Generator Feed Conductors

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ehawks

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Where are the rules that determine the ampacity of the emergency feed between the generator circuit breaker and the automatic transfer switch? Same questions about overcurrent protection of these conductors?
 
I think I know

I think I know

I needed to give an answer and did not get any input in time. See if you agree with my response.
Someone questioned our sizing of the generator output feeder between the generator breaker and the transfer switch. Below are the code referances I cited.....See if you agree. I used the 90 degree rating of 4/0 becuase we do have 90 degree terminals on the breaker and xfer switch.


NEC 240.4 Protection of conductors indicates the conductors need to be protected in accordance with their ampacities from table 310.16. In this case 260 amps but because 260 is not a standard amp setting (see 240.6) which allows you to select the next highest standard trip setting which is 300. A 300 amp breaker is being provided with the generator.

Using the table NEC table 310.16, 90 degree C rating of the 4/0 wire it is rated for 260 amps which is 115 percent more than the nameplate amp output rating of the generator.
 
Make sure that ALL of your terminals are rated 90 degrees, not just the terminals in the generator. My understanding is that 90 degree terminals are fairly rare, but I may be wrong.
 
I agree with Mr. Ben A Round. 115% of nameplate rating or 100% if generator has overload protection.
 
spsnyder,

The OP'er stated 260a was 115% of nameplate rating, I was saying the load

calc should be less than that because of the 300a breaker.
 
Just because the terminals are listed for 90?C does not mean that you can use the 90?C ampacity. I am not aware of any breaker in that size range that is suitable for use with 90?C conductors.
Don
 
benaround said:
Don, How do you make that little ' degree' mark, if it's not to hard to explain?
Click to expand...
Press ALT + 0176 on the keypad by your right hand..?

ALT + 0216 = ?

You can find these symbols and others right on your computer....
Start>Programs>Accessories>System Tools>Character Map

charactermap.jpg


:)
 
benaround said:
Thanks, Celtic !! I guess that shows my limited computer skills. Agian Thanks
Click to expand...

There is actually some usefull some that actually comes pre-loaded on the computer :grin:

Have fun.
 
celtic said:
There is actually some usefull some that actually comes pre-loaded on the computer :grin:
Click to expand...
Indeed. Check out the Accessibility for Special Needs topic on the Contents tab in Windows Help in the Start-button menu.
 
don_resqcapt19 said:
Just because the terminals are listed for 90?C does not mean that you can use the 90?C ampacity. I am not aware of any breaker in that size range that is suitable for use with 90?C conductors.
Don
Click to expand...

Adding to what Don stated, it is not just the breaker terminals. The enclosure has to also have a 90C rating.
 
benaround said:
spsnyder,

The OP'er stated 260a was 115% of nameplate rating, I was saying the load

calc should be less than that because of the 300a breaker.
Click to expand...


Sorry Frank.

I thought you were saying to size the conductors based on load calcs. I think we all agree they should be 115% of nameplate (or 100% with overload protection) and in the 75? column.

Also thanks for the degree symbol info.

Regards,
 
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