I'm taking an informal poll here.

Should the table apply to a feeder run from a dwelling to a detached shop?

No, it is only for the main feeder to the dwelling.

The detached shop is not a dwelling unit so that table can not be used.

Another no here.

Roger

No, it is only good for the main feeder and to other panels within the same dwelling. Conductors feeding a detached "shop" must comply with 310.16. So it's ok to run #4 copper feeders to a subpanel on the 2nd floor of a dwelling for 100 amps, but if 100 amps is desired for a detached shop, #2 copper should be run.

That's kinda dumb ain't it?

Shock, a sub panel is not a "main feeder" unless that is the source of all current to a dwelling. For example, if you had a 100a disconnect at ther meter feeding a distribution panel that would be a main feeder. If you come to a main panel with other loads and then feed another sub, that is not a main feeder and you us 310.16.

A main feeder, and all other feeders within the same dwelling, shall comply with Table 310.15(B)(6).

Not sure where you are getting this from. 310.15(B)(6) can't be used for subpanels.

310.15(B) (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(s) between the main disconnect and the lighting and appliance branch-circuit panelboards(s). 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.

Curt

Isn't any panel located downstrem of the main disconnect a "subpanel"? Or does the main disconnect have to be an overcurrent device, to have any panel downstream a "subpanel"?

steve

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).]

Gentlemen:
I have to say this:
As an AHJ (NJ) it is my responsibility to do Plan Review and Permit Approvals, and sign off on plans and the permit applications.

It is my State Licences that I execute on each and every 'job' that I sign off on Plan Review. Licences that I worked very hard to get, BTW.

The purpose of Plan Review is to basically do a 'double check' for NEC compliance. In addition, we also are obligated to enforce the EE/PE/AIA's 'spec' if and when it is above and beyond the NEC.

Yes, we are all human, and humans do commit errors, both AHJ's and PE/EE/AIA's. NJ has a law that all work in comm jobs be signed/sealed by an EE/PE/AIA, so we are not 'anti-engineer'

Plans conform to the NEC, they get approvals, plans do not conform to the NEC, they get a rejection. Courtesy phone call, then, if no reply, a formal Notice of Denial.

So, based on the above, I say NO, the Seal/Signature does not get the stamp of approval.

John

There are certain features of the code that specifically admit the use of 'engineering supervision'.

Relevant to the present discussion: 310.15(C)

Given that some parts of the code admit of 'engineering supervision' and other parts do not, it seems pretty clear an engineer's stamp is not a blank check to go around code requirements, unless the government authority which adopts the code provides this exception.

-Jon

Wouldn't a PE design use accepted practices?? The PE is one who would be liable if the design failed. I believe in MAine a PE can overrule(override) the NEC but not sure where I'd find a link to prove it. I believe its done quite often in Paper Mills?? Probably PoCos also?.

I would be intrested to see it.


I am not sure they supposed to 'override' the NEC but they may well be their own AHJ.


The NEC does not apply at all to power company distribution systems.

If the power company builds a new office building for themselves that office building will have to conform to the NEC.

Take a quick look at 90.2(A) and 90.2(B).




[This message has been edited by iwire (edited 02-10-2007).]

The PE stamp does not permit one to "overrule"the NEC. It does permit a PE to provide an alternate method that may be equivalent or more strict than the NEC.

I also am an inspector, and there are many times that prints have to be adjusted and thus may not make it past us. That is when we have discussions with the PE so they can make the corrections and then the prints are submitted.

iwire
I believe you are correct in that paper mills perform AHJ duties. I don't believe the state inspectors go into the mills.

This is all anecdotal from stuff I've heard over the years. I was always under the impression that a PE could do as he wanted but it was his butt on the line. Never seen it in practice.

electure ---

I have posted substantiation in the thread about the number of conductors in a conduit. But I will continue here also.

---

I would expect that the moderators and those who claim to be inspectors would have read the local laws that adopt the building codes.

Usually the process is that a national building code is adopted and that building code includes reference to the NEC.

All national building codes allow engineering. That includes engineering of the electrials.

The national building codes and the NEC are prescriptions. That is, based on general assumptions general engineering solutions have been produced and reduced to the tables and text of the codes and the NEC.

The engineering allowed by the national building codes and by included reference by the NEC consists of project specific assumptions and produces project specific engineering solution.

In general, an engineered solution will not "meet" the NEC. It will not "meet" the NEC because the design assumptions more accurately reflect the needs.

---

I suggest that those of you who hold a differing opinion consult your attornies before you reject an engineer's work.

George I suggest you find some real references or admit your mistaken.

Here we do not use a national building code.

George, we're still waiting.

It's apparent that you have gotten in over your head and simply can not back up your statements can you?

Telling us to contact an attorney is not substantiation to your claims.

Roger

George- I have no problem approving your plans when they meet or exceed the minimum requirements of the NFPA standards, it's when they don't that I, not unlike any other inspector or plan review department would reject your plans. I don't know where are you from because you've chosen to be silent with respects to your location but I'd be surprised if what you are indeed claiming is accurate. Your creditability would be increased if we knew your background. Chances are you are a newbie in the electrical field and don't know your role in relation to the rest of the industry.



[This message has been edited by George Little (edited 02-10-2007).]

Heres what some PEs think about code vs engineering http://www.eng-tips.com/viewthread.cfm?qid=104152

I find it interesting the predominant reply is "If we ever find a situation where we need to violate code for a safe and practical design, that just means the code is wrong and we need to change it." That's a forum full of engineers for ya!

[This message has been edited by SteveFehr (edited 02-11-2007).]

This rule is very poorly written. Even though it uses the word "main" there is nothing that says that the conductors question must carry the main or any other portion of the load. This is because the term "main power feeder" is defined in the section and the definition says nothing about the load.
The wording of the section does match the intent of the rule. In my opinion all feeders are installed between the main disconnect and the lighting and appliance branch circuit panelboard(s). There is nothing that says that there can't be another feeder or OCPD between the main and the panel. I would agree that it can only be used for panels that actually serve the dwelling unit. I know that few agree with me on this, but in my opinion, that is what the words actually say. As I said, I know that this is not the intent of the CMP.
Don

I read this as applying to "dwellings" in the same way that IRC applies to shops and garages, as opposed to IBC-type commercial buildings which are subject to more stringent codes. As such, small outbuildings like sheds, garages and workshops detached from one or two-family homes are still considered "dwellings" for the sake of code compliance and 210.15(B)(6) would apply.

[This message has been edited by SteveFehr (edited 02-13-2007).]

Don, Not sure what your position is after reading your post. Can feeders go to the 'shop' or not? Seems like you say yes and no all at the same time.

SteveFehr, a 'shop', 'detached garage', 'shed' etc. is definitely not a dwelling in any actual or intended code I have ever read. Also, I felt there was a balance in the eng. forum on using the code. I do agree that some engineers on that thread are presumptuous and arrogant.

There is no architect or engineer of any field who can submit something less than the intent of the code and pass (if the AHJ catches it) based on the way the laws are written and interpreted where I come from.

Any town can adopt any code they want and if it way above or below engineering standards (whatever those may be) the AHJ can do whatever they wish. But that's where I come from. Laws could be different in different places and both opinions could be right.

Tom, see what you started!! My opinion is no as well. But, I also think a dwelling unit panel that subsequently feeds a 'shop' should not be allowed to follow the section either as the feeders are not feeding just a dwelling (which I believe is the intent of the section.) I may be wrong, but the substantiation for this section came from data supplied from utility billing showing that dwelling loads rarely ever reach the ampacity level of the wiring, therefore the allowance for the reduction in the size of the wire. I highly doubt, the data included buildings with down-stream 'shops'.

Can we define 'shop' please?

You can parse the language all you want but at the end of the day you are still stuck with A feeder to a detached garage is not the "main power feeder to a dwelling unit" unless that garage complies with article 100 "Dwelling Unit".

"Living"


A shop is no different than a sewing room or rumpus room or pool room or any other hobby space. If this was a detached practice room for a band, would anyone have a problem with considering it dwelling space? Adding some receptacles so that a tool bench and some tools doesn't change that it's still residential and falls under residential rules vice commercial rules.

Steve it would be interesting to get you out of your present employment situation and get you working under the typical AHJ / NEC enforcement situation.

I think your head would be spinning, in no shape or form would I ever expect an AHJ to call a detached garage a dwelling unit.

Most of our Municipal Codes out here specifically prohibit living in a garage or shop.
If you want to remodel an existing garage for use as living space, you must also build a new garage.
It used to be a pretty popular thing to convert the garage to a rumpus room, apartment,etc. (of course sans permits)

Through the years, there have been occasional Code Enforcement sweeps that targeted these bootleg "dwellings".

If you want to cal your shop a dwelling unit, fine. Where is the bathroom, kitchen and laundry with required 20a circuits? Which part are you calling the sleeping quarters and where is your AFCI?

Maybe it's just a hang-up I have with the way some of the codes are worded, and a tendancy I have for trying to apply logic to a legal document. If I have a room that shares a common wall, it's treated one way, but if I double that wall up for extra fire safety and move it 12" away, all the sudden NEC wants me to treat it completely differently, which I think is BS- a room is a room whether it's sharing a wall or 30' away and should be treated the same way. I see outbuildings as merely extra rooms associated with the primary dwelling, maybe I'm wrong- as noted, this is not exactly my realm of expertise... But I see the shop as a dwelling sub-unit ("living") and see no logical reason it should be treated any different than a dwelling unit.


[This message has been edited by SteveFehr (edited 02-22-2007).]

Steve, it all has to do with diversity of the load. In a dwelling unit we put a lot of things in the load calculation that will not usually be going at the same time. Certainly with a house full of people on Thanksgiving with someone in the shower, washer/dryer going, every light in the house on and the stove/oven going on all burners that 310.15(B)(2) table is probably not going to be "enough" but most times it reflects the actual diversity a dwelling will have.
In the case of your garage/shop, you have usually overbuilt but the answer is just to protect your feeder with 310.16. If you are tripping that you probably underbuilt the feeder.

Tom, you said the panel agrees it is only for feeders carrying 100% of the dwellings diversified loads. So what about a circuit to the garage? If you have a detached garage (with electric) the table won't apply?

I was thinking when you said shop, that maybe you meant a business of some sort. Of course if you are making kitchen cabinets in your garage and selling them, it is a business, right? Of course if you give the cabinets away then it's just a hobby.

I'll have to make sure our zoning officer checks the wiring before approving home based businesses.