ECN Forum Forums Code Related Discussion NEC & other Code issues Table 310.15(B)(6)

As I read 310.15(B)(6), it applies to the specific listed conductors that supply the _main_ load of a residence. This could include feeders to subpanels, as long as what you have at the end of the chain is the _main_ load of the residence.

For example, if you have a 'meter-main' on the side of the house, with a 200A breaker, followed by a 200A feeder to a panel in the basement, with the loads of the residence connected to branch circuits at the panel in the basement, then the feeder between the meter-main and the _subpanel_ in the basement would fall under 310.15(B)(6).

As I read this, a random subpanel for a single floor or a garage would _not_ qualify for inclusion under 310.15(B)(6).

Now if I read the original question to mean _should the code be adjusted to permit feeders to garages to be sized using 310.15(B)(6)_, then my hunch is: probably. Residential loads are very diverse with short duration peaks, and I don't see common garage loads being much different. A 100A feeder to a garage sized using 310.15(B)(6) is probably just fine. I don't see it as meeting current code, however.

-Jon

"the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit panelboards(s)."

The subpanel in the detached building is a "lighting and appliance branch-circuit panelboards." The feeder for the subpanel is between the main disconnect and a "lighting and appliance branch-circuit panelboards(s)" and is therefore a "main power feeder."

One vote for use of the table. (Being an engineer my stamp allows it.)

There is no reduction
allowed after the lighting appliance branch-circuit panel(s).

310.15(B)(6) specifically allows reduction to the first lighting appliance
branch-circuit panel(s) down line of the service equipment.

Using a lateral in the following example

400A service
2-200 amp lighting appliance branch-circuit panels.

Service lateral --400KCM copper per article 310.15(b)(6) to 400A OCPD.

We still have not made it to our lighting appliance branch-circuit panels
yet.

For sake of coversation we install 2-200 amp enclosed breakers adjacent to
this 400 amp OCPD and feed these from parallel lugs.

We use 2/0 copper per 310.15(b)(6).

We still have not made it to our lighting appliance branch-circuit panels
yet.

We feed 2-200 amp lighting appliance branch-circuit panels with 2/0 copper
per 310.15(b)(6)and make all terminations.

We have finally made it to our lighting appliance branch-circuit panels.

Now 310.15(b)(6) has seen it's end and if we feed any sub panel, say a 100 amp, from one of these aforementioned lighting appliance branch-circuit
panels, this 100 amp sub panel can not use 310.15(b)(6)

Roger

All this may become clearer in 2008. The has been an acceptance in principle that will change the wording. Anyone who has downloaded the ROP can look at 6-61 Log #194 NEC-P06.

I think the statement of the panel sums it up.
" The panel agrees that the present wording is ambiguous. It is the panel’s intent that this allowance apply only to conductors carrying 100% of the dwelling unit’s diversified load."

BTW, thanks for all the replies.

[This message has been edited by Tom (edited 02-06-2007).]

I don't understand the rational that argues:

One wire size if I put the outbuilding service at one place and a different wire size if the service is elsewhere.

Certainly the diversity of load at the outbuilding is identical. And the current demands on the wire are identical.

George- I'm not in agreement with your understanding of feeding a detached building sizing the conductors per- 315.15(B)(6) because it specifically says "Dwelling Unit" and even with your "Seal" I would not approve it nor issue a green sticker.

The AHJ has no authority to not approve work that is engineered and installed according to the engineering.

That is quite untrue.

It staggers the mind that you feel a PE seal circumvents the adopted codes.

The AHJ does not have to accept any work not conforming to the NEC.

Where is it you work and what is it you do?

Bob

Thanks for the support Bob- I agree with you. I usually work very well with the engineers and have learned from them in many cases. I do not have a degree but I teach for Mighigan State University and have worked with Dr. Truman Surbrook for about 15 years and I do realize my role in the electrical industry. Having been a Master electrician for 25 years and maintaining my education with CEU's doesn't hurt either. Maybe George is from a State where there is little or no inspection activity. And maybe the Engineer is king. Hope he has insurance.

[This message has been edited by George Little (edited 02-07-2007).]

George, (not Little)
Do you have anything we could see to substantiate these things you say?

Show us!



[This message has been edited by electure (edited 02-07-2007).]