SER Cable Ratings

[raider1]

If it is installed in the interior of a building, one cannot use Table 310.15(B)(6) for ampacity values, one has to use Table 310.16, 60C column for the final value.

I disagree.

334.80 states "The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15." It then goes on to say "The ampacity shall be in accordance with the 60 degree conductor temperature rating."

So the first sentence says to comply with 310.15.

310.15(B) says to use Tables 310.16 though 310.19 and ampacity table 310.20 and 21 as modified by (B)(1) through (B)(6).

310.15(B)(6) modifies the general rule to use Table 310.16 and permits the use of the ampacities given in Table 310.15(B)(6) provided that you meet the requirements in (B)(6).

I don't see anything in 334.80 that states we can't use 310.15(B)(6) and must use Table 310.16.

Chris

 

[Dennis Alwon]

If it is installed in the interior of a building, one cannot use Table 310.15(B)(6) for ampacity values, one has to use Table 310.16, 60C column for the final value.

I disagree. T310.15(B)(6) mentions nothing about 60C wiring. Simply stated it says se cable may be used whether it enters the house or not. I see nothing in the nec that limits the use of this table for main feeder or service conductors.

I agree that 338 limits SE cable to 60 C but where in 310.15 does it says temp. of the conductor is a factor.

 

[Pierre C Belarge]

There is nothing wrong with disagreeing.

Did you see the post about the CMP stating the use of SE cable? I posted it a few posts back.

 

[Dennis Alwon]

There is nothing wrong with disagreeing.

Did you see the post about the CMP stating the use of SE cable? I posted it a few posts back.

Pierre I am curious as to where in the code you came up with your point. I don't think the words are there. Almost a year ago I thought the same thing and brought this concept up because it does appear the CMP missed it. Unfortunately as I see it T310.15 does not forbid it.

Yes I saw the CMP statement but it addresses temp. of the conductor. Table 310.15 does not.

 

[raider1]

There is nothing wrong with disagreeing.

Did you see the post about the CMP stating the use of SE cable? I posted it a few posts back.

Yes I did see that, but like Dennis said, I see nothing in their comment regarding not being able to use Table 310.15(B)(6) for SER cable serving as the main power feeder interior to a dwelling unit.

Chris

 

[cpal]

Yes I did see that, but like Dennis said, I see nothing in their comment regarding not being able to use Table 310.15(B)(6) for SER cable serving as the main power feeder interior to a dwelling unit.

Chris

I gotta tell ya Chris I was leaning towards your argument. But I have re-read 334.80 and I see it is constructed of short sentences that really form a complete thought when read in unison. I believe that one can make an argument that the CMP did intend to limit SE in the same manner it restricts NM. Both NM and SE are required to be loaded IAW 310.15, but nobody questions the logic that NM's ampacity is limited to that of the 60 degree col. In a manner of speaking where SE is to be installed per 334.80 , and I believe we all agree that NM is limited to the 60 deg Col pe 334.80, then why wouldn't SE which must be installed under this same restrictive language be limited in the same way.
To apply your logic, nothing in 334.80 nor 338.10(4)(a) makes an exception for installations that would fall under 310.15(B)(6).

There should be an opportunity to address this thru comment and maybe this issue can be clarified.

 

[Dennis Alwon]

and I believe we all agree that NM is limited to the 60 deg Col pe 334.80, then why wouldn't SE which must be installed under this same restrictive language be limited in the same way.

Agreed one would think it should be the same as NM but the fact is the words do not support your argument. It is very clear as written and we cannot guess the intent of the CMP.

To apply your logic, nothing in 334.80 nor 338.10(4)(a) makes an exception for installations that would fall under 310.15(B)(6).

Nothing in 334 or art. 338 needs to make an exception. The NEC is a permissive code thus we look for words that disallow the install. IMO, there aren't any words to negate T. 310.15

There should be an opportunity to address this thru comment and maybe this issue can be clarified.

Perhaps so but until then I see no reason to not use se in T.310.15.

 

[cpal]

Agreed one would think it should be the same as NM but the fact is the words do not support your argument. It is very clear as written and we cannot guess the intent of the CMP..

just be clear I never mentioned guessing anyones intent, and I do not agree that the language is clear.

Nothing in 334 or art. 338 needs to make an exception. The NEC is a permissive code thus we look for words that disallow the install. IMO, there aren't any words to negate T. 310.15

Again I disagree, I would not paint the entire Code as a permissive Code. There is plenty of restrictive langauge.

Perhaps so but until then I see no reason to not use se in T.310.15.

No one suggested changing your business practice. My comments suggested that this language would be better served if it could be clarified. Its an observation not a decree.

 

[Pierre C Belarge]

I am not sure if you are disagreeing with me or not.

My Stance:
One cannot use the rating of Table 310.15(B)(6) for SE cable if, the SE cable is installed in the interior of a building.
Section 310.15(B)(6) is a general rule, with specific wiring methods/conductors that are spelled out.

Section 338.10(B)(4)(b) is specific in referencing 334.80, without stating there is an exception for Main Power Feeders. The CMPs were aware of this issue, and did not provide for an exception.

Here is the substantiation to the proposal sent in to change this.

CMP's
"Substantiation:
When Type SE conductor are used for interior wiring, as a replacement for Type NM cable, the ampacity of the conductors should be the same as permitted for NM cable since the insulations used ar the same both NM and SE conductors."


There is no exclusion for Main Power Feeders.

This is what I see and read, its my story and I's sticking to it.

 

[Dennis Alwon]

Charlie, I do not use SE cable. I will pipe my service conductors and large feeders or I will use NM. You misunderstood my intent. I was only trying to say that the wording is there to support using SE cable under T310.15 as long as it is for the service entrance or the feeder that does the entire load.

The other articles, 338 and/or 334, restrict SE cable under different circumstances then what is being addressed in T. 310.15

Perhaps it was overlooked but IMO the wording is very clear to support Chris and my thinking on this. I see no wording that restricts it.

 

[cpal]

Charlie, I do not use SE cable. I will pipe my service conductors and large feeders or I will use NM. You misunderstood my intent. I was only trying to say that the wording is there to support using SE cable under T310.15 as long as it is for the service entrance or the feeder that does the entire load.

The other articles, 338 and/or 334, restrict SE cable under different circumstances then what is being addressed in T. 310.15

Perhaps it was overlooked but IMO the wording is very clear to support Chris and my thinking on this. I see no wording that restricts it.

thanks for clearing that up. I also do not wish to be miss understood. I have mixed feelings on this issue and it is of great interest to me. I for one am enjoying the exchange on the topic.

 

[Pierre C Belarge]

Does the wording in 310.15(B)(6) permit THHN to be installed without the proper wiring method...No.
310.15(B)(6) is limited to itself, and does not override what is written in 338.

The wiring method, 338, does have reference over 310.15(B)(6)
If Table 310.13 had more restrictions for THHN, those restrictions could override what 310.15(B)(6) permits.

 

[don_resqcapt19]

My Stance:
One cannot use the rating of Table 310.15(B)(6) for SE cable if, the SE cable is installed in the interior of a building.
Section 310.15(B)(6) is a general rule, with specific wiring methods/conductors that are spelled out.

Section 338.10(B)(4)(b) is specific in referencing 334.80, without stating there is an exception for Main Power Feeders. The CMPs were aware of this issue, and did not provide for an exception.

Here is the substantiation to the proposal sent in to change this.

CMP's
"Substantiation:
When Type SE conductor are used for interior wiring, as a replacement for Type NM cable, the ampacity of the conductors should be the same as permitted for NM cable since the insulations used ar the same both NM and SE conductors."


There is no exclusion for Main Power Feeders.

I see it the other way around...the specific rule is 310.15(B)(6) and it modifies other rules. I don't see a need for an exception to use SE or NM as the main power feeder using 310.15(B)(6). Note that 310.15(B)(6) does not change the ampacity of the cables, it only permits them to be used for specific sized services. This works just like 240.4(B) which does not change the ampacity of the conductor...it only permits an oversized OCPD.

As far as the substantiation, that was from the submitter, a representative of a cable manufacturer, not from the CMP. There was no technical substantiation for this change.

 

[M. D.]

I disagree.

334.80 states "The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15." It then goes on to say "The ampacity shall be in accordance with the 60 degree conductor temperature rating."

So the first sentence says to comply with 310.15.

310.15(B) says to use Tables 310.16 though 310.19 and ampacity table 310.20 and 21 as modified by (B)(1) through (B)(6).

310.15(B)(6) modifies the general rule to use Table 310.16 and permits the use of the ampacities given in Table 310.15(B)(6) provided that you meet the requirements in (B)(6).

I don't see anything in 334.80 that states we can't use 310.15(B)(6) and must use Table 310.16.

Chris

Well said Chris

 

[Dennis Alwon]

Does the wording in 310.15(B)(6) permit THHN to be installed without the proper wiring method...No.
310.15(B)(6) is limited to itself, and does not override what is written in 338.

The wiring method, 338, does have reference over 310.15(B)(6)
If Table 310.13 had more restrictions for THHN, those restrictions could override what 310.15(B)(6) permits.

All articles 338 says is that we must use 334.80 when installing se cable in the interior of a dwelling. That means the wiring is limited to 60C. Okay, I agree but now we go to T. 310.15(B)(6) and the 60C doesn't enter into the equations. Where is the restriction in 334.80 or 338 that says we cannot use T. 310.15.

Here is the problem. If I run PVC with 2/0 copper I can use it for a 200 amp service. Now if that wire runs thru an attic with ambient temperatures of 130 degrees I still do not have a restriction on that wire being used for 200 amps. Bad idea? Perhaps but the table does not take into account any of that info. So are you to be the one who decides what is allowed and what isn't based on temp., derating etc.

I just don't see the code to back up your thinking. I mentioned this a long time ago and got no support on this issue from the forum. I believe it is an oversight.

 

[Pierre C Belarge]

Lets look at another section of the code, related in theory.

NM cable is restricted to the 60C column as per 334.80.
Table 310.16 tells us the amperage for the conductor size according to the column.

Sec 240.4(G) permits a reduction in the size of the conductors under specific applications. Yet it does not give permission for overriding 334.80, as 334.80 is specific to the NM cable.

The same principle is used for SE Cable for interior installations. The tables do not override 338 qnd 334.

 

[augie47]

All articles 338 says is that we must use 334.80 when installing se cable in the interior of a dwelling. That means the wiring is limited to 60C. Okay, I agree but now we go to T. 310.15(B)(6) and the 60C doesn't enter into the equations. Where is the restriction in 334.80 or 338 that says we cannot use T. 310.15.

Here is the problem. If I run PVC with 2/0 copper I can use it for a 200 amp service. Now if that wire runs thru an attic with ambient temperatures of 130 degrees I still do not have a restriction on that wire being used for 200 amps.

No ? Would the correction tables at 310.16 not apply ? To me it's the same argument. Does 310.15(B)(6) overide the temperature adjustment factor ? What if the ambient was 175? ? Would we allow a 80 amp rated conductor on a 200 amp breaker ? Actually what you describe is the basis of Southwire's argument in support of 338.10/224.80. They state the rule was supposed to apply to SE in insulation due to conductor being damaged by temperature.

Is Bad idea? Perhaps but the table does not take into account any of that info. So are you to be the one who decides what is allowed and what isn't based on temp., derating etc.

I just don't see the code to back up your thinking. I mentioned this a long time ago and got no support on this issue from the forum. I believe it is an oversight.

It is going to continue to be controversial until the CMP's straighten it out by a 2011 or TIA change.

 

[Pierre C Belarge]

I see it the other way around...the specific rule is 310.15(B)(6) and it modifies other rules. I don't see a need for an exception to use SE or NM as the main power feeder using 310.15(B)(6). Note that 310.15(B)(6) does not change the ampacity of the cables, it only permits them to be used for specific sized services. This works just like 240.4(B) which does not change the ampacity of the conductor...it only permits an oversized OCPD.

As far as the substantiation, that was from the submitter, a representative of a cable manufacturer, not from the CMP. There was no technical substantiation for this change.

Yes, Don I understand that. The CMP accepted this proposal, with the substantiation.

There are times people put proposals in, not so much to get a proposal accepted, but to see what the CMP has to say about the topic. I believe that the CMP accepting this proposal also means they agree with the substantiation.




BTW:
I do not always agree with the Code, or CMPs, but they generally have access to much better/detailed info than I have and I use the ROPs/ROCs as informational.

 

[raider1]

No ? Would the correction tables at 310.16 not apply ? To me it's the same argument. Does 310.15(B)(6) overide the temperature adjustment factor ? What if the ambient was 175? ? Would we allow a 80 amp rated conductor on a 200 amp breaker ? Actually what you describe is the basis of Southwire's argument in support of 338.10/224.80. They state the rule was supposed to apply to SE in insulation due to conductor being damaged by temperature.

It is going to continue to be controversial until the CMP's straighten it out by a 2011 or TIA change.

Gus I'm going to have to disagree that the temperature correction factors of Table 310.16 would apply to 310.15(B)(6). Those correction factors are specific to that table and not a general adjustment factor required in 310.15 such as the factor for more than 3 current carrying conductors is.

Chris

 

[pete m.]

From NFPA an answer to a request for a Formal Interpretation

From NFPA an answer to a request for a Formal Interpretation

Date: 5/8/09

This replies to your E-mail of requesting information on NFPA 70, National Electrical Code ?, 2008 Edition or NFPA 70 ?.

A revision to the 2008 NEC resulted in a new provision in Section 338.10(B)(4) that required application of the ampacity rule for Type NM cable in Section 334.80 to Type SE cable where it is used as an interior branch circuit or feeder. This provision limited the final load ampacity of the conductor within an SE cable to the 60?C ampacity column. When contrasted to the allowance of Table 310.15(B) (6), this 2008 revision results in larger conductor sizes than would have been required by previous editions of the NEC.
The substantiation supporting these accepted proposals (7-88 and 7-90) cited temperature concerns associated with using Type SE cable as an interior wiring method. Proposal 7-90 cited a 1987 NEMA study in which the effect of embedding a cable in thermal insulation was deleterious to conductor insulation unless the conductor?s ampacity was reduced. There was no data included in either of these proposals indicating that application of Section 310.15(B)(6) to Type SE cable installed as a service or feeder wiring method, in which the conditions of use specified in Table 310.16 were not exceeded, resulted in the cable operating at temperatures exceeding its insulation temperature rating.
This brings us back to the premise of my original response and the decision that has to be made by the AHJ for feeders that ?supply all loads that are part of or associated with the dwelling unit?. One approach would be to use the Type NM cable ampacity requirement, that is now tied to Type SE cable by the revision to Section 338.10(B)(4), for all interior feeder and branch circuit installations without considering the installation conditions. Alternatively, the AHJ could use Section 90.4 and assess the particular installation and make the decision that the conditions of installation are such that application of the ampere ratings specified in Table 310.15(B)(6) does not result in the feeder conductors being exposed to operating temperatures that exceeds the conductor?s insulation temperature rating. If that is the case, the goal of the performance requirement specified by Section 310.10 can be met and the overall safety objective to maintain the integrity of the conductor insulation, by judiciously applying the ampacity and operating temperature requirements that have been cited in this response, can be achieved.
To summarize this, Section 310.10 is the performance requirement that the prescriptive ampacity rules and tables in Articles 310 and 338 are used to satisfy. Because there are some questions related to the revision of 338.10(B) (4) and how that correlates with Section 310.15(B) (6), the use of Section 310.10 can be used as the controlling requirement. Granted, that may not be as cut and dry as what you were hoping to learn, but it does provide a means by which to make a prudent determination that helps ensure conductor insulation integrity. Additionally, the 2011 NEC revision process is underway and the Report on Proposals will be available at the NFPA website around the middle of June. I know that there have been proposals directed to CMP-6 and CMP-7 on Sections 310.15(B) (6) and 338.10(B) (4). I urge you to review these proposals and submit any comments you deem appropriate so that the CMPs have the benefit of your expertise and field experience. The strength of the NEC is the process by which it is developed and you have an opportunity to help make the Code stronger.



Paul Choiniere
NFPA Senior Electrical Specialist


Important notice! This correspondence is not a Formal Interpretation issued pursuant to NFPA Regulations. Any opinion expressed is the personal opinion of the author, and does not necessarily represent the official position of the NFPA or its Technical Committees. In addition, this correspondence is neither intended, nor should be relied upon, to provide professional consultation or services.