Electrical question on using conduit part II

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Bend a saddle in the conduit.
Try locating an Uglies book.
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I can't bend a saddle, as the double 2x4s are against the side of the electrical panel, they are part of the framing holding the panel. I'd like to just go through the 2x4s, as they don't support anything else.
I'm just wondering if I should switch from 3/4" EMT with setscrew connectors to a different kind of conduit and connector that would require a smaller hole. There will be a box near the panel, so it will just be a short run. I could even butt the box up against the 2x4s and use NMB, since it wouldn't be exposed. What would be best?
On a related note, the KO I want to use is 1/2", how hard would be to enlarge to 3/4"?

Thanks.
Cheers, Wayne
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On Thu, 23 Sep 2004 09:55:02 -0700, Wayne Whitney wrote

Wayne,
You certainly can use NM for the run from the panel to the first box - but that's 3 pieces of NM so you're going to end up with more drilling - you'll need to use multiple knockouts to get the NM into the box and panel - so it won't be a neat job. I recommend you just drill the studs for the EMT. You'll need about a 1-1/2" hole to accomodate the connectors.
Alternatively, you certainly can use 1/2" EMT for this section or for the whole run for that matter. Still don't understand why you're running 3/4" for 7 #12 + EGC.
There are knockout punches (Greenlee Slugbuster) available which can easily enlarge the KO from 1/2" to 3/4" - the tool consists of a punch, a die and a draw stud and usually comes in a set that can handle 1/2" to 2" KO's. They're expensive, but you can rent a set, or try eBay - there are usually used sets listed there.
I agree with SQLit on the book - Ugly's Electrical Reference by George Hart - much cheaper than the other references I recommended.
Be sure to read up on maximum box fill. If I understand your design, you'll have 3 branch circuits running through some of the boxes, with two of them connected to duplexes. With allowances for the duplexes and the EGC, that would require a 4x4x2-1/8 (deep) box with a raised cover, or a 4-11/16 deep box.
Good Luck,
Kenneth
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KJS wrote:

Yeah, it would take two holes, and two extra connections, since one of the 3 circuits just runs through the first box. So I decided against that.
My current plan is just to use a 1/2" x 6" RMC nipple. Then I don't have to enlarge the 1/2" KO, and I can drill a fairly small hole. I know that connecting RMC to a box requires a plastic bushing and a locknut inside the box, but does one normally use a second locknut outside the box? If so, I was thinking that on a 6" nipple secured with a 2-hole RMC strap, it would be OK to omit the second locknut on one side.

Well, there are two reasons, one is that like most beginning DIYers, I tend to overengineer a bit. The other is to allow room for future expansion, for example in case I ever want to put in bigger conductors on the 240V circuit. In fact, I wonder if it is worth using a #10 EGC now for that reason.

That what I've bought. Thanks for the calculation, I went over it and concur. I was surprised to find that the 4x4x2-1/8 box would be too small without the raised cover.
Cheers, Wayne
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On Thu, 23 Sep 2004 15:38:54 -0700, Wayne Whitney wrote

Rigid requires two locknuts plus a smooth bushing. There are combined locknut/bushings which can be used on the inside of the box. Or you can use a rigid compression connector which is NOT the same as an EMT fitting.

Fine. It's a good idea to allow for future expansion. BTW, you could run the 240V circuit and EGC in #10 and still use 1/2". If you're expecting to install a large power tool, why not run the circuit in #10 now?
You may even need to go larger depending on the expected motor load. A 3HP motor has a Full Load Current of 17A at 230V, and a 5HP one has an FLC of 28A. The motor branch circuit conductors should be sized at 125% of the FLC using the appropriate table 310.16 column for the terminal temperature - 75C or 60C. Notice that for 90C wire like THHN, you DON'T use the 90C column. So, a 5HP table saw with 75C terminals requires #10 THHN conductors at 35A. The CB would be 30A - you can't fuse #10 at more than that.
However, it gets more complicated. If the motor starting current draw is high, this size CB might not be enough, so you might want to go to #8 conductors. And for a motor circuit, the CB cannot be larger than 1.15 or 1.25 times the nameplate FLC - which factor depends on the temperature rise and service factor ratings of the motor. Take a look at NEC Article 430 if you want to sweat the details.
A 5HP table saw is pretty big. I've never owned more than a 3HP myself, and that's adequately served by a #12 THHN 230V circuit fused at 20A.

Good. Glad you're up to speed on that. You're now ahead of 95% of DIY electricians.

Regards,
Kenneth
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KJS wrote:

Of course, the motors on consumer brands of stationary power tools don't draw anywhere near that because they lie about the motor HP -- like the 4.5 HP air compressors that operate on 120V and have a 15A plug. They make up for it by also lying about the CFM air capacity. While air compressors are the worst offenders, all power tools do the same thing.
The only 5 HP compressor I've ever seen that said it drew 28 amps was a Quincy 2-stage [industrial] compressor.
It's best to ignore the HP rating and go with the current rating on the motor itself.
Best regards, Bob
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OK, it is done, thank you for all the wonderful advice. I ended up using a 1/2" x 6" rigid nipple, 4 locknuts and 2 bushings. I thought I could achieve a smaller hole using rigid instead of EMT, but then I had to allow for the exterior locknut.
BTW, these bushings are nice, should I use them on the EMT connectors as well? I'm assuming here the threads on the EMT connector match the threads on the rigid conduit. I guess the bushings are not required on EMT since the connectors are made smooth and there are no field cut ends inside the box.

That's a good idea, I'll put in a 20 amp receptacle and a 20 amp breaker, but just run it in #10 wire. That also conveniently distinguishes the circuit.
Thanks again for all the guidance.
Cheers, Wayne
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On Thu, 23 Sep 2004 19:33:12 -0700, Wayne Whitney wrote
wrote:

Glad to hear of your progress. You certainly can use insulating bushings on the threads of EMT connectors, but they're not required by code. There's also generally not enough thread on an EMT fitting for the locknut and a bushing. It's sometimes useful to use a bushing for the pull (to protect the outer nylon coating of THHN), then remove it.

Regards,
Kenneth
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<< BTW, can anyone suggest a good practical reference on using EMT and other conduits? >>
Get a copy of the Benfield Conduit Bending Manual, ISBN 0-87288-510-0. It will give you detailed tips for working with EMT and other conduit. Over the years I have noted that the journeyman most electricians grant the greatest respect is the man on the crew that can run hundreds of feet of complex conduit every day. You hear comments like, "He did the whole darned twenty-third floor sub and they carried out the scrap in a wheelbarrow." Good conduit installations are the hallmark of good electrical work. The man who can get it done without a big flock of adapters, offsets and widgets IMO is a real pro. HTH
Joe
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<snip>
Not for nothin', but more time has been spent researching, questioning, debating and re-debating this little project than it would have taken an electrician to install the damn outlets.
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Here wrote:

True, but everyone has to start somewhere.
Thanks Wayne
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On Thu, 23 Sep 2004 15:40:05 -0700, Wayne Whitney wrote

Yes, a lot of thought and postings. And now Wayne will probably be better at his DIY electric project than 95% of those who attempt a similar one. If minimal postings were the measure, Budy, there'd be no purpose to this NG - the only response would be: call a pro :)
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Too true, now... let's get on to the buss trolley option which we haven't even begun to dabble in.
If the op were to excersize this option, in say the 40a model, there'd be no need for understanding box fill, conduit bending methods, or the pros/cons of leaving room for future upgrades! :-)
http://www.uecorp.com/trolley-system.asp
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