Safety: testing Electrical outlets

[x-pro]

Grounding, marking, designations!
You forget that the user has a device that in most cases is not new. This means that something in it may no longer meet electrical standards. The safety of the owner must be ensured by himself, especially in important places. Whether he does it himself or has a specialist do it is up to him. It is good to have a document of such verification.
It is better if a specialist checks the instrument before the artist's performance. But where and who does this? Only what owner would give his favorite expensive props to be checked by a specialist)?

Maybe I'm wrong.

[g1]

Are the articles suggesting that the hot is connected to the neutral leg of the socket AND the ground lead of the socket Without a real ground back to the box, and the neutral is connected to the hot leafld on the outlet?

Yes. Post #26 has a working link to the article.
He calls it 'reverse bootleg ground'.
Here are the images of the wiring, and how the outlet tester does not register a fault:

[Greg Robinson]

Here in Australia (and there are similar requirements in other countries - Japan, much of Europe, etc), these outlet testers often feature a ground fault test button that places a resistor between active and ground, allowing at least 30mA of current to flow. Any new installation (or modification to an existing installation) now requires a RCD/GFCI with maximum 30mA trip current, and the test button will identify any such "bootleg groound". Unfortunately you're unlikely to get invited back anywhere if you try that during soundcheck, as it will trip the RCD which will be hidden in the electrical panel somewhere. Rather inconvenient, but at least possible to confirm swapped ground/neutral or "bootleg ground".

[g1]

Any new installation (or modification to an existing installation) now requires a RCD/GFCI with maximum 30mA trip current, and the test button will identify any such "bootleg groound".

I could be wrong, but I think this may be a uniquely North American or single phase issue. Our neutral and earth are connected at the distribution panel.

[Greg Robinson]

I could be wrong, but I think this may be a uniquely North American or single phase issue. Our neutral and earth are connected at the distribution panel.

As they are here. But ONLY at the panel, else the function of protective earth and RCD/GFCI is defeated.

[Mars Amp Repair]

Yes. Post #26 has a working link to the article.
He calls it 'reverse bootleg ground'.
Here are the images of the wiring, and how the outlet tester does not register a fault:

Holy crap!
That's flat out frightening, esp that the testers won't catch it. You're right, DYI'ers who know nothing about electrical wiring could actually do this even unknowingly when replacing an already bootlegged outlet by switching the hot and neutral.
thanx for posting the diagrams.

[g1]

I could be wrong, but I think this may be a uniquely North American or single phase issue. Our neutral and earth are connected at the distribution panel.

As they are here.

Thanks, I'm guilty of being ignorant of other power systems, or at least not giving it enough thought. I was unaware that one side of your AC was neutral. Here our 240V is center-tapped (to make two 120V legs) and the CT is our neutral which is grounded. We do have some things running on 240V (like ovens) in the house and those things are grounded, but of course, neither side of the 240 can be neutral. I had just assumed that was normal 240V, but now understand no one else would have need for the center-tap.

[DrGonz78]

Thanks, I'm guilty of being ignorant of other power systems, or at least not giving it enough thought. I was unaware that one side of your AC was neutral. Here our 240V is center-tapped (to make two 120V legs) and the CT is our neutral which is grounded. We do have some things running on 240V (like ovens) in the house and those things are grounded, but of course, neither side of the 240 can be neutral. I had just assumed that was normal 240V, but now understand no one else would have need for the center-tap.

It’s the same here in the USA, essentially. My neutral connection is the center tap to a big drop down transformer device. We have both 120 and 240vac. We reserve the additional 120v line for water heaters and dryers, possibly heavy duty ovens and run those on 240v.

Open neutral is what I am currently chasing in a circuit in my house. We have crappy aluminum wiring in the house that requires checking of the connections at the box and the outlets. Never trust aluminum connections mated to copper. I was using an anti-oxidant compound on it and it improved water heater connections by 100%. That’s because the wiring had melted!!

[R.G.]

This set me off wondering about ground safety again. I speculated a widget that you could touch to your guitar strings and then to a mike stand or other equipment and have it glow red if "hazardous".

Did some reading; human skin is ~100K ohms dry, may be as little as 1K through a human if they're sweaty. Indicator would need some way to indicate red if there was more than ~1ma flowing through 1K, and reliably. Mind jumped to a uC PIC running from a coin cell and some sensing Rs and Cs. Clip one end to a guitar string, touch the probe to the other thing, red = Oh Sh!!
PIC could even leave itself running in nano-watt mode all the time, so no on/off switch maybe.

Sigh. So many designs, so little time.

There is a low-tech, slam-dunk method to increase safety here. Just make up some ground cables with clips to tie the mike stand and other stuff you'll touch to a ground stud on the back of your amp. If you get BIG hums or melting, smoking insulation on the ground wires, it's probably better not to touch the equipment.

[loudthud]

What we used to do back in the early 70s was leave your guitar strings long sticking up from the headstock of your guitar. Before you touched the microphone, you would hold the headstock of your guitar up to the microphone and let the strings touch it to see if there were any sparks. No, I'm not kidding.

I worked in an old Paramount Theater in the 70s that stopped showing movies and had Rock and Roll Concerts. The place was built in the 30s for Vaudeville and never updated their stage wiring, it was all two wire. The guy who ran sound there when the road bands didn't bring their own used a bunch of the Shure mixers. Each one had it's own ground cap internally with no switch. The combination gave a random Voltage on the signal ground because some were connected to Neutral and some were connected to the Line. The Union guys that ran the stage during the shows didn't listen to me, an 18 year old kid with long hair.

[R.G.]

Yikes!!!
I started and stopped few times suggesting this one: One way to ensure a long(er) life as a gigging guitarist is to measure the actual AC line draw of your amplifier setup, and get an isolation transformer or better, a constant voltage/ferroresonant transformer from ebay to power your rig. A good iso or ferro will completely isolate you from the wall socket ground, however good or bad that is. A live mike stand can then only shock you through your sweaty shoes on the stage, not your guitar or amp. About the only drawback is the weight. A good 250-500VA trannie will weigh 30 pounds or so. But that's easily in the range of a one hand handle.

[Helmholtz]

My simple mains testing screwdriver (containing a neon bulb) tells me if there's a dangerous voltage wrt ground on accessible metal parts.
Particularly used it to test mic shells as well as my own stuff on stage.

[R.G.]

That's one approach. Neon bulbs break over at 45 to 65Vac for the standard type, 75 to 95Vac for the high brightness type. So the actual voltage sense point is a little fuzzy. The reason I was mentioning other voltages and currents is that the shock you get depends on the current you get; the voltage may not matter much if the source impedance can't supply current through the body of about 1ma or more. It it won't fire the Ne bulb, then it's probably safe, at least until your hands get sweaty. If it fires the bulb, it may be deadly, but also might be no shock at all, depending on the source impedance of the leakage versus the internal resistance of the current limiting resistor in the probe.
I mentioned the PIC approach because I envisioned the controller sensing that there was ...something... and spending some milliseconds running a few tests for whether the current got over 1ma with 100K, 10K, 1K series resistance to sample the human skin resistance range.

[Helmholtz]

Regarding guitar string grounding, I always thought that lifting the string ground is kind of illusive as long as there are other hard grounded accessible metal parts on a guitar like jack nut, plug shell, PU height screws, metal PU covers, control knob pointers etc. depending on guitar type..
Much safer to use the mains tester before plugging in.

[R.G.]

Regarding guitar string grounding, I always thought that lifting the string ground is kind of illusive as long as there are other hard grounded accessible metal parts on a guitar like jack nut, plug shell, PU height screws, metal PU covers, control knob pointers etc. depending on guitar type..
Much safer to use the mains tester before plugging in.

I agree - and that's why guitar grounding needs carefully thought out.