SER ampacity

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Stubbie

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This code quandaries (4th question) article spurred some conversation with some co-workers and we are in disagreement on calculating the ampacity for SER cable ran for sub feeds to panelboards indoors in the same single family dwelling.

http://www.ecmweb.com/mag/electric_code_quandaries_18/index.html

Some of the electricians at work and on the forums are saying that SER can be approved for table 310.15(B)(6) ampacity and AHJ's routinely do this. I say no and in my experience they dont.
I'm curious as to the change in code from 1999 to 2005 on SER cable ampacity. In the 1999 code sec. 338.4(a) says SE type cables will be subject to the ampacities of sec. 336.26.
In 2002 or 2005 that language apparently changed... 2005 now states in sec.338.10(B)(4)(a) SE is subject to parts 1 and 2 of 334 excluding334.80.
My question is two parts....

1.) Why was the requirement for the 60C ampacity column for SER apparently removed?
2.) Would an inspector be correct in allowing table 310.15(B)(6) for SER cable indoors for sub feeds?
 
This code quandaries (4th question) article spurred some conversation with some co-workers and we are in disagreement on calculating the ampacity for SER cable ran for sub feeds to panelboards indoors in the same single family dwelling.
Click to expand...

I don't see how 310.15(B)(6) could apply to this. This table is for services and feeders that feed the main panel for a dwelling, not sub-panels.

As far as your questions:
1) I don't know
2) IMO, i don't see how (for the above reason) 310.15(B)(6) can be applied to sub-panels.

Eric
 
Stubbie,

There is another reason why the installation described in the ECM article is not allowed to use 310.15(B)(6). That system is 120/208. That excludes it.

(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Ser-vices
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 con-ductors,
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 sec-tion,
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.
Click to expand...
A proposal for the 2005 cycle to include 120/208 was rejected, because the submitter's substantiation was along the lines of "What's the difference?" The CMP said it was insufficient substatiation to justify a change, which tells us two things: they know it applies only to 120/240, and they intend for it to be applied that way.

Maybe Don or someone with the ROP to the 2002 NEC can explain the change to exclude 334.80 from SER. If I were to guess, it would be the old rule made it a huge leap to use Table 310.15(B)(6) when sizing feeders for indoor runs.

Looking at the table, I'd imagine that they might not have originally intended for 334.80 to apply in the first place, they might have been looking to use all the securing and supporting rules for NM without duplicating them in Article 338. But that's just a guess on my part.

Stub, what year code are you under where you are? Here, we've adopted the 2005 NEC as of last July. It can get real confusing real quick to try to learn your way around several editions of the code at once, just a thought. :)
 
guess I just dont understand the table language.. It says services and feeders which a sub panel feed is just that a feeder. but then in the main body of the language it specifies panelboards for lighting and appliance branch circuits. confusing. I think some inspectors are cofused also. I have used this table language and never been called yet........
 
There is another reason why the installation described in the ECM article is not allowed to use 310.15(B)(6). That system is 120/208. That excludes it.
Click to expand...

Yes, that would. I should have mentioned this was a dated article and created a conversation on SER used in sub-feed applications in single family dwellings. This spawned the additional questions. We have always sized it using 310.16 and typical temperature termination rules when not using it under 310.15(B)(6) in a dwelling using 120/240 3 wire. Never as a 60C conductor only... like NM-B.
I just couldnt see how you could continue with 310.15 (B)(6) once you changed its intended application. But I'm told the AHJ's can approve it in a sub-feed application and do approve the use of the dwelling feeder table in many parts of the country, though I dont know if its SER in all cases. I just thought I was in one of those "being misinformed conversations"... :)

Stub, what year code are you under where you are? Here, we've adopted the 2005 NEC as of last July. It can get real confusing real quick to try to learn your way around several editions of the code at once, just a thought.
Click to expand...

George we are under 2005 also....this was just an archived article I came across and when I saw that the author of the answer to that question considered SER to be a 60C ampacity like NM-B, I was confused as we have never treated it that way. Upon researching it I saw the change in language between the code editions. Sometimes I take the dirt road instead of the pavement..... :)

Thanks for your time...I'll keep watching the post if anyone else makes additional comments.
 
guess I just dont understand the table language.. It says services and feeders which a sub panel feed is just that a feeder. but then in the main body of the language it specifies panelboards for lighting and appliance branch circuits
Click to expand...
.

Stew I think the catch here is it specifies conductors that serve as a main power feeder to a dwelling and between the main disconnect and the lighting and appliance branch circuit panelboard or panelboards.

For application of this sec-tion,
the main power feeder shall be the feeder(s) between
the main disconnect and the lighting and appliance branch-circuit
panelboards(s).
Click to expand...

This would seem to exclude a sub-feed as it is not a main power feeder to a dwelling as defined in the section language.

I would agree that sub-feeds in single amily dwellings are being sized with table 310.15(B)(6)and are passing inspection.

My stance is that these feeders, sized with the dwelling feeder table, are not in compliance with the wording of the section and therefore cannot be sized as main power feeders. You must use table 310.16 to size the sub-feeder.
 
In the recent thread on this subject, it was brought up that 310.15(B)(6) can't be applied to a feeder originating in a Lighting & Appliance Branch Circuit Panelboard (see 408.36-ish for a definition of it), because 310.15(B)(6) states that the feeder is between the main disconnect and the L&ABCPB's.

For example, if you decided to be a good samaritan and install a feeder to power your neighbor's entire house, and pulled it off a L&ABCPB in your house, then it would have to be sized to 310.16, because it's not in sync with what (B)(6) is allowing. :)
 
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