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What Are Forms R641, R642, and R643 On NEMA Lighting Contactors?

Published date: 16 June 2020

Issue:
Identify the forms of a NEMA lighting contactor

Product Line:
Class 8903 Lighting Contactors

Environment:
NEMA Lighting Contactors

Resolution:
These forms add interposing relays to a mechanically held lighting contactor.
There are three different control voltage options:
Use Form R641 for 120VAC coils on the interposing relays.
Use Form R642 for 24VAC coils on the interposing relays.
Use Form R643 for 277VAC coils on the interposing relays.
This form is typically used for long distance control installations.
Addition of two 8501XO11 interposing relays and terminals for customer connections per wiring diagram 31091-354 (see attached files).

Typical connection diagram of mechanical held lighting contactor with Form R64x.  Form R64x allows the latch and unlatch signals to be momentary.  If, for some reason, the voltage on terminal 19 remains while voltage to terminal 18 is applied, the electrical interlocks will prevent the unlatch coil from being energized (typical electrical interlock configuration).

Because the latch and unlatch coils of the contactor may or may not be in the power circuit (common control) and the coils of the relays could in a separate control circuit, the use of a voltage code to specify both line and control is necessary.  Example, if the line voltage for the power contacts is 480V, and if the control voltage for the latch and unlatch coils are at 120V, and if the voltage for the interposing relay coils are at 277VAC the device would be specified as:  8903SMG11V81R643.

See attached file.

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