Devices Rated Over 800 Amperes

[Jeff Fairfax]

I have run across this topic more than enough times, but, would like someone else's opinion. Installing a 1200 amp overcurrent device, many times customers, and or engineers request 3 runs of 500kcmil conductors. The code reads that anything 800 amperes or over must have conductors equal to or greater than o.c. rating. This would lead me to believe that 3 runs of 600 kcmil would be necessary to meet code. Since 3 runs of 500 kcmil is equivalent to 1140 amperes, it would be necessary to drop the o.c device to 1000 amperes. I've spoken to several local people about this and get the same reaction, "we've been installing 1200 amp services with 3 runs of 500 kcmil for years" is this wrong or am I misinterpreting this particular code article? I always get questions why my price is higher than my competitor when it comes to 1200 amperes services. Any thoughts?

 

[infinity]

Your interpretation is correct. You would need a minimum of 1200 amps worth of conductor for a 1200 amp OCPD. If you used 3 sets of 500 kcmil you would have to protect those conductors at 1140 amps or less. Over 800 amps you cannot use the "next standard size" rule.

Welcome to the forum.

 

[augie47]

Depends
Do the services they describe have a main or are they MLO services ?
You are correct that (3) 500s are not adequate for a 1200 amp main, so often a 1200 MLO panel will be installed with a load calculation below 1140 amps.
I'm sure there are some inspectors who might allow (3) 500s for a 1200 amp main service especially if you install an underground service and take in account the 70-77 ambient correction factor.

 

[Rockyd]

Looking at the chart (310.16) and looking at 310.15(B)(2) ex 4, and with the use of 90'C terminations 380A a@ 70'C vs 430A@90'C would we see any excption ina legal sense? As far as I can remember 90'C is rserved for 5Kv, but always willing to see/learn something new. As long as all parts could be elevated to 90'C then a whole new can of worms would be opened in regard to 1200 amp service at FULL rating.

 

[infinity]

Looking at the chart (310.16) and looking at 310.15(B)(2) ex 4, and with the use of 90'C terminations 380A a@ 70'C vs 430A@90'C would we see any excption ina legal sense? As far as I can remember 90'C is rserved for 5Kv, but always willing to see/learn something new. As long as all parts could be elevated to 90'C then a whole new can of worms would be opened in regard to 1200 amp service at FULL rating.

I don't think that you'll ind equipment rated for use a 90? C.

 

[Rockyd]

That was my original thought, then started wondering how far the manufacturers lobby might want to bend temp ranges in the future on any of their equipment. Assuming we won't see any foolishness like that in the 2011 code cycle hopefully.