Harmonics with computers and lighting

[lady sparks lover]

Question??

For fluorescent lighting, I assume the neutral carries current, so I make it a current carrying conductor and derate the feeders for the panel.

But for a panel with all computer loads, if i call for a double sized neutral, should I still derate the wire??

What do you think??

 

[dereckbc]

Re: Harmonics with computers and lighting

Long time no hear from you. If you are using a "K" rated rated transformer or increasing the size of the neutral for whatever reason, then it is assumed the neutral is a current carrying conductor and should be counted. Dereck

 

[ron]

Re: Harmonics with computers and lighting

Unfortunately 310.15(B)(4)(c) does not differentiate between a single neutral carrying the full brunt of the harmonic load, or a double neutral each carrying half the harmonic load. So technically, when exceeding 4 current carrying conductors you must derate, even if two of the conductors are sharing the load.
This is reasonable, since it is possible in a heavy harmonic scenerio, that the neutral current may exceed the full load current of a single ungrounded phase conductor.

 

[bob]

Re: Harmonics with computers and lighting

I think you are asking if you should derate the neutral. You are derating the phase conductors.
You double the phase conductor to get the neutral size, therefore you have already derated the neutral.

 

[bennie]

Re: Harmonics with computers and lighting

Make the load fit the wire or make the wire fit the load.

 

[lady sparks lover]

Re: Harmonics with computers and lighting

Thanks for the info, as always, you guys are great.

Oh dereck, you are making me feel bad. I'll drop by more often. I miss you guys!!

Originally posted by dereckbc:
Long time no hear from you. If you are using a "K" rated rated transformer or increasing the size of the neutral for whatever reason, then it is assumed the neutral is a current carrying conductor and should be counted. Dereck