400 amp install

[hillbilly]

Here is an interesting scenario for those who use aluminum for se conductors and feeders.

400 amp meter base with 2- 200 amp panels. In the past we could run 4/0 aluminum to each panel and everyone would be happy. Then the CMP changed art. 310.15(B)(6) to clarify that in order to use T310.15(B)(6) the conductors must carry the full load of the service. So for a 200 amp service 4/0 SE cable is still good if it carries the full load of the service. Why? Because T310.15(B)(6) allows 4/0 aluminum for 200 amps and se cable is an acceptable wiring method.

Okay now back to the 400 amp service stated above. Se cable cannot even be used. Why because 4/0 seu to each panel will not satisfy Art. 310.15(B)(6).



Now we must use Table 310.16 which states we must use 300 KCM aluminum for 200 amps. 250 KCM is only good for 170 and 175 is next higher size breaker so you cannot use that conductor. 300 KCM is what must be used.

Let's install the seu cable from the 200 amp and use firecaulk around it into the building and that does not change a thing even though that is the main reason - as Bob pointed out- that SE cable has been derated to 60C.

So 200 amp service 4/0 se cable is fine for a SFD however 350 KCM must be used for a 400 amp service that utilizes 2-200 amp panels.

This is what I was getting at in my first post (#8).:smile:

steve

 

[Dennis Alwon]

This is what I was getting at in my first post (#8).:smile:

steve

I realized that my response (#9 post) was misdirected. I was thinking just about T310.15(B)(6). I keep forgetting about se being 60C.

 

[Brad Baxter]

really

really

I was told all over florida that they have been doing this method for forever. 2 #4/0 al use-2 to both panels and no inspector complaints.

I realized that my response (#9 post) was misdirected. I was thinking just about T310.15(B)(6). I keep forgetting about se being 60C.

 

[hillbilly]

I was told all over florida that they have been doing this method for forever. 2 #4/0 al use-2 to both panels and no inspector complaints.

I believe that the rule (310.15(B)(6) was changed....well maybe not changed...just clarified...in the 08 Code.
I don't as yet have (nor need) a 08 code, so this is what I've heard.

Until then, IMHO, the wording of the rule allowed the installation that you propose.
Now, you can only use 310.15(B)(6) to size the Main power Feeder (singular)....not Feeder(s) (plural).
This eliminates using this rule to size two seperate Service Feeders into a residence.

This is just my interpretation and opinion
steve