A Shocking Problem...

T

toddimac

New member
Hi All,

I am getting small shocks in my studio. Quick explanation: my guitar rig is powered by a Furman PL8. All my studio gear (mixer, computer, etc.) are powered by a separate PL8, plugged in to the same circuit in the room where my studio is. If I am touching any metallic part of the guitar system, and touch any metallic part of the studio gear, I get a shock.

Any advice is much appreciated to resolve this "shocking" problem. Sorry...

toddimac
 
My first thought is to try a different guitar amp if that's what you're playing through. Does it have a 3 prong plug or ground switch?

You should get it sorted out immediately. Something's wrong, unless you're talking about a static electricity kind of shock, and then maybe the problem is everything is ground-isolated by the Furmans. Don't know how they work as I've never used one. I have seen stars when my lips touched a mic playing through my buddy's ancient Mesa with 2-prong plug and ground switch in the wrong position, though!
 
Small test:

Touch metal. You get a shock.

Repeat immediately.

Is the shock considerably less?

You're dealing with electrostatic charge. Harmless for humans. Not wearing plastic shoes and synthetic clothing will lessen the problem. It's also less of a problem if the air is humid.

Is the shock equally disturbing?

Consider getting an electrician to check everything, as this is potentially lethal. You're feeling a ground leak. That could come from one piece of your gear, or it could be a problem with your electrical system. It needs to be taken care of, because it will get worse.

And, no, a typical multimeter won't help at all. You need an isolation measurement device and a ground tester. Usually, these are combined in what's referred to as a "megger". A professional electrician will have one and know how to use it.

It can be a simple matter and it can be infuriating difficult to find the culprit. I was in a studio once that had a problem like yours, albeit, it was the gear, not the people who "felt" the shock. You could see all VU meters on the desk moving, fi, when it occurred.

After some weeks we discovered that behind the building was a railroad marshalling yard that used a small 550 VDC locomotive. Whenever it passed the building, the loc injected several hundred volts DC via the ground into all equipment in the studio, but only after weeks of very dry weather. Because it wasn't AC, all filtering failed and it took us weeks to find.
 
Love the Megger comment. Very few electricians use them nowadays, and modern test meters can certainly measure current and voltage to do the testing - slapping umpteen hundred volts down the mains cable to check for leakage is still a function, but normally integrated into loads of others, at much gentler currents and voltages. There is still a need for one in installation testing, but PAT testers check leakage more gently.

The static charge is a rapid discharge event - so you touch a piece of kit and a small spark jumps to your finger, and is gone. One single discharge . If the shock is a continuous current then you feel it as a kind of 'purring' sensation. This is bad. A continuous current flowing is bad. Remember the old saying - Volts Jolts, but Mils Kills. As in 100th of an Amp. Even a cheap test meter that's digital will indicate the presence of voltage. Touch the probes between say a guitar bridge, and a piece of kit in your rack, and there should be zero. In fact, a couple of volts or so can be quite common where they get their grounds from different locations, and this often causes hums in the audio system, but once you see 60 or more volts - something is wrong. Often faulty power supplies where the mains voltage gets rectified, and it's not uncommon for faults here to put half of the mains voltages onto the ground. In Europe it's worse - half of our mains voltage is 120V our so - so getting a bit of that through your lip via a microphone can be quite unsettling. A cheap meter will show this.

However - if you get a shock, and you are not competent in electrics, find somebody who is to check it for you. Over the years I have had many shocks, most small, but a few nasty ones. A guitar amp with an internal transformer that failed and the front panel socket was live at 240V! Two faults it turned out - the transformer BUT also some idiot had removed the ground cable inside, not because of the usual hum, but because it kept tripping out his house protection. Instead of fixing it, he removed the safety earth! I was side stage, and he was playing on stage - working perfectly fine, until he went too far forward and the jack pulled out. His guitar cut out, and he kept waving at me to fix it, so I saw the plug on the floor, so I approached from the rear of the amp (a old Marshall combo) I crept up, and reached over the top, leaning on the reverb unit he had sitting on top. As soon as I picked up the metal jack, and put it into the amp, the pain went up my arm, and then out where my elbow was touching the reverb unit grounded case. It threw me backwards. I was damn lucky.
 
Because you say "Furman" I am guessing you are on 115V and not dead yet?

Yes, get a good sparks in to check the system. There is the possibility that the mains conditioners are injecting mains current into the earth line. This is not a problem so long as the gear is solidly earthed, it would seem yours is not.

This 'filter current' is not, of itself, likely to be lethal (and is only 1/2 what it would be here) but it does indicate to me that you have a problem with the mains wiring in the studio.

Dave.
 
cyrano said:
And, no, a typical multimeter won't help at all. You need an isolation measurement device and a ground tester. Usually, these are combined in what's referred to as a "megger". A professional electrician will have one and know how to use it.
Click to expand...
'Ground Tester'....
Are you referring to the 3 or 4 pole fall of potential ground test used to evaluate the effectiveness of an earth grounding system?
AEMC Instruments model 4620 ground resistance testers | Electro-Meters

'Megger'....
Insulation tester that applies 50 or higher vdc to a circuit under test, either to ground or between conductors and/or shield of a cable to determine electrical leakage. Maybe of some value if wetness of internal house wiring is suspected, but to do properly the electrician would need to ensure every electrical device is isolated away from what is being tested. Not worth the effort in my view.

I've used the two testers above somewhat frequently through about 29 years of a career with an electrical utility, so I have a pretty fair familiarity with what they are used for.

My guess on the OP's issue is much of his 'studio' gear is powered from 2 pronged wall warts which may not be well grounded and there is some capacitive coupling of the AC into the studio gear. A digital multimeter could be used to see if there is AC between the guitar amp and the studio gear, but I would probably use an old analog Simpson type meter to start as it would tend to load down capacitive coupled voltage more than a DMM. Usually switching a Simpson to a lower voltage range will reduce the voltage if capacitively coupled.

Wouldn't be a bad idea to get one of these testers to ensure the outlets the gear is plugged into are properly wired (Walmart, Lowes, or Home Depot type stores will have these)
Power Gear 3 Wire Receptacle Tester, Outlet Tester, 6 Visual Indications, Light Indicator, UL Listed, Yellow, 50542 - Voltage Testers - Amazon.com
 
Is the earth on the actual power outlet earthed correctly? First thing I would check, I once moved into a house where the whole house was not earthed due to a broken main earth wire within the house.

Alan.
 
arcaxis said:
'Ground Tester'....
Are you referring to the 3 or 4 pole fall of potential ground test used to evaluate the effectiveness of an earth grounding system?
AEMC Instruments model 4620 ground resistance testers | Electro-Meters
Click to expand...

Yes. For me, that's THE starting point. Check if the groundpin(s) do effectively sink current into the earth.

Over here, a lot of groundpins in sandy soil run dry in the summer and don't work. Not a problem in new buidlings, but often a problem in older ones. Stuff works well when it's wet, but gets spooky when it's dry.

'Megger'....
Insulation tester that applies 50 or higher vdc to a circuit under test, either to ground or between conductors and/or shield of a cable to determine electrical leakage. Maybe of some value if wetness of internal house wiring is suspected, but to do properly the electrician would need to ensure every electrical device is isolated away from what is being tested. Not worth the effort in my view.
Click to expand...

Well worth the effort in very old buildings. Sometimes leakage occurs in the wiring. But it's just one of the tests if it isn't clear from the beginning what the cause is.

I've used the two testers above somewhat frequently through about 29 years of a career with an electrical utility, so I have a pretty fair familiarity with what they are used for.
Click to expand...

They only come out once or twice a year. But when you need them, they are irreplaceable. Mine is a combined one.

I do use a DMM if I don't have one on hand, but that gives only an impression. And that impression can be completely wrong. It also produces mysteries. Over here, most mains nets are symmetrical. If you measure mains between one wire and ground, you should have half voltage. We've got 230 VAC; so you should measure 115 VAC to ground. I have one outlet in my house that measures 140 VAC. In theory, there should be 280 VAC on the wires. Of course, there isn't...

My guess on the OP's issue is much of his 'studio' gear is powered from 2 pronged wall warts which may not be well grounded and there is some capacitive coupling of the AC into the studio gear. A digital multimeter could be used to see if there is AC between the guitar amp and the studio gear, but I would probably use an old analog Simpson type meter to start as it would tend to load down capacitive coupled voltage more than a DMM. Usually switching a Simpson to a lower voltage range will reduce the voltage if capacitively coupled.
Click to expand...

I know enough about mains in other countries to be extremely cautious. I lost a dear friend to electrocution...

Wouldn't be a bad idea to get one of these testers to ensure the outlets the gear is plugged into are properly wired (Walmart, Lowes, or Home Depot type stores will have these)
Power Gear 3 Wire Receptacle Tester, Outlet Tester, 6 Visual Indications, Light Indicator, UL Listed, Yellow, 50542 - Voltage Testers - Amazon.com
Click to expand...

I hate those. Just like a DMM, they lead to wrong conclusions in rare cases. And that's when it becomes very dangerous. And we even threaten them with reporting to the authorities.

I do trouble digital/analog shooting. But repairs in ground installations are always left to qualified technicians from one company. We know they don't cut corners. And they know we test again after repair. If a customer refuses repairs, we don't consider them customers any more.

I don't mind patching an audio cable with tape, if there's no time to solder.

That's something I will NEVER do with mains.

My friend who got electrocuted is dead. He wasn't even on the ground, he was up in the rigging, checking cables. It was a festival, so an outside rig and someone had decided to disconnect the proper power from the distribution box and connect it to a very long cable going to a standard wall socket in a nearby bar. That was enough to power the drill and a few pieces of gear. The main PA wasn't installed yet. How was he to know there wasn't a ground connection in that one wall socket?

We have strong rules for electricity. I follow those, even when some people consider me over-cautious.
 
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