Since you will be driving the compressor from a 30A breaker/fuse, you can either
use a dryer cord, or the proper sized SO cord with a 30A twist lock which will work
very well. A disconnect is not required with a plug, but is with a direct wired
installation (no plug).
Uncle Bob
The disconnect is NOT required in his case as he says he has line of sight (and I have to assume less than 50 ft) from the circuit breaker. In this case, the CB is the disconnect.
Most plugs and receptacles in the 30 amp range are not, I suspect, motor rated for the horsepower he will be running.
NEC 430.109(F) governs most plug and cord connected motor installations.
430.108 Every Disconnecting Means. Every disconnecting
means in the motor circuit between the point of attachment
to the feeder or branch circuit and the point of connection
to the motor shall comply with the requirements of 430.109
and 430.110.
430.109 Type. The disconnecting means shall be a type
specified in 430.109(A), unless otherwise permitted in
430.109(B) through (G), under the conditions specified.
(A) General.
(1) Motor Circuit Switch. Alisted motor-circuit switch rated
in horsepower.
(2) Molded Case Circuit Breaker. A listed molded case
circuit breaker.
(3) Molded Case Switch. A listed molded case switch.
(4) Instantaneous Trip Circuit Breaker. An instantaneous
trip circuit breaker that is part of a listed combination
motor controller.
(5) Self-Protected Combination Controller. Listed selfprotected
combination controller.
(6) Manual Motor Controller. Listed manual motor controllers
additionally marked “Suitable as Motor Disconnect”
shall be permitted as a disconnecting means where
installed between the final motor branch-circuit shortcircuit
protective device and the motor. Listed manual motor
controllers additionally marked“Suitable as Motor Disconnect”
shall be permitted as disconnecting means on the
line side of the fuses permitted in 430.52(C)(5). In this
case, the fuses permitted in 430.52(C)(5) shall be considered
supplementary fuses, and suitable branch-circuit shortcircuit
and ground-fault protective devices shall be installed
on the line side of the manual motor controller additionally
marked “Suitable as Motor Disconnect.”
(7) System Isolation Equipment. System isolation
overcurrent protection and its disconnecting means. The
disconnecting means shall be one of the types permitted by
430.109(A)(1) through (A)(3).
Paragraphs (B) thru (E) are not relevant to this discussion.
(F) Cord-and-Plug-Connected Motors. For a cord-andplug-
connected motor, a horsepower-rated attachment plug
and receptacle, flanged surface inlet and cord connector, or
attachment plug and cord connector having ratings no less
than the motor ratings shall be permitted to serve as the
disconnecting means. Horsepower-rated attachment plugs,
flanged surface inlets, receptacles, or cord connectors shall
not be required for cord-and-plug-connected appliances in
accordance with 422.33, room air conditioners in accordance
with 440.63, or portable motors rated 1⁄3 hp or less.
While the OP does not say, a 23 amp motor is most likely a full 5 hp motor. Code tables list 28 amp for 5 hp, but I find the table is usually a little higher than what you find listed on the motor. In this case we really need to know the actual horsepower of the motor. if it is 5 hp, then you are required to calculate wire size based on 125% of the value given in NEC table 430.248 and NOT use the FLC given on the motor data plate. You DO use the FLC given on the data plate for calculating the Circuit Breaker size that protects the circuit.
Its quite possible the OP needs to use #8 wire with his compressor supply, and something heavier than a 30 amp dryer plug.
The easiest way out of this is to use a 60 amp outdoor disconnect as shown above, it is designed for air conditioner units and will carry the starting loads, it will provide a good place to connect the circuit wires and the wires from the compressor, and it will be relatively inexpensive at $12 to $15. A box, cover plate, splices for the wire sizes involved will run this much and you don't have the local disconnect (which while not needed, is an nice feature)
Charles
