What is the minimum size grounded conductor required for the following installation?
A service consists of a NEMA 3R service-rated fusible disconnect. The load supplied is a 100 hp, 460V, 3-phase motor for a pump in the middle of a field (with appropriate motor controls and equipment). The ungrounded service entrance conductors are 2/0 AWG XHHW. The electric utility supplied service is 3-phase, 4-wire grounded.
- 1/0 XHHW (70% of 2/0)
- 2/0 XHHW
- No. 1 XHHW (2 sizes smaller than 2/0)
- No need for a grounded conductor since the motor is 3-phase.
Because the electric utility service is grounded, a grounded conductor must be installed. As noted in 250.24(C)(3), the grounded conductor shall have an ampacity not less than that of the ungrounded conductors. This is a new requirement in the 2011 edition of the NEC.
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