3 Ph.4W

[kiss]

I looked at a commercial installation with the following. 800 Amp 3P4W distribution board(not service equipment) 1-switch feeds a 3p 4W panel fused at 100Amps. The nuetral in this panel is feed with #8 wire and the feeds are # 2THHN.
The load is only 6 cirts. all 120V low amps.
Is this a code violation?
If I increase the neutral to a # 3 THHN would this meet code ? Since feeds are # 2THHN. #3 for the neutral since its rated for 100amps and the panel is fused at 100Amps. Thanks

 

[nvcape]

Re: 3 Ph.4W

NEC 220.22 requires neutrals to be sized for the maximum load, this could even include harmonic loads. NEC 110 requires the 60 degree column for 100 amps and less. It appears you don't think the number 8 is enough, and you are probably correct.

 

[steve66]

Re: 3 Ph.4W

If there are only two 20A single pole breakers on each phase (for a total of 6 breakers), the maximum unbalance would be 40 amps on the neutral. #8 is rated for 40 amps at 60C.

But, if another breaker is added to the panel, the neutral would be overloaded. I would only allow this if it is a six space panel, or if there was some way to ensure another breaker isn't added.

See 220.22 and 215.2 of the 2002 NEC.

Steve

 

[kiss]

Re: 3 Ph.4W

I was away for a few days, no Inter. access.
The existing panel is a 42 ckt M.L.O. panel with a #8 Neutral. The additional load that will be added to this panel is 80 Amps 3phase 4wire. So I will change the existing neutral to a # 3THHN.

 

[ryan_618]

Re: 3 Ph.4W

Originally posted by nvcape:
NEC 220.22 requires neutrals to be sized for the maximum load, this could even include harmonic loads.

In your opinion, would harmonic currents on the nuetral of a setup like the one described be a violation of 310.10?

I realize that FPN's are not enforcable code, but it almost seems to me that 310.13 is a performance requirement, and not entirely a prescriptive one. In particular, see the FPN (2).