On Mon, 10 Sep 2007 23:00:19 -0500, homebrewdude
wrote:

The breaker never tripped.

The power dropped and lights went out, pumps turned off.

But all the other lights and TV stayed on.

All on one breaker, which did not trip.

Voltage drop means the whole overall circuit will be drawing less
current , not more (due to the added resistance). If the voltage gets
too low, you might have problems with dim bulbs and a slow-to-heat
fish tank, but it sounds like you are not there yet.

If you continue to add load, you will be drawing more current and may
reach the tripping point of the breaker. (It may not be exactly 15
amps). The reason it trips can be a complex function involving time,
thermal delay, and factors like surge intensity. Residential circuits
are usually derated to 80% of the breaker rating for maximum
continuous load.

If the breaker is a GFCI breaker, it might trip for apparently no
reason at all. Usually, though it is caused by actual leakage to the
ground circuit. I've also had several trips due to nearby lightning
strikes, but the new GFCI's are supposed to be better for this.