4000 amp 480v 3ph switch gear

[freddy.cage]

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?

 

[iwire]

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?

What I have seen is 10 sets of 600 copper for a 4,000 amp service. (10 x 420 = 4,200 amps)

You cannot round up as you can with smaller services so if you have a 4,000 amp breaker you need at least 4,000 amps of conductors.

 

[dionysius]

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?

500 kcmil at 90 degC 430 amps
12 * 430 = 5160 derate 20% 5160 - 1032 = 4128

So 12/phase

A set is defined as A, B, C, N

 

[don_resqcapt19]

500 kcmil at 90 degC 430 amps
12 * 430 = 5160 derate 20% 5160 - 1032 = 4128

So 12/phase

A set is defined as A, B, C, N

We don't have any information that says we have an ampacity adjustment issue for this installation.

 

[iwire]

A set is defined as A, B, C, N

By who?

 

[infinity]

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

 

[charlie b]

12 * 430 = 5160 derate 20% 5160 - 1032 = 4128

Why are you derating? I would not go into this design assuming that the neutral would count as a current-carrying conductor, especially at the service.

A set is defined as A, B, C, N

You need to include some type of ground wire to that set. Usually the first OCPD is at the switchboard. So there will be one Supply Side Bonding Jumper that has to be run between the transformer and the switchboard.

 

[infinity]

You need to include some type of ground wire to that set. Usually the first OCPD is at the switchboard. So there will be one Supply Side Bonding Jumper that has to be run between the transformer and the switchboard.

You may be right I was thinking service switchgear but this could be a feeder instead of SEC's.

 

[dionysius]

Why are you derating? I would not go into this design assuming that the neutral would count as a current-carrying conductor, especially at the service.

I'll buy that if the Inspector does. So let me recompute:

10*430 = 4300 so 10/per phase

Run the phases in separate conductors to make it easy......

[FONT=&quot]
[/FONT]You need to include some type of ground wire to that set. Usually the first OCPD is at the switchboard. So there will be one Supply Side Bonding Jumper that has to be run between the transformer and the switchboard.

Point well taken. Safety first.
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.

Now tell me what is the absolute min size neutral and ground to use????
I have my own ideas but I would like to see someone else jump in.

 

[electrofelon]

I'll buy that if the Inspector does.

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."

You need to include some type of ground wire to that set. Usually the first OCPD is at the switchboard. So there will be one Supply Side Bonding Jumper that has to be run between the transformer and the switchboard.

I would think the transformer would be bonded by the neutral conductor (assuming this is a service).

Run the phases in separate conductors to make it easy......

I concur that makes for a much neater easier job, however we should note that there are restrictions on running isolated phases. This being a switchboard should make it doable.

 

[topgone]

We don't have any information that says we have an ampacity adjustment issue for this installation.

This is very important. Running more than three, current-carrying conductors in a raceway requires adjustment on the ampacity of conductors.

 

[Ingenieur]

It would be nice to know a few basics
distance: side by side on a pad or a few hundred feet apart?
concrete duct bank?
service or feeder?
load: balanced N or considered i carrying ie derate > 3 cond

grouping phases is seldom done
usually on pads where there are bending radius constraints

 

[don_resqcapt19]

This is very important. Running more than three, current-carrying conductors in a raceway requires adjustment on the ampacity of conductors.

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

 

[infinity]

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

I agree, maybe we'll hear back from the OP to hear what the setup looks like beyond the number of sets he's using. For a 4000 amp service we would use a custom made auxiliary gutter for the 10 sets of SEC's between the POCO and the service equipment.

 

[augie47]

It would be nice to know a few basics
distance: side by side on a pad or a few hundred feet apart?
concrete duct bank?
service or feeder?
load: balanced N or considered i carrying ie derate > 3 cond

grouping phases is seldom done
usually on pads where there are bending radius constraints

I agree...more info for a more assured answer. It appears we are all approaching this as a 4000 amp main also. Probably is, but there's a possibility we are dealing with MLO so clarification of that and the calculated load would also be important.

 

[Smart $]

... For a 4000 amp service we would use a custom made auxiliary gutter for the 10 sets of SEC's between the POCO and the service equipment.

The wiring method employed will be subject to site criteria. An auxiliary gutter (or wireway) is typically only used for near and adjacent equipment.

A major advantage of using gutter or wireway is no derating for up to 30 ccc's.

 

[dionysius]

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.

We have covered the CCCs fairly well in this thread.

Anyone here want to take a stab at what is the absolute min size neutral and ground to use????

Also do all agree that same phases in separate raceways is the easier and acceptable way to go????? Assume side by side raceways with no airspace.

 

[roger]

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.

What are going to do if there is no CEE present?

Also do all agree that same phases in separate raceways is the easier and acceptable way to go????? Assume side by side raceways with no airspace.

To bad it won't work with 10 or 11 conduits per the NEC.

Roger

 

[don_resqcapt19]

...
Anyone here want to take a stab at what is the absolute min size neutral and ground to use????
...

The neutral would be based on Table 250.102(C)(1), so if you are using 500 kcmil conductors it would be 1/0 in each raceway, but if you are using 600 kcmil it would be 2/0 in each raceway.
If by ground you mean grounding electrode conductor, the minimum would change based on the grounding electrode that is used. The absolute minimum would be a #6. The maximum required by the code would be 3/0 no matter what type of electrode is used.

 

[Ingenieur]

...
Also do all agree that same phases in separate raceways is the easier and acceptable way to go????? Assume side by side raceways with no airspace.

no, a common grouped phase is seldom the way to go
we have no information to determine that
having seen it rarely used in 30 years imho it is likely NOT the way to go
but not enough info to say one way or the other

my WAG's
10 sets 750's in a 2x5 duct bank or
9 sets 1000's in a 3x3 bank
no derating

need to cost it out to the most efficient/economical method
lugs/terminations
Duct bank
conduit
length
etc

need more info
swatting a flea with a tennis racket lol