4 posts / 0 new
Last post
Bundling NM wire together??

Here is another question related to running NM wire through tight spaces:

I know that there are code restrictions on bundling NM wire together for long distances due to induction currents, wire heating, etc. How close to the wires need to be for this to occur? I can see the situation developing if they were tightly ty-wrapped together for several feet, but what if they were just strung loosely together, following the same pathway thru ceiling joists, access points, etc. How close to they have to be before you violate the code and run into problems with induction currents?

Gray Watson
Re: Bundling NM wire together??

Your location? I recall your mentioning BC Canada in a prior post. You can update that information on your profile using the USER CP link.

Re: Bundling NM wire together??

Hi Gray...yes, it is BC, Canada. I'll upgrade my profile when I get a chance.

I'm kind of more interested in the physics behind bundling wires, and less so about the Code restrictions. What actually happens if you ty-wrap a whole bunch of NM cable together for a run of several feet? :confused:

Re: Bundling NM wire together??

Rick ... if i remember correctly you're allowed to "bundle" up to 9 conductors if they are not running through wood framing.
For a 14/2 cable it has 2 current carrying conductors .... 14/3 cable has 3 ...... etc..
For example you could bundle 3 ... 14/3 cables.

BTW .... an inspector would likely not be happy to see cable ties.

The physics .......

Current passing through a wire generates heat, which adds to the temperature from outside the wire, further heating up the copper wire, insulation and jacketing.

Overloaded wires can sometimes heat to beyond their rated capacity — 194°F (90°C) resulting in permanent damage to the plastic insulation and jacketing and fire hazards as well. Even when they do not exceed their temperature rating, they may operate for significant periods of time at high temperatures that waste energy, putting additional loads on equipment. In general, heat is the enemy of electrical equipment, whether transformers, motors or cable, and the cooler a product runs the longer it can be expected to last.

When electrically loaded cables are "bundled" together in a restricted area, a further heating effect can occur. It is even suggested that a "runaway" situation can occur in some cases, where heat from the loaded conductors, being unable to escape, further heats the conductor raising the conductor resistance which causes more heating, increasing the temperature still further, and that this cycle can continue to lead to failure.

These considerations are very important when the ambient temperature within the enviorment the cables lay. For example .... cables that are run within a hot attic space.

Hope this helps. :)

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.