Is this Neutral current carrying?

[smallfish]

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

 

[Dennis Alwon]

Since fluorecents are considered non-linear loads then the neutral needs to be counted as a ccc assuming a 4 wire, 3 phase wye

 

[infinity]

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

What size conductors are you using? For #12 THHN you're correct that 8 CCC's will get you 21 amps at 70%.

 

[ike5547]

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.

 

[infinity]

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.

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.

 

[steve66]

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