gwandsh wrote:
This weekend I had planned to add a 1000 watt electric heater to an
existing circuit with three similar heaters on it. The other heaters
are 750 watt, wired 240, and draw 2.7 amps each. The circuit is 30
amps, so I expected to pony the new heater (4.5 amps @ 240V) off the
wire to one of the existing heaters, and still not challenge the
breaker.

I was surprised to find the wire to the circuit I planned to pony from
was a 14/2. I traced it back to the junction box, and found each of
the heaters was serviced by a 14 gauge wire. Then I was horrified to
find that the wire from the panel to the main junction box for all
circuits was also a 14 gauge. Even at low amperage, I would expect at
least a 12 gauge, maybe 10?

The existing circuit is fine with 14 ga wire (but it should have a
15A breaker or fuses, not 30A). You can load it up to 12A, because
resistive heating circuits are limited to 80% of their ampacity --
so adding a 1000W heater (14 guage wire is good enough) takes you
pretty close to the limit but you're still under.

Make sure that the breakers or fuses are the right size for the
wires -- 15A. This is important. The rest, not so much.

Bob