new 400 amp resid. service

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fisherelectric said:
Is it because there are 2 feeders?
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Yes, because neither feeder carries 100% of the dwelling units load.

I believe it has to do with the lack of load diversity in multiple feeders.

BTW, the rules did not change, they just changed the wording to make it clear.
 
fisherelectric said:
I'll have to check the wording in the '08. The '05 says "feeder(s)" between "panelboard(s)"...plural.
I don't have the 08 code book.
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Let me save you the trouble. The bold is the new wording


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 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.
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fisherelectric said:
I'll have to check the wording in the '08. The '05 says "feeder(s)" between "panelboard(s)"...plural.
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Here is part of the proposal that brought about the change in wording only. Be sure to check out the panel statement at the bottom.

6-61 Log #194 NEC-P06 Final Action: Accept in Principle
(310.15(B)(6))

Recommendation: Accept the panel action in principle. Clarify the
permissible application of the multiple feeder allowances as one of the
following four options:

1) ?? the main power feeder shall include the feeder(s) serving only loads
associated with a single dwelling unit and running to but not originating in the
lighting and appliance branch-circuit panelboard(s) serving the dwelling unit.?

OR

2) ?? the main power feeder shall include the feeder(s) serving only loads
associated with a single dwelling unit and running to the lighting and appliance
branch-circuit panelboard(s) serving the dwelling unit.?

OR

3) ?? the main power feeder shall include the feeder(s) serving only dwelling
loads and running between the main disconnect and the lighting and appliance
branch-circuit panelboard(s) serving the dwelling unit.?

OR

4) ?? the main power feeder shall include the feeder(s) serving only dwelling
loads and running to but not originating in the lighting and appliance branchcircuit
panelboard(s) serving a particular dwelling unit.?


Substantiation: By clarifying that this note applies to dwelling units within
multifamily housing, which is well advised, the proposal raises important
questions as to exactly which panelboard feeders are within the scope of this
allowance. Options 1 and 2 exclude feeders that are comprised of dwelling
loads, but that serve multiple dwelling units. Options 3 and 4 allow such a
feeder. Options 1 and 2 as a group and options 3 and 4 as a group sort out
whether this allowance applies to subpanel feeders within a dwelling unit.
Dwelling unit subpanel loads do not present the same diversity as dwelling unit
panels serving the entire dwelling unit, and thereby undercut one of the
traditional supporting assumptions underlying these allowances. However, all
of these interpretations are possible given the ambiguous ?(s)? endings on the
word ?feeder? and ?panelboard.? CMP 6 needs to clarify exactly which feeders
qualify for this allowance.

Panel Meeting Action: Accept in Principle
Remove the 2 sets of parentheses and the duplicate ?s? on panelboards so that
the section reads:
(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 between the main disconnect and the lighting and appliance
branch-circuit panelboard. The feeder conductors to a dwelling unit shall not be
required to have an allowable ampacity rating greater than their serviceentrance
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.

Panel Statement: 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.
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They definitely took out the plurals...like on purpose. That'll change the way I do 400 amp services with remote panel boards if they ever adopt the 08 here in Va. They only just adopted the '05 in April here. Thanks for the info....now back to my fiddle playin..
 
Although the 400 amp combo meters are perceived as big, I tend to disagree. The milbank meter base i use is 30" wide by 33" tall and is quite compact for what it is. It includes 2 200 amp breakers as well as an 8 space subpanel for outdoor circuits, AC's, etc. The only drawback i can see is the fact that it is only listed for GE breakers, but i get over it. Maybe later I will post some pictures of one installed.
Jacob
 
charlie said:
Having the ability to bury conduit in the crawlspace without requiring a concrete cap. :smile:
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No Charlie, that's not what I was referring to, although it is really a gift.

What I was referring to was the re-wording of 310.15(B)(6) in the 08 code as compared to 05 and before.

The following posts on the subject argue the point that I was trying to make.

In my opinion, the 05 code would allow the twin 4/0 al feeders from a 400A Main to supply the two MLO panels......thus the "As I read it" quote.

A literal reading and the application of your own "Charlie's Rule" leads me to believe it true.

Opinions vary, so the re-wording in the 08 to clarify.

Just my opinion
steve
 
Dennis has a good point about using 240.4(B), the "next standard overcurrent device rating" rule. I think that in most houses it would be a rare case that the calculated load on a 200 amp panel would exceed 180 amps.
 
hillbilly said:
A literal reading and the application of your own "Charlie's Rule" leads me to believe it true.
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You got the wrong Charlie-- There is chalie and charlie B. To make matters worse they are both mods.:smile:

Charlie B has the infamous Charlie's Rule
 
Oops

Oops

fisherelectric said:
Dennis has a good point about using 240.4(B), the "next standard overcurrent device rating" rule. I think that in most houses it would be a rare case that the calculated load on a 200 amp panel would exceed 180 amps.
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It is unfortunate that I can't always be correct (I've got to work harder on that :smile: ). I have searched the Code to back up my point and have come to the conclusion that you are indeed correct and I was wrong. Would someone pass the salt, this crow is a bit flat.
 
That's what makes this forum such a great resource. We just need to find a way to make the forum findings legally sanctioned to overule the sometimes mistaken opinions of AHJs.
 
ok, i know i'm late to this discussion, but let me give you this scenario....
i have a double with a 100 amp main for each apt...i use #4 feeder to feed the mlo panels inside...right????

ok, i have a single home with a 200 amp mlo panel...i have two 100 amp breakers in this panel feeding a mlo panel upstairs and down.....lets say teh demand is 200 amps for teh entire house...according to the nec, i can use 2/0 copper to feed the meter and panel....and i would have to use #3 for the feeders??? am i understanding this right?...i can't use #4 in this situation?
 
NolaTigaBait said:
ok, i have a single home with a 200 amp mlo panel...i have two 100 amp breakers in this panel feeding a mlo panel upstairs and down.....lets say teh demand is 200 amps for teh entire house...according to the nec, i can use 2/0 copper to feed the meter and panel....and i would have to use #3 for the feeders??? am i understanding this right?...i can't use #4 in this situation?
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This is correct.
 
NolaTigaBait said:
than you dennis...
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You are welcome but I should have added that a #3 if part of a se or nm cable is only good for 85 amps in which case it will not be sufficient. You would have to use #2 as long as the calculated load is not more than 95 amps on each panel served.
 
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