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Sizing Equipment Ground #92201
03/07/05 08:19 AM
03/07/05 08:19 AM
S
sparkync  Offline OP
Member
Joined: Oct 2002
Posts: 830
NC
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

2017 / 2014 NEC & Related Books and Study Guides
Re: Sizing Equipment Ground #92202
03/07/05 10:37 AM
03/07/05 10:37 AM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,166
Estero,Fl,usa
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
Re: Sizing Equipment Ground #92203
03/07/05 10:41 AM
03/07/05 10:41 AM
R
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
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


Don(resqcapt19)

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