Nmb electrical wire insulation coat is thinner...

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Old 09-13-07, 03:21 PM
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Nmb electrical wire insulation coat is thinner...

...than it used to be.

Is there any new code requirement on how wires are packed in an electrical box because of this? Keeping the hot wires separated from the neutral and ground. back behind switches and outlets? Or don't most electricians worry about this?
 
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Old 09-13-07, 03:26 PM
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There is a box fill calculation done to determine max conductors in a box per the NEC (314.16(a)). It all depends on what size box, and what size and quantity wiring.
 

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Old 09-13-07, 03:49 PM
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Not the number of wires. I want to know if there is a requirement on how the wires are jammed in the box. If one has to take dilegent care in making sure when the excess wire folds back in there - that pressure is not exerted where a bare ground wire or especially one of those pigtail crimps on ground wires, tries digging into a hot wire.

Today I had to replace an outlet with a short in the wire because that is the very thing that happened! I had to section out that piece, rather than electrical tape around it, because the gauge size of the wire was greatly compromised, by maybe 1/2. In essence, it became like a fusible link. And people wonder what some reasons are for electrical fires?
 
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Old 09-13-07, 03:56 PM
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If it is an older house, the box size and # of wires does not likely meet current code. That is what those calculations are for, so the wires are not crammed into the back of the box. But your old box is legal, it just takes careful work to pack the wires so there are no problems. If you have an especially busy box with lots of wires, I would replace it with a new deeper box. Old work boxes are good for this type or replacement.
 
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Old 09-13-07, 05:48 PM
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Code fill is based on the circular mil, of the conductors (copper) not the insulation, and associated connectors etc..

I would not be surprised if, at some time in the future these guidlines are changed, based on the new technologies afforded us.
 
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Old 09-13-07, 05:55 PM
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Suppose there are only 6 wires in an outlet box. By 6, I do not mean 6 romex. I mean only 6 twelve or fourteen gauge wires, as you would find in an outlet box. What I want to know is if there is some (new?) code requirement to how a person folds those wires back in there to make sure the hot wire does not touch the bare ground wire. Do electricians even bother with this, or do they just shove the outlet back in there with no regard to what is going on behind or alongside the outlet? That is obviously what the electrican did that wired this not-that-old condo! It's the fact that the insulation is so thin, coating the wires today.
 
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Old 09-13-07, 05:58 PM
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Originally Posted by lectriclee View Post
Code fill is based on the circular mil,...
Could you translate that please?
 
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Old 09-13-07, 06:18 PM
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The insulation is less thick than it used to be, that is true. However, it is still rated the same, as far as being able to stand up to the temperature, voltage and current flow.

To address your question, there is no explicit code in regards to fitting the wires in the box. Some generic terms apply, but nothing specifically talks about how the wires are folded, etc.
 
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Old 09-13-07, 06:39 PM
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Originally Posted by ecman51` View Post
Suppose there are only 6 wires in an outlet box. By 6, I do not mean 6 romex. I mean only 6 twelve or fourteen gauge wires, as you would find in an outlet box. What I want to know is if there is some (new?) code requirement to how a person folds those wires back in there to make sure the hot wire does not touch the bare ground wire. Do electricians even bother with this, or do they just shove the outlet back in there with no regard to what is going on behind or alongside the outlet? That is obviously what the electrican did that wired this not-that-old condo! It's the fact that the insulation is so thin, coating the wires today.

With the boxes sized correctly, and a neat and orderly install.

This they did not do. The only code here is a minium of six (6)inches of wire at the box, More is better.

Originally Posted by lectriclee
Code fill is based on the circular mil,...

Could you translate that please?



The conductors are sized in circular millimeters. That is the guage. Based on that some very smart people(in other areas) came up with the fill requirements.
 
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Old 09-14-07, 05:31 AM
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Yep, new is thinner, but

is it worse for cut-thru resistance? 50 year old 14AWG romex measures about .030 insulation thickness on the conductors, the new stuff is .020, a pretty big change. Note, however that the new stuff contains a thin nylon outer coating that significantly reduces the tendancy to cut thru. Which is better? don't know for sure, but the new stuff takes up less space in the box, and no doubt, is cheaper to make.
 
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Old 09-14-07, 07:20 AM
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The concern of the original poster is not related to box fill, nor to the fragility of the insulation, nor to the possibility of metal-to-metal contact. It seems the concern is in regard to the insulating value of the newer, thinner insulation.

My understanding is that the newer, thinner insulation still provides the same insulating value as the older, thicker insulation--probably even better. A bare wire, resting directly against an insulated hot wire, is still safe. The difference in voltage potential between the two is only 120 volts (in North America), and the insulation is good up to 600 volts. It should be fine.
 
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Old 09-14-07, 08:55 AM
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Originally Posted by ecman51` View Post
What I want to know is if there is some (new?) code requirement to how a person folds those wires back in there to make sure the hot wire does not touch the bare ground wire.
There is no specific code related to folding wires back, however the length and fill of the wires is regulated by code. Furthermore, NEC has a blanket requirement that all wiring be installed in a "neat and workmanlike manner", which inspectors sometimes use to fail shoddy workmanship in the absence of a specific code violation.

Originally Posted by ecman51` View Post
Do electricians even bother with this, or do they just shove the outlet back in there with no regard to what is going on behind or alongside the outlet?
A quality workman will take the time to do the job right. The low bidder that builder hired? Probably not.
 
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Old 09-14-07, 01:23 PM
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The old "thick" insulation on NM cable conductors was good for 60 applications. It also had a tendency to get brittle under certain conditions.

The newer insulation on the conductors (type NM-B) is good for 90 applications. Not all of it has the nylon covering.

About the same time NM-B became required the requirement for 2 deductions rather than 1 for each yoke mounted to the box went into effect - in essence there can be less of the new smaller wire in a box than than when the older type was common simply because of the new device allowance requirements.

The why has partially to do with the preponderance of stuff that takes more room in the boxes like GFCIs, dimmers, and similar stuff.

The insulation on the new wire is pretty rugged stuff and it really takes abuse to pinch it to the point that a short develops. I use the deepest boxes that will fit in a given location and frequently remove old metal device boxes and replace them with deeper ones when installing GFCIs and similar stuff. Just a bit of care and simple folding of the wires generally results in a good device installation that won't have problems.

As to the box fill, the tables still apply no matter the insulation type of the wire. And the 2 wire deduction of the largest size wire in the box per device applies as well. Some of the smaller boxes don't have the volume to allow you to feed through a #12 if a device is present - something to keep in mind if you are remodeling and are tempted to re-use old metal boxes.
 
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Old 09-14-07, 04:29 PM
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Thanks to all who answered so far. Interesting.

After reading all that has been said, I get the impression that the new stuff is actually better. Now I wonder why there was that insulation missing, more than I was before reading your responses. Perhaps the insulation was damaged prior to the wire even being packed in the box! Maybe it was just a coincidence that it appeared the insulation was worn through by the pressure of it up against the ground wire, and this was just an accident waiting to happen. Maybe this all happened because the bare spot in the hot wire happened to be up against the bare copper wire, and for no other reason.

It's actually reassuring to know that this newer wire insulation is better. The initial perception that thicker is better sounds like it is not true in this particular case.
 
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Old 09-14-07, 04:46 PM
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New technology Vs Cheaper Manufacture?
Go to the big box stores and feel a roll of Romex. Then pick up a roll of "FRED's" wire. I looked 2 or 3 times, To make sure I actually bought 12/2 wg , because it really did feel "Cheesy". "Just as good"? maybe so, But Im a firm believer in quality work with a quality product. How Proffessional can you be if the outlets you install are 5 for a dollar?
 
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Old 09-14-07, 06:02 PM
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How does 5 for a dollar receptacles enter into a discussion about NM-B?

NM hasn't been legal for a long time, and the lighter they can make a product (like eliminating all that paper wrap) and slicker they make it for easier pulling, the better. Sweating an extra 2 gallons a day because of the wire type you use contributes nothing to quality. Just exactly what are you expecting to happen to the wire after it's installed?

50 cent receptacles frequently outlast $30,000 automobiles, even in high use areas. Quite honestly in spite of the bad rap they get, they happen to be cheap, for among other reasons, they are made in huge quantities. Double the price gets you a pretty decent receptacle.
 
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Old 09-14-07, 07:16 PM
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The point was'nt necessarily outlets.

In any field, there is the product, and the cheap counterpart. The cheap outlets-(the ones with no screws, "Backstab" only)
are available only because Someone insisted on saving 50 cents an outlet and was willing to buy them. This same guy cant understand why he continuously has problems with them.
When I bought my house, in the garage were two rolls of 12/2 wg NM cable. when I unrolled one of them it was night and day as compared to what was already run. When I was in big box, The same wire I had, was less than half the price of Romex. Maybe I'm off base with the quality issue, but why half the price?
 
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