The Dreaded SubPanel

Status
Not open for further replies.
R

Rerhasaurus

New User
Location
Washington
Ok Guys and Gals, I have a Sub Panel question. 320 amp service, one panel is just a 200 amp main with empty load lugs. I have a barn approx 300 ft away from the home (and the main service) I have 330 ft of 4/0 4/0 2/0 4awg quadplex aluminum wire. What is the largest sub panel I can install in the barn?
 
Hmmm, sounds like a homework question, give us your answer and how you arrived at it and then someone can critique your answer.

Roger
 
Rerhasaurus said:
Ok Guys and Gals, I have a Sub Panel question. 320 amp service, one panel is just a 200 amp main with empty load lugs. I have a barn approx 300 ft away from the home (and the main service) I have 330 ft of 4/0 4/0 2/0 4awg quadplex aluminum wire. What is the largest sub panel I can install in the barn?
Click to expand...

The largest panelboard you can install is 1200 amps. That is as large as they get. Ok, more details required. Is the run to the barn a set of service entrance conductors installed per 230.40 exception #3? Thats what I would do, less equipment and less wire but since you speak of a 4th wire, then maybe this is a feeder?
 
Rerhasaurus said:
Ok Guys and Gals, I have a Sub Panel question. 320 amp service, one panel is just a 200 amp main with empty load lugs. I have a barn approx 300 ft away from the home (and the main service) I have 330 ft of 4/0 4/0 2/0 4awg quadplex aluminum wire. What is the largest sub panel I can install in the barn?
Click to expand...

4/0 aluminum is good for 180amps @75C so that's what you have unless you have to derate for temperature. @60C it's 150 amp. It's a feeder not a service so you can't run it at 200 amps
 
Eddie702 said:
4/0 aluminum is good for 180amps @75C so that's what you have unless you have to derate for temperature. @60C it's 150 amp. It's a feeder not a service so you can't run it at 200 amps
Click to expand...
Being a feeder vs a service has no bearing on whether you can use the table for dwellings in order to use a lesser AWG conductor. The rule is for service or feeders that serve the entire load. If you have a disconnect outside that just feeds the inside panel, the conductors from the disc to the panel are feeders. If the inside panel serves the whole house, then you can use reduced the AWG according to the table even though they are feeders.

This reply has nothing to do with the OP's question or situation.
 
Last edited:
Your question is not correct, largest subpanel could mean size. 180 amp feeder breaker to what ever size panel you want.
Now the 300 ft is another issue altogether. You would need to determine what 3% volt drop results in at 180 amps, if VD is excessive then back down on the size of the feeder breaker
 
Lots of online voltage drop calculators. Use two of them and see what they say!

Voltage drop is clearly the determining factor of amps useable at this distance. The voltage drop will limit the feeder size before the wire does using any table.:thumbsup:
 
You can use a large a panel as You want.
Someone pointed out to make sure the lugs in the panel that You choose are large enough for the wire.
Size the feeder breaker to protect the wire.
Voltage drop calcs wont require You to put in a smaller breaker; it is a suggestion.
 
Little Bill said:
Being a feeder vs a service has no bearing on whether you can use the table for dwellings in order to use a lesser AWG conductor. The rule is for service or feeders that serve the entire load. If you have a disconnect outside that just feeds the inside panel, the conductors from the disc to the panel are feeders. If the inside panel serves the whole house, then you can use reduced the AWG according to the table even though they are feeders.

This reply has nothing to do with the OP's question or situation.
Click to expand...

310.15(B)(7) is not applicable here, it's a feeder for a barn, not a dwelling. Just as a note as well, Quad-plex is not rated to be run inside a build or structure.
 
swptln said:
310.15(B)(7) is not applicable here, it's a feeder for a barn, not a dwelling. Just as a note as well, Quad-plex is not rated to be run inside a build or structure.
Click to expand...

If you read the last line in my post you will see that my reply didn't apply to the OP's situation since it was a barn.
I was replying to Eddie702, explaining there is no difference between a feeder and service as far as 310.15(B)(7) is concerned.
 
swptln said:
310.15(B)(7) is not applicable here, it's a feeder for a barn, not a dwelling. Just as a note as well, Quad-plex is not rated to be run inside a build or structure.
Click to expand...

It depends on the specifics of the quad. If it is just use-2 then true. Often the quad I get is use-2/rhh-2 which is ok inside. "Quad", "4 wire URD", "mobile home feeder" are rather general terms with the insulation type varying by manufacturer.
 
Status
Not open for further replies.
Top