ECN Forum Forums Code Related Discussion NEC & other Code issues 334.80

Does anyone else see a problem with the wording in the new paragraph of this article?

Where more than two NM cables containing two or more current-carrying conductors are bundled together and pass through wood framing that is to be fire-or draft-stopped using thermal insulation or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a)

Or maybe the question should be "HUH"?

If the cables meet the definition of being bundled this is already required and why would "thermal insulation or sealing foam"
be singled out?

If we used a fire caulk, would we not need to adjust the ampacity even if the cables were bundled?


Roger

Roger, I am guessing and not looking at the ROP or ROC. Fire stopping with this foam or insulating material is different from the standard fire calking or other type of intumesce material that expands upon the presence of fire. Under normal conditions, heat will not be dissipated so Panel-7 has accepted the requirement to protect type NM cable irrespective of the length of the bundling.

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Charlie Eldridge, Indianapolis, Utility Power Guy

The more interesting turn of phrase, to me, is draft-stopped.

I take this to mean the sealing that insulators do to minimize air flow through stud cavities by squirting foam into the holes I drill for my NM-B.

I don't see the term draft-stopped as minimizing. With foam and thermal insulating material, you are blocking all airflow now and adding heat-retaining material. Therefore, the need for the new rule (this is a guess).

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Charlie Eldridge, Indianapolis, Utility Power Guy

Are you suggesting that this Code language is not applicable to the scenario I'm describing? It seems to me that the sealing foam that is squirted into the hole that I drill for my NM-B will stop the draft through that hole. In my experience, the insulator will leave framing irregularities and joints un-stopped. The stud cavity will still draft, but at a lesser level, perhaps a minimized level, after the electrical penetrations are stopped.

Some of the fire stopping is done with intumesce material that expands upon the presence of fire. In other words, it does not stop all movement of air until a fire activates the material and it will expand to fill the opening.

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Charlie Eldridge, Indianapolis, Utility Power Guy

The wording is chosen carefully so that the electrician is not sent to the bundling section, but rather directly to the table. This requires us to derate cables, no matter how short the distance, when they are routed through a fire-or draft-stopped thermal insulation or sealing foam.

This is another reason not to adopt the 2005 Code.
The situation is that the Romex cables pass through a 1 1/2" thick stud and the rest of the hole is sealed with foam. It should be emphasized that this is only for a distance of 1 1/2".
Earlier editions of the Code recognized that the copper will conduct away any built-up heat. Thus the permission to bundle for up to 24" without derating.
This section of the Code should not be adopted. The Code panel doesn't understand the physics involved.
~Peter

I assure you that that is not the case. Without substantiation, this proposal would not have been accepted.

This was a panel proposal 7-150a. The substantiation was:

Code-Making Panel 6 Rejected Proposal 6-31 to add the proposed text to 310.15(B)(2)(a) and provided the following Panel statement:

"The Panel agrees with the intent of the Proposal, however, this material is more appropriately addressed in 334.80 since the Proposal only applies to one type of cable, and Code-Making Panel 6 covers all wiring methods. Therefore, Code-Making Panel 6 has forwarded this Proposal to Code-Making Panel 7 for action."

The substantiation provided by the submitter, Travis Lindsey, of Proposal 6-31 was:

"Recent experimentation shows the possibility of dangerous conditions when loaded circuits are brought into close proximity to each other inside a fire- or draft-stop, where the ability to dissipate heat is extremely limited. Cable temperatures well in excess of their 90°C rating were encountered, with no overcurrent protection present for these conditions. Results indicate that immediate adjustments should be made to the NEC to apply at least to the specific case represented by the experiment. Such a proposal is being made, with a supplemental report offered as technical support."

This was accepted by panel 6 by a vote of 15 - 0.

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Charlie Eldridge, Indianapolis, Utility Power Guy

I believe that Peter is correct and that the submitter, Travis Lindsey, is wrong.

If Mr. Lindsey is correct, a single NM cable also has the problem.

If Mr. Lindsey is correct, we can also look at foam insulated walls and discover that NM cable should never be used in those.

I will continue to do engineering for heat related derating and continue to use "old" code methods.