Motor Overload Relay - Heater Elements

[nhee]

My understanding is that if you remove the heater(s) from a standard 3-pole thermal overload relay, the aux contact on the overload relay should open.

Today we came across a couple at a site where the OL contact remained closed with the heaters removed. We disconnected leads to ensure our continuity measurements were not through the starter coil or other circuit devices.

Is this normal?

 

[bphgravity]

Re: Motor Overload Relay - Heater Elements

The aux contact is just a switch that is engaged by one of the heaters. Upon removal of the heater, the switch should open as you describe.

Check to see if the switch is jammed closed or stuck. Also, is it possible that the aux contact has been changed out to a normally closed operation for whatever reason.

 

[electricman2]

Re: Motor Overload Relay - Heater Elements

Depends on the brand. On some Cutler-Hammer OL relays, the heater coils can be removed without tripping the switch. Removing the solder pots will cause the switch to trip.

 

[Ed MacLaren]

Re: Motor Overload Relay - Heater Elements

As John has stated, it depends on the type of trip mechanism.

In the bi-metallic units the heater does not make physical contact with the trip bar.
In the molten alloy (solder pot) units, the contact is actually "latched" closed by the heater assembly.

Ed

 

[bert47]

Re: Motor Overload Relay - Heater Elements

The NEMA rated older Allen Bradley OL relays do not trip when the type "N" heater coils are removed. The solder pot ratchet wheel stays in the trip circuit. Same for type "J" heaters. The newer type "W" heaters have the ratchet wheel built into the heater coil and will trip upon removal. Square D styles will trip also. Generally if the ratchet comes out the unit should trip.

 

[steve66]

Re: Motor Overload Relay - Heater Elements

Bert:

I tried thinking positive, but it seemed to attract all the negatives