4000 amp 480v 3ph switch gear

[electrofelon]

Lets assume the switchboard will be directly connected to rebar ufer ground.
Bond that ground back to the metal case of the trafo. Run one insulated Cu grd wire in with the neutrals.

I am not sure why you want to run a ground back to the transformer (true we dont know for sure it is a service and not a SDS, but your comment about connecting the UFER to the switchboard strongly implies that you are assuming the service disconnect(s) are in the switchboard). The utility transformer would not be under the NEC, and besides the transformer case would be bonded to the XO (even if the NEC applied, see 250.92(B)(1)).

 

[dionysius]

I am not sure why you want to run a ground back to the transformer (true we dont know for sure it is a service and not a SDS, but your comment about connecting the UFER to the switchboard strongly implies that you are assuming the service disconnect(s) are in the switchboard). The utility transformer would not be under the NEC, and besides the transformer case would be bonded to the XO (even if the NEC applied, see 250.92(B)(1)).

Assumption is it is a service transformer 480Y/277 4 wire. Assume the service disconnects are in the switchboard as is the metering (CT). So what you are saying in this case is that the service is a SDS (separately derived system) and its GEC is connected to the UFER ground with the neutral bonded to the grd. The point of service is defined as the secondary 4 wires leaving the trafo. The service provider (PUD) will be responsible for having the trafo case grounded.

 

[mstrlucky74]

We use 10 set's of 600 kcmil for 4000 amp services. As Bob stated 420*10 gets you over 4000 amps.

If it so happened the equipment lugs were rated fro 90 degree you could use (10) sets of 500, correct?

 

[mstrlucky74]

Its is very rare to count the service neutral as a CCC. Even something like a high rise or server complex will probably have a high enough AC load that the linear loads wont be a "majority."

So when are neutrals counted as CCC's? I'd like to read up on that. Thanks

 

[iwire]

If it so happened the equipment lugs were rated fro 90 degree you could use (10) sets of 500, correct?

The lugs most likely will be, the equipment will not be.

It is my understanding that there isn't any 90 C rated equipment for 600 volts or less.

 

[infinity]

So when are neutrals counted as CCC's? I'd like to read up on that. Thanks

This little list may help:

Neutral Conductors:
Here's some examples of when to count and not count the neutral as a current carrying conductor or CCC:

3Ø- 208Y/120 or 480Y/277 volt system-different circuit types:
A) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B) 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C) 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*

Notes:
A) A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B) In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C) In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with an exception, *if the current is more than 50% nonlinear (see below for NEC article 100 definition) then the neutral would count as a CCC.

1Ø- 120/240 volt system-different circuit types:
D) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E) 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's
Notes:
D) A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
E) In this circuit the neutral will only carry the imbalance between the two ungrounded conductors so the neutral is not counted as a CCC.

 

[kwired]

If it so happened the equipment lugs were rated fro 90 degree you could use (10) sets of 500, correct?

The lugs themselves may actually have markings on them that indicate they are 90 degree, but I'm pretty sure you won't find a under 600 volt breaker or fused switch that is listed as 90 degree for terminations and the lug(s) still need to make that connection - @ 75 deg.

 

[kwired]

I need help on determing what size wire and how many per phase for 4000 amp run of 480v 3ph between a tranformer and switch gear. I know that 500 is 380. if I multiply that by 10 it is 3800 and by 11 it is 4180. Would that be 10 or 11 sets? And is a set defined as A,B,C,& GRD?

The answer to your question depends on a few other factors. Many of them have already been mentioned.

1. are you supplying a single service disconnecting means?
if not, your minimum conductor ampacity may be allowed to be less then 4000 amps, but must be at least the calculated load.
if yes, for over 800 amps the minimum conductor ampacity must be equal or greater then the overcurrent protection level - no rounding up to next standard size for over 800 amps.

2. number of current carrying conductors in raceways
If you have ABCN per raceway there is no ampacity adjustment unless there is a high amount of non linear load - unless you are supplying a data center this is probably not a concern.
If you have all one phase per raceway - then 10 or 11 conductors in raceway must have a 50% adjustment - 500's go from being marginally sized to well undersized in that situation, let alone the fact those raceways will be huge even without considering adjustments needed.

 

[electrofelon]

Assumption is it is a service transformer 480Y/277 4 wire. Assume the service disconnects are in the switchboard as is the metering (CT). So what you are saying in this case is that the service is a SDS (separately derived system) and its GEC is connected to the UFER ground with the neutral bonded to the grd. The point of service is defined as the secondary 4 wires leaving the trafo. The service provider (PUD) will be responsible for having the trafo case grounded.

Its either an sds or a service. I have been assuming it is a service. Yes utility will bond the transformer. Gec goes from the switchboard (most likely, it doesn't have to however ) to the first grounding electrode. Maybe it's an UFER, maybe it's just two rods.

 

[Phil Corso]

I need help on determing what size wire and how many per phase for 4000 amp run of 480v 3ph between a tranformer and switch gear. I know that 500 is 380. if I multiply that by 10 it is 3800 and by 11 it is 4180. Would that be 10 or 11 sets? And is a set defined as A,B,C,& GRD?

Freddy...

Because of inductivity effects it is better to bundle 3 (or 4) single-conductors carrying the 3-phases between source and load, when running parallel cables, in a tre-foil arrangement!

Regards, Phil Corso

 

[mstrlucky74]

This little list may help:

Thanks.

 

[topgone]

But it is somewhat rare that the neutral in a system like this would be required to be counted as a current carrying conductor.

Agree. Neutrals do not count as current-carrying.

IIRC, the conditions where one does not apply ampacity adjustments on paralleled conductors are:
376.22(A) ". . . sum of the cross-sectional areas of all contained conductors at any cross section of a wireway shall not exceed 20 percent of the interior cross-sectional area of the wireway"
"and"
376.22(B) . . . .if the total number of current-carrying conductors does not exceed 30.

The first condition is what we don't know.

 

[iwire]

Freddy...

Because of inductivity effects it is better to bundle 3 (or 4) single-conductors carrying the 3-phases between source and load, when running parallel cables, in a tre-foil arrangement!

Regards, Phil Corso

Phil,

Because of different perspectives and goals better to one person is not always better to the other.

As an installer this is better to me.

Regards, Bob

 

[Besoeker]

I need help on determing what size wire and how many per phase for 4000 amp run of 480v 3ph between a tranformer and switch gear. I know that 500 is 380. if I multiply that by 10 it is 3800 and by 11 it is 4180. Would that be 10 or 11 sets? And is a set defined as A,B,C,& GRD?

Would busbars be an option?
That's what I would do. But then I'm a Brit. And a Scot at that........................

 

[iwire]

Would busbars be an option?
That's what I would do.

In an industrial location here that would be a common solution.

On the other hand if this is say a hotel, an office building, data center or something of that nature they will usually want the installation done underground to hide it which in my experience ends up being wire type conductors.

 

[Besoeker]

In an industrial location here that would be a common solution.

On the other hand if this is say a hotel, an office building, data center or something of that nature they will usually want the installation done underground to hide it which in my experience ends up being wire type conductors.

Fair comment.

 

[Phil Corso]

Phil,

Because of different perspectives and goals better to one person is not always better to the other.

As an installer this is better to me.

Regards, Bob

Bob,

What you illustrated is correct for phase leads! But, it is incorrect to have all groundED leads together separated from the phase leads! Was the distance from the source to the load significant in length?

Regarding my reply to paralleled cables, I was referring to the case where individual conductors (would be 4-sets in your case) are installed horizontally in a cable tray!

Phil

 

[roger]

Bob,

But, it is incorrect to have all groundED leads together separated from the phase leads!



Phil

And why do you think that? If the non metallic raceways are run in close proximity to one another it doesn't matter anyways.

Roger

 

[iwire]

Bob,
But, it is incorrect to have all groundED leads together separated from the phase leads!

Phil, that statement is incorrect.

Was the distance from the source to the load significant in length?

How far is significant and how will that change circuit operation in an unsafe way?

Regarding my reply to paralleled cables, I was referring to the case where individual conductors (would be 4-sets in your case) are installed horizontally in a cable tray!

But the OP is running this in conduit ...

 

[Ingenieur]

Phil,

Because of different perspectives and goals better to one person is not always better to the other.

As an installer this is better to me.

Regards, Bob

That is a clean installation but could have been done by sets too
the conductors were derated since >3, correct?
does the cond area < 20% cnd area? How long was the run? In feet
short no big difference, long Cu and cnd add up fast
you have 8 cnd = 8 sets, could have rotated cnd 90 deg and been pretty clean
could have possibly used 6 smaller sets (conductor and cnd at 40% fill) without derating?
easier manipulating into position then

there is no right or wrong, these are preferences and judgement
as long as code compliant doesn't matter