Electric shock

[ryan0583]

I recently had a gig and got a small shock off the mic. This was the first time this has happened and I want to try and get to the bottom of why this happened.

I've bought a socket tester and check all the sockets on my extension lead - no problem there. I've also bought a multimeter, and there seems to be a small AC voltage (0.1 V) when i touch the red lead to the switches on my effects pedals and have the black lead connected to earth. Is this normal? It happens with any of my effects pedals and with two out of the three 9 volt adaptors I have.

I haven't been able to test the outlets at the venue as I haven't been back, so it could still be that. If anyone has any experience getting to the bottom of problems like this it would be appreciated.

[JapanAxe]

This has happened to me too. I don't think it would be the 0.1V AC - too small to feel. I wonder whether it's a DC offset at the input of the PA or the bass amp?

[KiOgon]

Hopefully it won't be the equipment or the mains supply at fault, I'd say it's more likely to be static from your body discharging to earth via the mic or anything that is earthed.

It's a good idea to check the supply with your socket tester wherever you're gigging though, if there is/was a fault with the mains it could be lethal, as I'm sure you already know..

[skidder652003]

[quote name='KiOgon' timestamp='1355444405' post='1898617']
Hopefully it won't be the equipment or the mains supply at fault, I'd say it's more likely to be static from your body discharging to earth via the mic or anything that is earthed.

It's a good idea to check the supply with your socket tester wherever you're gigging though, if there is/was a fault with the mains it could be lethal, as I'm sure you already know..
[/quote]

ok going to a proper noob here, how does one test the mains sockets at a pub? Is there a "plug in" device that tells you its ok?
would deffo get one if there was. Some of the dives we play have well dodgy power supplies.

[Musky]

[quote name='skidder652003' timestamp='1355468939' post='1898687']
ok going to a proper noob here, how does one test the mains sockets at a pub? Is there a "plug in" device that tells you its ok?
would deffo get one if there was. Some of the dives we play have well dodgy power supplies.
[/quote] They're sold as socket testers in DIY stores, but often called Martindale testers after the brand (like Hoover).

Testing the socket for wiring faults is never a bad idea, but it still leaves you open to faults to the chassis of the amp. The amp needs to be checked over as well.

Edited December 14, 2012 by Musky

[stingrayPete1977]

I'm a sparky and this is normally caused by what we call a floating earth, the most obvious causes would be either a lack of earth at the socket at the venue or a faulty ext lead/4 way adaptor etc. Obviously you can't check the venues sockets now so double check the leads and fwiw a proper pat test could reveal a fault that the multimeter can't as a proper pat tester or a insulation resistance tester 'megger' puts a high voltage through as it tests where a multimeter does not.

The reason for the shock is because all the gear we use especially stuff with windings or moisture has a very small leakage to earth hence why we can't have rcd's set at 0mA (usually 30mA instead), if the venues socket was taking the leakage as it should everything works fine but if that earth is missing in the chain then that little bit of voltage goes down the mic's earth as everything is connected obviously, you are then the easiest path to earth. Now imagine if the lead entering your pa had a loose wire that suddenly came free of its terminal and landed on the metal casing inside straight to earth, the only earth is the next poor bugger who grabs a mic to see why the pa has gone quiet who gets the whole 230v until they either drop the mic or the fuse blows!

Plug in testers that show 3 lights for live neutral and earth can be bought for a few quid at maplins, b&q or even ebay, a local sparky should be able to pat test your leads for a couple a quid per lead and a mug of coffee

Did that make any sense?

Edited December 14, 2012 by stingrayPete1977

[EBS_freak]

Who do you think you are Pete? Some sort of expert?

[stingrayPete1977]

[quote name='EBS_freak' timestamp='1355478566' post='1898814']
Who do you think you are Pete? Some sort of expert?
[/quote]
I will put up some graphs later

[EBS_freak]

[quote name='stingrayPete1977' timestamp='1355479765' post='1898832']
I will put up some graphs later
[/quote]

Cheers.

[stingrayPete1977]

Obviously the temperature of the venue and the type of underpants you wear will alter the figures but I am having a room built to test this at the moment

[EBS_freak]

[quote name='stingrayPete1977' timestamp='1355480233' post='1898847']
Obviously the temperature of the venue and the type of underpants you wear will alter the figures but I am having a room built to test this at the moment
[/quote]

Obviously you wear rubber pants and rubber soled shoes.

[charic]

[quote name='EBS_freak' timestamp='1355484537' post='1898947']
Obviously you wear rubber pants and rubber soled shoes.
[/quote]

and nothing else? Are all bassists this kinky?

[tonyf]

I find the best bassists wear rubber pants, shoes and swing around a metal precision whilst standing in a bath of water in the middle of an open air gig in a thunderstorm. Whilst under a tree.

[BILL POSTERS]

[quote name='KiOgon' timestamp='1355444405' post='1898617']
Hopefully it won't be the equipment or the mains supply at fault, I'd say it's more likely to be static from your body discharging to earth via the mic or anything that is earthed.

It's a good idea to check the supply with your socket tester wherever you're gigging though, if there is/was a fault with the mains it could be lethal, as I'm sure you already know..
[/quote]

a shock from static - or DC offset whatever that is - would be more of a sharp sting. Mains feels different, it sort of buzzes if its a little one, or bloody hums if its full mains across your body. Trust me, after donkeys years repairing stuff live, I know.

If it feels like AC, but doesnt actually hurt, theres probably just not enough current available. so probably, as has been said, a dodgy earth somewhere. Needs checking out properly though. A good earth might save your life one day.

[stingrayPete1977]

I must point out I am sat here with a broken arm that was caused by electrocution!

+1 on the static being a quick snap of a shock where as the bad earth will usually make you have a tingly lip thing or your hairs prick up if you rub you arm over it, its quite nice sometimes but I would not suggest it.

[charic]

[quote name='stingrayPete1977' timestamp='1355489062' post='1899050']
I must point out I am sat here with a broken arm that was caused by electrocution!
[/quote]

More details please!

[stingrayPete1977]

[quote name='charic' timestamp='1355489419' post='1899063']
More details please!
[/quote]

[url="http://basschat.co.uk/topic/192248-which-idiot-has-broken-his-left-wrist/page__hl__broken%20wrist"]http://basschat.co.uk/topic/192248-which-idiot-has-broken-his-left-wrist/page__hl__broken%20wrist[/url]

I have not updated it for a while so will do shortly

[charic]

Oh yeah! I remember now!

[Musicman20]

What is the best socket tester for metal?

[flyfisher]

[quote name='stingrayPete1977' timestamp='1355473327' post='1898718']
Plug in testers that show 3 lights for live neutral and earth can be bought for a few quid at maplins, b&q or even ebay,
[/quote]

Yep, I have one of these in my gig bag: http://www.maplin.co.uk/mains-socket-tester-9800

I also use an RCD adapter for my amp.

Maybe not 100% exhaustive in the safety stakes, but pretty close and at minimal cost.

[stingrayPete1977]

[quote name='flyfisher' timestamp='1355497321' post='1899260']
Yep, I have one of these in my gig bag: [url="http://www.maplin.co.uk/mains-socket-tester-9800"]http://www.maplin.co...ket-tester-9800[/url]

I also use an RCD adapter for my amp.

Maybe not 100% exhaustive in the safety stakes, but pretty close and at minimal cost.
[/quote]

You would be very unlucky to get anything worse that a tickle using that lot, you could add a big lump hammer in the kit for bopping guitarists on the head that refuse to use your RCD in case it goes off and recks a valve, la dee darr!

[flyfisher]

The RCD is just for my amp. The guitarists can look after themselves (as long as they don't touch me!)

[Phil Starr]

It's pretty rare to get static shocks off a mic, so it is safer to assume that something else is wrong. If a venue tells you they get a lot of 'static' they have unsafe wiring, don't trust them or their wiring.

PAT testing your gear makes a lot of sense but a surprising number of mains sockets are incorrectly wired or faulty in other ways. I'd completely back up using RCD's and socket testers but there is one other precaution worth taking and that is to run all your gear off a single socket (obviously this only works if you have less than 3kW of gear, which is your 13A worth) If your earth is floating then at least all the earths on the amps/instruments/mics are at the same potential and you shouldn't get a shock in this way.

[rmorris]

I'd have to go with recommending you use an RCD plug for your multi way mains block but you could still get an issue if the mic / pa system is run off a different socket. Hopefully the venue would have RCD protection where the power enters the building but it's possible that it might not and just be relying on fuses. It shouldn't be the case of course but it may not be practical to verify in all cases.
Classically you can get a problem if the 'earth' on the bass is significantly different to the 'earth' on a mic. High Power installations may use different 'phases' of the electricity supply ( ref 3 phase power ) and problems, possibly lethal, can result. People have been killed as a result. If I recall correctly, someone in the 'Sensational Alex Harvey Band' was killed like this in Swansea many moons ago.

[JapanAxe]

[quote name='stingrayPete1977' timestamp='1355473327' post='1898718']
I'm a sparky and this is normally caused by what we call a floating earth, the most obvious causes would be either a lack of earth at the socket at the venue or a faulty ext lead/4 way adaptor etc. Obviously you can't check the venues sockets now so double check the leads and fwiw a proper pat test could reveal a fault that the multimeter can't as a proper pat tester or a insulation resistance tester 'megger' puts a high voltage through as it tests where a multimeter does not.

The reason for the shock is because all the gear we use especially stuff with windings or moisture has a very small leakage to earth hence why we can't have rcd's set at 0mA (usually 30mA instead), if the venues socket was taking the leakage as it should everything works fine but if that earth is missing in the chain then that little bit of voltage goes down the mic's earth as everything is connected obviously, you are then the easiest path to earth. Now imagine if the lead entering your pa had a loose wire that suddenly came free of its terminal and landed on the metal casing inside straight to earth, the only earth is the next poor bugger who grabs a mic to see why the pa has gone quiet who gets the whole 230v until they either drop the mic or the fuse blows!

Plug in testers that show 3 lights for live neutral and earth can be bought for a few quid at maplins, b&q or even ebay, a local sparky should be able to pat test your leads for a couple a quid per lead and a mug of coffee

Did that make any sense?
[/quote]
Excellent explanation.

I always plug into an RCD on gigs, and carry a ring-main tester to use if I have any concerns about the venue mains supply. Biggest worries are extension leads at outdoor/marquee jobs. Most common faults are no earth (which equals no protection from lethal faults), and live/neutral reversed (which may not be as bad as it sounds if all the band are on the same supply, but is not recommended!)