Andy Hill wrote:

Derek Broughton wrote:
Yeah, but the pond's probably a long way from the nearest outlet on a
too-small extension cord. 1250/15 = 83V, which is one heck of a voltage
drop, but perhaps not impossible if the house is on the end of a long
rural run - where voltages tend to fluctuate quite a bit anyway.

C'mon Derek, that dog don't hunt. We ain't dealing with a motor here --
this is just a big honkin' resistor (11.5 ohms, more-or-less), which isn't
going to
change resistance significantly, no matter what the line voltage. 15
amps through a 12.5 ohm resistor is nearly 2600 watts (which also implies
188 volts
across the resistor). Nope.

Doesn't work that way. Line voltage drops. Line voltage _always_ drops, we
just try to keep it minimal based on sizing the wire. Line voltage drops
_a lot_ when you run it through an 18Ga extension cord. Your "volts across
the resistor" is not across the heater, it's across the heater and all the
cable leading to it - which is why it's a fire hazard. All I showed there
is that the voltage would have to be down to around 83V to blow a 15A
breaker, which (I agree) even on an extension cord seemed too much.

Either the breaker / fuse is weak, or there's another 500+ watts of other
load on the circuit.

Yeah, like the _other_ pond heater. Ruth - just because you have two pairs
of outlets doesn't mean you have two circuits. Did both heaters stop
working when the breaker blew?
--
derek