310.15(b)(6) vs. 310.16 for panel feeder

[DavidTu]

200A service for single family residence (in Seattle)
Demand load calcs come out at 105A for load and 65A neutral. So we have already installed 4/0-4/0-2/0 AL Triplex from the weather head. Original plan was to have panel back to back with meter but now the room is supposed to become a bedroom and GC wants to move the panel about 25 ft away on interior wall.

At this point, we were planning to swap the meter for a meter/distribution panel with 200A OCPD at the meter, then use feed-thru lugs to run 4/0 AL SER cable to a 200A MLO panel at the new location; so all protection at the meter.

If we want to run feeders from the meter/distribution to detached garage and a detached (finished) out-building (not a dwelling) can we do so and still use 310.15(B)(6) to size the SER at 4/0 or (as I've seen in other threads) does 310.16 apply in that case? Isn't the remote panel STILL taking all the load for the dwelling and therefore should 310.15(B)(6) still not apply? OTHERWISE, do we need to put a smaller breaker at the meter or use a 150 at the remote panel (MBP then)?

 

[ActionDave]

Does 230.40 Exception 3 fit your needs?

 

[Smart $]

Hmmm... I think you need to back up a bit. The service entrance conductor on suuply side of meter/MDP serves all three buildings... so 310.15(B)(6) is not applicable to that portion as it serves more than just the dwelling unit.

IMO, you can use 310.15(B)(6) for the portion between MDP and MLO house panel... but it is a hard call that only AHJ interpretation can answer.

 

[Dennis Alwon]

Are you all still on the 2011? The 2014 code cycle changes things and IMO is probably the way 2011 was meant to be interpreted. In that case running 4/0 alum ser that passes thru insulation or thru a caulked hole must be rated at 60C and therefore would not be compliant as the feeder to the sub panel. Again it depends on which cycle you are under

 

[ceb58]

Hmmm... I think you need to back up a bit. The service entrance conductor on suuply side of meter/MDP serves all three buildings... so 310.15(B)(6) is not applicable to that portion as it serves more than just the dwelling unit.

IMO, you can use 310.15(B)(6) for the portion between MDP and MLO house panel... but it is a hard call that only AHJ interpretation can answer.

IMO you cannot do what you are proposing. The only way to be able to use 310.15 (B)(6) would be to feed the other two buildings from the 200 amp sub panel.
That is the problem with that code. If you use a meter/combo with a load center and you feed say an A/C unit from it you cannot use 310.15 (B)(6) but if you feed the same A/C unit from your sub panel you can use the table. You reduce the load on the feeder so you must make it larger :slaphead:

 

[charlie b]

Are you all still on the 2011?

I can answer that for the OP, since we are both from Seattle. The state of Washington never adopted the 2011, and never will. As a cost-saving measure, the (former) governor placed all code-making activities on hold a couple years ago. We will be under the 2014 edition later this year (July, I think).

 

[Smart $]

IMO you cannot do what you are proposing. The only way to be able to use 310.15 (B)(6) would be to feed the other two buildings from the 200 amp sub panel.
That is the problem with that code. If you use a meter/combo with a load center and you feed say an A/C unit from it you cannot use 310.15 (B)(6) but if you feed the same A/C unit from your sub panel you can use the table. You reduce the load on the feeder so you must make it larger :slaphead:

Not your normal design. Consider...

 

[Dennis Alwon]

I can answer that for the OP, since we are both from Seattle. The state of Washington never adopted the 2011, and never will. As a cost-saving measure, the (former) governor placed all code-making activities on hold a couple years ago. We will be under the 2014 edition later this year (July, I think).

Thanks Charlie-- I saw he had 2008 but I didn't know if he had updated that info

 

[ceb58]

Not your normal design. Consider...

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.

Don't see your set up complying. The detached garage and other building would be associated with the dwelling. The dwelling would be the main point.

 

[Smart $]

Don't see your set up complying. The detached garage and other building would be associated with the dwelling. The dwelling would be the main point.

Read the quoted code sentence you posted.

Is the feeder between the main disconnect and the dwelling panelboard? [Yes]

Does it carry all loads part of or associated with the dwelling? [Yes]

 

[GoldDigger]

Restating:
Does it mean all the loads associated with the dwelling building?
Or does it mean all of the loads associated with all of the buildings associated with the dwelling?
The interpretation is easier to make in the case of service wires than feeders, IMHO.

Tapatalk!

 

[Smart $]

Restating:
Does it mean all the loads associated with the dwelling building?
Or does it mean all of the loads associated with all of the buildings associated with the dwelling?
The interpretation is easier to make in the case of service wires than feeders, IMHO.

It says dwelling unit, which is not defined in terms of structure. We deduce it to be not more than one building... but if it were to be more than one building, those buildings would have to provide facilities per the definition. The problem with the way the definition is worded, the facility categories are not limited to those stated.

 

[Dennis Alwon]

It says dwelling unit, which is not defined in terms of structure. We deduce it to be not more than one building... .

Not necessarily true-- a garage detached or attached is IMO associated with the dwelling unit and thus would be a part of the load. Why would a detached garage be looked at separately??? A garage door opener or a freezer should be in the calculation in either case--- of course this is my opinion

 

[Smart $]

It says dwelling unit, which is not defined in terms of structure. We deduce it to be not more than one building...

Not necessarily true-- a garage detached or attached is IMO associated with the dwelling unit and thus would be a part of the load. Why would a detached garage be looked at separately??? A garage door opener or a freezer should be in the calculation in either case--- of course this is my opinion

I thought I covered that interpretation in the latter portion of my post...

...but if it were to be more than one building, those buildings would have to provide facilities per the definition. The problem with the way the definition is worded, the facility categories are not limited to those stated.

 

[DavidTu]

Wasn't able to reach the inspector the other day, but I did get ahold of a guy who does Electrical Plan Reviews here in Seattle (Charlie might know him -- Tim Porter) and he thought what I was describing was pretty typical for a mobile home installation--haven't done any. He agreed with the premise that the 4/0 SER feeder was in fact supplying all the loads of the dwelling and thus could be sized according to 310.15(B)(6). The feeders to garage and shed would have to be off 310.16, of course.

Discriminating between an attached an a detached garage does seem sort of arbitrary--but no more arbitrary to me than comparing feeding the garage load (and shed) off the main load center at the end of those same cables sized via T310.15 versus if we REMOVE those loads from those same cables at the meter we would somehow size more restrictively by T310.16 with LESS load?

 

[Dennis Alwon]

Discriminating between an attached an a detached garage does seem sort of arbitrary--but no more arbitrary to me than comparing feeding the garage load (and shed) off the main load center at the end of those same cables sized via T310.15 versus if we REMOVE those loads from those same cables at the meter we would somehow size more restrictively by T310.16 with LESS load?

Yes and the same holds true for ac units. If you install a circuit for the ac from the main panel then the feeder to the sub, even with less demand, must be size to 310.16