Still trying to make sense of SER wire size.

[jwelectric]

(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.

Understanding this section is easier than falling down. The sentence that is in bold and underlined above is the key to the whole section and does not allow the installation that is being mentioned concerning the AC unit.

To have a 30 circuit panel with a main breaker and then install a 100 amp breaker in the panel to supply another panel whether or not it is a lighting and appliance panel would not be a feeder that is between the main and the panel.
The feeders would have an overcurrent device that separated the feeders from the main and the panel; the 100 amp breaker would be between the main and the panel.

I could turn the 100 amp breaker off and not the service to the house. This section is clearly meaning that the feeders have to be controlled directly by the main service disconnect with no other overcurrent in between the feeders and the main.

In the first sentence it also states that if supplying feeders these feeders have to be the main power feeders to the dwelling unit. I don?t think that feeders supplying a second panel from the first panel would fit the description of the Main Power Feeders.

 

[M. D.]

Mike, are you saying that if I have a house with 100 amp service #4 cu. and I put a 100 amp sub panel on the second floor that I now have to run a # 3 cu?
What would be the point in that??

 

[jwelectric]

Mike, are you saying that if I have a house with 100 amp service #4 cu. and I put a 100 amp sub panel on the second floor that I now have to run a # 3 cu?
What would be the point in that??

If the panel on the second floor is fed from a panel on the first floor then Table 310.15(B)(6) would not apply but the feeders never have to be larger than the service conductors as outlined in 215.2(A)(3).

 

[suemarkp]

To have a 30 circuit panel with a main breaker and then install a 100 amp breaker in the panel to supply another panel whether or not it is a lighting and appliance panel would not be a feeder that is between the main and the panel. The feeders would have an overcurrent device that separated the feeders from the main and the panel; the 100 amp breaker would be between the main and the panel.

I could turn the 100 amp breaker off and not the service to the house. This section is clearly meaning that the feeders have to be controlled directly by the main service disconnect with no other overcurrent in between the feeders and the main.

In the first sentence it also states that if supplying feeders these feeders have to be the main power feeders to the dwelling unit. I don’t think that feeders supplying a second panel from the first panel would fit the description of the Main Power Feeders.

It doesn't seem so cut and dried to me. If you know what they're trying to say, that is a logical interpretation. But I don't know what they are trying to say and can interpret it multiple ways. The words highlited above seem to reinforce this -- you say this feeder is between the main and the panel which sounds a lot like main disconnect and L&A panelboard.

The use of "main power feeder" connotes a certain thing in my head. But in this section, they define what those words mean, and I think that is the crux of the problem. Everyone wants the whole dwelling load to be on this feeder, and I'm not convinced it really says that (and it shouldn't have to as long as the feeder is mostly full of diverse loads).

If you have an 4 unit apartment with a 400A main and 4 100A feeder breakers in that panel, could you use 310.15(B)(6) to size each of the feeders to the individual unit from its 100A breaker at the main to the L&A panelboard at each apartment? If there was no 400A main, but just 4 grouped 100A disconnects instead could you use the table for those same feeders?

 

[racerdave3]

OK, so if I'm following this correctly, If I were to install a 100 amp service on a house and install a meter socket with a 100 amp breaker incorporated in it, thus making this breaker the main disconnecting means, then I would be feeding the meter with a #2 aluminum SE cable, but would have to change over to a #1 aluminum SER cable to come from the meter can into the house and the breaker panel? Help me understand the logic as to why they would require this. I'm having a hard time trying to understand this scenerio. :-?

 

[jwelectric]

you say this feeder is between the main and the panel which sounds a lot like main disconnect and L&A panelboard.

This is why there is so much confusion about this table. You are seeing a panel and calling that panel the main disconnect. This is not true. The breaker that is in this panel that turns everything off is the main and the rest is not part of the main disconnect but instead are feeders and branch circuits.

The use of "main power feeder" connotes a certain thing in my head. But in this section, they define what those words mean, and I think that is the crux of the problem. Everyone wants the whole dwelling load to be on this feeder, and I'm not convinced it really says that (and it shouldn't have to as long as the feeder is mostly full of diverse loads).

This is exactly what it is saying just as you have outline below.

If you have an 4 unit apartment with a 400A main and 4 100A feeder breakers in that panel, could you use 310.15(B)(6) to size each of the feeders to the individual unit from its 100A breaker at the main to the L&A panelboard at each apartment?

Most certainly as is noted in the definition of the section and is again established in 215.2 for feeders.

If there was no 400A main, but just 4 grouped 100A disconnects instead could you use the table for those same feeders?

There would be no question as to this being compliant. What I wouldn?t be allowed to do would be to install a 200 amp 20/40 circuit lighting and appliance panel in my home and use #2 aluminum protected with a 100 amp overcurrent device to supply a panel installed elsewhere in the home.

 

[suemarkp]

So why is it OK to have a apartment 400A main disconnect with four 100A feeder breakers use 310.15(B)(6) but not do a similar thing in a house (a 200A main with one 100A feeder breaker plus a bunch of little branch circuit breakers)?

Either the feeders conected to those 100A breakers are between the main disconnect and a L&A panelboard or they are not, and it should be the same answer in both cases.

I also wonder why a "main power feeder" must contain all of the dwelling load. Take a house with a 125A service with a 125A main breaker in a meter main with two other breakers -- a 30A for an outside HVAC unit and a 100A for a feeder to the rest of the house. To me, the 100A feeder is just as diverse as any other house with a 100A feeder and the HVAC unit should not come into play.

 

[M. D.]

So lets see if I have it right , we can only use 310.15(b)(6) if the conductors supply the whole house ? But if we run a sub panel we now have to use 310.16 to size the feeder? This does not make sense to me at all , am I missing the point ??

 

[jwelectric]

From the 400 amp main to each unit of the apartment would be the same size conductor as if it were coming from the meter base to the main breaker of each unit. These feeders would be the main power feeder for the unit.

From the lighting and appliance panel of a house the feeders supplying another panel would not be supplied with the main disconnecting means for that unit. The feeders would not be the main power feeder for the unit.

 

[stickboy1375]

Look at it this way, if table 310.15(B)(6) did not exist, what size breaker would you be installing? This table allows you basically to reduce the conductor size for dwelling services only... For what reason I do not know, but its only for a service...

 

[M. D.]

Look at it this way, if table 310.15(B)(6) did not exist, what size breaker would you be installing?

It does exist and it is for feeders. When I feed the sub panel for the second floor I have run a feeder, haven't I???

 

[jwelectric]

It does exist and it is for feeders. When I feed the sub panel for the second floor I have run a feeder, haven't I???

Yes I agree that these feeders and they must comply with Article 215. The first three sections of that article should help you choose the proper overcurrent device to protect these feeders.

 

[Dinspect]

Ser

Ser

To all check 110.14(c)(1) Temp limitations,sends you to 310.16.

 

[dnem]

(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.

Understanding this section is easier than falling down. The sentence that is in bold and underlined above is the key to the whole section and does not allow the installation that is being mentioned concerning the AC unit.

To have a 30 circuit panel with a main breaker and then install a 100 amp breaker in the panel to supply another panel whether or not it is a lighting and appliance panel would not be a feeder that is between the main and the panel.
The feeders would have an overcurrent device that separated the feeders from the main and the panel; the 100 amp breaker would be between the main and the panel.

I could turn the 100 amp breaker off and not the service to the house. This section is clearly meaning that the feeders have to be controlled directly by the main service disconnect with no other overcurrent in between the feeders and the main.

In the first sentence it also states that if supplying feeders these feeders have to be the main power feeders to the dwelling unit. I don’t think that feeders supplying a second panel from the first panel would fit the description of the Main Power Feeders.

“The feeders would have an overcurrent device that separated the feeders from the main and the panel; the 100 amp breaker would be between the main and the panel.”

The service conductors [like tap conductors] are protected at their load end. . Feeder [& branch circuit] conductors are protected at their source. . Feeders will always be separated from the main [service equipment] by an OCPD. . So by definition there will always be 2 overcurrent considerations before the feeder conductors begin. . Both functions [service conductor protection and feeder conductor protection] can be accomplished by a single OCPD or by separate OCDP. . As long as this is all within the service equipment enclosure(s), there’s no difference, the feeder originates from the service equipment either way.

The Article 100 definition of Feeder says, “All circuit conductors between the service equipment, the separately derived system, or other power supply source and the final branch-circuit overcurrent device.”
Service Equipment is “The necessary equipment, usually consisting of a circuit breaker(s) or switch(es) and fuse(s) and their accessories, connected to the load end of service conductors to a building or other structure …..”

Feeders will can be separated from the main OCPD by a feeder OCPD. . That’s not going to impact the application of 310.15(B)(6).

You’re trying to single out the words “main disconnect” and apply that as meaning something other than the whole of the service equipment. . But if that was true, you would have to more narrowly restrict the use of 310.15(B)(6) farther than you have already.

If the main disconnect was a switch with fuses, you couldn’t use 310.15(B)(6) according to your reading. . The “main disconnect” is the switch and the feeder isn’t “originating” from the “main disconnect” directly. . It could be feeders to separate dwelling of a multi-dwelling building, that wouldn’t matter. . According to your reading of the words “main disconnect”, they wouldn’t originate from the “main disconnect”. . They would be on the load side of a OCPD that would be positioned after the disconnect [230.91]. . Even if it was one OCPD for both service and feeder protection.

If the main disconnect was a breaker and the feeder conductors were not large enough to be protected by that one breaker but needed individual lower amperage protection, you couldn’t use 310.15(B)(6) according to your reading. . There would be a feeder OCPD that would be separate from the “main disconnect”. . Once again, it could be feeders to separate dwelling of a multi-dwelling building, that wouldn’t matter.

“I could turn the 100 amp breaker off and not the service to the house.”
And that’s not an issue. . The 310.15(B)(6) wording adds (s) for plural, “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).” . If this was talking about separate feeders to separate dwellings, then it should have said, “For application of this section, the main power feeder shall be the feeder between the main disconnect and the lighting and appliance branch-circuit panelboards for each individual dwelling unit.”

David

 

[M. D.]

215.2 Minimum Rating and size


215.2(A)(3) Individual Dwelling Unit or Mobiloe Home Conductors .Feeder conductors for individual dwelling units or mobile homes need not be larger than service conductors. Paragraph 310.15(B)(6) shall be permitted to be used for conductor size.

This seems to say that from a 200 amp m.b. panel I could run a feeder from it based on 310.15(B)(6)


Question 1 are these conductors feeders?
I think we all agree that they are?
If not, then these conductors must be something other than feeder conductors.

 

[jwelectric]

Like I already said this is easier than falling down.

What is being addressed in this thread? (answer) Feeders

What article of the NEC covers feeders? (answer) 215 and 225

Which one of these are being addressed? (answer) 215

What does 215 have to say about feeders? (answer)
215.1 Scope.
This article covers the installation requirements, overcurrent protection requirements, minimum size, and ampacity of conductors for feeders supplying branch-circuit loads.

215.2 Minimum Rating and Size.
(A) Feeders Not More Than 600 Volts.
(1) General. Feeder conductors shall have an ampacity not less than required to supply the load ????.., shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.
Additional minimum sizes shall be as specified in 215.2(A)(2) and (A)(3) under the conditions stipulated.

(3) Individual Dwelling Unit or Mobile Home Conductors. Feeder conductors for individual dwelling units or mobile homes need not be larger than service conductors. Paragraph 310.15(B)(6) shall be permitted to be used for conductor size.

If the feeders don?t fit into the category of 215.2(A)(3) then Table 310.15(B)(6) shall NOT be permitted to be used.
This is why the words ?main power feeder? are included in section 310.15(B)(6).

It seems that those that want to use Table 310.15(B)(6) for every residential panel totally disregard Article 215 as though it was never printed.

All feeders MUST comply with either Article 215 or 225 before any other section of the NEC can be applied.
We can?t just say that we have found the word feeder and panelboard(s) mentioned in the same sentence and this is the section that I think I will use for this installation.

 

[suemarkp]

I don't see how 215.2(A)(3) is being disregarded. Aren't all of these feeders (whether one main one or a substantial one and a smaller one) "for" a dwelling? It doesn't say "to" a dwelling.

I now see you interpretation, but why would "Paragraph 310.15(B)(6) shall be permitted to be used for conductor size" have to be stated, as the previous sentence should be adequate (you don't have to use feeder conductors larger than the service conductors)? This 310.15(B)(6) sentence is redundant if it applies only to feeders that match the amp rating of the service. That is why I'm saying you can apply it to all dwelling feeders.

Dnem: You can have a feeder with only one overcurrent device in front of it. An example would be a house with a 200A disconnect outside and a 200A MLO panel inside.

Either way, the interpretation that Mike has (which seems to be the more prevalent view on this site) makes for some strange things. Given two houses with a meter main containing a 100A feeder to the inside loads, and one has airconditioning and one doesn't. If you put the air conditioning on its own breaker in the meter main (and the service is 125A instead of 100A), then all of a sudden that 100A feeder in the airconditioned house can no longer use 310.15(B)(6) because it doesn't contain all the loads of the dwelling (but it has the same loads as his neighbor does).

 

[jwelectric]

What is being overlooked or misunderstood is what is being said in 215.

215.2(A)(1) says that the conductor must be sized by 100% of the noncontinuous and 125% of the continuous
215.2(A)(3) says that if it is a feeder that is supplying a individual dwelling unit or mobile home it can be sized using Table 310.15(B)(6).
215.2(A)(3) does not say the feeders supplying individual panels in a dwelling unit.

215.3 says that the overcurrent must be sized using Part I of 240
In Part I of 240 we find 240.4(B) which allows for the next higher overcurrent device to be used unless the ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker
240.6(A) lists a 90 amp overcurrent device and the ampacity of a #2 aluminum conductor from the 75 degree column of 310.16 is 90 amps.

Using the rules found in 215 we are not allowed to use a 100 amp breaker for #2 aluminum feeders unless they are the main power feeder supplying an individual dwelling unit or mobile home.

 

[dnem]

To Mike,
Now that I understand that you?re position is that, for a feeder, 310.15(B)(6) can not be accessed directly until 215 & 225 are consulted, I have to rethink the scenerio. . My initial thought is that the repeated use of the word ?individual? stands out in 215.2(A)(3).

I need to think about it and respond tomorrow if I have the time.

To Mark,

Dnem: You can have a feeder with only one overcurrent device in front of it. An example would be a house with a 200A disconnect outside and a 200A MLO panel inside.

I know. . That?s why on post #34 I said

The service conductors [like tap conductors] are protected at their load end. . Feeder [& branch circuit] conductors are protected at their source. . Feeders will always be separated from the main [service equipment] by an OCPD. . So by definition there will always be 2 overcurrent considerations before the feeder conductors begin. . Both functions [service conductor protection and feeder conductor protection] can be accomplished by a single OCPD or by separate OCDP.

David

 

[suemarkp]

What matters is what the code says, not what it doesn't say. 215.2(A)(3) says feeders for individual dwelling units can use 310.15(B)(6) for conductor size. It is not clear if that last sentence is modifying the previous sentence (which would be redundant since service conductors we know can be sized by 310.15(B)(6)), or it if it is a separate statement.

It is not clear what feeder is being referenced -- one as big as the service or any dwelling unit feeder. All it does is send us back to the confusing wording of 310.15(B)(6) which does limit the use to main power feeders and the specific definition of that feeder type defined in that section.