Thread: Lengths of conductor leads

is there any provision limiting the length of the conductor leads being exposed pass the terminal screws? Or am i being nit-picky again.

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Off the top of my head, I'm not aware of any limits on neutrals and grounds. I've heard of at least a 1/4" so you could verify the wires pass all-the-way through. Now you got me thinking...

I know you didn't ask, but just in case, are you aware that you can only have one neutral per terminal and double grounds would depend on the panel listing?

Not that I've heard of, but an electrician or two have told me that you shouldn't see any copper at the breaker connections.

Without reference to any code, I would say its not a problem. Also the lay of the wires is neatly done. Personally I would not write it up as an issue.

Also shouldn't the two 20 amp breakers be tied together at the handles as its actually a 220 volt circuit?

The only code I can think of which could address that would be 110.3 (B) Listing and labeling. And then if you were to dig into the specifications you would likely find detailed information about terminating conductors in those terminals which would specify that the insulation be stripped back enough to allow the conductor to be fully inserted into the terminal but not project beyond the terminal.

Being as that is service equipment and those are the grounded conductors (no voltage on them) and they are bonded to ground at those terminals, there is no potential risk of problems created if the long exposed ends were to touch ground.

A bit sloppy on the workmanship side, but not really a problem.

The multiple tapped neutrals are a problem.

The real issue here would be 2 neutrals under the same screw. As for the the lengths in this case you should be fine.

Originally Posted by Mbrooke

The real issue here would be 2 neutrals under the same screw. As for the the lengths in this case you should be fine.

The drawing you provided is of "typical" allowed terminations, the correct answer for each panel is "read the label" as some allow 3 of the same size if either#14 AWG or #12 AWG - but not all allow 3, many are limited to 2.

Thanks everyone.....I knew about the multiple neutrals....but according to the diagram, multiple equipment grounds under a single terminal screw is acceptable. Dang....I've been writing those up!

Originally Posted by brianmiller

... but according to the diagram, multiple equipment grounds under a single terminal screw is acceptable.

They are acceptable *only if* so specified on the labeling.

And then only in accordance with the labeling (which typically allows to groundING conductors, of the same size and of the same material and from #14 to #10 in size, in one terminal, however, as mentioned above, some allow 3 #14 and #12 in one terminal (of the same size and the same material), and some even limit the multiple conductors to 'copper only', which means no aluminum multiple tapped groungING conductors ...

... it is best *not* to make blanket statements on this issue as it all depends on ... what is stated in the labeling - DO NOT "assume" anything other than one conductor in one terminal if it is not stated or if the label is not legible or is missing.

Without the label it is one conductor in one terminal, says so in the code: (bold and underlining are mine)
- 110.14 Electrical Connections. - - (A) Terminals. Connection of conductors to terminal parts shall ensure a thoroughly good connection without damaging the conductors and shall be made by means of pressure connectors (including set-screw type), solder lugs, or splices to flexible leads. Connection by means of wire-binding screws or studs and nuts that have upturned lugs or the equivalent shall be permitted for 10 AWG or smaller conductors.
- - - Terminals for more than one conductor and terminals used to connect aluminum shall be so identified.

Originally Posted by brianmiller

Thanks everyone.....I knew about the multiple neutrals....but according to the diagram, multiple equipment grounds under a single terminal screw is acceptable. Dang....I've been writing those up!

The unfused service lateral conductor is in the wrong wiring space. The service equipment should have been employed in conformance with its limited vintage listing which includes the wiring diagram and the provisions "when used as service equipment". Space (bending sp, heat dissapation/sink, shielding, separation sp, flash chute) requirements were less with older equipment; however highly dependent on following the appropriate vintage limitations for the Standards for Safety AND the conditions (and limitations) outlined in the labeling & wiring diagram in addition to the vintage edition of the NEC referenced at the time of manufacture & listing/labeling.

DSC04027.JPG

Originally Posted by H.G. Watson, Sr.

The unfused service lateral conductor is in the wrong wiring space. The service equipment should have been employed in conformance with its limited vintage listing which includes the wiring diagram and the provisions "when used as service equipment". Space (bending sp, heat dissapation/sink, shielding, separation sp, flash chute) requirements were less with older equipment; however highly dependent on following the appropriate vintage limitations for the Standards for Safety AND the conditions (and limitations) outlined in the labeling & wiring diagram in addition to the vintage edition of the NEC referenced at the time of manufacture & listing/labeling.

DSC04027.JPG

I hope you are kidding. In over 30 years I have never seen the SE conductors run in any place besides the wiring gutters. The limited instructions that do come with the panel do not say that only the branch circuit wiring is allowed in the gutters. Where do you expect the wiring to be installed?

As far as the vintage, those are the current style CH breakers being manufactured. You can see the plastic mounting foot.

Canadian inspectors should ignore the 3 posts above.

Under the CEC, service entry conductors are not allowed in the area of the panel that contains the branch circuit conductors.

Originally Posted by John Kogel

Canadian inspectors should ignore the 3 posts above.

Under the CEC, service entry conductors are not allowed in the area of the panel that contains the branch circuit conductors.

That reminds me, I was talking with an electrician and we were talking about a certain show and the topic of panels in Canada came up. We both noticed that there was separate covers on the panels in the background. One for the service conductors, and the second cover for the branch circuits. Are these panels made just for Canada? I have never seen them around here, and the electrician said he has not seen them in supply houses. Your comment answered our question if this was required in Canada, and seems like a good idea...

Originally Posted by Jim Port

I hope you are kidding. In over 30 years I have never seen the SE conductors run in any place besides the wiring gutters. The limited instructions that do come with the panel do not say that only the branch circuit wiring is allowed in the gutters. Where do you expect the wiring to be installed?

As far as the vintage, those are the current style CH breakers being manufactured. You can see the plastic mounting foot.

The panel is also of current vintage as the main breaker handle operates sideways as opposed to the older vertical operating handle,which is not shown in the pic though. Too bad a neat panel job was ruined by placing 2 neutrals under one set screw.

Originally Posted by Mike Kleisch

That reminds me, I was talking with an electrician and we were talking about a certain show and the topic of panels in Canada came up. We both noticed that there was separate covers on the panels in the background. One for the service conductors, and the second cover for the branch circuits. Are these panels made just for Canada? I have never seen them around here, and the electrician said he has not seen them in supply houses. Your comment answered our question if this was required in Canada, and seems like a good idea...

Yes, Combination breaker panels in Canada have either two covers or an interior removable panel over the SEC's.

Also, there is no rule in the CEC forbidding mounting the panel on its side, although this is seldom done, except in basement upgrades. I've seen it once in new construction and can only guess that somebody was bent out of shape.

There are dozens of differences in the Canadian codes pertaining to the service entry alone.

Canadian inspectors need to buy the books and read them.

Originally Posted by John Kogel

Canadian inspectors need to buy the books and read them.

Why? Do you mean that contractors buy the books and "read them"?

I did an electrical final today where the service equipment had been replaced and new ground rods driven: (I'll keep the list shorter than it really was) the ground rods were 3 feet apart; the first ground rod clamp was not listed for direct burial use; the first ground rod clamp was not listed for two conductors but had two grounding conductors in it; the grounding electrode conductor come down through a piece of EMT and was not bonded at either end; the contractor knocked a hole through the wall twice as large as was needed for the conduit going from outside to the inside - I could fit my hand into the hole around the conduit; obviously, I could see plenty of daylight to the outdoors (probably not enough for a raccoon, but something a little smaller); and there were more items which were not correct ... no, I did not 'pass' it. The longer I stood there, the more I saw wrong with it ... so I had to leave ...

Oh, and one item was one I have contemplated bringing up here before, so here it is:
Dwelling unit service:
- a) Service entrance conductors come to the service equipment panel which has a main disconnect only and then feeders go to an interior panel. The service disconnect is 200 amps.
- b) Service entrance conductors come to the service equipment panel which has a main disconnect and branch circuits and then feeders to to an interior panel. The service disconnect is 200 amps.

What size feeders are allowed for a) and for b)?
- a) copper =
- a) aluminum =
- b) copper =
- b) aluminum =

This is only a test, do not adjust your set, regular programming with return in 30 seconds ...

Oh yes... just another case where licenced so called qualified professionals screw up. If you can't rely on licenced electricians, who ya gonna call?

Due to gray matter farts, I don't remember the brand, but one manf. allowed 3)#14's or 2#12's in the buss bar. Back when there isn't any mention of stranded vs solid either.
I know some Electricians who don't know where J.P. is going with his question. If any of U H.I's are hep to it, your doing pretty good.

- - - Updated - - -

Due to gray matter farts, I don't remember the brand, but one manf. allowed 3)#14's or 2#12's in the buss bar. Back when there isn't any mention of stranded vs solid either.
I know some Electricians who don't know where J.P. is going with his question. If any of U H.I's are hep to it, your doing pretty good.

Originally Posted by bob smit

I know some Electricians who don't know where J.P. is going with his question. If any of U H.I's are hep to it, your doing pretty good.

Bob,

All they need to do is read what is written in the 2008 NEC Handbook to confirm the wording in the code is meant as the wording in the code was written.

This is one of those sections which some electricians, and some electrical experts, have continued to state that the code does not really mean "all" when the code uses the word "all". The Handbook clears that up by stating that it means "100 percent" ... which, at least to me, is the same as "all" ...

Originally Posted by Jerry Peck

The drawing you provided is of "typical" allowed terminations, the correct answer for each panel is "read the label" as some allow 3 of the same size if either#14 AWG or #12 AWG - but not all allow 3, many are limited to 2.

The drawing is based on the newer NEC requirements.
I cant speak as to what code cycle the article was introduced, but in all cases now the requirement is one neutral per hole. The only exception would be paralleled circuit conductors, not ones of different branch circuits like we see here:



408.41 Grounded Conductor Terminations. Each grounded
conductor shall terminate within the panelboard in an individual
terminal that is not also used for another conductor.
408.30 ARTICLE 408— SWITCHBOARDS AND PANELBOARDS
70–276 NATIONAL ELECTRICAL CODE 2011 Edition
Exception: Grounded conductors of circuits with parallel
conductors shall be permitted to terminate in a single terminal
if the terminal is identified for connection of more
than one conductor.

Originally Posted by Mbrooke

The drawing is based on the newer NEC requirements.
I cant speak as to what code cycle the article was introduced, but in all cases now the requirement is one neutral per hole.

I was referencing the groundING conductors, not the groundED conductors: (bold and underlining are mine)

Originally Posted by brianmiller

... but according to the diagram, multiple equipment grounds under a single terminal screw is acceptable.

Originally Posted by Robert Meier

Since Mike Holt's graphic is from 2001 I would guess that the wording was added into the 1999 NEC. However the requirement for one grounded conductor per hole was in effect for many years prior to the inclusion of the words in the NEC. This had long been part of the UL requirement for panelboards but no one really knew about it.

I know that it has been in the code prior but I am clue less. I think the 80s? Dunno In my 2011 code book the section was been switched around from the 1999 code book, but the same theory holds true.

On a side note, I can understand doubled up grounds and neutrals if there are no remaining holes left, a really common problem in older panels and panels that use all twins (heck Ive let those slide), however, when there are remaining holes left with doubled up neutrals its just poor workmanship.

Originally Posted by Mbrooke

On a side note, I can understand doubled up grounds and neutrals if there are no remaining holes left, a really common problem in older panels
.
.
its just poor workmanship.

I can't understand doubling up the neutrals and the grounds, any holes left or not - all they have to do is to remove the grounds and use the holes for the neutrals, then add a ground bar for the ground conductors.

And it is not just poor workmanship, it was typically done that way because, well, because that is the way they were taught and the difference was not readily understood by all back then, even some electrician today still multiple tap the neutrals, and the reason they give is: "I've always done it that way" or "that is the way I've always seen it done by everyone else", neither of which gets a pass with me.

OR--just pigtail them with a wire nut and terminate the single wire. That would solve the workman like manner problem (it is only an opinion anyway).

Splicing neutral could result in improper multi wire branch circuits. The panel should have enough terminals for the neutrals. If needed a ground bar would be added.

- - - Updated - - -

Splicing neutral could result in improper multi wire branch circuits. The panel should have enough terminals for the neutrals. If needed a ground bar would be added.

Originally Posted by Jim Port

- - - Updated - - -

Splicing neutral could result in improper multi wire branch circuits. The panel should have enough terminals for the neutrals. If needed a ground bar would be added.

WOW--I am baffled on this one???Taking two grounded conductors from under a single screw and pigtailing them would not change anything electrically. If your "improper multiwire branch circuit" existed after pigtailing it certainly existed before it was done. It would solve the 2 conductors under a single screw violation.

Originally Posted by Jerry Peck

Oh, and one item was one I have contemplated bringing up here before, so here it is:
Dwelling unit service:
- a) Service entrance conductors come to the service equipment panel which has a main disconnect only and then feeders go to an interior panel. The service disconnect is 200 amps.
- b) Service entrance conductors come to the service equipment panel which has a main disconnect and branch circuits and then feeders to to an interior panel. The service disconnect is 200 amps.

What size feeders are allowed for a) and for b)?
- a) copper =
- a) aluminum =
- b) copper =
- b) aluminum =

This is only a test, do not adjust your set, regular programming with return in 30 seconds ...

215.2 (A) (4) says that on an individual dwelling unit the feeder doesn't need to be larger than the service entrance conductors, and doesn't specify only the main feeder, meaning all feeders.

In both cases the feeders can be 2/0 CU or 4/0 AL - - - but, only if the SE conductors are 2/0 CU or 4/0 AL on the panel with branch circuits. If the SE conductors are larger another rule applies and the feeder would need to be fully sized for 200 AMPs - 3/0 CU or 250 KCMil AL because the feeder is not considered a main feeder.

On the main disconnect only, the feeder can be sized from table 310.15 (B) (7) regardless of the SE wire size (see 310.15 (B)(7) definition of a main feeder)

Pretty much a stupid series of rules as the feeder from the panel that also contains branch circuits would in all probability see a smaller load than the one that feeds the main panel.

Originally Posted by Robert Meier

Yes it could. Splicing two neutrals together that are for two wire circuits on the same phase will create additive current on the pigtail. Two 20 amp loaded circuit would impose 40 amps on the pigtail.

Using two circuits not on the same phase will create a MWBC.

The same condition exists with 2 neutrals under the same screw. I would use #10 THHN--problem solved.

Your math is correct, you are missing my point..

Originally Posted by Roland Miller

The same condition exists with 2 neutrals under the same screw. I would use #10 THHN--problem solved.

Your math is correct, you are missing my point..

The same condition absolutely would not apply as each neutral is only carrying the current from its associated hot to the neutral bar.

A pigtail from two hots on the same leg could carry up to twice the load on the hots. The current from two 20 amp circuits could be more than the #10 can carry.

Originally Posted by Jim Port

The same condition absolutely would not apply as each neutral is only carrying the current from its associated hot to the neutral bar.

A pigtail from two hots on the same leg could carry up to twice the load on the hots. The current from two 20 amp circuits could be more than the #10 can carry.

My code book says #10 THHN's rated ampacity is 40 amps. And the overcurrent device should not exceed 30 amps. Looks like it will work to me. What does your code book say?

And what difference would it make if it is or becomes a MWBC?

Originally Posted by Robert Meier

The same condition doesn't exist when you have two neutrals under one screw. By using your method you're correcting one violation with another.

What is the violation I am creating. Give me some NEC stuff..

First you need to understand what a proper MWBC is and how it works.

Secondly you are ignoring the note at the bottom of the ampacity table. Thirdly, the 90 degree column is only used for derating.

**Refer to 240.4(D) for conductor overcurrent protection limitations.

By that note #10 is limited to 30 amps.

Originally Posted by Roland Miller

My code book says #10 THHN's rated ampacity is 40 amps. And the overcurrent device should not exceed 30 amps. Looks like it will work to me. What does your code book say?

And what difference would it make if it is or becomes a MWBC?

The 40 amp rating is not what it is allowed to be used at, that is the rating you would use to derate from.

If you have 2 circuits with 20 amp breakers you are allowing 40 amps on that #10 wire, and even you said the maximum allowed breaker size is 30 amps - that is a code violation ... and I included the NEC stuff you wanted.

Originally Posted by Jim Port

First you need to understand what a proper MWBC is and how it works.

Secondly you are ignoring the note at the bottom of the ampacity table. Thirdly, the 90 degree column is only used for derating.

**Refer to 240.4(D) for conductor overcurrent protection limitations.

By that note #10 is limited to 30 amps.

I see this is getting no where fast.

1. I do understand MWBC.
2. I didn't ignore the note.
3. The overcurrent device is 20 amps-well under the 30 required.
4. #10 THHN will carry 40 amps all day and all night and not be damaged, by design.

What difference does having a MWBC make? So if you are not happy with #10THHN I will use a #8 whatever. Show me the code references that say I couldn't do this. And please don't derail this discussion with smoke and mirrors...

Robert supplied part of the answer in post #38.

200.4 Neutral Conductors. Neutral conductors shall not
be used for more than one branch circuit, for more than one
multiwire branch circuit, or for more than one set of un-
grounded feeder conductors unless specifically permitted
elsewhere in this Code.

I also supplied the Note from Table 310 that states the #10 needs to be protected at no more than 30 amps.

Originally Posted by Robert Meier

Here you go, again:

So we now have code that says it is ok to do this, as long as you have created a MWBC.. And I know eveyone agrees with this so no further comments need to be made...

Nothing has appeared that says I can't put the #10 THHN on 2- 20 amp branch circuits. Even though by code it should not be subjected to more than 32 amps for the same phase, it is still well under its 40 amp ampacity..

Just to make everyone happy and focus in on the question. I will use #8 TW(if I can find some)..

The question is specifically--Can you splice the neutral in the panel to prevent putting 2 conductors under on screw? And I will give you all the answer--YES..

The correct code compliant answer is NO. It is obvious that you do not agree with the rule that has been posted several times. Regardless that does not mean it can be ignored.

Why do you think the return current would be limited to 32 amps? With both legs on the same hot the current is additive. Lets do the math, 20 + 20 = 40, not 32.

I see 200.4 that says I can do it as long as the circuit I have created is a MWBC. Pretty basic.

The NEC limits the current on a 20 amp breaker to 80% unless it is listed for 100% which I have not seen. Hence 20 X .80 X 2 = 32.. Also a very basic concept in the NEC..

Splicing is also a very basic concept in the NEC.. Why do all you respondants insist that a splice as discussed is a violation of the NEC?

200.4 Neutral Conductors. Neutral conductors shall not
be used for more than one branch circuit, for more than one
multiwire branch circuit, or for more than one set of un-
grounded feeder conductors unless specifically permitted
elsewhere in this Code.

I have 2 neutrals under one screw on the neutral bus. One supplies a circuit for A phase the other a circuit on B phase. I choose to splice them and terminate a single conductor on the neutral bus because an inspector said I couldn't do that. I have created a MWBC at the panel and terminated it with a single neutral. "shall not be used ........,for more than one multiwire branch circuit" which I have just created a single MWBC. Code compliant so far.

The bottom line is no one can predict how much current will flow on the single neutral and how long it will be there. So we all jump to 32-40 amps because we want it to sound sensational like the news, right? I don't sense that you all respondants comprehend conductor ampacity. #10 THHN CU will carry 40 amps all day long without damage by design.. The NEC chooses to limit the overcurrent protection to 30 amps (my circuits are on 20 amp breakers).

The discussion was about the possibility of wily-nily combining 2 neutrals from the same leg of the panel and overloading the neutral. The reason the 20 amps was used is that would be the maximum current from one or both of the hot legs. If both hots were at capacity the return current could be 2x 20 or more. A breaker can allow 125% of its rating for 2 hours, depending on the rate of rise and ampacity. Thus the improperly combined neutral could be carrying up to 50 amps on a 20 amp circuit. There is also no guarantee that the loads were line to load only.

The pigtailed neutral would also not satisfy the recent requirement for the simultaneous disconnect of both hots.

Originally Posted by Robert Meier

The bold part I agree with, in that case you have created a MWBC which is code complaint. The current on the pigtail will never be greater than the maximum current on any one circuit.

Bingo! (And I was still on the other circuit). We have a winner

Some might see this as a paralleled neutral. As such it would be way too small to meet the paralleling requirements along with other issues regarding paralleling.

You would also have the issue as not all conductors of the circuit being grouped together in the same raceway or sheath.

Originally Posted by Jim Port

Some might see this as a paralleled neutral. As such it would be way too small to meet the paralleling requirements along with other issues regarding paralleling.

It wouldn't meet the definition of parallel conductors.

You would also have the issue as not all conductors of the circuit being grouped together in the same raceway or sheath.

May or may not be an issue depending on which edition of the NEC you are under.

We already have a winner. Late submissions are not accepted

I moved the quote bracket

The paralleling requirements have not changed, nor have the grouping requirements in the last 20+ years IIRC.

Originally Posted by Jim Port

The paralleling requirements have not changed, nor have the grouping requirements in the last 20+ years IIRC.

WELL, I will just say you are half correct on this and I will let you figure out why...Have a nice day!

Not quite correct.

Originally Posted by Bill Kriegh

215.2 (A) (4) says that on an individual dwelling unit the feeder doesn't need to be larger than the service entrance conductors, and doesn't specify only the main feeder, meaning all feeders.

While 215.2(A)(4) does say "the feeder doesn't need to be larger than the service entrance conductors", it also says "Paragraph 310.15(B)(6) shall be permitted to be used for conductor size."

(I was referencing the 2008 NEC, you are referencing the 2011 NEC, but not really any difference between the two)
Note that in the 2011 NEC 215.2(A)(4) still references 310.15(B)(6) - however, the 2011 NEC had a new section inserted and 310.15(B)(6) was re-numbered to 310.15(B)(7), which says: (bold and underlining are mine)
- (7) 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)(7), 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 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. 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.

Note that in order to apply the above section "For application of this section" a main service disconnect ONLY (no branch circuits in the service equipment panel) the feeders do, indeed, supply "all loads that are part or associated with the dwelling unit.", however, when there are branch circuits provided for in the service equipment in addition to the main service disconnect, then the feeders from the service equipment 'do not supply' "all loads that are part or associated with the dwelling unit." and, as such, this section { 310.15(B)(7) } is not allowed to be applied.

That means that the feeders, and the service conductors, are to be sized in accordance with Table 310.15(B)(16) (formerly Table 310.16)

In both cases the feeders can be 2/0 CU or 4/0 AL - - - but, only if the SE conductors are 2/0 CU or 4/0 AL on the panel with branch circuits.

Incorrect.

When no branch circuits are provided for in the service equipment, you are correct, 2/0 copper would be permitted, however, when branch circuits are provided for in the service equipment, the feeders no long supply all the loads in and related to the dwelling unit and neither 310.15(B)(7) no Table 310.15(B)(7) is permitted to be applied ... thus Table 310.15(B)(16) (formerly Table 310.16) is to be utilized and that requires 3/0 copper.

If the SE conductors are larger another rule applies and the feeder would need to be fully sized for 200 AMPs - 3/0 CU or 250 KCMil AL because the feeder is not considered a main feeder.

The service conductors are permitted to be sized to 310.15(B)(7) like the feeders are permitted to be ... under the conditions permitted for the feeders.

Go back to the 2008 NEC, in your Handbook, and you will see where the Handbook specifically addresses the above condition of "all loads that are part or associated with the dwelling unit" as it appears that many electrical contractors AND inspectors were not getting what the code was saying, to the Handbook says this: (remember, in 2008 the numbering was 310.15(B)(6) )"Section 310.15(B)(6) permits the main feeder to a dwelling unit to be sized according to the conductor sizes in Table 310.15(B)(6). For the 2008 Code, the panel clarified that this permission to use this table applies only to conductors carrying 100 percent of the dwelling unit's diversified load."

I clarified this with two questions to NFPA through the ask a technical question section and received two answers back - both confirming what I stated above and what is stated in the code and in the Handbook - "all loads that are part of or associated with the dwelling unit" and "this table applies only to conductors carrying 100 percent of the dwelling unit's diversified load".

The reason for that specificity may be hard to wrap one's head around, but in essence it is to make sure that ... "all" ... "100%" ... of the dwelling unit's load is carried by the conductors and, as such, they can then apply their theoretical "diversified load" calculations to it and allow a reduction in the conductor size.

Take away some of that load and their calculation goes out the windows, and so does the permission to apply that table for reduced conductor sizes.

Electrical Engineering

Scroll down to Case #4. This seems to illustrate what you guys are discussing.

Regarding feeders, two things. The handbook isn't the legal document used for enforcement so whatever explanation they throw at things doesn't matter. And, as is the case many places in the NEC, the language contradicts itself so you play pick and choose. Around here, common practice is to use the reduced size feeder in both circumstances because 215.2(A)(4) says it's OK by not specifying only a main feeder can be reduced.

The NEC reminds me of the old Mad Magazine "What people say and what they really mean" series of articles. If they don't want 215.2(A)(4) applied in all resi circumstances it's a simple matter to change the language. If the language isn't clear and doesn't say what they really mean, they can change it. After all, a special resi situation is specified by the paragraph in the first place and if omitted then the language in 315 would be the only reference and the confusion wouldn't be there.

I would find it very unusual to find that a panel doesn't have load diversity simply because it isn't the first panel in line. And, if the first panel has several loads that would otherwise be on a panel at the load end of a feeder, the feeder wouldn't be needing to carry that load anyway. Load diversity isn't not a hard concept to wrap your head around. Load diversity in a residence is like balanced loads in resi situations - it may exist or may not and either circumstance is possible and just as likely on a panel that supplies all loads or one that is supplied by a feeder - these guys need to get out of the office a bit more.

All that aside, you can either ignore what 215.2(A)(4) says, pretend it doesn't exist, or apply it.

Originally Posted by Bill Kriegh

215.2 (A) (4) says that on an individual dwelling unit the feeder doesn't need to be larger than the service entrance conductors, and doesn't specify only the main feeder, meaning all feeders.

Originally Posted by Bill Kriegh

All that aside, you can either ignore what 215.2(A)(4) says, pretend it doesn't exist, or apply it.

Or you can do what 310.15 (B)(7) says and properly size the service conductors as stated in 310.15 (B)(7) - you seem to keep ignoring that the service conductors are included in that section - thus there would not be a conflict with between any of the sections.

All of the sections would fall into alignment and the code would not be inconsistent with itself.

Originally Posted by Jim Port

The paralleling requirements have not changed, nor have the grouping requirements in the last 20+ years IIRC.

Maybe Jerry Peck could help you? He does a great job with NEC history.