Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums > AC Power and Grounding
Dangerous AC situation in reception hall - PLEASE READ
Steve-White:
--- Quote from: Mike Sokol on May 03, 2012, 07:39:04 PM ---A hot-ground swap will cause the 3-light outlet tester to show red, warning you that the ground is hot. But a RPBG (Reverse Polarity Bootleg Ground) will appear to be wired properly using a 3-light outlet tester. And it will meter as correctly wired using a voltmeter as well. Even a $300 GLIT (Ground Loop Impedance Tester) like I use in my proof-of-concept video will not recognize a RPBG outlet. The only way to know for sure is to reference the earth itself by using a non-contact tester which capacitively couples to the earth via your body, or run a wire to known good ground (vice grips on a cold water pipe in the basement).
I'm pitching the idea of adding the VoltAlert test to the NFPA 70E National Electrical Code. This should be performed on EVERY outlet in any facility that had strange power problems. It only takes one RPBG outlet to trash your sound system.
BTW: I have a new test I've developing that will predict ground loop induced hum without having to plug in a single piece of audio gear. More fun!!!!
Mike Sokol
--- End quote ---
Wow, I've been doing this for a long time and it never occurred to me. I've always used the cheap 3 light Edison type plug-in tester. I am adding the capacitance voltage tester to my bag.
This can't be over-emphasized enough! Be safe gentlemen (and ladies), a non-contact voltage tester can be had for under $20 and could be a lifesaver. You could also test mics, amp cases, etc for voltage.
Really smart advice.
Craig Hauber:
--- Quote from: Jonathan Johnson on November 19, 2016, 12:25:06 AM ---I NEVER trust the terminal colors when wiring up plugs and receptacles, ever since I discovered a duplex receptacle that had been shipped from the factory with the brass and silver screws reversed.
How many others actually wire according to the position of the terminals rather than the color?
--- End quote ---
Which reminds me, and I may have posted this here years ago, but check your detachable cordsets (IEC, mickey-mouse, appliance-type as well as any powercon ones)
I have experienced factory-made molded ones that are reversed.
Anything with a aftermarket cord-cap is obvious suspect too, -especially when repairs have been made to it and blue-brown-yellow wiring is encountered by the unwitting handyman.
So if you find yourself pulling-your-hair out frustrated then check all the cords, power strips and rackmount power centers in your own system for factory errors. They may be rare but out of 500+ IEC cords in my own collection I found 2! -and it only takes one to screw the whole rig up.
Nathan Vanderslice:
--- Quote from: Guy Luckert on May 03, 2012, 08:11:18 PM ---whether it's a stove and a refrigerator or a guitar and a mike a "perfect storm" would be both plugged into hot grounds of opposite phase for a whopping 208 or 240 volts passing through your heart at 60 time a second U.S.A. (55 times a second at higher voltage abroad)
hot sticks are a good idea
now I'm gonna watch the video
--- End quote ---
I will post this here, and I know it's an old post. I've seen several posts on here that suggests that people are forgetting that it is not voltage that kills, it is the current that kills. I've heard of stories of electricians who will touch a wire on a circuit, probably where they are installing a light or fan or some such thing and just get a bit of a tingle. That's because they are fairly well grounded and only a very tiny amount of current is getting through. Years ago, I was working on an old B&W TV, trying to center the picture on the screen when I brushed a finger on the flyback transformer. 18 kv at 15750 cycles per second. If it were voltage the kills, I wouldn't be here to write about it.
Geoff Doane:
--- Quote from: Nathan Vanderslice on April 01, 2021, 07:27:42 PM --- ... I've heard of stories of electricians who will touch a wire on a circuit, probably where they are installing a light or fan or some such thing and just get a bit of a tingle. That's because they are fairly well grounded and only a very tiny amount of current is getting through...
--- End quote ---
It's not because they're fairly well grounded, it's because they aren't well grounded. No ground (or a very poor one)= nowhere for the current to flow.
Or it's possible that their hands are well callused and a high resistance, resulting in low current.
GTD
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