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dpb

On 4/14/2014 10:31 PM, wrote:
On Tue, 15 Apr 2014 00:38:06 +0000 (UTC),
(Larry W) wrote:

In ,
Mike wrote:
...snipped...
Not to mention that the themal overload in the switch has no idea at all
what the motor is seeing.

Not necessarily true either. I didn't look in detail at theat switch's
specifications, but I believe it had current-sensing heaters in it
matched to the motor size, similar to what a magnetic starter with overload
protection uses.
Which will PREDICT temperature based on load, but cannot take into
consideration reduced air flow and other factors.

It has nothing whatever really to do with predicting the motor
temperature, per se, it's simply overcurrent motor protection (as
opposed to overcurrent _circuit_ protection that is the function of the
breaker/fuse). Sizing is based on FLA and motor rating of how long is
allowed before protection kicks in.

The devices have colloquially been called "heaters" at least in the US
(I don't know about the frozen north jargon