Grounded (Neutral) Conductor Sizing NEC 220.61

[cdcengineer]

The saga continues... Alright, so here's where we're at:

It turns out that the calculated load for the new panelboard is approximately 325Amps, 208Y/120V. This panel is actually served with #300AL & #250AL neutral w/ #1 AL EGC.

The feeders were originally upsized due to voltage drop concerns as the load was closer to 400 Amps. However, the original installation was done in 1974, and they failed to upsize the EGC. My first code book dates to 1987, and at that time it was required to upsize the EGC per NEC 250.122(B) (2008 NEC then 250.95) proportionately with the phase conductors. My question is this, now that our load would adequately be served with 325Amps, and knowing that we would not have to upsize the feeders due to voltage drop, is the #1 AL EGC adequate despite the fact that the 250.122(B) would require that we upsize EGC regardless? What if I fuse the main at the switchboard feeding this new panelboard at 350Amps, what's the opinion? Would it be acceptable to leave the #1AL EGC rather than installing a new #1/0 (which would be proportionately increased)?

It's been a battle dealing with an owner who doesn't want to spend $ and keeps requesting that we find a way to make it work. The alternative isn't easy, but if it has to be done than he'll have no choice. I wanted to ask the AHJ for thoughts, but the owner sees that as a last resort.

Thanks to all.

 

[Dennis Alwon]

Okay so we have parallel runs, I assume , with 2 conduits??? Yes,

Here is the crazy thing if you had 60C wire in there then you would be req. to use 300KCM but you probably have 75C so now the 300KCM is upsized. This makes no sense to me to have to upsize the egc in this situation. This, I believe, is one of the absurdities of this section. So, the breaker size in this case would not make a difference esp. since 350 would req. the same size egc. as a 400 amp breaker.

Why would the temp. difference in the insulation make for a larger size egc. I guess one could argue that at 60C a 300kcm is req. so you really haven't upsized the conductor size at all. I would run that by the inspector.

 

[cdcengineer]

Thanks Dennis..

Question, of your opinion. I don't know that I should throw the owner under the bus by calling the inspector to discuss this specific project. I will (again notify the owner of my recommendations (that we speak to AHJ). However, if he refuses, do I:

1. Go behind his back.
2. Talk to AHJ about hypothetical project.

And finally, will a letter to the owner of my recommendations cover me (i.e. professional liability) in the event that he says the heck w/ you, we're going to let "sleeping dogs lie"..

I know you're not able to give legal advice, but from an ethical standpoint, thoughts please..

 

[Dennis Alwon]

Well , as a engineer you probably know better than an inspector about the reality of this situation. If it were me, I would call our NC department of insurance and ask the head engineer or electrical inspector what his feelings are on this since he would not be involved in the specific project. I would bet he would say upsize the egc. I guess I would prefer to err on the side of safety and repull but that can be very expensive.

I would let the owners know what the code says and I would recommend pulling the correct size. If he says "To heck with you", then you did your job.

It's a hard one because I really don't see what difference it would make but I understand that the longer the pulls the more chance that the breaker may not trip on a ground fault so upsizing will help.

Remember that the full size egc must be in both pipes of a parallel run.

I don't think we ever covered this but I am assuming the conduit is non metallic.

 

[cdcengineer]

PVC - right you are..

Thx