thermal overload relay contact convention

[JMJM]

While helping my son add an additional pump motor to a control panel, we noted that the designation of NO and NC on an older AllenBradley thermal overload relay was opposite that of the newer version from Schneider. Checking the current AB thermal overload relays, the NO and NC labeling is the same as the Schneider unit. In the older unit, the labeling corresponded to the tripped state while in the newer units, it corresponds to the untripped state. When did the convention change and what is the reference standard? Thanks !

 

[Jraef]

It does not correspond to the tripped state on the melting alloy, bimetallic or E1 SSOL relay. If you are looking at a programmable SSOL like the E3 or E300 network relays however it’s different. The reason is that in those versions the contact is network controlled and is also the Run Command contact, not just the OL trip contact. So you tell it to close and the motor runs, if anything makes the relay trip, the contact opens and drops out the contactor.