When to use 250.66 over 250.122

[AOGrady139]

Background for the question:

We ran a 400 Amp 3 Phase 120/208V parallel feeder from an already installed 400A MDP breaker. MDP was properly bonded to all required electrodes (building steel, rods, and concrete). The feeders ran to a panel in a retail space for a strip mall. We had an inspection by our state inspector for the energizing of this service and he informed us that the grounding conductor had to be sized per 250.66 Grounding Electrode Conductors. In the past we have always used 250.122 EGC's for this as it is only needed to supply return path for tripping of the OCPD. We sized each equipment ground conductor in the parallel runs at 1 AWG as it states for 400A OCPD under aluminum. Anyone have any idea as to where he is coming up with it? He is telling me it needs to be a 1/0 per 250.66.

 

[charlie b]

Is the retail space in a different building than the MDP? If so, then that separate building needs a grounding electrode system (GES) of its own, and it needs its panel to have a grounding electrode conductor, sized per 250.66, connected to its GES.

But I think the answer is no, the retail space and the MDP are in the same building. If that is the case, then there are no grounding electrode conductors (GECs) involved in the power supply to the retail space. All you need is the EGC, sized per 250.122, as you have already described.

Bottom line: exactly where does the inspector expect this wire, sized per 250.66, to be connected at each of its two ends?

 

[Smart $]

You are correct. Gets sized per 250.122(F).

 

[augie47]

It appears the inspector is incorrect.
250.66 is used when the conductors are not directly protected by an overcurrent device such as service conductors and SDS secondaries.
250.122 is the correct Table when the associated conductors are protected by an overcurrent device.

 

[AOGrady139]

MDP is in the same building. I have to email him for more info on as to where he came up with this. It didn't sound right to me at all.

 

[infinity]

I agree the inspector is not using the correct table. If the feeder conductors were up-sized then the next size up EGC would be #1/0.

 

[mistermudd]

What code section did you inspector refer to? An inspector (such as myself) writes a correction, it needs to be backed up by the NEC or the local AHJ rules?

I can't think of anything that would have these equipment grounding conductor sized per 250.66???

 

[MasterTheNEC]

Maybe the inspectors confusion stems from his lack of understanding that the term "grounding conductor" is no longer in the National Electrical Code.:happysad:

Da man needs to CLARIFY what he wants...lol