Is the neutral required in a panelboard

[steve66]

We had an existing 208V 3 phase, 3 wire motor control center. We used it to feed a new panelboard for 208V loads. The feeder was 3 phase, 3 wire with ground and no neutral (since there wasn't a neutral in the MCC). Now the inspector says the panel has to have a neutral wire to clear faults!! What code article would require this?

Steve

 

[bphgravity]

Re: Is the neutral required in a panelboard

There isn't one. The equipment grounding (bonding) conductor's purpose is to clear the fault back to the main service disconnect. From that point, the grounded (neutral) conductors takes over carrying the fault. Only the service requires a grounded conductor, 250.24(B).

 

[charlie]

Re: Is the neutral required in a panelboard

Keep in mind that the grounded conductor is a normal current carrying conductor and not there for fault return. The grounding system is for fault currents. The main bonding jumper carries the fault current to the grounded service conductor so the fault current can return to the source.

 

[rbalex]

Re: Is the neutral required in a panelboard

Steve,

I'm beginning to see a trend where some of our colleagues are put into the position where they feel they need to "prove a negative."

I believe the first response (with respect, of course) needs to be along the line of requesting the inspector explain how they derived their Code interpretation directly from the text. I confess I just haven't faced it that often, but if 90.4 is the only answer, I'd say you had solid grounds for an appeal.

BTW, in this case if you carried the neutral, what would you connect it to?

[ December 06, 2004, 03:50 PM: Message edited by: rbalex ]

 

[steve66]

Re: Is the neutral required in a panelboard

BTW, in this case if you carried the neutral, what would you connect it to?

I believe the panelboard does have a neutral bus.

Steve

 

[steve66]

Re: Is the neutral required in a panelboard

I have talked to the inspector, and I will get a code reference tomorrow. Apparently, the Motor Control Center and the panelboard are both labeled "120/208V 3 phase, 4 wire". Does a panelboard or MCC require a neutral if it is labeled "4 wire"?

Steve

 

[charlie]

Re: Is the neutral required in a panelboard

I don't see why it would need one if it is not going to be used, what would be the point?

 

[jim dungar]

Re: Is the neutral required in a panelboard

Grounded conductors are not part of the fault clearing path. Maybe your inspector need to be reminded about the difference between grounded and grounding conductors?

There are panelboards that are rated as 480Y/277 or 208Y/120 or even 600Y/347. These panels are UL Listed for a maximum voltage to ground of 277, 120 and 347V respectfully. Many inspectors mistakenly see the voltage to ground rating as a requirement for a neutral.

As long as your system is solidly grounded, there is no need to carry an "unused" conductor.