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
Interesting outlet at show last night
Aaron Maurer:
As I have learned from all the great folks on this site I always test each outlet with my non contact voltage detector. Found an outlet with both hot and neutral energized and ground was fine. To be honest I wasn't going to use it anyway as the venue plugged something into it which I think were Christmas lights. All other outlets were in good shape and the night went without issue. The one thing I learned to be most valuable was to test the microphones and all the chassis on the instruments. Had I not tested the outlet and potentially plugged into it I suppose conditions would/could have changed?
So the question is what may have caused this? Is this the floating neutral syndrome? Why none of the other outlets in the room were effected and is it common to see this in one singular outlet?
Mike Sokol:
--- Quote from: Aaron Maurer on March 20, 2016, 11:39:42 AM ---Found an outlet with both hot and neutral energized and ground was fine.
--- End quote ---
One thing I can think of is that someone wired a standard 120-volt "Edison" receptacle with 240-volts. I've seen this a number of times at churches and gas stations as "special" outlets for the floor buffer or air compressor. Yes, that would probably cause your sound system to burn up anything that didn't have an auto-switching power supply. Always best to test first.
John Roberts {JR}:
--- Quote from: Aaron Maurer on March 20, 2016, 11:39:42 AM ---As I have learned from all the great folks on this site I always test each outlet with my non contact voltage detector. Found an outlet with both hot and neutral energized and ground was fine. To be honest I wasn't going to use it anyway as the venue plugged something into it which I think were Christmas lights. All other outlets were in good shape and the night went without issue. The one thing I learned to be most valuable was to test the microphones and all the chassis on the instruments. Had I not tested the outlet and potentially plugged into it I suppose conditions would/could have changed?
So the question is what may have caused this? Is this the floating neutral syndrome? Why none of the other outlets in the room were effected and is it common to see this in one singular outlet?
--- End quote ---
The floating neutral will only be energized if there is something plugged into that outlet, since the current path is through whatever is plugged in. You mention something was plugged in so perhaps an open neutral connection at that outlet.
JR
Corey Scogin:
I wouldn't think that a receptacle and the wires in a receptacle box are isolated enough to guarantee that an NCVT would not light up in the neutral slot. I would imagine that often, even being that close to the hot may cause some NCVTs to alarm.
Jonathan Johnson:
--- Quote from: Corey Scogin on March 20, 2016, 02:46:28 PM ---I wouldn't think that a receptacle and the wires in a receptacle box are isolated enough to guarantee that an NCVT would not light up in the neutral slot. I would imagine that often, even being that close to the hot may cause some NCVTs to alarm.
--- End quote ---
If the run from the panel is particularly long, and the NCVT is particularly sensitive, there could be capacitive charging of the neutral wire detected by the (extremely high impedance) NCVT.
If in doubt, check with a voltmeter.
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