I would like to know some specific information about electrical wires and cables and how to run them properly...seems simple enough but wonder if there are specific code requirements:

1. When running a NM-B cable in the attic or basement and you need to go from one beam/joist to another - what is the allowed length of the run before you should support the cable with some piece of plank

2. Is there any rule as far as positioning electrical junction boxes in the attic ? Can I just attach it to any joist ? How would you ensure that in the unlikely event of roof leak, you don't have a serious electrical short? Are you OK to use plastic or metal boxes ?

3. I understand that if you want to run any cable along or across the wall - there are some rule that would require the cable to be inside a conduit. When is it OK to run the cable out on the wall and when you must use conduit

4. Depending on Answer to Q3.....Say you running a NM-B cable above the garage ceiling...and then you need to transition to the inside of the garage...so you use Sch40 conduit... would you strip the sheathing for the length of the conduit run so that you only have the individual insulated wires (black,white,) or you just run NMB Cable inside the conduit ? I ask this question because I notice that all specification around Conduit fill rate talk about number of wires, and never seen how many NMB Romex cables you can run inside a conduit.

thank you

 

The key to running NM-b cable is that is must always be protected. If you are running it across the tops of the ceiling joists..... keep it close to the low part of the roof so that it can't be stepped on. If you need to run it down the center of the attic.... perpendicular to the joists.... then you need to either drill the joists or fasten to the side of an added 2x3 or 2x4.

You can use plastic or metal for splices. Any location where it's protected and accessible is fine.
You can have a water leak anywhere in the house.

Technically NM-b is not run in conduit. It is sleeved in certain areas for protection. The sheath does not get removed as the wires are not rated to be installed individually in a conduit.

In a place like a basement... you could staple the wire along the top of a wall or down a wall. As long as it was fastened to the wall it would be protected. NM-b cannot be run exposed on a wall in a garage.

 

The cable must be supported at a maximum of 4.5 foot intervals.

 

thank you guys.

As far as the NM-b not being run in a conduit but rather "sleeved" ....what kind of sleeve would that be? Like if I need to run NM-b from the top of my garage ceiling down the wall to about 4 ft off the flooring....?

 

An example of this is using a short piece of conduit to sleeve a cable where it passes through a masonry wall.

 

EMT or PVC conduit are commonly used as sleeves for cables.

 

thanks for clarifying...I misunderstood the comment above

 

Related question:
I already have 4 cables of AWG12 inside this 1inch conduit - would I be OK to pull AWG14 or is it already at its max?

the conduit goes from the garage attic down to the main panel - as you can see.
The top of the panel is about 6.5 ft of the ground - that's where the conduit enters

thanks!

 

Conduit fill tables are for single conductors, not multi-wire cables.

 

ok..so does that mean that in those cases when you need to run sleeved cable inside conduit (like in my case cable running down the wall in the garage)...I can put as many as I can fit...?? there is no concern that all those wires bundled together can get really hot ?
I feel I can still "comfortably" pull one cable.

I thought the reason for conduit fill tables is to avoid the risk of fire due to inability to dissipate heat....same should apply to running multi-wire cables...no?

 

Fill needs to be 40% of the of the conduit or less You would figure the area of each cable and add them together and compare to the area of the conduit.

You might want to look at this: http://www.codebookcity.com/codearti...onduitfill.htm

 

Ray; all the cables I can find are THHN or THW etc... nobody seems to show calculation for Romex type cables.
How can I calculate area of Romex?

 

You could measure the width and thickness then multiply to get the area. There may also be a problem with bundling. When you get two many wires in a bundel they have to be derated. This is really something the pros would have to explain. Weather the conduit would be considered bundling I can't say. You'll have to wait for the pros.

 

by the way....this is as close as I was able to find...old post here:
http://www.doityourself.com/forum/el...4-1-emt.html#b

ONly 1 Romex 12-2 in 1inch ???
Running it for the entire length or only a few feet for protection of an exposed run seems like overkill....I have the 1inch conduit and single Romex cable inside is like barely filling in anything.

 

NM fill is based on the major diameter of the cable. The percentage of fill will vary.

I am not sure why you are even sleeving the cables.

 

pcboss; My main panel is in the garage....any new wire run to the breaker will be exposed on the garage wall - which I understand is NOT allowed.
It is my understanding that you can't run unexposed Romex cables along the garage wall and they have to be protected by conduit.
Once I get the cable up to the garage ceiling then it goes behind the walls or runs up on the attic...so I don't intend to run conduit for the entire length of the cable...but it is my understanding based on what has been written here and other electrical Forums that the 6ft of Romex cable that is exposed inside the garage - must be protected by a sleeve.

 

NM is allowed to be run on the surface where not subject to physical damage. However, physical damage is a subjective call. I would not consider above the panel to be subject to damage. Your inspector is the one to ask.

 

so IF the cal is made that the cable needs to run inside the conduit.... just for protection from possible damage...would I still need to comply to the same fill rate rules....which would put me at maximum 2 Romex NM-b AWG12 inside 1inch PVC conduit ?