250.122 interpetation

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puzzled22

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first time poster... dealing with a new inspector.. installing a 480/277 400 amp service.. fused disconnect.. 2 200 amp subpanels fed with 3/0 conductors...my question is about ground size... 250.122 has the phrase "ahead of equipment , conduit.. ect. " my inspector interpets that phrase as my grounding should be sized "ahead" meaning the 400 amp rating instead of the 200 amp rating of the conductors feed the subpanel...specifically i am referring to the ground conductor to be carried with the 3/0 conductors.. thank you in advance..
 
The inspector is correct. The Equipment Grounding Conductors between the 400 amp OCPD and the 200 amp panels is required to be sized based on the 400 amp OCPD.
 
I must have missed this or forgot about it as I see 250.122(G) was added in the 2005 code cycle, which means you will be required to run a #3 instead of a #6 EGC for the feeders, it does make sense for feeder taps because a #6 might not clear a 400 amp breaker fast enough before the fault can damage the insulation of the conductor, but then again with a 25 foot limit on the tap you would think there would still be enough available fault current to clear the 400 amp breaker or fuses? specially if we are in the over 25k AIC range?
 
hurk27 said:
I must have missed this or forgot about it as I see 250.122(G) was added in the 2005 code cycle, which means you will be required to run a #3 instead of a #6 EGC for the feeders, it does make sense for feeder taps because a #6 might not clear a 400 amp breaker fast enough before the fault can damage the insulation of the conductor, but then again with a 25 foot limit on the tap you would think there would still be enough available fault current to clear the 400 amp breaker or fuses? specially if we are in the over 25k AIC range?
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That was not really a code change...the code rules have always required this. The only reason for the new wording was because too many were missing that. The rule was found in the heading of T250.122 in the 2002 and previous codes.
Rating or Setting of Automatic Overcurrent Device in Circuit Ahead of Equipment, Conduit, etc., Not Exceeding (Amperes)
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don_resqcapt19 said:
That was not really a code change...the code rules have always required this. The only reason for the new wording was because too many were missing that. The rule was found in the heading of T250.122 in the 2002 and previous codes.
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IMO the wording was needed, I still see this just about everywhere someone installs tap conductors.
 
infinity said:
IMO the wording was needed, I still see this just about everywhere someone installs tap conductors.
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I didn't say the additional wording was not needed, I am just saying the code required this long before 250.122(G) was added to the code.
 
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