400 Amp Service Conductors

[jmellc]

Hate to sound totally dumb, but I haven't calculated service feeders for some time. I'm rusty and I know there have been some changes.

I am quoting a job to replace an old 200 amp panel in a church with a 400 amp outdoor meter/panel combo. Can someone help me nail down the code sections to properly calculate this? I get 500 MCM from 90 degree chart, 600 from the 75 degree chart and 750 from the 60 degree chart. I haven't had a chance to examine the equipment for temp ratings on it. Last time I saw a similar combo, it sure didn't have lugs big enough for 750. Some lugs are hard to find larger replacements for.

Thanks for any assistance. Yes, I have been slack not to keep up
with calculations.

 

[hardworkingstiff]

Hate to sound totally dumb, but I haven't calculated service feeders for some time. I'm rusty and I know there have been some changes.

I am quoting a job to replace an old 200 amp panel in a church with a 400 amp outdoor meter/panel combo. Can someone help me nail down the code sections to properly calculate this? I get 500 MCM from 90 degree chart, 600 from the 75 degree chart and 750 from the 60 degree chart. I haven't had a chance to examine the equipment for temp ratings on it. Last time I saw a similar combo, it sure didn't have lugs big enough for 750. Some lugs are hard to find larger replacements for.

Thanks for any assistance. Yes, I have been slack not to keep up
with calculations.

The 75 degree column will be used for your ampacity. You can use the 90 degree column if you need to apply derating factors but you cannot load the conductor to over the ampacity of the 75 degree column. This is assuming all of your connections are rated for 75 C.

If the calculated load for the service is 380 amps or less, then the 500 cu. is fine.

Personally, I prefer to parallel a couple of 3/0's in separate conduits or 4/0's in one conduit.

Are you able to use two 200-amp panels instead of a 400-amp panel? It sometimes is easier and more cost effective.

 

[jmellc]

Thanks for the quick reply. I haven't done total load calculations, I need to do that. My usual supply house does not have a 400 amp meter base to feed the 2 panels you suggest. They only have the Siemens combo. They also carry GE, which I try not to ever install. The combo has split bus with a 200 main on 1 part and space for 2 DP breakers separate from it. I don't think the combo has double lugs to allow this. I can usually find those lugs though.

 

[infinity]

According to 110.14(C)(1)(b) your lugs would need to be rated for 75 degrees C so you can use the 75 degree C ampacity of the conductors. If you calculated load is 380 amps or less you may use 500 kcmil THHN as HWS suggested because those conductors have an ampacity of 380 amps. 240.4(B) will allow you go up to the next standard size OCPD since 380 is not a standard size listed in 240.6(A).

 

[Buck Parrish]

Thanks for the quick reply. I haven't done total load calculations, I need to do that. My usual supply house does not have a 400 amp meter base to feed the 2 panels you suggest. They only have the Siemens combo. They also carry GE, which I try not to ever install. The combo has split bus with a 200 main on 1 part and space for 2 DP breakers separate from it. I don't think the combo has double lugs to allow this. I can usually find those lugs though.

mellic , a 400 amp ( 320) meter base for 2 - two hundres amp panels is readily available in central NC.

 

[LarryFine]

mellic , a 400 amp ( 320) meter base for 2 - two hundres amp panels is readily available in central NC.

If you're in Dominion territory, they provide meter bases free (or at least they used to.) All you'd need to buy is two 200a disco's if the panels won't be nearest the entrance point.