View Full Version : Overload sensors

Lew Hartswick
05-16-2012, 03:49 PM
Does anyone have or know where to find a cross ref. to the sensors
in motor starters for the overload "heaters"? I have tried to find any
thing on them in a dozen places on the net starting with a search on
"motor starters" or controllers and the results are less than helpful.
I think it' a Cuttler Hammer and the number on the sensor is:
C250B The cover is not at hand but is available so am not 100%
sure of the company. Did write down the number though. :-)
We want to use it on a 5 Hp 240V 3 Phase motor and would like to
see if the sensors are appropriate or get the right ones.
Thanks for any info. or pointers to a source.

05-16-2012, 04:29 PM
"Heaters" are simply auto-resetting (normally) thermoelectric switches. They're current sensitive - as the current increases they get hot, it they conduct too much current for too long they get too hot and open. The neat thing is that they're naturally load averaging - they'll take a pretty good pulse of current (think of the starting inrush) without opening, but a lower current for a little longer will get it too hot and it'll open the circuit.

Gerneric contactor information:


Cutler-Hammer heater selection:


Without knowing the contactor and motor current I couldn't say, but the C250B is a 21.8 amp heater and would be (roughly) appropriate for a 7HP motor. You'd want something more like a C198B, at 17A it's more appropriate for a 5HP motor.

Lew Hartswick
05-17-2012, 09:24 AM
For anyone who may be interested, the starter was a GE and if you
ever want info on the sensors etc. here is a link to tell you more
than you want.