"Ned Simmons" wrote in message
...
In article ,

I think it may have been legal at one time to switch only
two leads of a three 3 phase motor. My 60s vintage IR
compressor has a Square D pressure switch nameplate rated
5HP @ 240V, 3 phase, but is only a 2-pole switch.

I know that it used to be acceptable to put overload
heaters on only two poles of a motor starter, and this is
no longer the case.

Ned Simmons

From the 2002 NEC

Article 430.84
The controller shall not be required to open all conductors
to the motor.
Exception: Where the controller serves also as a disconnection
means, it shall open all ungrounded conductors to the motor
as provided in 430.111
---A controller that does not also serve as a disconnecting
means must open only as many motor circuit conductors as
may be necessary to stop the motor, that is, one conductor
for a DC or single-phase motor circuit, two conductors for
a 3-phase motor circuit, and three conductors for a 2-phase
motor circuit.---


Nate

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