirement to say, the solution to an untraced fault causing electric shocks via the mic is NEVER to remove more earth connections. This is a potentially (geddit) lethal scenario.

 

If you have any doubts at all about a venue's electrics or your gear, at least plug in through a decent RCD. For god's sake don't try and work around it by removing earths!

 

By the way, a local RCD on your gear is safer than relying on an RCBO back at the distribution board, because RCD effectiveness is influenced by length of a cable run.

I cut through the cable of a hedge clipper I was using, once. So glad I had a plug-in RCD.

[Huge Hands]

Hi @LawrenceH - I don't know if that was aimed at me, but I was not suggesting moving physical earths from PAs or equipment.

 

I was suggesting disconnecting the signal shield from the microphone.   This would avoid a "bridge" between varying earth planes (existing or not) in various equipment plugged into various sockets in the building.  A signal "ground lift" is a common option in DI boxes to isolate this to stop hum and no different to what I am suggesting here. 

 

I totally agree with the safety precaution of carrying a socket RCD and have one in my gig bag too.

 

However, I think people need to understand the difference between serious electrical faults like mains voltage/current shorting to earth and small potential differences caused by less resistive paths to earth, which can happen due to bad connections, or some poor wiring in venues.  Still not great and should be looked at by the venue and resolved, but if a microphone genuinely had mains voltage flowing through the casing, your mouth would have to be peeled away with a wooden pole once you'd burnt to a crisp (assuming a RCD hadn't tripped and saved you).   These shocks are generally like static from your shoes or when you used to rub a balloon on your jumper.

 

I am not belittling them by the way, I know they can bloody hurt, I have had a few myself in the odd venue over the years. 

[TimR]

7 minutes ago, Huge Hands said:

A signal "ground lift" is a common option in DI boxes to isolate this to stop hum and no different to what I am suggesting here. 

 

A ground lift inserts a small resistor, it doesn't disconnect the earth.

 

The issue is if a fault develops in the PA and a signal wire becomes live, there's nothing preventing the microphone casing becoming live.

 

If the guitarist had touched any other grounded component in the setup while touching his strings, he'd still be getting a shock.

 

Essentially, it sounds like it was his guitar that was live, but without a multimeter that would be difficult to determine. Usually opening the plugtop reveals a multitude of dodgy DIY wiring. 

 

Edited 3 hours ago by TimR

[Dad3353]

4 minutes ago, TimR said:

... there's nothing preventing the microphone casing becoming live...

 

I'm pretty Shure that mics casings are not connected to the signal wires or capsule. If the cable shielding (ie : earth...) has been cut, the mic casing is essentially 'floating', connected to nothing. 

[TimR]

10 minutes ago, Dad3353 said:

 

I'm pretty Shure that mics casings are not connected to the signal wires or capsule. If the cable shielding (ie : earth...) has been cut, the mic casing is essentially 'floating', connected to nothing. 

 

Assuming there's no fault in the mic wiring. 

[LawrenceH]

This'll be my last post. But in the scenario above where someone is already getting electric shocks possibly due to a faulty amp, removing the earth from the mic wire is NOT an acceptable solution. If the fault is in the guitar amp (or the supply feeding it), removing the path to earth means they are still building potential which can easily be earthed through another path, like a different mic or some random bit of stage kit or touching someone else who is earthed. Especially dangerous if it's one where the potential slowly floats up over time. The ONLY safe solution is to stop using that guitar amp/supply.

 

Hum is not necessarily a sign of serious danger. However, an electric shock is a damn good indicator (nylon trousers notwithstanding). The point is not that the fault is definitely lethal, but that you don't know it isn't 

Edited 3 hours ago by LawrenceH

[Huge Hands]

Hi @TimR, most DI boxes I have opened up over the years just have a simple switch that causes a break in the connection to pin 1 of the XLR, there is no resistor.  I think it would have to be of a pretty high resistance to give the same noise cancelling effect, which would be the same as a break in the connection. 

 

Mic cable shielding is not designed as a safety earth plane.  It just happens to connect to earth in the mixer to aid with signal shielding if there isn't inherent noise being inducted it on the run.

 

I have seen installations with all shields removed at 1 end on multi-channel snakes in noisy environments before.   It wouldn't be my choice as it limits your options for noise issues, but I have seen it done.   

[Huge Hands]

22 minutes ago, LawrenceH said:

This'll be my last post. But in the scenario above where someone is already getting electric shocks possibly due to a faulty amp, removing the earth from the mic wire is NOT an acceptable solution. If the fault is in the guitar amp (or the supply feeding it), removing the path to earth means they are still building potential which can easily be earthed through another path, like a different mic or some random bit of stage kit or touching someone else who is earthed. Especially dangerous if it's one where the potential slowly floats up over time. The ONLY safe solution is to stop using that guitar amp/supply.

 

Hum is not necessarily a sign of serious danger. However, an electric shock is a damn good indicator (nylon trousers notwithstanding). The point is not that the fault is definitely lethal, but that you don't know it isn't 

My point is, I am not a qualified electrician but am qualified in audio tech and have worked with it and single/3-phase electricity enough over the years to have the experience to know it is not direct mains electricity flowing through these people.  If it was, they would definitely know about it and would have probably bitten their tongue off at the very least!  However, I agree that precautions are obviously best and having socket testers/inline RCDs  is good for peace of mind. 

 

What these people experience is a static and sometimes impressive looking small blue flash like you would get from Nylon trousers, or poor shoes, or a balloon..   It is caused by small static or potential build up on a ground plane, because for whatever reason any inducted voltage caused by nearby noise or whatever, thinks your mouth is a faster route to earth than its current connection.    It is not caused by a fault causing the live mains to somehow connect to the casing of the microphone. 

 

It is also worth noting that with the example I quoted, the guitarist did the whole gig with no problems.  He then turned up the next year with the same setup and never mentioned his amp killing him in that time. 

 

I have also seen this issue with RCDs in place and they don't blow as it is not seen as a leakage to earth from another conductor.

 

Edited 2 hours ago by Huge Hands

[TimR]

1 hour ago, Huge Hands said:

What these people experience is a static and sometimes impressive looking small blue flash like you would get from Nylon trousers, or poor shoes, or a balloon.. 

 

One band I was in had this scenario. I took the amp home and measured 60volts to earth. It's not static. 

 

It's caused by the 0v of the transformer output not being at Earth potential as it's not grounded via the mains plug.

 

The potential problem is a fault inside the amp causes a fire or the case to become live.

 

An RCD detects an imbalance between the neutral and live. Which you won't get as the 240v side of the transformer is working as expected.