NEC says this?

[kwired]

I don't have a copy of the 2014 so I'm going solely on the pasted section Infinity posted.
I don't see the language that 310.15(B)(6) [2008 code] had concerning the service or feeder serving the entire load. Or as it put it, "serves as the main power feeder"

I guess I'm asking if that language is necessary since if you have a subpanel the 83% could be used but based only on the service size? Or the language may be there and I can't see it because I don't have the actual code to read.

It is (B)(7) in 2011 and 2014 - but I think it was changed in 2011 and was (B)(6) in 2008. Anyway, here is all of (B)(7) from 2014. There is no more table, just the 83%, and some details to go with it, and the fact there is no table with specific values makes it easier to determine that they intend to make adjustments for number of conductors in raceway or ambient temp. Some say we had to do that before - but was not really all that clear just how to do so, now you are doing same thing you do with any other conductor just with a final result that is otherwise 83% of the usual method. This is also mentioned in informational note1.

This means for a 100 amp service, conductors are selected just like they normally are for other applications, but instead of needing a final ampacity of 100 amps it only needs to be 83 amps if they are conductors that supply the entire dwelling unit load.

I bolded some key items that seem to get asked about frequently here on the forum when talking about this section.

(7) 120/240-Volt, Single-Phase Dwelling Services and Feeders.
For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, service and feeder conductors supplied by a single-phase, 120/240-volt system shall be permitted be sized in accordance with 310.15(B)(7)(1) through (4).
For a service rated 100 through 400 A, the service conductors supplying the entire load associated with a one-family dwelling, or the service conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the service rating.
For a feeder rated 100 through 400 A, the feeder conductors supplying the entire load associated with a onefamily dwelling, or the feeder conductors supplying the entire load associated with an individual dwelling, unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the feeder rating.
In no case shall a feeder for an individual dwelling unit be required to have an ampacity greater than that specified in 310.15(B)(7)(1) or (2).
Grounded conductors shall be permitted to be sized smaller than the ungrounded conductors, provided that the requirements of 220.61 and 230.42 for service conductors or the requirements of 215.2 and 220.61 for feeder conductors are met.
Informational Note No. 1: The conductor ampacity may require other correction or adjustment factors applicable to the conductor installation.
Informational Note No. 2: See Example D7 in Annex D.

Format or links/special characters (because it was copied from E-book version of NEC) may have not copied exactly as printed in hard copy NEC, but main content is still there AFAIK.

 

[Smart $]

...
I don't see the language that 310.15(B)(6) [2008 code] had concerning the service or feeder serving the entire load. Or as it put it, "serves as the main power feeder"

I guess I'm asking if that language is necessary since if you have a subpanel the 83% could be used but based only on the service size? Or the language may be there and I can't see it because I don't have the actual code to read.

Here's how it is stated in 2008...

... 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.

 

[FionaZuppa]

... 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.

so this says "whatever the poco does up to meter then its ok to use that wire size, or larger". but a few pages back it was mentioned NEC does not apply to to poco. thus very odd the linkage, and even if it was changed in newer NEC versions we still have this 83% rule, which i guess is what the poco commonly installs when this 83% is compared to the std ampacity table.

 

[Dennis Alwon]

so this says "whatever the poco does up to meter then its ok to use that wire size, or larger". but a few pages back it was mentioned NEC does not apply to to poco. thus very odd the linkage, and even if it was changed in newer NEC versions we still have this 83% rule, which i guess is what the poco commonly installs when this 83% is compared to the std ampacity table.

The power company wire size has nothing to do with the NEC. We use the NEC and the power company have their own guidlines but that will not influence our work.

 

[kwired]

... 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.

so this says "whatever the poco does up to meter then its ok to use that wire size, or larger". but a few pages back it was mentioned NEC does not apply to to poco. thus very odd the linkage, and even if it was changed in newer NEC versions we still have this 83% rule, which i guess is what the poco commonly installs when this 83% is compared to the std ampacity table.

They are still referring to NEC service conductors. Anything ahead of the "service point" which is a art 100 defined term (but was added in 2011) is not covered by NEC.

 

[FionaZuppa]

They are still referring to NEC service conductors. Anything ahead of the "service point" which is a art 100 defined term (but was added in 2011) is not covered by NEC.

isnt this from poco xfrmer to service meter ("the 1st disco of the service", aka "1st main disco") ?? the feeder from that 1st disco to main panel is allowed the 83% rule, which for the most part is because poco uses smaller wire than what ampacity table says.

... 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.

 

[kwired]

isnt this from poco xfrmer to service meter ("the 1st disco of the service", aka "1st main disco") ?? the feeder from that 1st disco to main panel is allowed the 83% rule, which for the most part is because poco uses smaller wire than what ampacity table says.

[/I]

NEC does not apply to anything ahead of (NEC defined) "service point.

In most instances conductors from POCO transformer to point of attachment (for overhead services) is on the POCO side of the service point. For underground applications the service point varies a little more, but is usually somewhere on the supply side of metering equipment.

NEC does not care what size conductors ahead of the service point is - it doesn't apply to anything ahead of the service point and those conductor sizes are not considered when using the section you have quoted.

... For application of this section,
the main power feeder the portion of conductor allowed to be sized per this section shall be the feeder between the
main disconnect and the panelboard that supplies they mean a feeder that supplies entire dwelling unit loads here - one example is a multi-tenant structure where you have service disconnect that supplies feeder breakers for each tenant- the load side of those feeder breakers is what conductors are under scrutiny here as long as they supply an entire individual dwelling unit 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. Last sentence is just saying the feeder conductor are not required to be larger then the service conductors(NEC covered service conductors) if they are supplying all the load to the dwelling they feed.

Should the dwelling be supplied by more then one circuit none of any of this material applies, those conductors default to standard ampacity calculations. If the dwelling has service/lateral -meter- service disconnect in a panelboard - the conductors ahead of the service disconnect can use the 310.15(B)(7) provisions for determining it's size. But if there is multiple circuits leaving that panelboard even if some are feeders to other panels in the dwelling - they are no longer feeding the entire dwelling load and this exempts them from being able to apply 310.15(B)(7), but the conductors on line side of service disconnect are still feeding the entire dwelling load.

Some may say this means those secondary level feeders need not be larger then the service conductors even if not supplying the entire dwelling load. I disagree. It says - The feeder conductors to a dwelling unit shall not be... those secondary level feeders are no longer the feeders to a dwelling - they only serve a portion of the dwelling. If this was not the intent of the CMP that wrote it then I feel they need to have some wording changes.

 

[FionaZuppa]

... For application of this section,
the main power feeder the portion of conductor allowed to be sized per this section shall be the feeder between the
main disconnect and the panelboard that supplies they mean a feeder that supplies entire dwelling unit loads here - one example is a multi-tenant structure where you have service disconnect that supplies feeder breakers for each tenant- the load side of those feeder breakers is what conductors are under scrutiny here as long as they supply an entire individual dwelling unit 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. Last sentence is just saying the feeder conductor are not required to be larger then the service conductors(NEC covered service conductors) if they are supplying all the load to the dwelling they feed.

that verbiage applies to single-family homes too, so what "NEC covered service conductors" are there if the feeder here is between the 1st disco (meter) and the main panel? there are none if the wire from xfrmer to meter is poco, thus i dont get the reference of feeder wire to service-entrance conductors.

 

[Smart $]

that verbiage applies to single-family homes too, so what "NEC covered service conductors" are there if the feeder here is between the 1st disco (meter) and the main panel? there are none if the wire from xfrmer to meter is poco, thus i dont get the reference of feeder wire to service-entrance conductors.

The meter is not the service disconnect.

The main feeder in this context is one which carries all the load of a single dwelling unit service-entrance conductor. The only difference between it and the service-entrance conductor is they are on opposing sides of the service disconnecting means.

 

[roger]

that verbiage applies to single-family homes too, so what "NEC covered service conductors" are there if the feeder here is between the 1st disco (meter) and the main panel? there are none if the wire from xfrmer to meter is poco, thus i dont get the reference of feeder wire to service-entrance conductors.

I think part of your confusion is that you think the meter is the service disconnect, it is not.

Just for sake of conversation let's use an overhead service, typically the service point is at the weatherhead, everything below that POA can be sized per 310.15(B)(7) until it splits into more than one set of conductors (feeders)

Now, looking at an underground service lateral and say the conductors from the POCO xfrmr go directly to the meter, then the conductors from the meter to the main (probably through a short nipple) would be the only conductors that could use 310.15(B)(7) and you wouldn't have a bidding issue because the POCO would be providing the conductors to the meter.

I don't see why this is such a big deal.

Roger

 

[FionaZuppa]

hmmm, the verbiage says between 1st dicso and main panel board. so from weatherhead to meter, then meter to main panel, where exactly is "the 1st service disco" ?? from weatherhead to meter, isnt that still on poco side (power there is always ON)?

 

[roger]

hmmm, the verbiage says between 1st dicso and main panel board. so from weatherhead to meter, then meter to main panel, where exactly is "the 1st service disco" ??

Spend a little time in article 100, it might clear up some of your questions.

Roger

 

[Smart $]

hmmm, the verbiage says between 1st dicso and main panel board. so from weatherhead to meter, then meter to main panel, where exactly is "the 1st service disco" ?? from weatherhead to meter, isnt that still on poco side (power there is always ON)?

Service Drop -> Service Entrance Conductors [and meter typically] -> Service Disconnecting Means -> [main] Feeder -> [main, sub-] panel.

In many cases there is no [main] feeder, [main, sub-] panel... just Service Drop -> Service Entrance Conductors [and meter typically] -> Service Disconnecting Means/panel.

 

[kwired]

Spend a little time in article 100, it might clear up some of your questions.

Roger

Also remember most of us are on either 2011 or 2014 NEC and the term "service point" was added in 2011. (I think, but could have been 2008). One reason for those added definitions at that time was to help clarify what NEC applies to and what it does not apply to. The text in question here is quoted to be from 2008.

Before those changes though 310.15(B)(7) still was able to be applied to any NEC covered conductor carrying the entire load to an individual dwelling unit, whether it be a service conductor or a feeder conductor. Branch circuit conductor supplying a dwelling unit seems to be written into the language there but it is pretty much impossible to have such a thing as a dwelling unit is required to have more then one branch circuit. One of easiest ways to claim this is that we need a minimum of two for SABC's before even doing any other calculating. If we don't have a kitchen requiring SABC's we don't fulfill the definition of dwelling unit either.

 

[FionaZuppa]

Service Drop -> Service Entrance Conductors [and meter typically] -> Service Disconnecting Means -> [main] Feeder -> [main, sub-] panel.

In many cases there is no [main] feeder, [main, sub-] panel... just Service Drop -> Service Entrance Conductors [and meter typically] -> Service Disconnecting Means/panel.

ok, i am seeing some definitions of things come into order, however, for a home, between meter and main distro panel you show "Service Disconnecting Means". what exactly is this item for a single-fam home? my home has feeder wires directly from meter to main panel OCD (a single chassis box).

 

[Smart $]

ok, i am seeing some definitions of things come into order, however, for a home, between meter and main distro panel you show "Service Disconnecting Means". what exactly is this item for a single-fam home? my home has feeder wires directly from meter to main panel OCD (a single chassis box).

Typically an exterior-mounted, service-rated fused disconnect switch.

Sounds like your home has service-entrance conductors to a service panel... no main feeder.

FWIW, most mobile homes are supplied with a main feeder.

 

[FionaZuppa]

Typically an exterior-mounted, service-rated fused disconnect switch.

Sounds like your home has service-entrance conductors to a service panel... no main feeder.

FWIW, most mobile homes are supplied with a main feeder.

arent service-entrance conductors the poco side? the wires from meter to main panel OCD are "feeder" wires (granted, just one panel for single-fam homes)? article 100, service is poco up to (and including) the meter, after that they feeder(s) to panel(s) with main OCD's. did i get that wrong?

 

[Smart $]

arent service-entrance conductors the poco side? the wires from meter to main panel OCD are "feeder" wires (granted, just one panel for single-fam homes)? article 100, service is poco up to (and including) the meter, after that they feeder(s) to panel(s) with main OCD's. did i get that wrong?

Yes, wrong.

Typically Service Drop is POCO.

From near-weatherhead terminations to Service Disconnecting Means are Service-Entrance Conductors.

 

[FionaZuppa]

ok, here's my house. thus #4 wire size can be 83% of #5 OCD (the main OCD is no larger than poco service) ??

For a service rated 100 through 400 A, the service conductors supplying the entire load associated with a one-family dwelling, or the service conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the service rating.

 

[don_resqcapt19]

Also remember most of us are on either 2011 or 2014 NEC and the term "service point" was added in 2011. (I think, but could have been 2008). One reason for those added definitions at that time was to help clarify what NEC applies to and what it does not apply to.
...

The term "service point" was added to Article 100 in the 1993 code (I believe it was in Article 230 before that, but did not check my old code books).

In the 2011 code, the terms "Service Conductors, Overhead" and "Service Conductors, Underground". These new terms apply to conductors that are covered by the NEC. The terms "Service Drop" and "Service Lateral" apply to conductors under the control of the utility and are not subject to the rules of the NEC.

In many area the utilities are requiring the customer to provide the conductors from their transformers to the building. When the customer supplies these conductors that are subject to the rules of the NEC and are called Service Conductors, Overhead, or Service Conductors, Underground as the case may be. When supplied by the utility, these same conductors are Service Drops or Service Laterals.