EMT Conduit Questions


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Old 02-27-21, 04:27 PM
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EMT Conduit Questions

I am working on a project to rewire my garage. I have romex cable that is stapled on the ceiling which I would like to replace and or sleeve inside EMT conduit.

- How is the conduit fill is calculated if its a complete conduit system (i.e. entire romex run is sleeved and both ends connect to a box)

- In the case of a junction box that is mounted on a ceiling and that has EMT conduit entering/exiting on both ends (both conduits bring a set of romex cable as sleeves) and both romex cables leave the junction box towards the back inside the ceiling cavity (romex cables are then fed to a lightning fixture that is flush mounted inside drywall), do I need to splice the romex cables and run an explicit ground wire to the electrical box OR can the EMT conduit serve as a means to ground the box and the romex cables can be left alone?

Unfortunately due to these lightning fixtures (and there are about 7 of them in a 2 bay garage), I cannot run a conduit to them directly as they are mounted on those flush mount octagonal boxes that you mount in between joists and as such running romex is the only way to them.
 

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02-28-21, 04:39 AM
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NM-b is allowed to be used in a complete conduit system but it is a dumb idea. Fill area is calculated using the widest diameter of the cable.
 
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Old 02-27-21, 05:17 PM
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NMB cable is not permitted in a complete conduit system.
 
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Old 02-27-21, 06:02 PM
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As long as you're running conduit, definitely go with THHN wires instead. It'll be MUCH easier to pull and you'll end up with a much more professional installation.

There's no issue going out of a box using a standard NM clamp to NM (Romex) up into the ceiling. The NM is protected at that point, so conduit isn't required. You'd just splice it in the box like you normally would.
 
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Old 02-28-21, 04:39 AM
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NM-b is allowed to be used in a complete conduit system but it is a dumb idea. Fill area is calculated using the widest diameter of the cable.
 
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Old 02-28-21, 06:23 AM
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Guys,

I understand NM-b in conduit is dumb and not ideal. If I could do it, I would do THHN all the way. I already ran over 100 ft of EMT in my basement. It is the way to go.

But this is different and I have no choice. There are flush mounted ceiling lighting fixtures and their octagon boxes are recessed "inside" the drywall. So right now I have romex stapled across the ceiling (to drywall) which enters inside the ceiling cavity from a hole and then to the fixture box.

I am converting everything in the garage to EMT (outlets, switches, etc). Where possible I will use THHN (and for example surface mount outlets or switches), but in the case of these lights, I cannot reach to the boxes with EMT directly. So I have no choice but to place a junction box (surface mount) where these romex cables enter the drywall and sleeve romex in between entries inside EMT. There will be parts of this run I will splice into THHN and run THHN between connection points (long runs). But at some point I have to transition to NM-b.
 
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Old 02-28-21, 09:46 AM
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You can install NM cable in conduit but conduit fill rules still apply. If you have one cable you may fill the conduit to 53%. If you have 2 cables you may only fill the conduit to 31%. If you have more than 2 cables you can fill the conduit to 40%. For cables that have an elliptical cross section, the calculation needs to use the major dimension of the ellipse as a circle diameter.
 
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Last edited by Tolyn Ironhand; 02-28-21 at 05:33 PM.
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Old 02-28-21, 10:45 AM
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Thank you, this is what I was looking for.
 
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Old 02-28-21, 12:40 PM
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Tolyn Ironhand
You can sleeve NM cable in conduit but conduit fill rules still apply.
Where are you getting that info from? NEC conduit fill tables apply only to complete conduit systems. See NEC Chapter 9 Notes to Tables.
 
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Old 02-28-21, 03:23 PM
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See chapter 9 Tables, Note 9
 
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Old 02-28-21, 05:06 PM
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Tolyn Ironhand
See chapter 9 Tables, Note 9
Note 9 is stating how to calculate the area of a cable such as NM-b when installed in a complete conduit system. I'm asking where are you getting the requirement of fill limits for conduit sleeves? Read Note 2, does not apply to conduit sections such as sleeves. I'm not aware of sleeves being subject to the same fill requirements as a complete conduit system.
 
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Old 02-28-21, 05:24 PM
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I have never seen a sleeve restricted to the same fill rules.
 
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Old 02-28-21, 05:32 PM
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It sounds to me that the OP is planning to run a conduit system and installing cable in it. The term "sleeving" the cable is not correct in this case.
 
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Old 02-28-21, 05:57 PM
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The OP asked about a complete conduit system, box to box.

How is the conduit fill is calculated if its a complete conduit system (i.e. entire romex run is sleeved and both ends connect to a box)
 
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Old 02-28-21, 06:12 PM
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Old 03-01-21, 07:45 AM
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I am not running the entire system in conduit. 70% or more of the current nm-b will be replaced with thhn. But there is still some that has to remain as nm-b. I have explained why that is. There is no way to run thhn in conduit to recessed light fixture boxes. So my two options are leave nm-b as is which is stapled (yes stapled) to drywall ceiling. Or do what I am proposing to do. I understand its not a great solution but it is better than whats there.

I will be using a T style rigid conduit pull box with two ends being EMT conduit and top (facing the ceiling) having a threaded small nipple which romex will be entering/exiting.
 
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Old 03-01-21, 08:34 AM
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Derstig-

Can’t you replace the current light fixture boxes with metallic old work fixture boxes, and then connect flex conduit from the new light fixture box to the surface junction box? Then you could run THHN from end to end and have no NM cable.

But I guess I’m assuming the current NM cable goes up into the ceiling near the light fixture box, so if you remove the light fixture box you have working space to add the flex conduit. But sounds too simple. Must be wrong! ( lol)
 
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Old 03-01-21, 11:22 AM
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Attaching some pictures so that you guys can see what I am dealing with. There are 7 total light fixtures with this problem. Some have 1 romex entering, some have 2 (incoming and outgoing). The light fixtures are mounted to a ceiling fan box (the one where you position a bar between joists and as you turn the rod, the teeth expands and grabs the joists). I am attaching a picture of the box of what they look like.

I want to try and avoid removing them all and doing extra work.

I thought about a flexible conduit but the issue with that is 2 fold:

1) Some of the romex runs are quite long (for example in a 2 bay garage, a run crosses the metal I beam of the house from one side to the next). Fishing THHN inside a flex metal isnt easy from prior experience and it is going to be too much work.

2) More importantly flex doesnt bend 90 degrees flat like the pull boxes or junction boxes do. In other words, flexible conduit has an arc and it wont lay flat on the ceiling.

See below for my proposed conduit solution. This is a RIGID conduit body with EMT compression fittings on both sides. At the center is a 2" RIGID nipple with a plastic threaded insert to protect the wire. This side would protrude inside the ceiling.

NOTE the compression fittings here screw on but their locking rings arent used. I dont know if this is okay. I dont know if its okay to mix and match EMT fittings with RIGID like this but I dont see the problem. There is no way those fittings can be removed without taking the entire system apart.

ANOTHER option is to use those old work boxes that has flaps on the side that you can install in a drywall and then use an extension ring on top of them to make the box extend below the ceiling. I dont know if this will work though as far as the junction box being sturdy enough. I was thinking using a ring like this (https://www.grainger.com/product/2DD...B&gclsrc=aw.ds)






 
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Old 03-01-21, 03:11 PM
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One other thing about MC cable is that (correct me if I'm wrong) but it is no different than a NM-b cable stapled on the ceiling as far as "subject to physical damage". Now granted, my NM-B cable isnt much subjected to physical damage anyways and you may even tell me why are you even doing this and the answer is because I hate yellow stapled cable on my ceiling that doesnt look neat. But with that said, as far as the engineering and rigidity of the system, MC is like somewhere between EMT and NM-B but not same as EMT, correct? It might bend, pierced, etc. If my wife is carrying a shovel for example and flips by accident and the tip hits the MC cable, yes it will protect it better than NM-B but it can still be damaged. The metal part of it easily bends and can pierce the insulation of the conductors.

The sleeved section of this run will be a 3/4" EMT with only a single 12/2 NM-B inside. The only portion where 2 of these cables will coexist is the threaded nipple part of it thats on the Tee pull box and that is less than 2" in length.
 
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Old 03-02-21, 10:12 AM
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There's nothing inherently wrong about your plan. You can run NM sleeved in conduit and connect it to your lighting as you've shown.

If I were doing it, I'd replace the tee with a 4" square box. The conduits going each direction would have THHN and would splice into the NM going up into the ceiling via a standard NM clamp. Basically keeping THHN in the conduits and NM in the ceilings.

In my opinion, most electricians would consider a sleeve to be a few feet down a wall or whatever. Though as far as I know, the NEC doesn't put any limits on sleeving, so I don't see any code-compliant reason to not do what you have planned.
 
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Old 03-02-21, 05:10 PM
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These sleeves will not be longer than 3' in each section. The challenge with what you are saying is the number of 4" boxes would be quite a lot. In one run, I would need 4 of these boxes 3' apart. And 2 more boxes elsewhere for a total of 6 boxes.

The other issue is where the light fixtures are (and hence where the romex enters into the ceiling cavity) is between joists. I cant place a junction box on anywhere but on a ceiling joist. Which means there is no way to place the junction box right where the hole is.

I looked into using those "remodel" boxes, the one you use the side flaps to tighten behind the drywall and an extension ring on top of it so that the box ends up being level with the EMT but the issue with that is those extension rings that fit the remodel boxes are not made with 3/4" KO which means no 3/4" EMT. And the funny thing is if I use a 1/2" EMT and THHN and splice in those junction boxes, its actually LESS available volume inside the EMT than 3/4" EMT and sleeves NM-B in it.

The last thing I looked into are these special extension rings that you can see below. This one would work (but still would need so many of them on my ceiling) unfortunately none of the electrical supply houses here stock this as they consider it a special item. And because its a special item, they have to buy it 1 carton at a time (25 in each carton).

https://www.homedepot.com/p/RACO-4-i...B&gclsrc=aw.ds
 
 

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