feeder and voltage drop

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alberto

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good evening everybody,
i have a big question, i need to feed a panelboard, i need to have 800 amperes in this panelboard, i am going to install that feeder on a cable tray, my question is,
may i install two conductors of 300 kcm in paralell, (i dont need neutral conductor), another question is:
how can i calculate the voltage drop?
 
Re: feeder and voltage drop

I don?t think I quite understand your situation. But to start with, you can put two 300 MCM conductors in parallel, but that will not be enough to handle 800 amps. Secondly, you can put two sets of parallel conductors in the same cable tray, but you will have to derate the conductors in accordance with 310.15(B)(2)(a). As to voltage drop, another recent topic on this Forum addresses that question. See this item.
 
Re: feeder and voltage drop

my question was if can i set a pair of 300 kcm conductors per phase on a cable tray?, because i was considering that posibility, i was reading the mexican code that is a copy of the nec code, but i don understand very well, 318-11(b) i understand that i dont need to derate.
800 amperes, 279 feet of lenth, 480 volts, i am going to install 9 conductors of 300 kcm (3 per phase) and a EGC of 1/0, the conductors in a single layer on the cable tray with a space no less of the conductor diameter.
is that correct or do i have to do something more? because i want to do the job very well, because you know most of the electrical instalations are aside of the code here in mexico.
 
Re: feeder and voltage drop

If there are three cable trays, and you're using copper conductors, you're fine. My fuzzy math comes up with 5 volts drop on each conductor.

If they are in one cable tray, you need to derate them.

(Editted to remove mistake before anybody saw it. a 1/0 CU conductor is good for the whole 800 amps per table 250.122. :D )

[ March 16, 2005, 07:29 AM: Message edited by: georgestolz ]
 
Re: feeder and voltage drop

Originally posted by alberto:I am going to install 9 conductors of 300 kcm (3 per phase) and a EGC of 1/0, the conductors in a single layer on the cable tray with a space no less of the conductor diameter.
Click to expand...
Now that I understand your intentions, I will change my opinion. I think you are reading 318-11(b)(3) (1999 version) correctly: You I don?t need to derate. More than that, since you can use the ampacities of Table 310.17, and since a 300 MCM is rated for 445 amps in that configuration, you only need two parallel sets to handle the load. With two sets of 300 MCM and the load and length you mentioned, I get a voltage drop of under 2%.

In fact, I think you could use two sets of 250 MCM. The ampacity (per 310.17) would be 810 amps, and the voltage drop would be about 2%.
 
Re: feeder and voltage drop

I get:

1.8% for two parallel sets of 300 MCM's
2.15% for two parallel sets of 250 MCM's
 
Re: feeder and voltage drop

So what did you do to goof it up George? :D

Edit: I think I'm close to what you did, I got about 10v. for single phase for one 300 MCM one way.

[ March 16, 2005, 05:41 PM: Message edited by: physis ]
 
Re: feeder and voltage drop

Don't you guys need a special union card or something to engineer work on the other side of the border? Or does NFTA cover that?
 
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