Mixing different voltages in panelboard??

Status
Not open for further replies.
I

innov8

Member
Hi all,
I'm helping to install a new service at a new restaurant/commerce center.

The 600Amp, 480/277Y service is terminated in a panelboard fed by 3 sets of 3/0,

450Amp CB into 225 KVA208/120Y XF with 2 sets 250MCM,

And then XF secondary feeding 2 identical 600Amp panelboards with either (3 sets of 3/0), or (2 sets of 300MCM). haven't decided yet. We are trying to keep the secondary conductors under 25 feet to comply with 240.21(B)(2).

The 3 panels (Main Disc.-600A 480v and 2 600A 208v) are mounted side by side with the 480v panel to the left, and the 208v panels to the right, with the transformer to the far right.
The upper area will not be used for load-side wiring. (everything going out on the bottom)

Is there any NEC rule that says I can't route the 480volt conductors out the top right-hand side (using metallic raceway) through the 2 208volt panels, down to the transformer, and then using the same raceway to route the secondary conductor back to the 2 208v panels?

Thanks
 
innov8 said:
Is there any NEC rule that says I can't route the 480volt conductors out the top right-hand side (using metallic raceway) through the 2 208volt panels, down to the transformer
Click to expand...

You can do what you described, see 312.8 but read the entire section, not just the first sentance.

and then using the same raceway to route the secondary conductor back to the 2 208v panels?
Click to expand...

You can do that as well, but derating will get you, the condutors will have to be larger if you run all six current carrying condutors in the same raceway.
 
Thanks for the fast reply

I'm running all Metal raceway and my conductor count is right at 30, so derating shouldn't be an issue.
am I right?
 
innov8 said:
I'm running all Metal raceway and my conductor count is right at 30, so derating shouldn't be an issue.
am I right?
Click to expand...

The raceway from the panel to the transformer will have six current carrying condutors, those condutors will have to be derated.

I would use two raceways from the transformer to the panel or panels.
 
iwire said:
The raceway from the panel to the transformer will have six current carrying condutors, those condutors will have to be derated.
Click to expand...

Bob, Why ? You lost me (not unusual). I would have thought 386.22 would allow him not to derate.
 
Last edited by a moderator:
So I should be good to go then...

except...I ran into this while searching through this forum: 408.3(A)(3)

Or maybe this applies only to Switchboards, and not to Panelboards?
 
Switchboard= MCC and other freestanding gear
Panelboard= Common CB panel, and intended to be fastened to wall

Am I right in assuming this?

Thanks for you replies
 
Status
Not open for further replies.
Top