Feeding a 1200 amp sub panel

Status
Not open for further replies.
M

milemaker13

Senior Member
Location
Suburbs of Chicago
Hey Gang,

I am installing a 1200 amp sub panel in our facility, and I am thinking of the best way to feed it. There isn't alot of room, and this will sit within about 6" from the MDP feeding it.

Orignally, I was thinking of using four 3" nipples (four sets of 500's) but looking at it out there I'm not sure I can fit 4 nipples in place... not to mention trying to manuver the cables thru them in this small space.

OK, so my box will sit maybe 12" off the ground, and its bottom fed, so I thought of maybe constructing a trough below the new panel.

It'll probably work great! But am I overlooking something code-wise? All edges would be smooth and/or protected...
 
milemaker13 said:
Hey Gang,

I am installing a 1200 amp sub panel in our facility, and I am thinking of the best way to feed it. There isn't alot of room, and this will sit within about 6" from the MDP feeding it.

Orignally, I was thinking of using four 3" nipples (four sets of 500's) but looking at it out there I'm not sure I can fit 4 nipples in place... not to mention trying to manuver the cables thru them in this small space.

OK, so my box will sit maybe 12" off the ground, and its bottom fed, so I thought of maybe constructing a trough below the new panel.

It'll probably work great! But am I overlooking something code-wise? All edges would be smooth and/or protected...
Click to expand...

Not sure why you are using 4 sets of 500. I come up with 1520 amps @ 75 degree. Three sets of 600 would be more appropriate.

Off hand,I think all 12 of them plus an EGC would fit in a single 6" nipple and still be less than 60% fill. Derating for number of conductors is not an issue here.
 
texie said:
Not sure why you are using 4 sets of 500. I come up with 1520 amps @ 75 degree. Three sets of 600 would be more appropriate.

Off hand,I think all 12 of them plus an EGC would fit in a single 6" nipple and still be less than 60% fill. Derating for number of conductors is not an issue here.
Click to expand...

maybe it is AL wire, although that seems kind of odd for such a short run.
 
milemaker13 said:
Hey Gang,

I am installing a 1200 amp sub panel in our facility, and I am thinking of the best way to feed it. There isn't alot of room, and this will sit within about 6" from the MDP feeding it.

Orignally, I was thinking of using four 3" nipples (four sets of 500's) but looking at it out there I'm not sure I can fit 4 nipples in place... not to mention trying to manuver the cables thru them in this small space.

OK, so my box will sit maybe 12" off the ground, and its bottom fed, so I thought of maybe constructing a trough below the new panel.

It'll probably work great! But am I overlooking something code-wise? All edges would be smooth and/or protected...
Click to expand...


You could also do 4 sets of 350's. (310a X's 4= 1240a). 350's are little easier to bend. Would all still fit in one 6" nipple.
 
Look at Carlon E996N 4" Box Adapters. Those with a coupling between your cabinets make a smooth transition that take up very little interior space.

996N.jpg
 
Last edited:
While the OP did not indicate, maybe there is no need for a full size neutral. By using a single nipple he is free to use the quantity and size of conductors as the load calc requires. for the neutral as long as it meets the minimum. Depending on neutral load it may even be possible to use a single conductor.
 
One of the first things I look at when doing this, is where are the wires landing in the MDP feeding it and where are they landing in the sub? Usually I'll put my nipples in a spot where it creates the shortest wire distance possible.
 
haha, I ran out of fingers and didn't want to remove my shoes to add it up! I will only be running 3 sets of 500s. Copper, 90* = 430 amps before any derating. I have to see my lugs on both sides before I can consider more lighter guage cables... not sure how many holes they have.


I would just cut an appropiate size hole in both and butt them together, but I don't have the new panel yet so I'm not sure how much room I have below the lugs. Thats how I landed on constructing a trough below the panel.

But judging from your awnsers it seems like I'd be ok to butt them together and cut a hole?

I guess one large nipple would also work ok. I'll have to wait and see what the panel looks like.

Thanks guys-:thumbsup:
 
milemaker13 said:
haha, I ran out of fingers and didn't want to remove my shoes to add it up! I will only be running 3 sets of 500s. Copper, 90* = 430 amps before any derating. I have to see my lugs on both sides before I can consider more lighter guage cables... not sure how many holes they have.


I would just cut an appropiate size hole in both and butt them together, but I don't have the new panel yet so I'm not sure how much room I have below the lugs. Thats how I landed on constructing a trough below the panel.

But judging from your awnsers it seems like I'd be ok to butt them together and cut a hole?

I guess one large nipple would also work ok. I'll have to wait and see what the panel looks like.

Thanks guys-:thumbsup:
Click to expand...

You need to rethink your ampacity calculation method. The terminals will be rated for 75 degree so you must use the 75 degree table for ampacity. There is no derating involved here as it is less than 24". But even if derating came into play, the final ampacity must be not more than what is allowed at the 75 degree value. And since this is above 800 amps, you don't get to use the next size up rule.
 
I agree with Texie, unless your terminals are rated 90 deg you will be 60 amps short with three sets of 500's

Roger
 
Yeah, dang.... That one still catches me... when did the term temp become the determining factor.. And why arn't all terminals now rated to 90* based on the new code? Well, no matter I guess.

OK, so I guess I have a choice (depending on how many holes the lugs have)..

3 sets of 600's @75* = 1260
4 sets of 350's @ 75 = 1240
5 sets of 250's @ 75 = 1275

I think the 600's will be too much to handle in the tight space. I guess if I have 5 holes then I'll go with the smallest 250's to make bending the cables in easier.

What do you all think?
 
What a butt.. Only 3 holes per phase.. Guess I'll be wrestling 600's into place.

Unless the lugs are 90*.. I don't see anything on them indicating the temp. Got a list of dif lugs and what size wire they will hold.. but it does not list the term temp.

I know if I cannot find a marking I must assume 75*.

So... what is the differance between a 75* lug and a 90* lug? Probably nothing but paperwork and $.
 
milemaker13 said:
What a butt.. Only 3 holes per phase.. Guess I'll be wrestling 600's into place.

Unless the lugs are 90*.. I don't see anything on them indicating the temp. Got a list of dif lugs and what size wire they will hold.. but it does not list the term temp.

I know if I cannot find a marking I must assume 75*.

So... what is the differance between a 75* lug and a 90* lug? Probably nothing but paperwork and $.
Click to expand...
I am not sure but I seem to recall that if you buy a 100% rated breaker the lugs are rated 90 deg C. Maybe my recollection is off.
 
milemaker13 said:
What a butt.. Only 3 holes per phase.. Guess I'll be wrestling 600's into place.

Unless the lugs are 90*.. I don't see anything on them indicating the temp. Got a list of dif lugs and what size wire they will hold.. but it does not list the term temp.

I know if I cannot find a marking I must assume 75*.

So... what is the differance between a 75* lug and a 90* lug? Probably nothing but paperwork and $.
Click to expand...

You can find lots of lugs rated for 90*. The issue here is that the equipment you are connecting to is not rated above 75*. In other words, you can't just change lugs and make equipment magically rated for 90*.
 
texie said:
You can find lots of lugs rated for 90*. The issue here is that the equipment you are connecting to is not rated above 75*. In other words, you can't just change lugs and make equipment magically rated for 90*.
Click to expand...

I agree, just forget the 90 degree ampacity.;)
 
Status
Not open for further replies.
Top