Where or how do I figure out Conductor Sizing for 3 Phase Service? Its a 600 amp main, according to table 310.16 its something like 1500 kcmil, that can't be right. This is the first job I have actually ran, and most prints have all this figured, atleast the jobs I have been on. So for a 208/3 phase service how do I calculate the service conductors, Thank you for helping out a green electrician.
3 Phase Service Conductor Sizing
- Thread starter dpandres
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- Connecticut
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- Engineer
Two sets of 350 MCM would have an ampacity of 620A, and would be acceptable for your service with a 600A main.
Thank you
Thank you
Thank you very much. So do tell, how did you come up with that, is there calculations that I have to do, or is it something I am missing in the NEC? I am thankful for your answer I just want to learn how so that I don't have to keep posting every time I cross a different size main. Thanks
Thank you
Thank you very much. So do tell, how did you come up with that, is there calculations that I have to do, or is it something I am missing in the NEC? I am thankful for your answer I just want to learn how so that I don't have to keep posting every time I cross a different size main. Thanks
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Are you familiar with parallel conductors?
kingpb
Senior Member
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- SE USA as far as you can go
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- Engineer, Registered
You are correct in the way you looked up the ampacity from 310.16. If you were to run a single set of conductors, they would need to be 1500KCMIL.
The issue becomes practicality, and you have to ask yourself, is running a set of 1500KCMIl conductors practical? This is where experience and knowledge of installation and product availability takes over.
First, you will not be able to purchase that size of conductor "off the shelf" it would have to be a special order. Sine it is a special order, it will probably have a minimum length which may be way more than you need. Second, say you can order the cable you need, what is your timeline to complete the job? If it is short, the order time for the cable may put you out past the completion date. Finally, working with anything over 750KCMIL is a nightmare, some say over 500KCMIL is a nightmare, because of the equipment you need just to handle it, and get it installed. Assume you bought XHHW-2 and it is going in a 4" conduit. Are you prepared to install a 4" run of conduit?
From a practical point of view, the 1500KCMIL is not a good choice, and so you need to look for alternatives, that being as mentioned, parallel conductors.
The 350kCMIL works nicely because you need 600A, and running two conductors per phase of 350KCMIL is 2 x 310A, so that works well. 350KCMIL is probably more quickly obtained in the quantity you need, and working with 2 x 2-1/2" conduit is going to be much more easily accomplished.
Remember, when using the NEC, it is the MINIMUM requirements to install a safe system, it is not meant to be a design guide.
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