Latching/unlatching contactor

[skishin]

On a project with an Owner-furnished 400A latching/unlatching type contactor. The contactor was designed to open upon signal from the FACP to shut down fans in the building. The FACP provides a constant 120V signal for this operation and when applied, it smoked the latch coil. Looks like this contactor is designed for momentary contact push buttons, but I might be missing something? When I look at the SqD website, it says something about the latch and unlatch not being rated for constant voltage and should be wired to the "coil clearing contacts" per the instruction sheet. Cant find an instruction sheet and don't know what this might look like??

The contactor is a Square D 8903 series SY.

Ideas?

 

[masterinbama]

You are correct. The coils in these contactors will not last with constant voltage.

 

[hillbilly1]

Where did you terminate the neutral? If directly on the coil, that is the problem, the clearing contacts on most latching contactors open the neutral. You will also need a slave relay to toggle from open to close and back since you only have a two wire control from the FACP.

 

[Jraef]

Sq. D Wiring Diagram Book

8903 type S is on page 80 (pdf file page 84)

 

[rcwilson]

A clearing contact is a contact that opens the circuit when the action is done.

Wire the "Close or Latch" coil through the contact that is closed when the contactor is open or unlatched and opens wehn teh contactor is fully closed.
Wire the "Open or Unlatch" coil through the contact that is closed when the contactor is closed.

That way as soon as the coil has done its job it is automatically denergized.

As stated above, many times these are factory pre-wired on the neutral side of the coil.