So if you got this service call tomorrow, just exactly how would any of you proceed to diagnose the problem? I'm really curious as to what gear you would bring and how you would begin testing.
I know how I would do it... I want to know how YOU would do it. Thanks in advance.
A simple extension cord plugged into a known good properly wired receptacle can make a great trouble shooting tool in finding a RPBG receptacle or any reversed polarity receptacle in a 2-wire system, while voltage sensors or "Tic-Tracers" as some may call them can have there place in a tool box we must keep in mind they have there limitations and these must be fully understood, as they do tend to produce many false positives that can throw off even the best trouble shooter if you don't understand how they function here are some points to ponder:
Voltage sensors can chirp on a conductor that is not even connected to any other conductors but is close enough to a live conductor for enough capacitive coupling to put a ghost voltage on it, it can also say there is a voltage on a cabinet or case just because there is no bond to the case by the same problem, and because of this should not be used by itself to verify the present of voltage without also using a low impedance meter such as a wiggy or a loaded DVM.
The most reliable method I have found is the extension cord to a known good receptacle or even to Earth.
I too am a certified sound tech and before Electro-Voice was bought out held a contractors certificate to install Electro-Voice PA systems spent many hours up at the Buchanan, Michigan plant going through their seminars to get it so I could purchase directly from them, I'm very impressed with your understanding of many of the problems with sound systems and how electrical problems can make for a bad show (most time they rare there ugly head right in the middle of the show no fun)
I have installed many PA/DJ systems in clubs only to find that the place was wired by any drunk who says they know how to do it and will work for drinks, some of the horror story's I can tell would make many on here run for cover only to have this type of wiring that in many cases been in place for years be cause it is so simple to cut the ground off or like you said many take light shocks as a norm in these kind of places and nothing ever gets done till some one dies or is badly hurt.
While I will agree with Don that RPBG is not a common find in a dwelling it happens and in my career I have run into it twice, in clubs and bars well more time than I should have, both times in a dwelling were a receptacle installed in a garage one for a refrigerator and the other a freezer, even taking the receptacle apart wasn't a clue as who ever installed the circuit ran back under the house which only had old cloth covered romex and tied both the new neutral and EGC to the hot because the wire was so old you could no longer tell which was which.
First thing I did was get a 100' extension cord off my truck and a tap receptacle and run it to the main service panel which was on the other end of the house in a bedroom and made a temporary tap right at the main panel so I would know how it was wired, using this cord and my test meter (Ideal Volt-Con) it confirmed my suspicion that both the neutral and the EGC were hot, using a wire tracer I followed the wire back under the house to a octagon box where I found the mistake, they had also reversed the polarity of several livingroom receptacles and two lights that was also coming from that box when they were putting the connections back together, what amazes me is this little old lady wasn't killed as this work was done a few years before and it was the first time she ever went to get something out of it without any shoes on, and the fact they had no grand children that could have been hurt or killed by this.
But in the bar's and clubs anything goes and I have learned to be on the lookout as any one working in them should for shoddy work, I tell them right up front if I find any dangerous wiring it will be fixed or I can't continue as the liability is just too great.
I made a post in another thread
"Audio Hum" that most hums in audio systems are cause by current on the grounding, while this can occur in a NEC compliant wiring and I gave the reason in most cases its because the wiring is not compliant.
While I had always kept in my stage tool box sets of 1 to 1 simple matching transformers or balaunes in about every configuration to get a show out of a jam (the show must go on sort of speak) but afterwords I made sure that the owner fully understood the dangers of using the grounding or having even un-intentionally grounded neutrals and or other problems that could come back and cost him dearly if it were to cause someone to get hurt of killed, I always left it up to them whether or not they wanted me to look at it or someone they know as they are paying the bill, but many times I would get the job, and what I find many time is where someone just missed wired a cord end and swapped the neutral and EGC but I would also find many violations that would take way more typing then I wish to type on here.
Over the years I have made many post on here of these problems and many solutions to how to find them, but a good knowledge in electrical theory is a must to understand that current takes all paths even the nice little shield that most audio cable has running with it, and since it is referenced at both ends it will capacitive couple this 60hz into the signal wire and since 60hz is right in the audio spectrum of that amplifier, it does what it is designed to do it amplifies it.
Why we haven't got away from un-balanced shielded audio cable that references the EGC at both end is beyond me, and yes it can be done, isolated shielding has been done for many years in some industries and has been taking a hold in the Data area as a few have started to realize we don't need to reference Earth to make things work, but then if they did we would not be finding all these grounding problems that audio equipment seems to find very well.
Ok fingers need a break
