Art. 310.15 (B) (6) 2002

[donnie]

Need some in put, According to 310.15 (B) (6), the feeder conductors between a Main Service panel and a Sub Panel, if it is # 4 copper NM cable, that conductor ampacity is only good for 70amps, and not 100amps as Table 310.15 (B)(6) implies, because it isn't considered a Main Power Feeder as 310.15 b6 indicates. But from a Main Disconnect to a Sub Panel it would be good for 100amps (Like an Apartment Setup.) Am I Looking at this right or Am I going off the deep end.

Thanks for any replies.

 

[roger]

Re: Art. 310.15 (B) (6) 2002

Donnie,you're right on the money.

Actually in your discription the "sub-panel" from the "Main Disconnect" would be the "lighting appliance branch-circuit panel"

Roger

[ October 07, 2003, 05:39 PM: Message edited by: roger ]

 

[bob]

Re: Art. 310.15 (B) (6) 2002

Donnie
I think 310.15B6 refers to the use of SE cable and not NM. Look at 310.15 B6 for uses.

 

[roger]

Re: Art. 310.15 (B) (6) 2002

Bob if we are using the NM between the Main Disconnect and the Lighting Appliance-Branch Circuit Panel, this would not be "Service Entrance" and could be used per article 334

Roger

 

[bob]

Re: Art. 310.15 (B) (6) 2002

Roger
I was not saying that you could not use NM from the main panel to the lighting panel. My point was that the ampacity shown in table 310.15.B is for SE type cable and has a higher rating than NM.
NM is listed in the 60C column in table 310.16.
If I am in error please advise.

[ October 07, 2003, 06:03 PM: Message edited by: bob ]

 

[roger]

Re: Art. 310.15 (B) (6) 2002

Bob, I would agree if the first sentence didn't contain this: "and feeder conductors that serve as the main power feeder to a dwelling unit and are installed in a raceway or cable".

With this wording it seems to imply any cable, and does not exclude NM for this portion of the article.

The beginning of the sentence "service entrance conductors, service lateral conductors," would disallow the NM being used for this portion of the article.

Roger

 

[curt swartz]

Re: Art. 310.15 (B) (6) 2002

Roger

That's an interesting point. The 99 NEC specified what types of wires were permitted to be use the reduced size and NM cable wasn't one of them. The 2002 NEC doesn't mention anything about what types are permitted so I guess it applies to all conductors and cables.

 

[donnie]

Re: Art. 310.15 (B) (6) 2002

I guess what I was trying to say is according to this article, that if you have (what we call around here (Romex) syle wiring,is that if you have a #4 copper cable run between a 120/240 v. Main Service Panel to a Dwelling and a Sub-Panel and you put this cable on a 100amp breaker then it is in violation, because it is then not a (Main Power Feeder).If I am seeing this correctly, then around this area this is being violated many, times.

Thanks for all replies, Just trying to get a grip on it.

 

[pierre]

Re: Art. 310.15 (B) (6) 2002

The restrictions (60 degree column of table 310.16 as per 334.80) that are outlined in Art 334 would preclude the use of NM cable from the use of Main Power Feeders at the ampacity reduction (possibly 334.12(2) also). That may be the reason that the classification of cable types was removed, they were not necessary.

Pierre

 

[tom baker]

Re: Art. 310.15 (B) (6) 2002

There is an errata to 310.15(B)(6). NM cable is not allowed to be used at the reduced ampacity show for other types of conductors.

 

[bob]

Re: Art. 310.15 (B) (6) 2002

Donnie
If you install #4 NM with a 100 amp breaker to feed a residential lighting panel it is a violation because #4 NM is rated for only 70 amps. However if you install SER type cable you may use #2 AL cable to the 100 amp panel. It is not a violation because the cable is rated a 100 amps per table 310.15B(6). I think is it common to see SER AL cable used frequently for this type installation.

 

[donnie]

Re: Art. 310.15 (B) (6) 2002

Bob

I agree with part of what you are saying, if you use A #4 copper NM cable from a Main Service Panel to a Sub-Panel then it only good for only 70amps per 310.16, but run as a main power feeder then it is good for 100amps per 310.15 (b) (6). But if you use a #2 alum. SER cable then as Service entrance cable or a Main power feeder according to 310.15 (b)(6)then it is good for 100amps, but if not then according to 310.16, 75deg. colum (of which SER cable amperage is taken from 338.10 (b)(4). ) it is good for 90amps.

 

[bob]

Re: Art. 310.15 (B) (6) 2002

Donnie
334.80 requires that NM cable ampacity be determined from the 60C listing. In the 99 code table 310.15b6 listed the type of cables that were to be used. This code does not list the cables but it seems to me that 334.80 determines the capacity for NM regardless of the use.

 

[tom baker]

Re: Art. 310.15 (B) (6) 2002

Donnie did you see my reply above:
There is an errata to 310.15(B)(6). NM cable is not allowed to be used at the reduced ampacity show for other types of conductors.

the conductors in NM cable are rated at 90 Deg C, this is used for derating, but the final ampacity can not exceed the 60 deg C rating per 334.80.

Go to the NFPA web site and get the errata.

 

[roger]

Re: Art. 310.15 (B) (6) 2002

Donnie, now that Tom has pointed out that the NEC did try to correct their deficiency, let,s address the other part of your question. Let's assume a #4 recognized cable assembly.

But from a Main Disconnect to a Sub Panel it would be good for 100amps (Like an Apartment Setup.)

Yes!

Main Service Panel (this has to be a lighting appliance branch-circuit panel, if it isn't go back to Main Disconnect, see 408.14) to a Dwelling and a Sub-Panel and you put this cable on a 100amp breaker then it is in violation, because it is then not a (Main Power Feeder).

Yes again.


The following is from an old thread, substitute your numbers as applicable.

This article specifically allows reduction to the first lighting appliance
branch-circuit panel(s) down line of the service equipment.

We will use a lateral in this example

400A service
2-200 amp lighting appliance branch-circuit panels.

Service lateral --400KCM copper per article 310.15(b)(6) to 400A OCPD.

We still have not made it to our lighting appliance branch-circuit panels
yet.

For sake of conversation we install 2-200 amp enclosed breakers adjacent to
this 400 amp OCPD and feed these from parallel lugs.

We use 2/0 copper per 310.15(b)(6).

We still have not made it to our lighting appliance branch-circuit panels
yet.

We feed 2-200 amp lighting appliance branch-circuit panels with 2/0 copper
per 310.15(b)(6)and make all terminations.

We have finally made it to our lighting appliance branch-circuit panels.

Now 310.15(b)(6) has seen it's end and if we feed any sub panel, say a 100
amp, from one of these aforementioned lighting appliance branch-circuit
panels, this 100 amp sub panel can not use 310.15(b)(6)

Roger

[This message has been edited by rp.deas@verizon.net (edited October 26,
2002).]

[ October 08, 2003, 07:57 PM: Message edited by: roger ]

 

[donnie]

Re: Art. 310.15 (B) (6) 2002

TOM

I went to the NFPA web site and got a copy of the errata for the 2002 NEC table 310.15 (B)(6).

Thanks a Lot. Donnie

 

[donnie]

Re: Art. 310.15 (B) (6) 2002

Has anyone seen the article in the Electrical Contractor Magazine (OCT-03) issue. Regarding Question and Answers on Pg.23 by George Flach. Must be a mis-understanding on the use of NM cable.