question regarding location receptacle wiring

stephen lamb · June 3, 2009

Hey all,

Have what I feel might be a silly question coming from an electrician. But I've sort of moved into this role recently-ish after being an AC, so forgive me if it's a little basic. anyways, here goes:

The other day I was lighting a small scene on location in a house. I had a 750w source four Leko on a steel combo stand outside on the grass. It was plugged into (via one stick of edison stinger) a three-prong receptacle. Once the lamp was up and running, I stood on the stand and grabbed the back end of the lamp to make an adjustment. I felt a buzz in my hand that quickly grew sharper and more intense. I jumped off the stand, and put my gloves on to unplug the unit! I checked the lamp housing/lamp cable for continuity between the ground and the housing, and it seemed fine. Also checked for continuity between the hot and housing, and the neutral and housing, again, seemed fine (no continuity). I then checked the house receptacle with one of those little sperry three-light testers, and got a "hot/neutral" reverse. After doing some research, I found that by having the hot/neutral reversed, you wind up sending your load through the grounded line, which can build a voltage potential on the surface of the housing. It seems that this is what happened? I had a potential build-up on the lamp housing and when i touched and was also touching the steel stand...well...seems like I was lucky. Can anyone here back up my speculation with more in depth detailed explanations? Or could I be off of the mark entirely? :)

Thanks,

Best!

Edited June 3, 2009 by stephen lamb

jeff woods · June 3, 2009

I may be off the mark here, but the S4 tungsten doesn't care which line it gets the hot from (the sockets are not polarity specific). So, if it was a single line to a single light, which leg the hot is on shouldn't matter.

And this may not be be knowledge to you, but the sockets are grounded to the cap of the fixture, and thus to the chassis of the light itself (primarily through the brass screw that keeps the cap on).

So, my two cents is that the swapped hot/neutral at the receptacle shouldn't make a difference. I'd continuity check your stinger.

Again, I could be completely off the mark.

-j

JD Hartman · June 3, 2009

You outlet tester also didn't tell you if the metal housing of the S4 was energized. Only a voltmeter would have enabled you to determine exactly why you felt a tingle. Since you couldn't isolate the cause, both the fixture and stinger should have been sidlined as defective. If by gloves, you mean your leather gloves, they serve as no protection from stray voltage either. Leather is, after all...skin. It would be safer for you to unplug the stinger at the source.

stephen lamb · June 4, 2009

Hey Guys thanks for the responses. As for needing a voltmeter...that would have of course been useful, but my little multi-meter broke, and only works for continuity. Also, along the same lines, using the continuity meter, I couldn't find any reason that the casing of the lamp would even BE energized, as there was no continuity between the casing and neither the hot nor neutral. This seems to indicate no problems with the lamp, or am I misguided here?

Jeff, that was my understanding as well, at least in terms of the globe itself, in that it will function (turn on) regardless of the direction of the flow of power. However from what I had read, it was my understanding that the trouble occurs with a hot/neutral reverse because of how the unit as a whole is wired. The unit itself is grounded in a particular way that the reverse will cause a voltage to appear on the unit. Maybe I am over thinking this?

For the gloves, that is a helpful tip, and one that seems obvious in retrospect...duh! ha ha. Any recommendations for safer gloves that can handle the heat? Thanks,

Best

Jim Hyslop · June 5, 2009

Hey all,
Have what I feel might be a silly question coming from an electrician. But I've sort of moved into this role recently-ish after being an AC, so forgive me if it's a little basic. anyways, here goes:

The other day I was lighting a small scene on location in a house. I had a 750w source four Leko on a steel combo stand outside on the grass. It was plugged into (via one stick of edison stinger) a three-prong receptacle. Once the lamp was up and running, I stood on the stand and grabbed the back end of the lamp to make an adjustment. I felt a buzz in my hand that quickly grew sharper and more intense. I jumped off the stand, and put my gloves on to unplug the unit! I checked the lamp housing/lamp cable for continuity between the ground and the housing, and it seemed fine. Also checked for continuity between the hot and housing, and the neutral and housing, again, seemed fine (no continuity). I then checked the house receptacle with one of those little sperry three-light testers, and got a "hot/neutral" reverse. After doing some research, I found that by having the hot/neutral reversed, you wind up sending your load through the grounded line, which can build a voltage potential on the surface of the housing. It seems that this is what happened? I had a potential build-up on the lamp housing and when i touched and was also touching the steel stand...well...seems like I was lucky. Can anyone here back up my speculation with more in depth detailed explanations? Or could I be off of the mark entirely? :)

You've got it, that's exactly what happened. The swap occurred somewhere "upstream" of where the neutral and ground were bonded together. Here's a diagram:

The black dashed lines represent a properly wired system. The red lines show the reversed wires. On the right is the supply from the main circuit panel. The thick line represents the instrument's chassis. The reversal could easily happen in an older home, where the ground wire was not part of the original wiring. The lamp doesn't care which of its two wires is hot and which is neutral, so it works OK. But following the hot line from the main circuit panel, you can see how the chassis would get energized.