hardworker
Senior Member
A 400 amp single phase subpanel is being installed 70 ft. from the main panel. What awg size of wire and what size of conduit is correct?
400 amp subpanel
- Thread starter hardworker
- Start date
- Status
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Its this a test question? Pretty basic question for most electricians.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
500 kcmil copper will probably work.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
or two runs of 3/0 in parallel.
hardworker
Senior Member
Just trying to see if there is more than one way to go about it.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
At 70' voltage drop shouldn't be too much of an issue. There are a few options, as mentioned 500 kcmil gets you 380 amps so if your load isn't greater than 380 you're OK with 500's. If you want the full 400 amps then you can opt for 600 kcmil @ 420 amps. Or you could use two sets of #3/0 in separate raceways which gives you 400 amps or you could use parallel sets of #3/0 in one raceway and end up with 360 amps. If you like smaller conductors you could use 3 sets of #1/0. in 3 raceways @ 450 amps or one raceway @ 357 amps. The ampacities that are less than 400 amps would need to comply with the next standard size up rule.
As you can see there are many variables depending on the parameters of you installation.
Carultch
Senior Member
- Location
- Massachusetts
If it is my choice, and copper is required, I would run 2 parallel sets of #4/0 Cu with a #3 Cu ground, all THWN-2, in a common 3" conduit, to get use of the full 400A.
Generally, parallel runs make more efficient use out of the conductor, and are easier to install than the single large conductor counterpart. You can combine parallel runs in a common conduit, as long as there is symmetry among the conduits when multiple conduits are in parallel.
Most equipment in the 250A to 400A range is built to handle 2 qty aught-range wires in parallel, or up to a single 600 kcmil wire. "Snowman" lugs are common, which allow either one big wire or two small wires.
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hardworker
Senior Member
If it is my choice, and copper is required, I would run 2 parallel sets of #4/0 Cu with a #3 Cu ground, all THWN-2, in a common 3" conduit, to get use of the full 400A.
Under the above scenario what is the exact amount of amps that would be achieved?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
It would depend on how many CCC there are which we do no have enough information to say for sure. Assuming three phase with the neutral not a CCC we have 6 CCC which is a .8 derating from the 90 degree value or 416 amps. If the panelboard is truly a 400 amp, 408.36 would not allow you to exceed a 400 amp OCPD to supply it.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
This thread has been brought to you by the copper lobby 
hardworker
Senior Member
This is single phase.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
There are many ways to go about it.
If you need 300 amps of capacity you very likely will need a panel with a 400 amp bus, but could supply it from a 300 amp overcurrent device and 300 amp conductors.
If you want or need 400 amps of capacity there is copper, aluminum, single or parallel conductors are all considerations.
Then there is the mentioned 500 copper is only good for 380 amps but can be protected at 400 as long as the load doesn't exceed 380, similar applies to some other options.
You need to know what your minimal design requirements are and then throw in optional design decisions and then consider price of different options as well.
hardworker
Senior Member
This is single phase.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
What is your preferred method, one raceway, parallel sets in two raceways, parallel sets in one raceway?
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