Derated Neutral

[dbailey0521]

I just got turned down for derating the neutral conductor on a single phase commercial service. It is a 400 amp with two 200 amp disconnects. One is just for the AC units. The other is for the main panel. The load calc has the main panel at 135 amps and the neutral at 70 amps, but he wants a full size neutral. 220.61 "A" states the neutral must carry the maximum unbalanced load. 220.61 "B" (2) states in excess of 200 amps can be derated. When did they change this? If you follow the examples in the back of the book, they are still reducing the neutral. Can anyone give me the correct code reference?

 

[jumper]

I just got turned down for derating the neutral conductor on a single phase commercial service. It is a 400 amp with two 200 amp disconnects. One is just for the AC units. The other is for the main panel. The load calc has the main panel at 135 amps and the neutral at 70 amps, but he wants a full size neutral. 220.61 "A" states the neutral must carry the maximum unbalanced load. 220.61 "B" (2) states in excess of 200 amps can be derated. When did they change this? If you follow the examples in the back of the book, they are still reducing the neutral. Can anyone give me the correct code reference?

Inspector is interpreting that incorrectly, those are additional reductions. Full sized noodle not needed.

 

[Adamjamma]

In that drawing you have an ocpd... but am I right that it only shows three wires going in the conduit towards the main panel there? Because it looks like ground is simply running to the neutral bar.
Or is it an assumption that this is an all metal system so is bonded?

I know, not part of thread... just asking though.

 

[infinity]

In that drawing you have an ocpd... but am I right that it only shows three wires going in the conduit towards the main panel there? Because it looks like ground is simply running to the neutral bar.
Or is it an assumption that this is an all metal system so is bonded?

I know, not part of thread... just asking though.

On the load side of the disconnect there is no wire type EGC because the raceway is presumably metal which qualifies as the EGC.

 

[Dennis Alwon]

The neutral can be reduced as small as the grounding electrode conductor size providing the load on the neutral is not more than that.

Article 230 is for services

230.23(C) Grounded Conductors. The grounded conductor shall not be less than the minimum size as required by 250.24(C).

250.24(C)(1) Sizing for a Single Raceway or Cable. The grounded conductor shall not be smaller than specified in Table 250.102(C)(1).

 

[Dennis Alwon]

To be more correct the neutral cannot be smaller than the bonding conductor. For most service sizes it is the same as the grounding electrode conductor but it changes when the service conductors are over 1100 kcm.