ECN Forum Forums General Topics of the Trade General Discussion Area Current on neutral

Yes positive out in the country everythings 120/240. So could it be because of the flourescent lighting or something else. Or is it normal because the lights are the only load ?

As I said above, it is _possible_ that the lighting is producing enough even harmonics to cause this current reading. However I don't think that it is particularly likely that the lighting would cause quite this much harmonic current flow on the neutral, and would be inclined to check for another problem.

You could try metering all of the currents in all of the wires (ungrounded conductors, grounded conductor, and _equipment ground_ conductor) with different combinations of load, eg. no lights on, then 1 bank on, then the first off and the second on, then all the lights on. How the currents change with load might provide a good clue as to what is happening.

-Jon

When you find the problem/answer please post your findings, I for one would be interested to see what did cause this phenom.

Jon,
I don't think so. If they are fed from the two hots, the same order harmonic from one hot will always cancel out the that harmonic on from the other hot on a true single phase system. The two hots come from opposite ends of the transformer winding are "in effect" 180 degrees out of phase. All of the harmonics, no matter what order they are, will also be 180 degrees out and cancel in the neutral.
Don

Don,

That is not correct. The phase displacement of the harmonics is equal to the phase displacement of the fundamental multiplied by the harmonic order.

In three phase systems, you take a fundamental phase displacement of 120 degrees, and any triplen harmonic will produce a phase displacement that is a multiple of 360 degrees.

In single phase systems, _even_ harmonics will take the phase displacement of 180 degrees in the fundamental, and produce a phase displacement of that is a multiple of 360 degrees, or _0_ degrees. As far as I know, people have not been seeing even order harmonics as a problem, they do, however exist.

-Jon

Do the fixtures have electronic ballast or coil ballast ?
Are the tubes "watt miser" type.
Need more information to make an educated guess.
Alan--

edited, guess I didn't read the orignal post very well Now I see both legs were at 7 amps

[This message has been edited by walrus (edited 11-25-2005).]

Wraiths,
Before we get into the possible quantum physics involved, did you check the current on the neutral after you turned either bank of lights off?
my suggestion would be to look at this the same way you would trouble-shoot a tripping breaker.
Turn each bank off one at a time, taking readings on the neutral after each time.
Is the neutral current only apparent with one of those circuits or is it additive between both?
Are the lights on both circuits the same make, model, amperage, etc?