215.2(A)(2) Ampacity Relative to Service Conductors

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Dennis Alwon

Dennis Alwon

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This may be a little off target with the OP's question but I will present it anyway.

I suggest reading art. 310.15(B)(6) very carefully. Here is what I understand it says I can do.

Scenario: Single family dwelling--One meter with 2 - 200 amp discos (400 amp service). The disco has feed thru lugs for 200 amps and 2- 200 amp sub panels are added inside the building.

The wires between the meter and the discos can be 2/0 copper since Table 310.15(B)(6) allows that for single family dwelling. My reason is that since the conductors between the meter and the main disco are service entrance conductors, art. 310.15(B)(6) states can use T310.15(B)(6).

Now what size copper conductors, in conduit, must I install from the main disco to the interior panel? Let's assume 90 C conductors --- anyone want to bite at this one.....
 
Dennis Alwon said:
Scenario: Single family dwelling--One meter with 2 - 200 amp discos (400 amp service). The disco has feed thru lugs for 200 amps and 2- 200 amp sub panels are added inside the building.

The wires between the meter and the discos can be 2/0 copper since Table 310.15(B)(6) allows that for single family dwelling. My reason is that since the conductors between the meter and the main disco are service entrance conductors, art. 310.15(B)(6) states can use T310.15(B)(6).
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Dennis, I'll bite sort of. This is really more a question.

Why could you use 310.15(B)(6) for a 400A service with two 200A panels?
Niether 200A disco or panel supplies all loads that are part or associated with the dwelling unit.

I know this is allowed everywhere that I work, but it really does not read that way to me.
 
C3PO said:
I know this is allowed everywhere that I work, but it really does not read that way to me.
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That should really stop with the adoption of the 2008 NEC as they tried to clear that up.
 
iwire said:
That should really stop with the adoption of the 2008 NEC as they tried to clear that up.
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I think so too. It will be interesting to see how it plays out in my area. (we are still on the 2002, should be on 2008 sometime this year)
 
C3PO said:
I think so too. It will be interesting to see how it plays out in my area. (we are still on the 2002, should be on 2008 sometime this year)
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IF TN adopts '08, that is one of many that will haunt us inspectors for a long while. The 2/0s may have been incorrect for a long time and, I agree, '08 clarifies, but it's gonna be hard teachin' that many dogs a new trick.
 
C3PO said:
Dennis, I'll bite sort of. This is really more a question.

Why could you use 310.15(B)(6) for a 400A service with two 200A panels?
Niether 200A disco or panel supplies all loads that are part or associated with the dwelling unit.

I know this is allowed everywhere that I work, but it really does not read that way to me.
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Well I don't think 2008 really cleared it up. Let's invoke Charlie's rule.
I don't think it say that the service entrance conductors must supply the whole load of the service? It says feeders must do that. Yes?

edit: Thanks Bob-- I was going to start a new thread but wasn't sure it warranted it.
 
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Dennis Alwon said:
Well I don't think 2008 really cleared it up. Let's invoke Charlie's rule.
I don't think it say that the service entrance conductors must supply the whole load of the service? It says feeders must do that. Yes?
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I am not going to go down that road here and sidetrack a brand new thread.
 
Dennis Alwon said:
I don't understand. Is this not what the thread is about?
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I understood your issue to be with 215.(2)(A) or was I mistaken?

Now we are moving back to 310.15(B)(6)?

I would like to keep the subjects separate because either one alone will be a handful.
 
iwire said:
I understood your issue to be with 215.(2)(A) or was I mistaken?

Now we are moving back to 310.15(B)(6)?

I would like to keep the subjects separate because either one alone will be a handful.
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Nope, I was dealing with just 310.15(B)(6) but am fully aware of it. We can go there once this is hashed out. :)
 
Dennis Alwon said:
Nope, I was dealing with just 310.15(B)(6) but am fully aware of it. We can go there once this is hashed out. :)
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Well I am entirly lost and am now going to step aside. :-? :-? :-? :-? :-? :-? :-?
 
iwire said:
Totally lost, no light at the end of the tunnel. :grin:
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What I am saying is that I don't think 310.15(B)(6) has been cleared up. If they wanted to say that the service entrance conductors had to carry the full load of the residence then I think they missed their mark.

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.
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They way I see it they should have had a comma after feeder conductors if they wanted the entire group to carry the full load. As it reads to me it says "feeder conductors that serve as the main power feeder to the dwelling. To further support this thinking it goes on to say "the main power feeder shall be the feeder between the main disco & the panelboard". Not between the meter and the discos.
 
It looks to me like they are calling either the service-entrance conductors, the service lateral conductors or the feeder conductors the main power feeder. I know that is not proper terminology, but that is how the sentence reads to me. (I am in Tennesse though):wink:
 
C3PO said:
It looks to me like they are calling either the service-entrance conductors, the service lateral conductors or the feeder conductors the main power feeder. I know that is not proper terminology, but that is how the sentence reads to me. (I am in Tennesse though):wink:
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I believe that is the intent but I am not sure it's there. The crazy part is we have the NC state inspector who is interpreting it this way. To go further he says now if I feed the interior panel with a feed thru panel I can go inside with the 2/0 copper. If I add a circuit to the outside disco (feed thru with say 8 cir) then I must install 3/0 copper to the interior panel.

It does not make sense esp. since the load for a dwelling is based on diversity of the load. If you split the load with 2 200 amp panels then that diversity is lost.

I get what he is saying and I agree the wording is poor but it does seem to support his thinking somewhat.

The only argument I really have is why would another circuit needed to be in the exterior panel to change the diversity. That interior panel will never carry the entire load of the dwelling and it is a feeder.
 
Dennis Alwon said:
I believe that is the intent but I am not sure it's there. The crazy part is we have the NC state inspector who is interpreting it this way. To go further he says now if I feed the interior panel with a feed thru panel I can go inside with the 2/0 copper. If I add a circuit to the outside disco (feed thru with say 8 cir) then I must install 3/0 copper to the interior panel.

The only argument I really have is why would another circuit needed to be in the exterior panel to change the diversity. That interior panel will never carry the entire load of the dwelling and it is a feeder.
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In this example I would think you could run 2/0 to both because of the sentence "The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors'"

So from the MB to the feed thru could be 2/0 and the feed thru to interior panel could also 2/0. JMSO
 
C3PO said:
In this example I would think you could run 2/0 to both because of the sentence "The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors'"

So from the MB to the feed thru could be 2/0 and the feed thru to interior panel could also 2/0. JMSO
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One would think and Bob's title I beleive should be 215.2 (A)(3) which reference 310.15.(B)(6) as you stated. but what is the ampacity of 3/0 copper?
 
Dennis I really think it says what the intent is, I do agree the use of the term "main power feeder" makes i less clear.

IMO The key to it is the term "that serve as"


  • service-entrance conductors that serve as
  • service-lateral conductors that serve as
  • 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.


Used in this particular code section "main power feeder" includes service conductors and feeder conductors.


Any of the conductors in that list that serve the entire dwelling unit can take advantage of the table.
 
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