480V 3PH Neutral Wire Sizing

[dcg4403]

Greetings,

I'm a EE and have installed many electrical systems but am now dealing with my first large 3PH install on our property. I'm not formally trained in this area but very familiar as a EE. Anyway, can someone help me with proper neutral wire sizing?

I've done a bunch of research and am finding mixed answers. It comes down to this:

I'm planning on running 1000 MCM aluminum underground from a main disconnect at the pole to a MLO panel at our building about 400 feet away. This is for a 480V Wye Configuration with 400A meter.

I know the safe bet is to use a 1000 MCM for the neutral. But how do I go about proper sizing? I could save quite a bit of money if I'm allowed to run a smaller gauge wire for the neutral.

 

[Megawatt]

Greetings,

I'm a EE and have installed many electrical systems but am now dealing with my first large 3PH install on our property. I'm not formally trained in this area but very familiar as a EE. Anyway, can someone help me with proper neutral wire sizing?

I've done a bunch of research and am finding mixed answers. It comes down to this:

I'm planning on running 1000 MCM aluminum underground from a main disconnect at the pole to a MLO panel at our building about 400 feet away. This is for a 480V Wye Configuration with 400A meter.

I know the safe bet is to use a 1000 MCM for the neutral. But how do I go about proper sizing? I could save quite a bit of money if I'm allowed to run a smaller gauge wire for the neutral.

A good rule is size it at 83% of the 400 amp panel for a single family dwelling. So size it for 383 amps

 

[Megawatt]

A good rule is size it at 83% of the 400 amp panel for a single family dwelling. So size it for 383 amps

I’m sorry it’s 332 amps

 

[Megawatt]

Greetings,

I'm a EE and have installed many electrical systems but am now dealing with my first large 3PH install on our property. I'm not formally trained in this area but very familiar as a EE. Anyway, can someone help me with proper neutral wire sizing?

I've done a bunch of research and am finding mixed answers. It comes down to this:

I'm planning on running 1000 MCM aluminum underground from a main disconnect at the pole to a MLO panel at our building about 400 feet away. This is for a 480V Wye Configuration with 400A meter.

I know the safe bet is to use a 1000 MCM for the neutral. But how do I go about proper sizing? I could save quite a bit of money if I'm allowed to run a smaller gauge wire for the neutral.

I also need to ask, is your building going to be used as a commercial building. If so you are not allowed to derate the neutral.

 

[Simon47]

Apart from any regs that apply in your location, you need to understand the loads.
At one extreme, if all loads have non-complex waveforms then there's scope to reduce the neutral. At the other extreme, you could need a neutral larger than the phase conductors as third harmonics add rather than cancelling. Things like computer power supplies have got a lot better (for regs compliance) over the years, but flouros with magnetic have a very peaky current waveform.