New service

[brichter]

Please comment on the following scenario:

Paralleled 2/0 Cu from meter can to 400 A breaker on ATS

2/0 Cu from ATS to two individual 200 Amp feed-thru panels WP main breaker panels

From each 200 amp panel the house is fed underground with 4/0 aluminum to two main breaker panels inside the house.

Inspector says wire to house must be 250 mcm al or 3/0 Cu.

I this installation nonm-compliant in your view.

 

[augie47]

I may be alone here, but to me the non-code portion is the 2/0 from the ATS to the disconnect.
Since you are not feeding ALL the load, 310.15(b)(6) would not apply to these conductors, rated at 175 amp.
If your load calculations on your interior panels is less than 180 amps the 4/0 AL would be o.k. per 240.4(B)

 

[brichter]

I guess I am having trouble with "all " the load. 310-15(b)(6) says dwelling unit service conductors as well as feeders.

 

[paul]

Did he give you a code article?

 

[Dennis Alwon]

I guess I am having trouble with "all " the load. 310-15(b)(6) says dwelling unit service conductors as well as feeders.

Yes it does include the feeder if the feeder served all the loads of the dwelling. Thus if you had a 200 amp service --meter and a 200 amp MB with no other circuits in the panel then you could use Table (B)(6) to feed a 200 amp sub panel. If you install another breaker in the service disco panel then the feed to the sub must follow T310.15


In the case of a 400 amp service with two 200 amp panels then neither panel serves the entire load of the dwelling so Table (B)(6) would not apply. You would need 3/0 Cu between meter and panels not 2/0 CU

 

[augie47]

yes. but in either case the service or feeder must carry ALL the dwelling unit load. Once you "split" to two seperate panels, those feeders are not carrying all the load.
Your service to the meter and to the ATS appears to carry ALL, once you divided to the two feeders, the load was split.
Your 4/0 al feeder (unless SE per 338.10) has a 180 amp ampacity and unless loaded beyond that can be on a 200 amp breaker.
Your 2/0 Cu to the panels is only rated 175.

 

[infinity]

your 4/0 AL feeder (unless SE per 338.10) has a 180 amp ampacity and unless loaded beyond that can be on a 200 amp breaker.
Your 2/0 Cu to the panels is only rated 175.

So by using the #4/0 Al you can go up to the next standard size which is 200 amps. Since 175 amps is a standard size you're stuck with increasing the #2/0 Cu to a #3/0 conductor.

 

[brichter]

I still don't understand where you are coming up with "all the load". Where is this referenced please.

 

[augie47]

i still don't understand where you are coming up with "all the load". Where is this referenced please.

2008 310.15(b)(6)

note especially the newly highlighted words added for clarity

 

[Dennis Alwon]

I still don't understand where you are coming up with "all the load". Where is this referenced please.

Here art. 310.15(B)(6)

6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder to each dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.

 

[brichter]

Does referencing the 2005 NEC change any of your answers?

 

[augie47]

note mine. the wording in 2008, for me, was clarfication of what I always thought it read.

 

[infinity]

Does referencing the 2005 NEC change any of your answers?

That might depend on who you ask.

 

[LarryFine]

Does anyone know if a 250mcm al SE/SER cable looms on the horizon?

We're gonna need it if we want to keep using cable instead of conduit.

 

[augie47]

Does anyone know if a 250mcm al SE/SER cable looms on the horizon?

We're gonna need it if we want to keep using cable instead of conduit.

It's in use in this area. Been used on 225A services.

 

[Dennis Alwon]

Does anyone know if a 250mcm al SE/SER cable looms on the horizon?

We're gonna need it if we want to keep using cable instead of conduit.

250 MCM will not do you much good for a 400 amp service since you must use the 60C rating. My understanding is that the wire manufacturers are working on manufacturing 300 mcm alum SE cable. Even with that we would be limited to 380 amps on a 400 amp service.

 

[acrwc10]

250 MCM will not do you much good for a 400 amp service since you must use the 60C rating. My understanding is that the wire manufacturers are working on manufacturing 300 mcm alum SE cable. Even with that we would be limited to 380 amps on a 400 amp service.

As long as your calculated load is not over 380 amps you would be good to go.

 

[LarryFine]

250 MCM will not do you much good for a 400 amp service since you must use the 60C rating.

I was talking about twin 200a panel feeders.

 

[Dennis Alwon]

I was talking about twin 200a panel feeders.

If you are talking about two 200 amp panels that are fed from a feeder then you would need a minimum 300 kcm alum to each panel. 250 kcm is only good for 170 used in a se cable as a feeder. Am I missing something?

 

[normbac]

are you supplying the house with two separate feeders?