Is this Neutral current carrying?

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smallfish

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Am I correct in considerating the neutral conductor as a current carrying conductor (ccc) when it is run in pipe with its three phase conductors as a mulitwire branch circuit from panel to flourescent lighting fixture loads? I refer to 08NEC 310.15 (B) (4).

I ask this because, if it is so, then I will be limited in pulling only two multiwire branch circuits instead of three in a pipe run due to adjustment factors of 08NEC 310.15 (B) (2).

Thanks
 
Since fluorecents are considered non-linear loads then the neutral needs to be counted as a ccc assuming a 4 wire, 3 phase wye
 
smallfish said:
I ask this because, if it is so, then I will be limited in pulling only two multiwire branch circuits instead of three in a pipe run due to adjustment factors of 08NEC 310.15 (B) (2).

Thanks
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What size conductors are you using? For #12 THHN you're correct that 8 CCC's will get you 21 amps at 70%.
 
Out of curiosity, has anyone ever checked to see just how much "non-linear" current really ends up on the neutrals of balanced 4-wire circuits connected to electronic ballasts? Not arguing with the code, just wondering.
 
ike5547 said:
Out of curiosity, has anyone ever checked to see just how much "non-linear" current really ends up on the neutrals of balanced 4-wire circuits connected to electronic ballasts? Not arguing with the code, just wondering.
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Good question. We all make assumptions based on what we've read or have been told. I've never made such a measurement. Maybe someone out there has.
 
Most electronic ballasts are rated at 20% THD, or 10% THD.

For a circuit with 10% ballasts loaded to 16 amps, that would mean 1.6 amps of harmonics. So if we consider 3 of these circuits, each on a separate phase, and they share the neutral, there should be a maximum of 4.8 amps on the neutral.

I haven't tested the calculation above, so I won't guarentee I haven't missed something.

So its not a lot of current, but more than the 0 amps you would get with purely resistive loads.

Steve
 
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