service feeders

[phil laxague]

our utility service is replaceing our 120/208v, 4 wire service transformer and installing a 480/277v' 4 wire 3 phase transformer. they are using the existing (2) parrallel 700 kcmil. the wires are going to a CT can. I will be going from the CT can to a fused disconnect then to a 600a breaker on a main distrabution panel. i was informed to go with (2) parrallel runs of (4)500 kcmil AL. and 1/0 ground. it seems to me that wire is incorrect. since we have to adjust for 4 current carrying condutors. i also was informed that for service feeders, you don't have to adjust for more than 3 wires. I feel that 400 kcmil CU would do the job! I need some assistance on this. Thanks, Phil.

 

[Smart $]

... i also was informed that for service feeders, you don't have to adjust for more than 3 wires. ...

You were misinformed.

BTW, "service feeder" is an Code oxymoron. It's one or the other, never both.

Welcome to the forum, Phil. :thumbsup:

 

[Smart $]

...I will be going from the CT can to a fused disconnect then to a 600a breaker on a main distrabution panel. i was informed to go with (2) parrallel runs of (4)500 kcmil AL. and 1/0 ground....

What is the disconnect/fuse rating? That determines what size grounding conductor you need.

If 600A like the panelboard MCB, you need 2/0 aluminum minimum. If copper 1/0 is fine as only #1 is required.

 

[Flapjack]

since we have to adjust for 4 current carrying condutors.

Is there a lot of harmonic current? On a 3 phase, 4 wire wye circuit, you only have to count the neutral as a current carrying conductor if the major portion of the load is nonlinear. See 310.15(B)(5)(c).

Or are you saying you are routing the parallel circuits in one conduit, so you will have 6 current-carrying conductors?

 

[dkidd]

our utility service is replaceing our 120/208v, 4 wire service transformer and installing a 480/277v' 4 wire 3 phase transformer.

That is not going to work unless a 480-208Y/120 transformer is also being installed.

 

[kwired]

Originally Posted by phil laxague
since we have to adjust for 4 current carrying condutors.

Is there a lot of harmonic current? On a 3 phase, 4 wire wye circuit, you only have to count the neutral as a current carrying conductor if the major portion of the load is nonlinear. See 310.15(B)(5)(c).

Or are you saying you are routing the parallel circuits in one conduit, so you will have 6 current-carrying conductors?

I agree, unless there is a high nonlinear load there is only 3 current carrying conductors per raceway, from what was mentioned I believe there is three phases plus a neutral per raceway.

 

[Smart $]

...Or are you saying you are routing the parallel circuits in one conduit, so you will have 6 current-carrying conductors?

Eight (8) 500kcmil conductors in one conduit sounds fun... :angel:

I'm leaning toward the OP misunderstanding the neutral conductor not being counted as a current-carrying conductor (ccc) and thought it meant no correction for more than three ccc's.

 

[Flapjack]

Eight (8) 500kcmil conductors in one conduit sounds fun... :angel:

I'm leaning toward the OP misunderstanding the neutral conductor not being counted as a current-carrying conductor (ccc) and thought it meant no correction for more than three ccc's.

haha, yeah that would be intense. It is unlikely that's the case, but it is possible to do.

 

[roger]

I would think the conductors are still under the POCO's rule (maybe not though) on the line side of the disconnect, and if that is the case the NEC adjustments may not be an issue anyways.

Roger

 

[kwired]

I would think the conductors are still under the POCO's rule (maybe not though) on the line side of the disconnect, and if that is the case the NEC adjustments may not be an issue anyways.

Roger

That would depend on where the "service point" is. Past the CT can in many instances is customer side of the service point.

 

[roger]

That would depend on where the "service point" is. Past the CT can in many instances is customer side of the service point.

Yes it would and that might be the reason I said (maybe not though). :roll:

Roger