"Dave Platt = Radio Ham


Why didn't the residential breaker trip instead?

Residential circuit breakers are typically of the "thermal" type.


** WRONG !!!

They require some amount of time to react to an overload... the higher
the degree of overload, the slower they trip.


** WRONG !!!


"Magnetic" circuit breakers will trip very rapidly in the face of even
a short overload... but I believe these are rarely found in
residential applications.


** WRONG !!!

Domestic breakers are of the " thermal/magnetic" type - ie there are two
distinct mechanisms in the same unit.

The greater the overload, the FASTER they will operate !!!!

Most will trip after a few minutes at 20% above nominal amp rating.

At double the rated current ( 100% overload ) operation is within about 10
seconds, depending on previous history.

The magnetic trip is set way higher ( about 10 times ) the nominal amp
rating - it responds in less than half of a cycle to such overloads and
will even break the severe arc that results from a dead short on the
circuit.



..... Phil