1200A Feeder Size 1

[birddogger]

Per NEC 240.4(B), a 277/480V, 800A feeder is allowed to be the industry standard of 2 sets of 3-1/2”C, (4)#500, (1)#2G even though the ampacity of the feeders are only 380A. However, it seems that I’ve seen this standard applied to 1200A and 1600A feeders as well, even though 240.4(C) requires any OC device over 800A to have conducters rated equal to or greater than the device rating.

So am I correct in assuming that the proper size for a 1200A feeder would be 4 sets of 3”C, (4)#350, (1)#3/0G? Or is there some loophole I’m not aware of that would allow three sets of #500's to be applied to this circuit as well?

 

[RonShap]

Although the actual terminal may carry a 90 deg rating from the terminal manufacturer, when it is installed in a piece of equipment, the equipment as a whole generally is 75 degrees (larger than 100A), because the manufacturers have not been testing equipment at the higher levels.

 

[alehman]

RonSharp's statement agrees with my understanding of the present UL listing situation.

jbartos,
See note below tables on page 31 here-

http://ecatalog.squared.com/techlib/displaydocument.cfm?id=3100CT9801&action=view

 

[busbar]

Code stranding on 500kcmil is 37 strand—where 600kcmil is 61 strand, making it a little easier terminate. [99NEC Ch9 table 5A]

 

[REDDOG]

The temperature rating applys to current montoring devises, OL Relay Blocks, Fuses,and Circuit Breakers (not 100% rated.
This derating only applies to equipment rated less than 600 Volts. Bolted Pressure Contact Switches and 100% Rated Circuit Breakers can be terminated a 90 degree if so labeled. Running a conductor at 90 degree rating is incresing circuit losses and voltage drop

 

[davidbeach]

Many 100% rated devices require the use of 90 degree conductors AT the 75 degree ampacity.

 

[jbartos]

Comment on the previous alehman posting: I agree that all devices that have temperature rating limit on the conductor temperature termination have to have these limits satisfied. Visit

http://www.nmsu.edu/~tdi/pdf-resources/cc47.pdf

for related examples

 

[alehman]

I think the previous posting sums it up.

Terminals are rated based on the mutual heating effects. If rated for 75C then the conductor terminated must be sized based on its 75C rating. This is because of the mutual effect of heat from the conductor and from the device. The concern is for effects of heat on the device, the connection itself and the insulation on the conductor. Using a compression lug vs. mechanical doesn't typically change the rating.

 

[jbartos]

Suggestion: Visit

http://www.nmsu.edu/~tdi/pdf-resources/cc31.pdf

http://www.bussmann.com/library/docs/spd02/SPDSection04.pdf

for more info on the 75deg and 90deg conductor insulation rating and application.

 

[jbartos]

Comment on alehman (Electrical) Mar 27, 2004 marked ///\\jbartos,
See note below tables on page 31 here-

http://ecatalog.squared.com/techlib/displaydocument.cfm?id=3100CT9801&action=view

///Yes, these are safety switches in Section 3 Class 3110 with advertised lug temperature ratings 60°C and 75°C. However, I was referring to disconnect switches Section 7 Class 9422, in my posting on Mar 27.\\