Sizing of parallel (or more) conductors to transformer

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andrewpineo

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310.15(B)(2)(a) shows derating of parallel conductors, but not how to size them. For a 2000 kVa transformer with a 480V secondary I have 2406A. What size conductors would I use for two (or three) conductors on each phase?
 
Are you sure you are an engineer? Depending on the actual calculated load, you are probably looking at approx. 6 sets of 500 kcmil or possibly 600 kcmil.
 
These would normally be ran in separate conduits to avoid the derating you mentioned. But you may need to derate the cables some if they are in a duct bank.
 
Just divide the load by the conductor ampacity(after any required derating). If the conductor ampacity is 380 amps, then you would need seven sets. Note that there are rules that differ between service conductors and feeder conductors as far as the conductor sizing and the OCPD. Also look at 250.122(F) if this is a feeder.
Don
 
Warning. Thread hijacking in progress.

Something I have often wondered.

Why is it that people even put in such huge transformers in the first place.

Why not scatter several smaller ones around the premises?
 
{MODERATOR'S NOTE: This member has been banned for rude and inappropriate behavior towards other members. All of his posts are being deleted.}
 
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petersonra said:
Warning. Thread hijacking in progress.

Something I have often wondered.

Why is it that people even put in such huge transformers in the first place.

Why not scatter several smaller ones around the premises?
Click to expand...
Good afternoon, Bob. One possibility is you're building a large manufacturing facility, and the utility is providing 12.47 kV. You'll probably want a pair of outdoor transformers for that. I don't think you run 12.47 kV around to a handful of smaller transformers in that scenario. You might step down to, say, 480V and distribute *that* to a handful of smaller ones.

The whole thread is of great interest to me. We'll be facing a similar problem with a pair of 2.0 kA 480V parallel feeds soon.

The problem with the outside transformer and 480v secondary is the sheer size of the duct bank. I'm not keen on it myself, but I haven't come up with an alternative in our case because the building simply wasn't designed with room for a pair of indoor substations.

Andrew, you'd better get a decent calc program for the duct bank you're going to have to build.

Dan
 
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Sorry for calling you into question Andrew. Based on your PM, I realize your question is not as basic as I assumed. It would be helpful if you posted the entire details of your installation so the scope and context of the question is better understood. Again, I apologize if I offended you in any way...
 
My nerves would also be shot, if trying to justify the cost & wiring methods for a 2400A feeder. May prefer feeding some MV equip., locked behind "High Voltage" signs.

If there is no choice, there are single conductors for this load that may save some cost.
2500A F.Bus, PI.Bus, & CL.Bus are available in CU or AL.
 
ramsy said:
If there is no choice, there are single conductors for this load that may save some cost.
2500A F.Bus, PI.Bus, & CL.Bus are available in CU or AL.
Click to expand...

I am not familiar with the F.Bus, PI.Bus ,and CL.Bus references. Could you expand.
 
kingpb said:
I am not familiar with the F.Bus, PI.Bus ,and CL.Bus references. Could you expand.
Click to expand...
My apologies for using those odd acronyms. some common amperages are listed below:
Code: 
Fuse Bus, Plug-In, Current-Limiting Bus
600 AL   800      1000
800      1000     1350
1000     1350     1600
1350     1600     2000
1600     2000     2500
2000     2500     3000
2500     3000     4000
3000     4000
4000     5000	
5000
 
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