How about an opinion on table 310-15 b

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macmikeman

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This is the sceneario for my question. I am doing a remodel in which we are relocating the kitchen from one end of a house to another. No real change in load, just relocating stuff. Due to slab / no attic construction I am putting a new sub panel at the new kitchen. The existing house has a 100 amp meter/ main combo can with a #2 alum ser cable to feed the mlo panel on the other end of the house. I am running another #2 alum ser cable to my new mlo panel back to the existing meter/main can. If I pigtail out of the double pole 100 breaker into a splice connecting the both #2 ser cables so that the one 100 amp breaker serves both ser cables, will I meet the requirements of table 310-15 b ? I kinda see this could either be looked at as one set of feeders carrying all the dwelling load and meeting code, or it could be looked at as two sets which I don't believe will qualify. By the way, there is no way short of major demo reconstruct work to get the sub feeder to the existing panel and just do another sub main there. And a two hundred amp upgrade will be pretty difficult also since its underground all the way under an existing driveway and the lateral pipe is only 2" but our poco requires 3" for 200 upgrades.
 
The more I think about this, it sure resembles a typical branch circuit splice in a junction box where there is a home run that branches out at the box. The big difference I can see is what it is I was thinking of splice branching out, and where I was thinking of doing it at the meter can load side. At any rate, it will be possible but a bit harder to just re-route the existing branch circuits for the existing kitchen, so I think that is the route I will take.
 
Mac, can you just feed the new panel with a 60 amp wire and put a dp 60 in the main panel? It sounds as though all the kitchen loads are coming out of the original panel and being moved to the new subpanel. I would bet a 60 amp sub would work. You could also use the #2ser and just put it under a 90amp breaker in the main panel. I am not sure why you want to pigtail the feeder.

Edit: Thought you were going to the original sub panel not the meter-- sorry.
 
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macmikeman said:
The more I think about this, it sure resembles a typical branch circuit splice in a junction box where there is a home run that branches out at the box.
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Yeah I can see that as well.:)

I think what you propose is perfectly safe but it still (IMO) does not meet the rules of 310.15.....


The more I think about this the less sure I become:roll:
 
iwire said:
The breaker may be carrying the full load but nether cable is.
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Bob, at first I wanted to agree with you but after re-reading the OP I'm not so sure. We all know that the breaker is there to protect the wire so irrespective of whether both or either of the SER cables allows the amperage to get to the threshold, the breaker is going to trip at (or about) 100 amps. However, I would think that if there were any NEC code violations or objections by the POCO it would be with pigtailing the SER's inside the meter pan. I've never had occasion to do something like this before but I would imagine that if you used Polaris (NSI) insulated bugs there shouldn't be a problem. IMHO I would get this cleared up with the inspector and the POCO and make sure it's acceptable before doing the job.

Phil,
Gold Star Electric
New Jersey
 
Phil, for us neither the Poco, or the inspectors care if we put taps onto the load side of the main feeders inside the customer section of the meters, so long as there is enough room to meet the code. I do this routinely for pool panels nippled off the meter/main can. I generally use the dukuyper insul eater's for this job.
 
goldstar said:
We all know that the breaker is there to protect the wire so irrespective of whether both or either of the SER cables allows the amperage to get to the threshold, the breaker is going to trip at (or about) 100 amps.
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Phil that is why I said IMO it would be safe. :)

But the wording of section 310.15(B)(6) does not support that application of Table 310.15(B)(6).

Table 310.15(B)(6) works and is safe because the NEC knows the diversity involved in a main feeder to a dwelling unit.

Once you split that two ways the diversity changes and in extreme cases could cause a problem.
 
Why are there "(S)"'s after Feeder(s) and lighting and appliance branch circuit panelboard(s)? It seems to imply that more than 1 feeder or panelboard can serve a Unit.

Also feeder conductors as applied here do not need to be larger than the Service Entrance conductors. What size are the SE Conductors coming in?

Doesn't 215.2(3) allow this?

Just a thought, what are yours?

Tom:confused:
Edited for bad spelling
 
iwire said:
The more I think about this the less sure I become:roll:
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Then I shall pounce on this insecurity. :D

I think it is one feeder. If these conductors were starting at an OCPD and ending at outlets, it would be one branch circuit, despite going two ways from the circuit breaker.

Davis9 said:
Why are there "(S)"'s after Feeder(s) and lighting and appliance branch circuit panelboard(s)? It seems to imply that more than 1 feeder or panelboard can serve a Unit.
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IMO, it is referring to a multifamily situation, where there are multiple 310.15(B)(6) feeders from the service, but still one feeder to each individual dwelling unit.
 
georgestolz said:
Then I shall pounce on this insecurity. :D

I think it is one feeder. If these conductors were starting at an OCPD and ending at outlets, it would be one branch circuit, despite going two ways from the circuit breaker.


IMO, it is referring to a multifamily situation, where there are multiple 310.15(B)(6) feeders from the service, but still one feeder to each individual dwelling unit.
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Right, but it says"main disconnect" not main disconnect(s)? If a multifamily would it not reflect so?

I'm reaching for the OP.

Tom
 
I don?t keep a code book at home, so I cannot be sure of my response. As I understand it, making the connections and the routing as you describe is not at issue. I think you can do that, and I have read no contrary statements.

The issue, then, is whether you can use the smaller cables that that table allows for services and main power feeders. In my opinion, you cannot. I believe that for any single dwelling unit, you can use that table one time, and one time only. If you have two panels being fed from the utility meter, then you cannot use that table to size both panel feeders. If one is sub-fed from the other, then you can use the table to size the first feeder, but not to size the feeder to the sub-panel.

However, you might be able to do the following:
(1) Call the existing feeder to the existing panel the ?main power feeder.? (I hope I got that term right. As I say, I don?t have a code book with me.)

(2) Take credit for the table as the means of sizing the feeder to the existing panel (in other words, claim that the existing feeder is acceptable as-is).

(3) Connect a new feeder, in the manner and location you describe. But size the new feeder per Table 310.16. It is not the ?main power feeder,? so it cannot use the other table. So instead of #2 SER, you use a larger conductor size.

Is that an option for you?
 
georgestolz said:
IMO, it is referring to a multifamily situation, where there are multiple 310.15(B)(6) feeders from the service, but still one feeder to each individual dwelling unit.
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I agree.

Davis9 said:
Right, but it says "main disconnect" not main disconnect(s)? If a multifamily would it not reflect so?
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I cannot address that without seeing the text of the paragraph. Since I don?t have my book handy, and haven?t the time to look at the free on-line version (gotta go paint the family room), can someone please post the article?
 
I can't figure out how to link it for you. Sorry.

"For application of this section, the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance panelboard(s)."


Why wouldn't the CMP state 1 feeder only if that is what they meant?

They must like reading the website for the discussion!

Tom:-?
 
Here you go, Charlie:
(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.
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mac,

am i correct in thinking that there is an existing 100A MCB disconnect at the meter, feeding an existing 100A MLO panel in the house. And that you want to add an additional MLO panel at the other end of the house?

why not replace the existing disconnect with a 4 ckt panel. put in the 100A CB and a 60A cb?

you have less than 6 means of disconnect, you aren't pigtailing, each is it's own feed...

code wise..i didn't look it up, so have at code guys.

would this work for your app?
 
Thanks, George. Every time I read that paragraph I wonder if there will be any hope that I will someday understand it. Indeed, I am beginning to swing the other way at the moment (no jokes, please :cool: :roll: ).

To help with my confusion, let me ask this: Can you start with a single disconnect that establishes the boundary between the utility and any user(s), and from that one disconnect provide power to two dwelling units?
 
charlie b said:
Thanks, George. Every time I read that paragraph I wonder if there will be any hope that I will someday understand it. Indeed, I am beginning to swing the other way at the moment (no jokes, please :cool: :roll: ).

To help with my confusion, let me ask this: Can you start with a single disconnect that establishes the boundary between the utility and any user(s), and from that one disconnect provide power to two dwelling units?
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I did as search of ROC and it seems that the "(s)" are being deleted for this very reason. If I'm reading it correctly, anyways!

Tom


http://www.nfpa.org/assets/files/PDF/ROP/NEC2008Article285-338.pdf
 
You may have another way out. WHat size are your service entrance conductors? If those are #2 AL, then there is a rule that says the feeders don't have to be larger than the service entrance conductors. Kinf od make sense -- if the feeder would melt, so would the service.
 
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