Running multiple NM cables to 2nd floor

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  #1  
Old 08-20-04, 07:31 AM
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Running multiple NM cables to 2nd floor

I'm rehabbing a 100 year old Baltimore rowhouse, and replacing all the wiring (as an indication of age, the knob and tube is a "recent" addition - I am cutting out the gas pipe that goes to each ceiling rose for gas light!). I need to get about 10 cables (mostly 12/2) from the basement to the crawlspace above the 2nd floor for distribution - a total of 20 feet from basement ceiling to 2nd floor ceiling (they built em big then).

At the same time, I am adding a full bath in the 2nd floor, and for simplicity I have run the pipes (3" PVC waste and 3/4" copper supply) inside the rooms, just inside the walls, and I will build a bulkhead around them. This runs the full 20 feet.

Can I run the cables up through this bulkhead? Can I put in a conduit (thinwall or PVC) to run them in? I have plenty of space - this could be as big as another 3" PVC pipe. I am running a conduit for all the low voltage wiring (six Cat 5E and six coax) to allow for expandability, and it would be handy to be able to do something similar with the power cables.

Thank you
Andy
 
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  #2  
Old 08-20-04, 07:46 AM
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Yes, you can run them through this space. I would strongly recommend against putting more than four cables in one conduit, however, because of derating problems. So you could use multiple conduits. But the conduit is probably not necessary and it might be better without it (the conduit contains the heat). You might also want to consider a subpanel. That might make it easier to add more circuits later, and you could just run one large cable up to the second floor.
 
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Old 08-20-04, 12:18 PM
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Thanks, John, as always yours is the authoratative answer. I will ponder putting in a subpanel, which may also be an advantage as the house is 60 feet deep and voltage drop is an issue. If I do run multiple 12/2 up the bulkhead, I will run them loose as if up a wall. I can always fish more later if I need to. I'll keep the conduit for the signal voltage cable which is bound to become obsolete/inadequate in time and will need replacing.

I'm saving my pennies for a coffee mug for your 10,000th post!

Andy
 
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Old 08-20-04, 01:28 PM
rlrct
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Originally Posted by Andy C
If I do run multiple 12/2 up the bulkhead, I will run them loose as if up a wall.
Andy,

NM has to be supported at least every 4 1/2'. If you leave the NM "loose" in that chase, that would almost guarantee a red tag from the AHJ. Something like that could also make an AHJ take a harder look at your overall installation, based on missing something basic like stapling the NM down. If anything, take the time to do it neatly and it'll be to your benefit.

You also need to be careful not to create "bundles" of more than 3 runs of NM stapled together/right next to each other. That would be cause for derating and you don't want to go there. You could avoid that simply by stapling a pair of 12/2 NM at a time (use staples rated for that) and spacing the pairs of NM 2" apart. That way you won't have created individual bundles of 4, and I don't believe there are commonly available staples that will let you staple 3 NM at a time. You could use cable standoffs, but that seems unnecessary.

I'd pursue the subpanel.

Rob
 

Last edited by rlrct; 08-20-04 at 01:35 PM. Reason: add bundling
  #5  
Old 08-20-04, 02:34 PM
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NM has to be secured unless fished through finished spaces. So if it is possible to secure it without damaging finished surfaces, by all means do so. Otherwise, don't sweat it.

Rob said not more than 3. I said not more than 4. My number is based on the trying to avoid more than 9 current carrying conductors run together, which is the point at which the derating of #14 or #12 requires a smaller breaker.

I'm not quite sure where Rob's spacing requirement of two inches came from.
 
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Old 08-20-04, 09:09 PM
rlrct
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John,

My number of 3 came an experience where I had to spread some NM runs to avoid a red tag. Our AHJ interpreted the section as meaning that we could only have a bundle of 3 NM cables before we had to derate.

The crucial point, though, isn't if we derate but what the result of derating is. We do have to derate at 3 runs of NM bundled. The important point is that the result of derating still allows for bundling 4 runs of NM without losing any ampacity. Naturally, you're the one who is correct.

Had I known that 4 years ago, I could have saved myself some work.

The 2" is just a swag at some distance to separate the bundles an AHJ won't consider the whole thing a bundle - could certainly be closer if an AHJ won't tag it.

I mentioned the support distance because Andy indicated he'd be building the bulkhead to cover the pipes/wiring, so it's not fishing through preexisting space.
 

Last edited by rlrct; 08-20-04 at 09:44 PM. Reason: clarification
  #7  
Old 08-20-04, 11:14 PM
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Thank you for the guidance. I should have defined 'loose' as being in cable standoffs (as opposed to being inside a conduit). I shall secure as you suggest. The subpanel is appealing, but my planned circuits are separated up/down stairs rather than front/back of the house, so I'd have to redesign for a 'front' and 'back' of house panel. If I had 'up' and 'down' statirs panels, there would be just as many long runs.

Just for interest's sake, I calculate 0.68 W/ft at full 20A for 12AWG (20^2 * 0.0017 ohm/ft). So each 20 ft run loses about 14W, *if* my chase were insulated I could get 140W building up in there from the 10 circuits. Actually twice that including the neutral conductors. But this is all dissipated over 20 ft. Interesting how it adds up though - but that is at full 200A, 24 kW capacity. That's one big hair dryer.

Thanks again
Andy
 
  #8  
Old 08-21-04, 04:48 AM
rlrct
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You still might want to consider a subpanel. You could run some conduit chases from the 2nd floor subpanel up into the attic so you could easily drop circuits for the second floor down from the attic. That would also make it easier to add circuits in the future if you ever feel the need to do so. My thought on the subpanel wasn't so much long runs as it was the number of runs it sounded like you were planning. A sub just sounds like less wiring and provides future flexibility if done properly.

If you were planning on cable standoffs, it's my understanding that those qualify as supporting the cable. If you're using those you should have no need to otherwise staple the NM between standoffs.
 
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