Residental mains wiring questions (USA)

The classic set-the-office-partition-on-fire situation is to have a y-connected 3-phase system, with a common neutral, and run a bunch of PCs off each phase. The PCs pull current at the peak of the AC line, at six different times each cycle, so even if the three load currents are equal and have the same waveshape, they don't cancel in the neutral.

John

From three different directions?

John

PCs? Oh..yeah..I hear there's a new Commodore Vic 20 available now. It has colour, sound, UPPER *and* lower case Fonts..wow.

Actually they did change the rule concerning derating a few years back, due to what you mention. Before, pretty much only that portion of the total building load comprising the lighting could NOT be derated. (and the first 200 amps of non-lighting load)**. The neutral was generally smaller than hots. Now, it's going in the other direction.

Lighting Ballasts were a big offender, with electronic ones even worse.

All the newfangled stuff seems to cause harmonics, which are additive in the neural conductor. That could make the Neutral current greater than the line current.

You inspired to me to find out how bad this stuff is. The following PDF file has some rather interesting tables.

It appears some electronic ballasts can have UP TO a thirty third degree Harmonic. Wow. That's more than Freemasonry has.

mike

Rectifiers generate harmonics (no surprise).

The "triplen" harmonics - 3rd, 6th, 9th, ... - add instead of canceling on a 3-phase wye neutral.

-- bud--

With their harmonicas.

Ed

AND BANJOES [:-) ouch !

I AM PROTEUS