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#92201 03/07/05 08:19 AM
Joined: Oct 2002
Posts: 830
S
Member
When running motor circuits in conduit, where the breaker size is 250% of the FLA, is there an exception to the rule of sizing the equipment grounding conductor, according to the rating of the OCD in the circuit? For example I have a machine with a total amperage of 39.8 amps X 250% = 99.5 amps which would put me at a 100 amp. breaker. Is the ground wire size for the conduit still a # 8 or am I missing an exception somewhere when dealing with motor circuits.. I have other smaller motor circuit conductors in the conduit also, but this is the largest. Thanks, Steve

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#92202 03/07/05 10:37 AM
Joined: Jul 2004
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250.122(A) General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122 but shall not be required to be larger than the circuit conductors supplying the equipment.


Greg Fretwell
#92203 03/07/05 10:41 AM
Joined: Nov 2000
Posts: 2,148
R
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If you are using a motor circuit protector or magnetic only breaker for the short circuit and ground fault protection then 250.122(D) lets you size the EGC based on the overload protection rating. In your case, it appears that you are using a thermal magnetic breaker and you must size based on the breaker rating, however as greg pointed out 250.122(A) says the EGC is not required to be larger than the circuit conductors, but that does not change anything for your example as the circuit conductors will be #8 and Table 250.122 calls for a #8 EGC for a 100A OCPD.
Don


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