Electrical wiring in attic and conduit size

Reply

  #1  
Old 09-28-15, 04:31 PM
P
Member
Thread Starter
Join Date: Jan 2015
Location: United States
Posts: 500
Received 2 Votes on 2 Posts
Electrical wiring in attic and conduit size

I am in NJ and want to run new wires up on the attic.
Few questions related to code / rules:

1. How much in length can I have unsecured NM-B cable or does it have to be always secured to a rafter / beam or other type of wooden structure? I believe I can have 12 inches of "free" cable...but want to confirm.

2. Are there any rules about the cable being certain distance from gable vents or can I run it along the beam next to the opening ?

3. Finally, once the cables are exiting the attic (going down along the wall in my garage to the main panel) - how many 12/2 cables can I put in 1 inch PVC conduit ? (I saw some reference to max 3....but I want room for future so ideally would like to know what size conduit to use for 6 runs.

Thank you!
 
  #2  
Old 09-28-15, 05:39 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,773
Received 1,322 Votes on 1,222 Posts
You can lay the cable on top of the rafters where the roof slopes down. As long as they are in a place where they won't get stepped on they'll be ok.

It can be pretty tough to run NM-B cable down PVC pipe. After you do get a few in there it's almost impossible to keep them from twisting making hard to run future cables.

A more ideal solution would be to run the PVC pipe from the panel to the attic and set a junction box at the top of the conduit. You would then pull in individual conductors of THHN/THWN wire. You would splice your NM cables in at the junction box.

Or... if you need to run NM cables down the wall..... set a splice box in the garage converting to PVC to the panel.
 
  #3  
Old 09-28-15, 05:58 PM
P
Member
Thread Starter
Join Date: Jan 2015
Location: United States
Posts: 500
Received 2 Votes on 2 Posts
thanks PJmax.... I thought cables always must be secured to some part of the structure.... so I guess there is no rule and i can have part of the cable run not secured to anything... ?

surprised about the difficulty with channeling cables through PVC conduit....I see all sort of sizes of conduit being sold at HD or Lowes so I assumed they worked well and allowed different counts of cables.... never having it done myself, I guess I don't know it is pain
 
  #4  
Old 09-28-15, 06:04 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,773
Received 1,322 Votes on 1,222 Posts
If you keep the wiring where the red dots are... you are ok. If you're traveling across the attic then you need to fasten to the sides of the joists or install a 2x4 as a runner where you can fasten to the side and the wire is protected from being walked on.

Name:  attic.jpg
Views: 2359
Size:  6.5 KB
 
  #5  
Old 09-28-15, 06:51 PM
P
Member
Thread Starter
Join Date: Jan 2015
Location: United States
Posts: 500
Received 2 Votes on 2 Posts
well....the new wire comes through the ceiling at a point in the attic that you cant reach unless you crawl....I want to then run it up to a nearest rafter and along the rafter to the ridge.....then just straight along the ridge to the other end of the attic where it would drop down thru the garage ceiling and to the main panel.

so imagine your drawing with 2 cables a bit more to the center and going up to the rafter with no support until they reach the rafter (that's about 25inches)
 
  #6  
Old 09-28-15, 07:08 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,218
Received 103 Votes on 89 Posts
Type NM cannot be used outside, even if in conduit. The junction box with a transition to THHN conductors is the way to go.

Fished cables are not required to be secured. If you can access the cables secure them at intervaLs of no more than 4 1/2 foot.
 
  #7  
Old 09-29-15, 06:30 AM
P
Member
Thread Starter
Join Date: Jan 2015
Location: United States
Posts: 500
Received 2 Votes on 2 Posts
going back to the conduit question....how many 12/2 NM-B cables can I run thru 3inch "pipe" ?
 
  #8  
Old 09-29-15, 07:41 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,943
Received 44 Votes on 42 Posts
That's a question more complicated than it seems as there is both physical "fit" in the pipe and derating which is due to heat build up. Essentially, you shouldn't put more than 3 cables in due to the heat derating. Code then requires you calculate the pipe fill based on the widest diameter of the cable, which is about 1/2" for 12/2. That means you should be using 2 pieces of 1-1/2" condiut for 6 runs of 12/2.

I'll throw out an alternate of solution of installing a subpanel in the garage. If you want to pull 6+ circuits along the same path, installing a panel instead might be a better option. For example, pull a 6-3/g NM-B cable from the main panel to a 16 space, 60A subpanel in the garage, then run as many circuits from that panel inside the garage as you wish.
 
  #9  
Old 09-29-15, 08:19 AM
H
Member
Join Date: Jun 2006
Location: usa
Posts: 274
Received 0 Votes on 0 Posts
I must have mis-read somewhere. Why exactly do you want to run the NM-B cable in conduit?
Usually, you would use conduit for a group of individual conductors....like THWN, THHN, etc.
If you are just assuring future access to the Breaker panel from the attic to install more branch circuits, simply run a 2" conduit from the ceiling, straight down into the panel and leave it empty for now. The NM-B cable doesn't have to be in conduit unless it's exposed to potential damage. If you enclose it inside a wall, that would meet the definition.
 
  #10  
Old 09-29-15, 08:45 AM
W
Member
Join Date: Feb 2006
Location: USA
Posts: 6,740
Received 22 Votes on 21 Posts
NM Support

I want to then run it up to a nearest rafter and along the rafter to the ridge.....then just straight along the ridge to the other end of the attic where it would drop down thru the garage ceiling and to the main panel.
NEC 334.30 requires support at intervals not exceeding 4.5 feet.
 
  #11  
Old 09-29-15, 12:49 PM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,943
Received 44 Votes on 42 Posts
...and if you continue down to the (B) of that article:

(B) Unsupported Cables. Nonmetallic-sheathed cable shall be permitted to be unsupported where the cable:

(1) Is fished between access points through concealed spaces in finished buildings or structures and supporting is impracticable.


There's a lot of on site interpretation about where fastening is practical or not and what's finished or not.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: