Rough-in for fluorescent wraps?
davidmeiland
| Posted in Energy, Heating & Insulation on
I have ~12 fluorescent ceiling fixtures going into my shop. They’re 4′ 2-bulb fixtures, very common in work areas. They have a number of knockouts at each end, and a few in the middle–on the “back” or “top” of the fixture, against the ceiling. It looks to me like a bushing or romex clamp could go into a knockout, and the wire brought into the fixture for stripping and nutting to the fixture wires. Is this correct? Is this done with a box roughed into the ceiling, or can the romex simply be stubbed out thru the drywall? In many cases there will be 2 romex at each light because they are chained together.
Replies
David,
It sounds like you are hanging common shop/workbench 4 ft fixtures with chain, correct? You plan to rock the ceiling? If so then you use rectangular boxes with duplex receptacles, and install a standard 3-wire pigtail on the fixture. The pig tail must have a clamp through the fixture punch-out or strain-relief (sometimes there is a smaller hole for this).
If you are screwing it to the ceiling, then an octagonal "ceiling box" needs to be over it, OR you can run conduit between the fixture ends.
Mention this only because I recently did it:
In my shop (a detached garage) I wanted to have the fixtures controlled by 3 switches. First switch for the bench lights, which are almost always on. The bay lighting 1/2 on one switch and 1/2 on the other alternating units. I can vary the light level this way. Arranged like this, imagine one bay lighting switch is off:
wall------------------------------------------wall
ON OFF - ON - OFF - ON - OFF (row of fixtures)
bench bay
ON ON - OFF - ON - OFF - ON (row of fixtures)
wall------------------------------------------wall
To do this for the bay lights a 12/3 plus ground went from box to box, with split receptacles (red on one yoke and black on the other).
Nothing astounding here, typical for commercial work to save energy.
I am going to screw the fixtures directly to the ceiling, not hang them from chains. I assumed that an electrical box should be mounted over each fixture, but I'm not clear from your post what's between the box and the fixture (which will essentially be in contact). I can imagine stripping the wire in the electrical box, and then extending it thru a bushing in the fixture KO and tying it to the fixture wires. I can also imagine extending it thru a romex clamp and a cover plate on the electrical box, and then stripping the wire that protrudes thru the clamp (the fixtures have a very large KO near the center).
Later on I'm going to dig out a couple of books and see if they show this.
I did exactly what you are describing in my workshop. I drilled a 1&1/2 inch hole in the OSB ceiling over a knockout on the fluorescent fixture, installed a romex connector into the knockout (the larger hole makes clearance for the connector), screwed the fixture up, and ran my feed cable in. Then I connected to the next fixture through more connectors at the end knockouts. At the end of a row of fixtures, I went back up into the ceiling the same way and back down again into t he first one in a new row. Etc. No boxes required.
If your fixtures are already mounted, drill a pilot hole in the center of the knockout, and go above and drill down with a spade bit to the metal. The just drop the fixture enough to attach the connector.
Some of the details of what is code compliant and what isn't depend on your specific fixture. Given your inquiry, I assume you want to be code compliant. I don't know anything about your fixture other than it is a 4 ft fluorescent unit with knockouts and no cord installed. You want to mount it directly to a sheet rock ceiling. I don't know if the rock is in place or if you have access from above.In my area, poking wiring through a ceiling without a box is not permitted. Even if it were "overlooked" I still won't do it, since the ceiling box provides more options for changing things later on and the NM is securely clamped where I can see it.First, I would want to be sure that the fixtures are not labelled "for suspended use only", like many shop lights are- but they usually have pre-wired pigtails and chains in the box. Just checking.Second, you said there was a larger knock out in the center of the back of the fixture. If it measures 1 1/2 inches, then it is the wiring access hole. You knock it out in order to mount over a ceiling box. Check that back of the fixture covers the boxes you pick. In some cases the plastic old-work boxes have flanges that the fixture doesn't cover. It's a cosmetic thing. I use metal octagonal boxes for new work as they are a bit smaller.Third, check for the wire temperature rating allowed in the fixture. My fixtures say the supply wires have to be rated 90C within 3 inches of the ballast. The center access hole is within 3 in. of the ballast, so the branch circuit 60C wires had to be pushed back up into the ceiling box after the wires were nutted.If you have the 90C requirement, check for a small knock out next to the big hole, and a plastic bushing in the box to fit the small hole. The manufacturer's diagrams showed the fixture wires going up through the bushing, then you pull them back into the fixture via the access hole. Make the connections and push it all back out of the fixture.Exposed NM (Romex) is not permitted in finished spaces. If that becomes an issue, you can run BX cable with 90C wire from end to end. Then BX is run to a box.
Edited 2/12/2007 3:42 am ET by lcdeyes
Unbelievably, the only electrical book I could find here is a Sunset book. It shows a ceiling box roughed in and the large diameter KO removed from the fixture. The fixture is placed directly over the box, so the KO is centered. The conductors are stripped inside the ceiling box and then brought thru into the fixture for connection. There is no cover plate on the ceiling box and no bushings or clamps shown. Thinking about it, this is what I have seen when I've demo'd fixtures like this for jobs in the past.
I'm going to rough the whole thing in using boxes. It's all open joists right now so I can do whatever I want.
It's hard to get info from the electrical inspectors here. They are not local, they fly or ferry over. Inspections are scheduled via answering machine. They do not give a time for inspection, and will come and inspect a job with no one there, sign the permit, greentag the panel, and leave. If I wait all day I can talk to whomever shows up and ask for his method.
I'm not sure if I'm picturing this correctly or not, but it seems to me that it would be easiest to surface mount a junction box, and extend conduit to one or more surface mounted light fixtures (make sure they are rated for surface mounting). Then use conduit to connect the light fixtures together.
No reason to run all that pipe on my new lid if I can run romex hidden above instead.
Please note my goof on modern non-metallic (NM-B) insulation ratings. It is 90C not 60C. The derating for ampacity calcs still use the 60C value, however. The source of my error."It's hard to get info from the electrical inspectors here. They are not local, they fly or ferry over."Wow. With all the constuction going on in the San Juans, you would think you'd have your own. Sounds like a nice job for someone who wants to live on a boat. No wonder all those waterfront mansions are burning! Or is that just eco-terrorism, island style?
Electrical here is run by the state, the Department of Labor and Industries to be exact. They send an inspector two days a week to inspect jobs over here. From what I understand, 1-2 guys are "assigned" to island duty for a period of a couple of years. Some of them like it, some want out. We recently got a new guy, I haven't met him yet. On clear days they make a short flight, and keep a jeep at the airport.
Where are you finding NM cable. I don't think that it has been made since the mid 80's, but it might have been made into the 90's.Anycase the current non-metalic sheathed cable is NM-B. It has 90C wiring.And the NEC specifically says that NMB can be run exposed. Two conditions. One it has to closely follow the building surface. The other is that if it is if it is "subject to phyisical damage" then it needs to be protected. That can be done with guard strips, put it in conduit, etc. Subject to phyiscial damage is undefined and up to the inspector.But otherwise it is allowed unless the local modified that section of the code when the adopted it.One common use where NMB exposed is for undercounter lighting. Runs the 10" or so from the wall to light under the bottom of the top cabinet..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Sheesh. You are correct about 90C insulation for the NM-B, which replaced NM in the mid-80's. I have always been derating it to 60C for ampacity, which today I checked and is still correct to do so for the NM-B. I never paid close enough attention (or forgot somewhere along the way) that the insulation rating upgraded from 60C to 90C.Edited my incorrect post, and noted my error.So I guess I've been shoving the 90C wires up into the ceiling box for nothing. Oh well, not a big deal. Now that I think of it, since the change was made in the mid-80's, I never had a need to use the fixture as a raceway for non-metallic cable. For any of the end to end wiring, like in a drop ceiling, I used armored cable.I checked, and yes, I still have a partial spool of old NM. Is it worth anything on the "Antique Roadshow"?Thanks for catching my error! BTW, is it ok to poke nonmetallic out of the ceiling w/o a box? Although I've never believed it to be good workmanship or wise, I have seen it done on a few occasions.Now you have me doubting all the finger wagging I've done.
"BTW, is it ok to poke nonmetallic out of the ceiling w/o a box? Although I've never believed it to be good workmanship or wise, I have seen it done on a few occasions."I don't think the poking out the ceiling or the wall is the problem. It where is whether the connections are made in a "approved" box or not. I used "approved" because like CAP said the flouscent fixtures are often used for connection although all them are not so marked.It is common in older house for bathroom fixtures to connected to rommex just sticking out the wall and the fixture screwed to the wall. When I see those I add an old work box.In my garage I had some extra 8ft-2 tube strip lights that I put up. I don't remember why I mounted them on the walls, but I did. About 3" below the ceiling. I put a romex connector in the side and punch the NM down the couple of inches to the fixture..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Yup, your first thought is correct. Stub out the cable and use a romex clamp in the KO in the fixture. The fixture itself serves as the junction box. If you're going to through-wire, a picky inspector might want to see the fixture listed for feed-through wiring. Every shop light I've ever see has plenty of room for the splices for feed-through wiring, however.
Now there are some fluorescent fixtures (the circline ones, for instance) that have no space inside the fixture for making the splices 'tween building wire and fixture wires. Those need a 4R fixture box or equivalent.
You cannot use a single-gang outlet box for a light fixture; fixtures are required to be mounted with 8-32 screws, and the outlet (switch) box is designed for 6-32 device mounting screws. It has to do with the fact that light fixtures are heavier than a receptacle or switch. You can however, hang a smoke detector from a switch box, because the smoke weighs 'bout nothing.
Cliff
NM wire (60C) is not allowed in a fixture rated for higher temperature wiring. [Whoops- I'm editing this: NM wire went out in the mid-80's. The NM-"B" conductor insulation does have a 90C rating. The conductor ampacity still has to be determined at 60C. That's why I goofed on the insulation temp rating]A fixture cannot be "used as a junction box", unless rated for that purpose. It does not matter if there is room inside or not. An example of fixtures typically rated for use as a junction box are recessed lights. Fixtures with exposed metal parts must be grounded, unless equipped with a two-prong plug.You cannot mount the light fixture directly to a device box, perhaps that is what you meant. A single gang box can be used with a ceiling fixture with a cord. The fixture must be designed for use with a cord. The fixture might not include the cord, so the temp rating of the cord's insulated conductors must be considered. An example of this is the suspended shop light, where the cord plugs into a receptacle. The receptacle is allowed to be in the ceiling, just like a garage door opener receptacle. Notice that the shop light cords are only a bit longer than the suspension chains. For a new installation consider where the receptacle needs to be, usually directly over the light for the cord to reach. The receptacle would likely be switched.If the same fixture is rated for permanent installation (screwed to the ceiling) it must be hard wired.Just to clarify your ceiling box statement: It is not a requirement that a fixture be screwed with 8-32's to a ceiling box, unless the fixture is designed for that type of installation. Obviously, a 4 ft. fluorescent is not provisioned to screw directly to the ceiling box, so it must be screwed to the rafters, toggle bolted, or securely fastened in some way. There are usually some dimples to drill or holes for that purpose.Edited 2/12/2007 3:44 am ET by lcdeyesEdited 2/12/2007 3:50 am ET by lcdeyes
Edited 2/12/2007 1:16 pm ET by lcdeyes