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| Subject - NM Trough? | |
| Dave Nix |
Here is an install in a new house I inspected last week. This is the first time I have seen this method for NM installs. The "rings" have a snap-around 3-sided cover to close the sides and bottom.  quote: Let's suppose that the securing is not an issue and see if: (1)the install will comply with the derating and (2)with the fill allowance of 40% specified by the manufacturer. (1). The install has six 12/3WG NM cables, six 12/2WG NM cables and one 8/3WG NM cable. Current carrying conductors: (12/2)= 6, (12/3)= 12 and (8/3)= 2, for a total of 20 current carrying conductors. According to the Table, the derating is 50%. The 12AWG would be reduced to 15A and the 8AWG would be reduced to 22.5A. The breakers installed are 20A and 40A respectively. (2.) Let's guess the size of the 12/2NM is 3/8", (.375 x 6) = 2.25 sq." Let's guess the size of the 12/3NM is 1/2", (.5 x 6) = 3.00 sq." Let's guess the size of the 8/3NM is 3/4" = .75" That would give us a total of (2.25 + 3.00 + .75) 6.00 sq." fill. The product has a cross section of 7.25 sq.". When we calculate 40%, we have a result of 2.90 sq.". Based on the above calculations, (if you agree they are acurate) would you agree that the install does not satisfy these code requirements? |
| cs409 | we understand...hope your getting a lot of apples LOL |
| JimmyDee | quote: Math is good for the figures you have, but 1/2" has an area of about .245 sq in for 1.47 sq in total, and 3/4" has an area of about .455 sq in and 3/8" has an area of about .116 for an area of about .68 sq in for a grand total of 2.04 sq in. It looks to me like he is ok as far as the fill is concerned. I wonder about the letter of the law on derating. They arn't tightly bundled and the whole idea behind derating is for wire insulation protection from heat. These cables clearly have lots of cooling room around them and it not as though they are going through conduit and the heat generated can't excape. It may be a wrong but if it were my house, I'd have no problem with going with full size breakers with that system. Jim |
| Dave Nix | Jimmy, HUH?? I think I did the math wrong! Please help me figure out what sq.in. a 12/2WG is. If we figue the dimensions (conservatively) of 3/8" x 1/4", we would have .09375 ?? |
| JimmyDee | What I did is went to table 4 of chapter 9 and took a quick look at a conduit that had 3/8" diameter, one that had 1/2" diameter and 3/4". Then just went across to the area of that size and I got about the correct area. I think the area of a circle is 3.141 or pi X r squared. Not sure of that so I looked it up where I knew the math was done. Looking at the rings, it looked like there was no where near the 40% fill from my angle. Also, are those floor joist sitting directly on the foundation block? Jim |
| JimmyDee | Area of a circle is R squared x 3.14 so, the area of a circle or wire .5" in diamater is found by dividing .5 by 2 to find the radius = .25 and then square it = .0625 x 3.14 = .19625 sq in. so the table was actually heavy. Jim |
| cs409 | 6 12/2 with ground equals =12 current 6 12/3 with ground equals =18 current 1 8/3 with ground equals = 3 current total wire count would be =33 derating would be 40% think u got a problem....But .... i see no bundling,or any cable with more than 3, so i see no reason to derate!,,,,so its down to the Raceway issue,,,,,so u made them use 3 of the funny/new brackets instead of one? what are these items? do they go on j boxes? what? any item number to serch for on line? thanks,,,,am tired,,,hope i got it right |
| Electricman | Is there a backer board behind the panel? Or is it mounted directly to the block wall? Also the 83 looks alot closer than 1.25 inches to the top of the floor joists.Gotta love them HVAC guys violating the work space. |
| JimmyDee | quote: I heard this argued both ways. I agree with this interpretation, however there are many that don't. I would like to hear from a few of the inspectors here and get some of their ideas. Jim |
| JimmyDee | quote: Ever get that blank, dumb look from one of them when you tell them you were there first and that they couldn't leave their duct there? Our inspectors here would make them move it. Thats always good for a fight. Jim |
| Ryan_J | When determining the area of an elliptical shaped cable, we are required to use the bigger dimension and treat it as a round conductor. Table 1, note 9:quote: |
| cs409 | to me,,,,i see nothing wrong with the nm run period...but what are these brackets/etc??? now if he tie wraps, tapes,,then bundling as NEC states would come into play.....but as above,,,,i see nothing but clean air flow LOL...but am an old dog.....hope all had a good holiday weekend.........Ryan,,,whats this, no see for a couple,,u come in here, jump in, jump out ,,,you got 2 or 3 women folk your trying to keep up with? LOL and that reply on inpections,,,geee, talk about a cheap out LOL....best to u |
| bigvic | It certainly looks like heck. |
| cs409 | what part would you call the "heck",,,,on a neat scale of 1 to 10, 10 being the better...i would put this at 7.... still waiting on name of product please????? oh Vic, if no one else welcomed you aboard, i will at this time...good to have your input. |
| David Hyatt | Has anyone noticed in the picture, all circuits are run in #12 romex, no #14. This is a guy after my own heart. I try not to use many 15amp circuits. |
| Ryan_J | quote: LOL Sorry, I've just so busy teaching lately. The sparkies have to have their licences renewed by July 31, so I'm buried with requests for CEU classes. Sorry, I'll try to stop by more and say more than two sentances at a time. :) :D |
| zapped208 | I myself have been using 1 1/2" pvc straps for about 4 years now. Beats drilling all the floor joists, and never any questions from our inspectors. |
| cs409 | how many nm runs will they allow in the 1 1/2........ |
| SteveMc | These things look like something designed for data networking cables. I don't think they were designed for Romex. Also, this looks like an unfinished basement, therefore, I would think that 334.15(C) would prohibit their use. Sorry I don't have the code on CD so I can't paste the article, but basically it says that in unfinished basements smaller sizes of Romex must be run through drilled holes or on running boards. |
| JimmyDee | quote: |
| David Hyatt | Wow, been wiring houses for years and never thought about that. I have stapled to bottom of joist. Never got called on that either. But good to know for future. |
| Ryan_J | quote: The apples I recieve are similiar to the ones that Snow White recieves....  LOL |
| cs409 | maybe Dave could add a bit to this issue,,,,is this going to be a dropped ceiling in the basement?..... on the issue of running exposed, across the bottom, probably didnt get called on it, for many reasons,,,think about it,,,its ok to run nothing smaller than 6/2 or 8/3,,,so whats the biggie on 12/2? or 10/2 etc etc?? |
| Scott Vickrey | Without knowing for sure, I tend to agree with Steve about the brackets being for data cabling. I searched high and low for a site containing the pictured brackets and could find nothing. Dave, do you know who makes these and if the are listed for this use? What about the mutual inductance. Would it be enough to be of concern? |
| Ryan_J | quote: Hi Scott. I' m assuming that you are talking about the proximity between conductors. If so, I think 725.55 affords enough protection, personally. |
| Dave Nix | Hi Guys, Here is a link to some scans of the literature. http://www.electricalmatters.com/gallery/One?page=2 The rings are not the entire system. |
| renosteinke | With the free air between brackets, I don't believe that it is necessary to de-rate. At least, that's how I would apply the 24' rule. Were the cables bundled/packed/twisted together, I would de-rate. I note that there is no requirement that the manner of attachment be specifically listed or approved. I think this is a good application of a data/com product. I note that there are in excess of the minimun number of supports- something that I encourage. This type of install will certainly make troubleshooting, tracing, and changes easier. |
| Scott Vickrey | I have to admit that I was impressed with this persons efforts to do a "tidy" install. |