On 1/26/2014 11:35 AM, Fred Abse wrote:
On Sun, 26 Jan 2014 08:13:56 -0500, Jim Wilkins wrote:

"DoN. Nichols" wrote in message
...
On 2014-01-25, Jim Wilkins wrote:

Why do you need two fuses for a single-phase motor?

In the UK, you don't, because 240 VAC comes with one side grounded.
However, in the USA, 240 VAC is normally supplied with a grounded center
tap, so if you have only one fuse -- or have two but only one blows, you
still have 120 VAC live in the motor's housing, and
potentially available for contact and personal zapping. :-)


I assumed it was wired with a 20A double-pole breaker at the panel
protecting from shorts and a smaller fuse sized (how?) to blow before the
motor burned out.


Panel breakers are there to protect the upstream wiring from excessive
load current, not to protect the load.

Matching the I-squared-t of a breaker, or fuse, to startup and running
conditions of a motor is not trivial. Motors are subject to starting
inrush currents sometimes tens of times the rated full-load current. Be
guided by the data published by reputable manufacturers. There's plenty of
it.

Most motors are tough old buzzards. Why the op needs more protection is
unknown, I would think some kind of thermal or time delay overload is
sufficient which may already be in the motor.

Jeff