We have a 1200 amp service with existing 3-4" PVC conduits from power company transformer to Main disconnect. We want to use 700 MCM XHHW-2 aluminum to feed the main. Is this acceptable. We realize that we are using the 90 degree rating of 420 amps for the aluminum. The terminal lugs are rated @ 90 degrees.
Aluminum feeder for Main Service
- Thread starter normrunk
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- Location
- Logan, Utah
Welcome to the forum.
You will not be able to use the 90 degree column of Table 310.16 for the ampacity of the conductors. The lugs may be rated for 90 degrees C but the equipment the lugs are connected to will most likely not be rated for 90 degrees C.
You would need to use the 75 degree column which would limit the ampacity of the 700's to 375 amps.
Chris
You will not be able to use the 90 degree column of Table 310.16 for the ampacity of the conductors. The lugs may be rated for 90 degrees C but the equipment the lugs are connected to will most likely not be rated for 90 degrees C.
You would need to use the 75 degree column which would limit the ampacity of the 700's to 375 amps.
Chris
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I agree with Chris. In fact with those conduits you may need to use copper if you need 3 phase with neutral and ground. Otherwise you can go with parallel 350kcm in each conduit depending on the neutral and ground and assuming the neutral is not a CCC
- Location
- New Jersey
- Occupation
- Journeyman Electrician
So you're talking about 6 sets of conductors in 3 conduits?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yes.....If you mean 6 conductors plus egc and neutrals. Is that not doable????
- Location
- Logan, Utah
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Dennis what is a CCC
Current carrying conductor
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Could be, I didn't do the math with the derating. I'll trust that you got it correct.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Could be, I didn't do the math with the derating. I'll trust that you got it correct.
Well I didn't do all the math since I didn't know what size neutral was required but it looked like it might make it.
Welcome to the forum.
You will not be able to use the 90 degree column of Table 310.16 for the ampacity of the conductors. The lugs may be rated for 90 degrees C but the equipment the lugs are connected to will most likely not be rated for 90 degrees C.
You would need to use the 75 degree column which would limit the ampacity of the 700's to 375 amps.
Chris
By what Chris is suggesting you are at 3 X 375 = 1125 Amps. I see no problem with that, unless you have a 1200 amp load.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
How can you have a 1200 amp service with only 1125 amps worth of conductor?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
So you were figuring:
350 Kcmil Al XHHW-2 = 280 amps
6-CCC's = 280 * 2 sets * 80%=448 amps in each raceway
448 amps * 3 conduits = 1344 amps
You don't. What you have is a 1125 amp service with a 1200 amp OCP
- Location
- New Jersey
- Occupation
- Journeyman Electrician
How is that permissible with a single OCPD?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
You cannot go to the next size breaker once you are over 800 amps.. 240.4(B)(3), 240.4(C)
For future reference and a better understanding of 110.14(C) application, the link below is to a Square D Data Bulletin titled: Wire Temperature Ratings and Terminations...
http://static.schneider-electric.us/docs/Power Management/0110DB9901.pdf
DARUSA
Senior Member
- Location
- New York City
Next size up rule is not permited to use over 800 amps .
Your wire will have to be rated at lest for 1200 amps or higher !!!
Forgot about that one, I don't normally do over 800 amp work.
That is what I like about the Forum, you get reminded really quickly. :grin:
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