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

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

Postby witzendoz » Mon Apr 29, 2013 8:12 am

Sorry if this has been mentioned, but I only zapped (excuse the pun) through the 5 pages.

One way you can get a shock between the mic and holding a guitar is if the PA system is plugged into one phase of a 3 phase supply and the guitar amp is plugged into a different phase of the 3 phase supply. This is because due to different loadings across the 3 phases there is sometimes a voltage differential. The volts you get hit with is unlikely to be the full 250 volts (thank goodness) but may be up to 50 volts which when hitting the lips feels like 1000 volts.

The PA and stage amps should be plugged into the same phase, then they should run the lighting rig from a different phase. This problem is hard to trace due to different nights / times of day, having a closer or wider voltage differential. The voltage differential also causes noise in the audio witch if often mistaken for a ground loop.

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

Postby dmills » Tue Apr 30, 2013 8:59 pm

Sorry but that is complete bullshit in almost all ways, if you do not understand three phase power (and you clearly do not), please do not repeat myths about it.
They do nothing to enhance safety and are counter productive as they cause people to worry about unimportant things (which phase) as opposed to critical things (is all the metalwork bonded).

Three phase power is routine on stages bigger then the one down the local pub, and many amp racks of the bigger sort are built with three phase inputs, so tell me how is a rack full of amps wired to a three phase input supposed to be run off single phase?
I do normally try to keep all the backline on the same phase just because I have a power distribution chain for the back of the stage that is single phase, but if it ends up on two or even all three phases, it is not something I loose sleep over.

The one case where it can make a slight difference is where you have class II appliances on different phases as the touch current if getting between them can be slightly higher then normal, not generally a problem, and class II with no earth path is not that common on stage anyway.

99+% of the time complaints about hum due to lighting are really comments that the sound guy does not know how to design a rig with acceptable noise immunity or is doing something daft, do it right and your rig will not hum even if you are on the same phases as the lighting and in fact even if your dimmers are parked right next to the amp racks. Most non trivial lighting by the way is three phase input to the dimmer racks, as it is difficult to get much more then 125A as a single phase supply.

Seriously there are enough weird myths about power distribution in this game without adding to them, and safety mythology does nobody any favors.

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

Postby Hugh Robjohns » Tue Apr 30, 2013 10:05 pm

Er... Yes! Well said Dan. Either Australia is a very scary place with a radically engineered three-phase system utterly at odds with the rest of the planet... Or our new friend is a tad confused!

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

Postby Bass Growler » Sat May 04, 2013 9:04 pm

What a fascinating thread! I'm a complete newbie as regards audio and completely out of my depth in this forum. As a newbie I'm taking the advice of all the folk who are replying to the threads for audio newbies - and I'm slowly learning about some of the basics.

Can I please appeal to all you audiophiles! Please pay the same respect to those who understand about AC power and its dangers and peculiarities when connected to sophisticated equipment.
Modern electrical kit has within its circuitry Safety Ground (Frame Ground) and many others. Logic Ground for electronic component circuits, Signal Ground for the Data path (Analogue or Digital) and I could go on. This is a complex subject. Many many electricians are connvinced that Ground is Earth and Earth is Ground so what does it matter - they all join up eventually!!! ------Wrong!!

Just as I will never know as much as recording engineers about recording - and as a result leave it to them for serious stuff - like recording our choir when it really matters, please hand over issues about electric shocks to folk who know their subject to a high level. I've been climbing up that learning curve for over 40 years and it includes attending more than one funeral, alas.

I don't want to get morbid - but please don't hand these issues over to the chap who knows how to wire a mains plug, and gets it right most of the time. This is serious stuff - and if I can lighten the issue - it has the potential to do significant damage to more than equipment. In the UK get a Martindale Tester to check all the outlets you use - if one fails - get help. Get all your kit PAT tested with a suitable tester - boring - yes - but the alternative is really shocking.







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

Postby dmills » Sat May 04, 2013 10:39 pm

Bass Growler wrote:
Modern electrical kit has within its circuitry Safety Ground (Frame Ground) and many others.
Which is usually the only one that matters from a safety perspective. All the others are merely functional not safety connections and so are not really a concern to the user (Particularly as they usually all come together inside the equipment anyway, "Technical earth" connections are not popular in live sound).

Many many electricians are connvinced that Ground is Earth and Earth is Ground so what does it matter - they all join up eventually!!! ------Wrong!!

Not really from the point of view of an electrician as opposed to an electronics engineer, what matters is the frame ground, and as long as that has a low enough Ze to make the disconnect time and keep the touch voltage reasonable that is really all that matters.
Sure you get some old kit that separates the functional earth and frame ground connections to support the old 'clean earth' thing, but that does not really work in this age of mobile phones simply because the inductance is way too high.
Of course you also get kit that gets the screen connections horribly wrong, and hums like a bad singer, for which the answer is either a fat PEC or to telescope the audio cable screens (NEVER disconnect the frame ground).

In the UK get a Martindale Tester to check all the outlets you use - if one fails - get help. Get all your kit PAT tested with a suitable tester - boring - yes - but the alternative is really shocking.
Also, get plug in RCDs and use them, they are a bit good at making most shocks merely painful rather then lethal.
I am a bit in two minds about the PAT thing for hobbyist musos mostly because IME a good visual inspection catches almost everything that the test box would, and that can and should be done every time the gear comes out, PAT is a bit like the MOT in that it only catches problems present when it is done, getting in the habit of inspecting for damaged cables and cord grips will catch most things as they happen.

I think however that for the most part we are in loud agreement!

My standard recommendation for papers by Walderon, Muncy, Whitlock and Ott goes here.....

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

Postby ef37a » Sun May 05, 2013 7:07 am

"Also, get plug in RCDs and use them"

You can also get RCDs that can be hardwired into dis'boards and socket strips and so cannot be forgotten.

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

Postby Bass Growler » Sun May 05, 2013 2:34 pm

Very happy with Dan and Dave's input. My comments regarding logic and Signal earths have been relevant in the past when equipment faults caused very unusual links between the differents earths.
To be fair, RCD has come to the aid of us all - before that, open circuit neutrals in particular have caused chaos, and the solution often tricky to sort out.
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Re: Well, yeah, again, electric shocks from mics !!

Postby planetnine » Tue Aug 13, 2013 8:24 pm

As much as I hate the "PAT test once a year regardless of use or environment" mentality, one thing that PAT does find is missing or disconnected earth leads on mains flex and IEC leads.

Flex and its plugs is the weakest link in electrical systems and the part most likely to be damaged or misused/altered in any electrical system such as a PA system or backline rig. The earth bonding test in the PAT sequence does root out some issues that might otherwise not be apparent, even after careful visual scrutiny, and if I only did one electrical test on flex it would be earth bond.

Try to get a electrician friend to do it cheaply for you, or club together and buy a tester yourselves, get trained up and use it. Even if you don't do the stickers and certificates thing, test the cables with it every month or so.

This depends of course on frequency and severity of use, and how far the casble trunk travels, etc, but you get the idea -learn about electrical safety and apply it.


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

Postby John Hewitt.71 » Thu May 10, 2018 9:47 am

I hear and see what you all say. There is another very real situation that a socket tester will not solve neither will all the PAT testing in the world. Mentioning that, in many cases PAT testing of equipment is required by many venues and councils ,including hotels, throughout the land. The very real situation of a building having been altered or extended can also create another far more dangerous situation. I worked in a school where the stage area had been the dining area for the previous building and the hall or seating area was built at a later date. All 3 phases were present on that stage in the sockets. Different phases on either side of the stage and the third phase on the sockets placed on the stage apron that formed part of the hall. Could have easily been rigged :- Bass to the left on Red Phase, Guitar to the right on Blue Phase and the PA plugged into Yellow Phase operated from the hall floor. At any point there could have been 415 volts. I reported it to the council. The result was that an electrician came to inspect the school stage and agreed the situation. His resolution of the matter was to put a 415Volt sticker on the 240Volt sockets in the hall. Sometimes things just don't go as you expected. The head teacher told me to "forget it. Just don't use those sockets for a school show." I wrote a H&S report. It was filed. Just remember that the Judge has a lot of power when it come down to a court case for negligence.
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Re: Well, yeah, again, electric shocks from mics !!

Postby MarkPAman » Fri May 11, 2018 12:19 pm

I think you're worrying unnecessarily here.

While it is still considered good practice to keep sockets near each other to one phase where practical, it is no longer a regulation (I forget when this changed, but it was quite a long time ago). The chances of two pieces of equipment both developing a fault that puts 240V through their casing, yet does not blow a fuse/trip is really incredibly small.

In the entertainment world, 3 phase lighting dimmers are very common, with adjacent lights almost certainly running on different phases.

Oh, and Red, Yellow & Blue were replaced by Brown, Black & Grey in 2006.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Hugh Robjohns » Fri May 11, 2018 12:58 pm

John Hewitt.71 wrote:All 3 phases were present on that stage in the sockets. Different phases on either side of the stage and the third phase on the sockets placed on the stage apron that formed part of the hall.

As Mark correctly says, this is not illegal or contrary to the current IEE/IET regulations (in the UK), and the arrangement is actually quite common -- although I should state that I'm not officially or legally qualified to make that comment! :o

The old guidance, as I recall, was to maintain at least 6 feet separation between sockets on different phases (to ensure one person couldn't touch both at the same time), but that guidance was withdrawn -- AFAIK, in the 16th Edition (we're now on the 17th Edition and the 18th Edition will be published this year). And sensibly so, in my view.

The only current ruling about different phases in the same room that I'm aware of is that all sockets within a single room in a medical environment should be on the same single phase, and the guidance discourages sockets on different phases in the same room in domestic environments. But elsewhere -- industry, offices, schools, etc -- there is no problem with it at all.

I reported it to the council. The result was that an electrician came to inspect the school stage and agreed the situation. His resolution of the matter was to put a 415Volt sticker on the 240Volt sockets in the hall.

...which was actually the incorrect response, highly confusing to anyone using those standard 230V supply sockets, and entirely contrary to the IEE/IET current (17th Edition) regulations which states that warning labels are required ONLY if the voltage between a socket's line terminal and the reference earth exceeds the nominal 230V. Nothing about the voltage between line connections of different sockets being more than 230V apart.

There is absolutely no requirement to label sockets on different phases in the same room; a warning label is required only when exposed terminals that are simultaneously accessible have a voltage between them greater than 230v.

While it's obviously true that 400+V exists between the Line terminals of mains sockets on different phases you would, as Mark says, need at least TWO CATASTROPHIC FAILURES to occur simultaneously AND all of the safety trips/fuses to fail as well for it to be a real problem... and that is vanishingly unlikely with modern equipment.

Just remember that the Judge has a lot of power when it come down to a court case for negligence.

That much is certainly true... as demonstrated in the ruling on the ROH musician's hearing damage claims, as discussed here: https://www.soundonsound.com/forum/viewtopic.php?f=28&t=60975&hilit=opera%20hearing%20damage#p549292
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Re: Well, yeah, again, electric shocks from mics !!

Postby John Hewitt.71 » Sun May 13, 2018 2:18 pm

I should have explained. The School was built in 1975. No only trips were fitted no RCDs. In fact that was the case up until 2008. I know. I put a nail through a PYRO cable to a light switch that was taken diagonally across the underside of a pin-board. There was quite a bang. No RCDs meant that there was quite a current until it tripped. That was 2004. I am not sure if the trips had been fitted as I seem to remember something about fuse capsules needing to be replaced. I agree that all this was some time ago. Yes regulations have changed. Not sure if all of the regulations are retrospective. If a church Hall /Club-house/ Pub back-room/ village -hall has not been updated with a current certificate. I one was involved in a fairly modest event in one of Cardiff's prestigious hotels. I received a demand for all my PAT certificates for the equipment I intended to use. This I forwarded with a request for a copy of the hotels electrical safety cert. so that I knew I was protected while using the building. They could not provide one. They said that I was not entitled to see it. I later found that they did not have one. Do not take anything on face value. Thanks to all who contributed to this.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Hugh Robjohns » Sun May 13, 2018 2:58 pm

John Hewitt.71 wrote:Do not take anything on face value.

Most definitely! I've lost count of the number of times I've found dangerously defective mains sockets at conference centres, churches, schools and elsewhere!

Always test before use, and always power your own gear via RCCBs!

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

Postby blinddrew » Sun May 13, 2018 4:21 pm

Probably the dullest bit of GAS I had after joining this site was a socket tester and a couple of RCCBs. :D
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Re: Well, yeah, again, electric shocks from mics !!

Postby Brian M Rose » Sun May 13, 2018 4:41 pm

And has been sad - hotels insisting on seeing printed PAT certificates before equipment can even get through the door. And then finding that their own PAT labels are two years out of date. Perish the thought that this has anything to do with their wish to hire you their rather expensive mixers, mics etc. In one case even the PAT tests for bedrooms were similarly out of date.
Hopefully, equally out of date is the old muso attitude of 'Well, no one has died yet dude!' Forums like this one have potentially saved lives.....
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Re: Well, yeah, again, electric shocks from mics !!

Postby Sam Spoons » Sun May 13, 2018 7:03 pm

Is there a problem with using a non polarised three conductor plug into the UK mains via an adapter with class 1 equipment using IEC three pin connectors (kettle leads). I think there is as the line and neutral can be transposed, my mate disagrees saying the RCCD would trip either way. We are not talking about poking about inside some kit here but in normal use.
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Re: Well, yeah, again, electric shocks from mics !!

Postby MarkPAman » Sun May 13, 2018 7:46 pm

An RCD trips when the current in phase and neutral is not the same. It does not care which is which.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Folderol » Sun May 13, 2018 8:26 pm

These days you can get individual combined RCD/MCB modules that directly replace the standard MCBs in domestic distribution boxes.
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Re: Well, yeah, again, electric shocks from mics !!

Postby Hugh Robjohns » Sun May 13, 2018 8:36 pm

Sam Spoons wrote:Is there a problem with using a non polarised three conductor plug into the UK mains via an adapter with class 1 equipment using IEC three pin connectors (kettle leads). I think there is as the line and neutral can be transposed, my mate disagrees saying the RCCD would trip either way.

Technically, it would not be deemed a safe way of working under all conditions, and the HSE would descend like a ton of bricks in the event of 'an incident'...

In practice, though, if -- but only if -- the circuit is definitely fed from a (double pole) RCD, it is actually fully protected and would be safe.

The potential problem is that if the line-neutral are swapped the on-off switch (and fuse) may end up not being in the line feed, and thus the unit remains powered (live) even when switched off, or if the fuse fails (through old age, say). Only the (high rated) fuse in the mains distribution feed would offer (minimal) protection against fire or electrocution.

Thankfully, in either situation, an RCD would detect the resulting imbalance of line-neutral currents and disconnect the device safely... But not all UK mains supplies feature RCDs, and so it cannot be guaranteed to be a safe way of working under all conditions.

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

Postby Sam Spoons » Sun May 13, 2018 8:39 pm

Thanks Hugh, that was what my mate reckoned...... Bugger! that means he was right again :tongue: Admittedly he is better qualified than me.

FWIW we always power the stage/mix position through RCCDs
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