Feeder to Sub Panel in residence ( Table 310.15(B)(6)

[Hairball]

I have a 800 amp single phase service (120/240) on a residence.The gear is made by AMP manufacturing and is a CT/Main combo unit SCT8 - 3T. The unit has 3-200 amp breakers and 1-125 amp breaker for distribution.
I think that I can use 4/0 SER Al to feed the 200 amp sub panels based on Table 310.15(B)(6). My inspector says that I need to refer to 334.80, which puts me in the 60 degree column for Alum and that puts me at 300 MCM Al. It seems to me that Table 310.15(B)(6) overrides Table 310.16 on single phase 120/240 volt feeders in residence(dwelling unit). I have read the handbook and Mike Holts changes to 2008 NEC and still think that I am correct. However my inspector is AHJ and says otherwise.
Does anyone have any input ?

 

[George Stolz]

I think that I can use 4/0 SER Al to feed the 200 amp sub panels based on Table 310.15(B)(6).

Unfortunately, the table is of no use for you.

If the table went up to 800A, then you could size the service conductors according to the table, because those conductors are serving the entire house load.

The feeders are not - each one is doing a piece of the house's load.

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.

Therefore, you must size your conductors according to 338.10(B)(4) and Table 310.15(B)(16).

 

[ceb58]

Unfortunately, the table is of no use for you.

If the table went up to 800A, then you could size the service conductors according to the table, because those conductors are serving the entire house load.

The feeders are not - each one is doing a piece of the house's load.



Therefore, you must size your conductors according to 338.10(B)(4) and Table 310.15(B)(16).

George is correct. The inspectors have even ruled if you have a 200amp meter combo and feed say a HVAC unit or well pump from it that you cannot use table 310.15 B 6.
Their reasoning is you are not feeding "ALL LOADS THAT ARE PART OR ASSOCIATED WITH THE DWELLING UNIT" per 310.15 B 6. Even though you are reducing the load on the feeder to the sub panel

 

[tryinghard]

I think the wording can be better (the red to me does not help the definition it confuses):
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.

to​

For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies all loads to the dwelling unit (the whole dwelling unit).

 

[kwired]

If the load on the feeder(s) is 150 amps or less you can use a 150 amp breaker. Otherwise a 300KCM SE cable is required. 4/0 conductors in a raceway are acceptable because they would be allowed to use 75degree column in T310.16.

 

[Dennis Alwon]

I don't have issues with the wording now however your statement would not include a detached shop or garage. The wording now includes detached structures associated with the dwelling., IMO

 

[tryinghard]

I don't have issues with the wording now however your statement would not include a detached shop or garage. The wording now includes detached structures associated with the dwelling., IMO

For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies the full downstream load and not a portion. :grin:

 

[iwire]

You can't word the section with panelboard singular, you must word it with panelboard(s)

 

[tryinghard]

You can't word the section with panelboard singular, you must word it with panelboard(s)

Agree; For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supply the full downstream load and not a portion.

 

[Hairball]

Thanks for all the input.

Thanks for all the input.

I see now that in 310.15(B)(6) the wording is " between the main disconnect and panelboard". However the wording when the NEC refers to " either by branch circuits, feeders, or both, all loads that are part or associated with dwelling unit". The wording is a little confusing when I see " feeders", I think multiple SER's to multiple sub panels. Then it says all loads that are "part or associated with the dwelling unit", I think the sub panel takes care of part of the dwelling unit. In the handbook there is a section that talks about the permission that to use the table applies to conductors that carry 100% of the diversified load. My thought was that the sub panels were all feeding deversified load so no problem. I fully agree if it was a AC unit or big Steamer, but was thinking that for branch it would be OK. The only other thing that I thought would help is the AMP does not have a main breaker, the 3- 200's and 1- 125 are the main disconnects. But can also agree that it applies to one panelboard per dwelling. I just don't like the thought of having to run 300 mcm SER ( I think they make it) or MC cable in a dwelling being wired in romex.

 

[tryinghard]

You can't word the section with panelboard singular, you must word it with panelboard(s)

Wait a minute now that I see it written I think the panelboard should be singular because the intent is to supply the whole and not a portion (short day skiing may have caused me a brain freeze - but it's worth it)
"For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies the full downstream load and not a portion."
Otherwise it just back to the scenario of the OP

 

[Little Bill]

What size house is this that it has an 800A service? What kind of loads in a residential setting would require such a large service?

 

[kwired]

I see now that in 310.15(B)(6) the wording is " between the main disconnect and panelboard". However the wording when the NEC refers to " either by branch circuits, feeders, or both, all loads that are part or associated with dwelling unit". The wording is a little confusing when I see " feeders", I think multiple SER's to multiple sub panels. Then it says all loads that are "part or associated with the dwelling unit", I think the sub panel takes care of part of the dwelling unit. In the handbook there is a section that talks about the permission that to use the table applies to conductors that carry 100% of the diversified load. My thought was that the sub panels were all feeding deversified load so no problem. I fully agree if it was a AC unit or big Steamer, but was thinking that for branch it would be OK. The only other thing that I thought would help is the AMP does not have a main breaker, the 3- 200's and 1- 125 are the main disconnects. But can also agree that it applies to one panelboard per dwelling. I just don't like the thought of having to run 300 mcm SER ( I think they make it) or MC cable in a dwelling being wired in romex.

In a single family dwelling the only feeder that would be allowed to be sized by 310.15(B)(6) would be a feeder between a service disconnect and the panel(s) it supplies, if it is the only feeder supplied by the service disconnect. If there is more than one feeder it does not apply because it is not carrying the load of the entire dwelling.

In a multi family dwelling you could have one feeder for each dwelling unit sized according to 310.15(B)(6) for the required load for each unit. Each feeder is supplying the entire load to an individual dwelling unit.

Why bother with 300 SER cable when 2 inch PVC and 4/0 XHHW is likely easier to handle and probably cost less? The cable will likely be about as hard or even harder to install. You may have issues with conductor bending space or main lug size with 300. Many supply houses probably do not stock 300 SER either - at least not in every location for the ones that have multiple locations.

 

[tryinghard]

In a single family dwelling the only feeder that would be allowed to be sized by 310.15(B)(6) would be a feeder between a service disconnect and the panel(s) it supplies...

Then how can this feeder supply more than one panel and still comply, tap?

 

[kwired]

Then how can this feeder supply more than one panel and still comply, tap?

Exactly, there is no rule to limit a feeder to supply only one panel or other device. If the feeder is supplying the entire dwelling what difference does it make if supplying a 30 circuit panelboard or 15 - 2 circuit panelboards, as long as overcurrent device does not exceed panel rating or if tap rules allow the installation.

 

[tryinghard]

Exactly, there is no rule to limit a feeder to supply only one panel or other device. If the feeder is supplying the entire dwelling what difference does it make if supplying a 30 circuit panelboard or 15 - 2 circuit panelboards, as long as overcurrent device does not exceed panel rating or if tap rules allow the installation.

For this table to be used the feeder can only supply one panel not more than one, any more than one is a portion not whole and these feeders cannot be sized from this table.

 

[kwired]

For this table to be used the feeder can only supply one panel not more than one, any more than one is a portion not whole and these feeders cannot be sized from this table.

OK, I had a whole paragraph telling information you may already know about feeders in general and that this section had nothing to do with panels and the word panel is not even in there. Then I read it one more time and the word panel is in there. And in singular form. Guess I was going the wrong way with some hypothetical installations that I have never done but could be legal. But the feeder would definately need sized by 310.16 and not 310.15(A)(6). And I have installed more than one panel on single 200 amp feeder before just happens that 4/0 aluminum is minimum size needed either way - as long as it is not required to be 60 degree conductor.

 

[Hairball]

9,000 sq ft house. I would prefer running conuit also, however too many bends between AMP gear on outside and Panel Locations on inside. Also nowhere for J - Box.

 

[George Stolz]

If the floor hasn't been poured yet, run it underground and have no j-box.