EMT Design Question

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I put a pdf file on my website which shows my current thinking about making an HTTN run through conduit. Evidentally, Rigid (EMT) is a better choice than Flexible Metal Conduit. BTW, the EMT that is not vertical will be on the ceiling; my SketchUp skills still need more work. Please take a peek:
http://web.newsguy.com/MySite /
As you can see from my pictures, there are 3 electrical boxes--the switch box mounted behind the wall and the other 2 bexes which are surface mounted. The pictures basically show my current idea. I am left with a question or two (if you would be so kind):
1. How is the weight of the vertical piece of EMT supported? It seems that there would be quite a bit of weight on the switch box on the bottom as I don't think the typical clamps that I've seen are designed to prevent the EMT from sliding underneath them. Maybe I need special clamps, extra support for the switch box, or something else?
2. I assume, that to attach the 2nd box (the one on the wall), that the end of the EMT (bent at 90 degrees) is pushed through a hole, connected to the box (with a screw-type connector) and then the box is screwed to the stud through the wall. Please correct me if I am missing anything here.
At least I came up with a way to avoid working at the top-plate near the eave (which I could not figure out how to deal with)!!! Thank you for your patience!
Bill
P.S. Doug taught me a little about LL (and LB,LR) conduit body connectors. These do not seem to make sense here unless you're want to run the wire before you finish the drywall. No one would use one of those in this model, would they?
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wrote:

Show your wiring and conduit maps, too, eh?

The nearly-a-pound is taken up by a strap screwed into the stud. ;) http://goo.gl/5AQO6 Or switch to stapled romex?

Ceiling box surface mounted with fmt to in-wall box might be my choice. Romex in wall, stapled to stud. http://goo.gl/UYFER

http://goo.gl/mKpvn
-- It is characteristic of all deep human problems that they are not to be approached without some humor and some bewilderment. -- Freeman Dyson
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Larry Jaques wrote:

I did those in pencil several times, except for necessary revisions. I'll update my SketchUp drawings. The drawings do force one to address the tough questions!

Stapled romex runs to the switchbox and HTTN in EMT runs up (behind the wall). Running romex after the switchbox may be unthinkable--UNLESS I color-coded the 3 cables (or use your long FMT solution). It also raises the wire count in the destination box.

I was thinking along these lines until I read: FMT is not intended to run farther than about 48", and that EMT was preferred to FMT. Your idea seems quite acceptable to me... Does the FMT just enter the wall through a hole in the drywall? That just cannot be right, can it?
White, right???
Bill
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wrote:

Right, get a deep one or use a duplex box for the room. But it's only 3 pieces of 14/2(grounded) romex and 7 14ga HTTNs (lone larger ground if OK by the NEC?)
I use very large needle nose pliers with heatshrink on the tips to bend wiring in breakout boxes, then stuff it so the lid closes without any problems. It works especially well with the dadgummed 10ga wire. That stuff might as well be steel, as far as bending it with human fingers goes. My fingers are like vise grips until it comes to stiff wire.

Ayup, but it plugs into fittings, then into a box. I've seen gray underground style PVC conduit used by itself, hanging into midair with wiring coming out. To code? Prolly not. ;) ENT is blue plastic conduit for use indoors. Time to research it, Bill! <evil grinne>

Walls, ceiling, and floor, yes. FMT/ENT? Up to you, but I thought you'd want color coordination in your EMT and FMT, so I mentioned painting the conduit and connectors. But the blue is awfully pretty. I'd leave it.
-- It is characteristic of all deep human problems that they are not to be approached without some humor and some bewilderment. -- Freeman Dyson
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Larry Jaques wrote:

You would be using all of the fixtures as "electrical boxes", correct?
So, if I understand your design correctly, I wouldn't need any more boxes other than the "switchbox".
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wrote:

Correctamundo. There are usually lots of knockouts in fluor fixture bases for connecting EMT fittings. Use those for runs for all three switches. Check the NEC for congestion. I think 3 pairs will be OK in 1/2" EMT with a single larger ground, but check.
-- It is characteristic of all deep human problems that they are not to be approached without some humor and some bewilderment. -- Freeman Dyson
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Larry Jaques wrote:

Yes, there are *lots* of knockouts on the fixture bases. I need to check the "wire space" of the fixture bases and of other pertinent specifications. If the fixture bases aren't large enough that will create mucho extra work.

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wrote:

I've never seen a fluor box which didn't have ample space for wiring. Mine are for T-12s, so there's room for about 150 extra 14ga THHNs in each. ;)
Even in the little T-5 HO boxes, there's probably enough room for a dozen extra wires. The further addition of half a dozen extra wirenuts is doubtful, though.
-- It is characteristic of all deep human problems that they are not to be approached without some humor and some bewilderment. -- Freeman Dyson
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Larry Jaques wrote:

I was thinking in terms of the "wire space" of the box (as in how many wires can be in there, not how much wire can I pack in there). As you know, most/all electrical boxes have their cubic inches written inside. I'll have to get out my chart to do the calculation.
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Bill wrote:

Larry Jaques wrote:

Not finding the "wire space" of my Lithonia fixture at Lithonia.com, I took out my ruler: The body of the fixture is 48" x 4" x 1.5" = 288 cubic inches.
This is an over-estimate becuase of the ballast, but it seems fair to say one can pass a Lot Of Wire (LOW) through this fixture, or a similar fixture!
Bill
*This is neither an offer to sell nor a solicitation of an offer to buy the light fixtures described above. An offering is made only by the prospectus. The sales and advertising literature, and in particular the LOW numbers, must be read in conjunction with the prospectus in order to fully understand all of the implications and risks of the fixtures to which the prospectus relates.
A copy of the prospectus must be made available to you in connection with any sale. No sale is made except by a prospectus filed with the Department of Law of the State of New York. Neither Home Depot, the Attorney-General of the State of New York nor any other state commissions has approved or disapproved of these fixtures or determined if the corresponding prospectus is truthful or complete. Any representation to the contrary is a criminal offense. (!)
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You cannot use these fluorescent fixtures for a wire raceway. Only the wiring necessary for the fixture and other daisy-chained units, downstream, on the same circuit, can be installed inside. Don't forget to subtract two wires for each wirenut connection inside,in your calculations...LOL
------------------ "Bill" wrote in message Not finding the "wire space" of my Lithonia fixture at Lithonia.com, I took out my ruler: The body of the fixture is 48" x 4" x 1.5" = 288 cubic inches.
This is an over-estimate becuase of the ballast, but it seems fair to say one can pass a Lot Of Wire (LOW) through this fixture, or a similar fixture!
Bill
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On 8/23/2011 9:05 AM, m II wrote:

That's all he's *planning* to put in there -- what made you think otherwise?
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--- Begin Quote ---
Section 410-31 of the NEC (1999 Edition) states:
Fixtures shall not be used as a raceway for circuit conductors.
Exception #1: Fixtures listed for use as a raceway Exception #2: Fixtures designed for end-to-end assembly to form a continuous raceway or fixtures connected together by recognized wiring methods shall be permitted to carry through conductors of a 2-wire or multiwire branch circuit supplying the fixtures. Exception #3: One additional 2-wire branch circuit separately supplying one or more of the connected fixtures described in exception #2 shall be permitted to be carried through the fixtures.
Branch-circuit conductors within 3 inches of a ballast within the ballast compartment shall have an insulation temperature rating not lower than 90 degrees C such as Types RHH, THW, THHN, THHW, FEP, FEPB, SA and XHHW.
--- End Quote ---
Most consumer grade flourescents aren't listed as raceways. That pretty much leaves exception #2 as the guidance for this application. It also limits you to 2 two-wire or 1 three-wire and 1 two-wire branch circuits for the string of fixtures.
Do note the "recognized wiring methods".
Please also be aware that the temperature rating of the conductors being passed through must be at least 90c (THHN should suffice, but never use NM or NM-B)
scott
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Scott Lurndal wrote:

Scott.
There is only 1 15A branch circuit. However, I had planned for it to "split" through 3 switches in the switchbox and pass the resultant 5 wires--3 hot, 1 neutral, 1 ground, through the fixtures as necessary to power them. If I understand correctly, this would qualify as a single 2-wire branch circuit, wouldn't it?
TYVM! Bill

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Absolutely. It's still one circuit, and it's still a "two-wire branch circuit" despite there being four wires (the ground is not counted) because your three hots are derived from the same point.
In any event, since the exception permits a multi-wire branch circuit, that particular point is moot anyway. It's clearly a single circuit: there's only one single-pole breaker.

Which would include, presumably, being connected by a properly-installed section of EMT.

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Doug Miller wrote:

Thank you for your confirmation Doug!

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Yes. The extra wires in this case do not matter[*], since they'll sum to the maximum branch circuit current (15a, in this case). This is would not be considered a multiwire branch circuit, however, per article 100 and 210-4, which requires a potential difference between the ungrounded conductors.
In other words, you have multiple paths for the same branch circuit.
scott
[*] subject to raceway fill guidlines.
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EMT and Rigid conduit are two different things. EMT uses setscrew or compression fittings, while rigid conduit is threaded and uses threaded fittings.

Flexible metal conduit is more often subject to local jurisdictional restrictions and is not suitable to be used as a grounding conductor.

Use EMT conduit clamps of the appropriate size. Check the NEC for the appropriate spacing (iirc, 3' from junction box, and every 6').
Or use unistrut and unistrut conduit clamps.

Either bend an offset in the emt (requires skill), or buy an offset setscrew connector to connect the box to the conduit (unless you're using the unistrut solution).
scott
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Scott Lurndal wrote:

I didn't know that. Thank you!

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THHN
Rigid metallic conduit (RMC) and electrical metallic tubing (EMT) are not the same thing. For your application, you definitely want EMT. Among other things, you can't bend RMC, and you can EMT. RMC is waaay overkill.

Agreed.
Just secure it to the wall in a couple of places. It really doesn't weigh all that much, not enough that you need to worry about it.

Depends on what type of box you're using.

I still think that's going to prove to be the easiest route for you (assuming you're still intending to surface-mount all of this).
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