ECN Forum Forums Code Related Discussion NEC & other Code issues Derating NM cable

I read somewhere recently (IAEI Mag?)
that the next code cycle is going to require derating NM that passes through bored holes that are fire stopped or otherwise "sealed".
Can anyone help me remember where I read this?

Redsy- your information is in 334.80 2005 NEC.

Now help me find the information that told us how to install "stove piping" of NM cables. I can't seem to find it. Probably was removed and no dot in the margin. I hate it when they do that.

Greg- I'm not going to pick on your graphic, since it's not your work. You, as an inspector and probably see the same things I see and we'll just leave it at that.

You get to see the 12" OD bundles of NM on jobs that have multi panel switch gear and someone thinks it's a good idea to enter all the cables for 8 or 10 - 42 circuit panels in one location.

If this is a 200amp service, there is no need to derate below 20amp for #12, 30amp for #10, 40amp for #8, and 50amp for #6.

I cannot pack NM close enough to keep the heat in. (I drill 3" holes in I-joists and pull a mix of #6 for subpanels and #12 for general circuits.)

312.5(C) exception? It survived into 2005 unchanged

Thanks Greg- I looked for about half an hour and had given up. Now I can sleep tonight.

When I read this code reference I'd say it is usually a violation on most of the jobs where they use "stove piping" and most contractors aren't up to doing the calculations. I personally don't think it's the most dangerous problem out there. If there were a number of other problems on the job I'd have a contractor fix the over fill on the stove pipes but if the stove pipes were the only problem I guess I'd pass the job. But don't tell anybody.

Can you explain this?

The size of the service has no bearing on the rules of 310.15.

You know, I'm kinda hackish, and that panel looks messy to me.

Real code issues aside.

The NEC should have an exception for single family for de-rating, just like the state of Wisconsin.

iwire ---

I just do electrial engineering. I am not responsible for the tables, the assumptions used in making the tables, or the errors in the tables.

One assumption that the tables make is that there is enough power from the service to allow all the circuits to draw their rated amps.

On a 200amp/220volt service, 4 50amp/220volt circuits draw a total of 200amps (average or 50), 8 50amp/220volt circuits draw a total of 200amps (average of 25).

The service derates the conductors. So if you pull either the 4 or 8 circuits through a single hole in the joists you will get about the same temperature rise.

I could do an example using 20amp circuits, but that requires actual math.