Electrical question on using conduit part II

Thanks to everyone who responded to my earlier query on conduit. BTW, can anyone suggest a good practical reference on using EMT and other conduits? I have "Wiring a House" by Rex Cauldwell, but that really only covers NM cable. I also purchased the 2002 NEC, but that's not a practical reference.

My last point of confusion is this: I want to put in a horizontal run of boxes to the left of the panel, but immediately to the left of the panel are two vertical 2x4s. They are part of a narrow stud wall built just to support the panel. How should I deal with this?

I assume I should just drill through the two 2x4s. That would be alot easier and require way fewer bends than going out somewhere else. Should I butt the first box up against the 2x4s and use NM-B just for this first run? Or should I use conduit?

For conduit, what type of conduit and connector should I use, in the interest of minimizing the hole size? Everywhere else I'm using 3/4" EMT with setscrew connectors, but I assume that would be a poor choice. There will 7 #12 wires, EGC plus 3 circuits, and the knockouts in the relevant area of the panel are all 1/2" only. So perhaps 1/2" conduit would be best for this very short run?

Any advice would be much appreciated, there seem to be too many options relative to my experience.

Thanks, Wayne

Reply to
Wayne Whitney
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Yah

This in a unfinished basement inna residence for a handful a branch circuits......

Last I heard the requirement for any conduit at all was for commercial use only...

String nm cable under the joists, and down the walls, leaving them exposed and just be done with it.

If the next owner dont like it then offer to disconnect and abandon the branches at the service panel before he takes possesion.

Local codes may vary, so be sure to check with your permitting authority.

HTH

Reply to
PrecisionMachinisT

On Wed, 22 Sep 2004 22:24:30 -0700, Wayne Whitney wrote (in article ):

Wayne,

Not sure why you're running 3/4" EMT. 1/2" is rated for up to 9 #12 THHN conductors, and that's not a hard pull by any means. If the studs are there only to support the panel and are not otherwise load-bearing, just drill them for the 1/2". A 1/2" right-angle drill and ship-auger bit is the preferred tool...

As to books on wiring methods: there's the American Electrician's Handbook by Croft, and Practical Electrical Wiring by Richter. They're both expensive, so I'd try to take a look at them first before buying to see if they're useful to you.

Good luck.

Kenneth

Reply to
KJS

rather than cutting a big hole for a fitting next to that panel perhaps just use a 90 deg connector or LB out of the panel bottom (or top)

Reply to
bumtracks

Bend a saddle in the conduit.

Try locating an Uglies book.

Reply to
SQLit

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

Reply to
Wayne Whitney

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

Reply to
Joe Bobst

On Thu, 23 Sep 2004 09:55:02 -0700, Wayne Whitney wrote (in article ):

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

Reply to
KJS

In article , PrecisionMachinisT wrote: ...

I respectfully disagree. Reason is: Exposed NM right on a wall surface doesn't pass the "subject to damage" test. I'm in the office now, so I can't quote chapter and verse of the NEC on it, but if I remember right, NM cable (a.k.a. Romex) always has to be protected by something (like a layer of drywall, some wood, conduit, etc.) at heights below 7', even in basements. Obviously, this does not apply in areas that are never used, like non-standing-height attics.

I'll try to look up the section in the NEC tonight at home.

Reply to
_firstname_

No prob, lemme know what you find--I would like to see it as basically this is how I wired our shop out of the top of the service panels and going up to the ratrace, and the local inspector passed the job and he even put a personal note on the ticket for me "Nice job!!!" or somesuch........

Do note the top of the panels is at appx 5'6" though, and NOT at bench height.

Reply to
PrecisionMachinisT

You can always use PVC but you don't get that industrial look guys like.

Reply to
Greg

"subject to physical damage" is really a judgement call. There are usually some local guidelines but thwe final answer is always going to be common sense or the inspectors opinion, not always the same thing. ;-) The compromise is Smurf tube (ENT) or MC cable.

Reply to
Greg

On Thu, 23 Sep 2004 11:16:13 -0700, _firstname_@lr_dot_los-gatos_dot_ca.us wrote (in article ):

Ralph,

I respectfully disagree in part with your respectful disagreement - Rx does not always have to be protected by a layer of something at heights below 7':

Article 336 specifically allows using NM for exposed work. It must be run in accordance with 336-6, which calls for protection from physical damage where necessary by conduit, guard strips, etc. Except for passing through a floor, no specific definition of where the cable would be subject to physical damage is given.

NM run in accessible attics has the same requirements as given in 333-12 for AC cable (guard strips under certain conditions), which also references

300-4(d) (protective plates if cable is less than 1 1/4" from stud surface).

You will find the 7' rule in 333-12(a) which calls for guard strips if the cable is run across the face of rafters or studs within 7' of the floor or joists in accessible attics. There is no exemption for "non-standing-height" attics, if they are accessible.

There is no 7 foot rule for unfinished basements.

However, I'm certainly far closer to your position than that of PrecisionMachinisT. Under 336-6(c), in unfinished basements, you have to protect NM "under the joists" unless it's larger than 8-3 or 6-2. Smaller cables have to be run through bored holes or on running boards. Under

300-4(d) NM run on the exposed face of studs has to be protected. If it is run on the side face at least 1-1/4" from both surfaces, it does not.

In the proposed installation, the question of whether and where the cable is subject to physical damage would be up to the AHJ. I have worked on many installations with exposed NM in unfinished basements, garages and attics which passed. It does take a bit of care to route the NM properly, and many DIY installations are inadequate.

All of that being said. I agree that the proper wiring method for this basement workshop is EMT, and I'm glad the OP is designing it that way.

Regards,

Kenneth

As a

Reply to
KJS

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.

Reply to
HA HA Budys Here

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

Reply to
Wayne Whitney

True, but everyone has to start somewhere.

Thanks Wayne

Reply to
Wayne Whitney

On Thu, 23 Sep 2004 15:38:54 -0700, Wayne Whitney wrote (in article ):

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

Reply to
KJS

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

Reply to
zxcvbob

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

Reply to
Wayne Whitney

Hi Greg.

I exaggerated a little mainly to get the ball rolling and to let the OP realize there are other easier and less expensive methods is all--not that I have any doubts a mettallic raceway isnt probably the most durable setup.

As I said before, I have kinda taken a liking to using emt and then transitioning to the liquidtite flex at a handy box

Reply to
PrecisionMachinisT

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