400 Amp Service - Residential

[Jimmy7]

I’m about to do this 400 amp service for a single family home. Can I run what I’m going to do by you.

1. I was going to run three 600 al XHHW underground outside.

2. I’m going to install a meter socket that has two 200 amp breakers with a barrier. The meter socket states 320 amps, is that okay? I’m going from 200 amps to 400 amps due to geothermal equipment, but it’s not too much additional load.

3. I was going to run 3/0 Ser copper ground from the Two 200 amp breakers in the meter socket to two 200 amp main breaker panels (Separating the grounds and the neutrals).

4. I was going to run a 1/0 copper ground from the water meter to the meter socket.

5. I was going to run a number 6 copper ground from the meter socket to two ground rods.

 

[Dennis Alwon]

1. Why are you running 600 al? That is only good for 340 amps at 75C

I would run a parallel run of 250 kcm al.

2. Meter sockets are rated 320 continuous and 400 non-continuous so you are fine for a residence.

3. That would work as 3/0 Cu is good for 200 amps

4. 1/0 is good to the water main

5. #6 to the rods is good.

 

[electrofelon]

I agree with Dennis, don't use 600. Besides not being large enough (although since you have two service disconnects you could size to the load which may be ok), it's an odd size , a pain to work with IMO, and probably won't fit in your lugs.

Sounds like you don't need main breaker panels FYI.

 

[Jimmy7]

1. Why are you running 600 al? That is only good for 340 amps at 75C

I would run a parallel run of 250 kcm al.

2. Meter sockets are rated 320 continuous and 400 non-continuous so you are fine for a residence.

3. That would work as 3/0 Cu is good for 200 amps

4. 1/0 is good to the water main

5. #6 to the rods is good.

Couldn't I use Table 310.12 for a Single Family Home?

Table 310.12(A) Single-Phase Dwelling Services and Feeders

	Conductor (AWG or kcmil)
Service or Feeder Rating (Amperes)	Copper	Aluminum or Copper-Clad Aluminum
100	4	2
110	3	1
125	2	1/0
150	1	2/0
175	1/0	3/0
200	2/0	4/0
225	3/0	250
250	4/0	300
300	250	350
350	350	500
400	400	600

 

[Jimmy7]

I have one 4" Pipe can I still use paralleled 250 AL with derating for 400 Amps?

 

[wwhitney]

Couldn't I use Table 310.12 for a Single Family Home?

Yes, which the responses so far have overlooked.

I have one 4" Pipe can I still use paralleled 250 AL with derating for 400 Amps?

Yes, because 250 MCM Al has a 90C ampacity of 230A, so after an 80% factor you get 2 * 80% * 230A = 368A, which is still greater than 83% * 400A = 332A.

Cheers, Wayne

 

[Dennis Alwon]

Yes and Yes.... 250 can work and I assume it will fit in 4" conduit

 

[Jimmy7]

Okay, in your opinion, which install do you recommend? Which is less headaches?

I haven't ordered the wire or the lugs yet. I have the meter socket.

 

[Little Bill]

Yes, which the responses so far have overlooked.


Yes, because 250 MCM Al has a 90C ampacity of 230A, so after an 80% factor you get 2 * 80% * 230A = 368A, which is still greater than 83% * 400A = 332A.

Cheers, Wayne

Given this install has two panels, one panel wouldn't serve the entire load. How can you use the table (83%) then?

 

[wwhitney]

Given this install has two panels, one panel wouldn't serve the entire load. How can you use the table (83%) then?

310.12(A) covers services. So if the service supplies the entire load of a single dwelling unit, then the 83% factor applies to the service conductors that supply both panels. If/once conductors split to the two panels, it no longer applies. Sounds like the OP is using a meter/main with two breakers, so all the service conductors do carry the entire load and the 83% factor applies.

Cheers, Wayne

 

[Little Bill]

310.12(A) covers services. So if the service supplies the entire load of a single dwelling unit, then the 83% factor applies to the service conductors that supply both panels. If/once conductors split to the two panels, it no longer applies. Sounds like the OP is using a meter/main with two breakers, so all the service conductors do carry the entire load and the 83% factor applies.

Cheers, Wayne

For the service, yes. I was speaking of the feeders to each of the 200A panels.

 

[Jimmy7]

I'm installing a single 4" pvc to 400 amp meter socket which does contain two 200 amp breakers. I'm always trying to learn (Excuse if I'm wrong), so isn't the two 200 amp panels now considered subpanels (That's why I chose 3/0 cu as a feeder, because they don't carry the entire load of the house). The service conductors to the line side of the meter carry the entire load, so can't I use 310.12(A)?

 

[wwhitney]

For the service, yes. I was speaking of the feeders to each of the 200A panels.

Agreed, but the bulk of the discussion so far has been about the service conductors. The feeders are mentioned in the OP as point #3, but the specified size (3/0 Cu) shows that the OP understands that 310.12 doesn't apply to them.

Cheers, Wayne

 

[wwhitney]

I'm installing a single 4" pvc to 400 amp meter socket which does contain two 200 amp breakers. I'm always trying to learn (Excuse if I'm wrong), so isn't the two 200 amp panels now considered subpanels (That's why I chose 3/0 cu as a feeder, because they don't carry the entire load of the house). The service conductors to the line side of the meter carry the entire load, so can't I use 310.12(A)?

Correct on all counts. 310.12(A) applies to your service conductors.

Cheers, Wayne

 

[Jimmy7]

With all this being said, is paralleled 250 Aluminum in one 4" pvc pipe the way to go?

 

[electrofelon]

IMO that is overkill. I would either use a single set of 500 or two sets of 4/0.

 

[wwhitney]

IMO that is overkill. I would either use a single set of 500 or two sets of 4/0.

If the OP wants a full "400A" service, those are both too small. A single set of 500 MCM Al service conductors gives a 310/0.83 = 373A residential service. While two sets of 4/0 Al give a 2 * min(180, 0.8*205)/0.83 = 395A residential service.

Of course, depending on the load calc, either of those is probably fine. Heck if the load calc is under 225A, you could put in a single set of 3/0 Cu per Table 310.12. And now suddenly your 3/0 Cu feeders are each good for 225A. : - )

BTW, the I think the OP's last question is whether you advise one larger set or two parallel sets, in terms of ease of installation, termination, etc. Not something I have any experience with.

Cheers, Wayne

 

[Dennis Alwon]

This thread has gotten convoluted and I am not sure what's what. I see there is a meter base with 2- 200 amp breakers in it. Where is the meter base. It appears it is away from the main building, is that correct? Or are you responsible for the runs from the power company pole to the meter base on the house?

If the second concept is what you have then you would need 2 sets of 250kcm. You have to use 80% based on more than 3 current carrying conductor's in the conduit. 250 kcm @90C = 230 amps x .8 = 184. Double for parallel and you have 368 amps. Since this is a residence you can use 83% of 400 amps = 332 amps so the 250kcm will work.

 

[qcroanoke]

1. Why are you running 600 al? That is only good for 340 amps at 75C

I would run a parallel run of 250 kcm al.

2. Meter sockets are rated 320 continuous and 400 non-continuous so you are fine for a residence.

3. That would work as 3/0 Cu is good for 200 amps

4. 1/0 is good to the water main

5. #6 to the rods is good.

Not so sure you should be taking grounds into Poco meter base. Not allowed here.

 

[Jimmy7]

This thread has gotten convoluted and I am not sure what's what. I see there is a meter base with 2- 200 amp breakers in it. Where is the meter base. It appears it is away from the main building, is that correct? Or are you responsible for the runs from the power company pole to the meter base on the house?

If the second concept is what you have then you would need 2 sets of 250kcm. You have to use 80% based on more than 3 current carrying conductor's in the conduit. 250 kcm @90C = 230 amps x .8 = 184. Double for parallel and you have 368 amps. Since this is a residence you can use 83% of 400 amps = 332 amps so the 250kcm will work.

The meter socket is on the side of a single family residence (There are no other buildings). I am responsible for providing the underground conductors from the meter socket to the utility pole.