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[Mike Sokol]

My article on measuring for Reverse Polarity Bootleg Grounds just published in Mike Holt's electrical safety newsletter last night. This newsletter goes out to 50,000 electricians and inspectors around the country every day. Below is one of the comments from another pro-sound tech.

http://www.mikeholt.com/newsletters.php?action=display&letterID=1804&email=#comments

Comment Posted:
I am a professional audio technician working in theater and corporate audio/visual(A/V). Fortunately, working with pro A/V companies, I rarely see bootleg gear come my way any more. Through experience, I guess that we have all learned that prevention, meaning properly wired gear, is cheaper than spending time troubleshooting ground problems in the field. The most important tools in my bag of tricks on every show are a three light outlet tester and a multimeter. Thank you for showing the false readings displayed when testing bootleg plugs using a three light tester. On shows, before anyone plugs anything in to the power distribution center(PD), which is usually a two or three phase unit, I check voltage to determine proper wiring from the disconnect panel. You would not believe the stupid and unsafe wiring that we encounter. Not only is hot to hot, hot to neutral, and hot to ground measured, I also check hot to chassis, neutral to chassis, and ground to chassis as well. I also measure the voltage between neutral and ground. When necessary I also identify the different phases of the plugs on the PD. These simple tests are very important in knowing what we are dealing with before using the venue electrical system as ground hums and buzzes in any part of the A/V system are highly undesirable. Quite often I find that the venue provides a three phase system using only 4 wires. The ground and neutral are improperly bonded inside the local PD. Usually, as you mentioned, a reading of absolute zero volts ground to neutral is the first identifier of this condition. I always wonder if the bonded connection is derived from the load panel ground buss or the neutral buss. One of the most frustrating things that we encounter is using power from separately derived sources/transformers within a building. This frequently occurs when the front of house(FOH) mix position is plugged into a different power source than backstage, hence, different ground p ath. If there is a buzz or hum in the sound system we have several tricks and tools to use. One solution is to run a power cable to the FOH position from the same PD that all of backstage is plugged into. Another might be to use digital snakes instead of a traditional copper snakes. These may include fiber, ethernet, or coaxial. These methods can sometimes help eliminate undesirable ground loops/noise in the system. As for individual "local" problems, as was the case recently, it turned out that a computer power supply was creating noise on one of the computer audio playback channels. I magically found a power strip with a missing ground pin to use on the computer PSU. That helped, even as illegal as its use may have been. Improvisation is a very big part of creating a "clean" temporary A/V system. In all my years of doing this I have hardly ever encountered a GFCI outlet in any venue unless there is a generator company supplying show power or we are plugging things in to the kitchen/catering outlets.

Zippy

[Mike Sokol]

Here's another response about RPBG's from my article on Mike Holt's newsletter.

Hi Mike,
It was exactly as you described.

1. Old, late 1940s to mid 1950s house.
2. All bedroom outlets un-grounded.
3. All bedroom outlets bootlegged.
4. One of the circuits, with bootleg outlets, became hot-neutral reversed for unknown reasons.
5. Home owner had a laptop plugged into a reverse bootleg outlet and an audio device plugged into a another bootleg outlet that was not reversed. There was an audio or USB cable between the laptop and the audio device.
6. Home owner watched as the cable burned up.

Ira Rubinson
Kestrel Electric
Ventura County, CA

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