Conduit to pick?

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  #1  
Old 08-17-04, 07:21 PM
isuras2
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Question Conduit to pick?

I am going to wire inside my garage. The wiring will not be in-wall so I will need conduit. The total length of wiring will be about 24 feet with about 8 outlets along the 24 foot length. My problem is I don't know which type of conduit to get. What are your thoughts?
 
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  #2  
Old 08-17-04, 07:28 PM
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EMT with set screw fittings. If you will ever do any conduit work again invest in a nice hand bender.
Depending on how many circuits/wires you will have " should be fine.
 
  #3  
Old 08-17-04, 07:48 PM
rlrct
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Are you planning on these outlets for a workshop? Are any of these going to be 240v circuits? If yes, you'll probably want to install multiple conduit runs because of derating. If you have more than 3 current carrying conductors in a conduit, you need to upsize your wire. If you were planning on (2) 120v circuits and (1) 240v circuit you'd clearly be into derating.

It would help if you could identify what you're planning for circuits.
 
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Old 08-17-04, 08:01 PM
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rlrct, what you are saying is absolutely true.
Fact is though he is only installing 8 receptacles so as long as the current carrying conductors are less than 10, which they will most likely be, derating is a non-issue.

Don't forget, derating is done from the actual amperage numbers, not the 15 & 20 amp figures for #14 & #12 as per 240.4(D).
#12 THHN, @ 30 amps actual, with 9 current carrying conductors x 70% derating factor is still 21 amps.
After ten current carrying conductors the numbers drop off dramatically.
 
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Old 08-18-04, 04:49 AM
rlrct
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Originally Posted by Speedy Petey
Don't forget, derating is done from the actual amperage numbers, not the 15 & 20 amp figures for #14 & #12 as per 240.4(D).
#12 THHN, @ 30 amps actual, with 9 current carrying conductors x 70% derating factor is still 21 amps.
Yeah - I was tired when I wrote that response.

It's my understanding of derating, though, that we need to take the temperature rating of the terminals into consideration. Even though THH(W)N is rated at 30 amps for #12, that assumes the 90* column. Our residential breakers are only rated for 75*, so we'd need to use the ampacity from the 75* column as a starting point. Granted, using 25 amps * an 80% derating factor which gives 20 amps still means 4-6 current carrying conductors in the conduit is fine. That would allow the (2) 120v + (1) 240v 20 amp circuits I quoted as an example, so he's still OK with the #12 (means I was still wrong). Am I misstating the derating process, based on my understanding of the need to consider temperature (let's not even go into ambient temp, like conduit through an attic)?
 
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Old 08-18-04, 06:20 AM
isuras2
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I am going to wire the 8 outlets for 110V at 20A. This should run anything I will have in there. I will eventually get an air compressor, but not sure about if it will be 110 or 220. Would it be better to wire it now so it is done or to wait until I get the compressor?
 
  #7  
Old 08-18-04, 07:51 AM
rlrct
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Originally Posted by isuras2
I am going to wire the 8 outlets for 110V at 20A. This should run anything I will have in there. I will eventually get an air compressor, but not sure about if it will be 110 or 220. Would it be better to wire it now so it is done or to wait until I get the compressor?
I would run (2) 120v circuits and alternate the outlets. 8 outlets over 24' means an outlet about every 3', so you'd have 2 circuit's worth of power within easy reach anywhere in the garage. If your compressor is 120v, you could simply use 1 circuit for that and the other for other tools/machines. With the conduit, you could always pull the wires for a 240v circuit if you need to.

When you run the conduit, don't forget to leave a pull string in each section for future pulls. I'd suggest putting your receptacles and conduit at least 4' off your garage floor so you can lean plywood against the wall and not have it covering/hitting stuff plugged in. Remember that garage outlets need to be GFCI protected, so the first receptacle in any 120v circuit should be a a GFI receptacle.

When you buy your conduit, get an extra stick to practice bending with. 90 degree bends are pretty easy, but your first pair of offsets won't be pretty (at least mine weren't). You need to bend offsets into the conduit because the knockouts in your boxes aren't flush to the wall. If you take a piece of conduit and, without bending offsets, run it from box to box, the conduit will be hanging in mid-air. Yeah, you can screw a block of wood/piece of plywood to the wall to use as a cleat to screw a conduit clamp to. The problem is that having a pipe hanging out in the air like that is an awfully tempting place to hang things and you can't do that (hang stuff on the EMT).
 

Last edited by rlrct; 08-18-04 at 08:15 AM.
  #8  
Old 08-18-04, 09:38 AM
isuras2
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Is the 1/2" EMT conduit big enough to put (2) 120v, 20a circuits with the possibility of a third 240v line & outlet for an air compressor? I am thinking of putting the 240v line/outlet in now while I am wiring the 120v stuff. If I try to put the 3 circuits into the same conduit, then I would run into derating?
 
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Old 08-18-04, 10:15 AM
rlrct
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You don't need to worry about derating with (2) 120v and (1) 240v 20 amp circuits run with #12 THHN/THWN in a single conduit.

3/4" EMT isn't a bad idea - the extra space will make it a little easier to pull stuff. If you ever decided you needed a 30 amp circuit, it would give you the room to redo things and pull larger conductors easily. It's a little stiffer to bend, but that's not really anything to worry about. I used 3/4" on the stuff I did.
 
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Old 08-18-04, 05:07 PM
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rlrct-

It is my understanding that even for derating you still start with the listed temp rating and ampacity of a conductor.
You are correct that the terminal temp has to be taken into account when figuring actual amperage. About the only thing rated at 90*c is wire. I don't think I've ever even seen a 90*c lug or terminal.
These are basically the reasons I don't usually bring up derating to a DIY'er since they usually don't get into an area where it is a factor. We on the other hand.....

Good discussion.
 
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Old 08-18-04, 06:20 PM
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For reference the last sentence of 110.14(C) is where it is permitted to use the 90 deg rating for derating purposes.
 
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Old 08-18-04, 07:11 PM
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Cool Ron. I knew it was in there. I had forgotten where it was and didn't look it up before. When I went there I already had it highlighted in my NEC.
Thanks for the reminder.
 
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Old 08-18-04, 07:39 PM
rlrct
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Originally Posted by HandyRon
For reference the last sentence of 110.14(C) is where it is permitted to use the 90 deg rating for derating purposes.
Thanks for the code reference!
 
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Old 08-18-04, 08:01 PM
isuras2
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Is Romex better to use or individual wires?
 
  #15  
Old 08-18-04, 08:06 PM
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Inside conduit, individual wires is the clear choice.
 
  #16  
Old 08-19-04, 09:48 AM
isuras2
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Originally Posted by John Nelson
Inside conduit, individual wires is the clear choice.
So individual wires is the clear choice, but it is possible to use Romex in conduit as I intend to use it? It isn't a code violation or anything?

GFCI outlets on the first outlet in the circuit. Are the GFCI required by code or just a good safety practice?

Thanks for all your help.
 
  #17  
Old 08-19-04, 09:57 AM
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1. Controversial. I'm not going to tell you not to. But code probably requires larger conduit than you might otherwise think. Give us details and we'll give you details.

2. Code required.
 
  #18  
Old 08-19-04, 10:22 AM
isuras2
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I plan on running 3 circuits: (2) 120V and (1) 240V circuits with 20A. First outlet on each circuit will be GFCI. The conduit will be 1" EMT. I would like to use 12/2 Romex wire because that is the wire I have. With individual wires the clear choice, is it possible to use Romex in conduit as I intend to use it? Will the 3 circuits of Romex wire fit into 1 EMT conduit?
 
  #19  
Old 08-19-04, 11:15 AM
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So you're asking if three 12/2 cables can be put in one 1" EMT conduit? I'd have to run the calculations later but I'm going to guess that the answer will probably be no. Even if allowed, it'll be as hard as the dickens to get them through and you'll probably damage the cable doing so. Use wire lubricant. If someone else doesn't beat me to it, I'll try to provide the calculations tonight.
 
  #20  
Old 08-19-04, 11:17 AM
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You would violate code to 3 12-2 NM-B in a 1" conduit. I believe that you would be pushing it even trying 2.

You will have fewer headaches running individual wires.

-Jon
 
  #21  
Old 08-19-04, 11:48 AM
isuras2
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Originally Posted by winnie
You will have fewer headaches running individual wires.
So I should get individual wires. So, for each circuit I need #12 THHN wires: black (hot) and white (neutral)? Do I need a third wire for ground?
 
  #22  
Old 08-19-04, 12:10 PM
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For each 120V circuit you will need 1 hot and 1 neutral. At a _minimum_, use Black for hot and white for neutral. Note however that it is important to keep separate circuits separate. I recommend that you try to use different colors for the different circuits, for example: black and white for 1 circuit, then red and white with red strip for the second circuit. You could also use _grey_ for a second neutral.

For each 240V circuit you will need 2 hots. Again, these could just be black, but I recommend that you pick two additional colors (say brown and purple) to identify this as a separate circuit.

For all the circuits you can share a single safety ground. Metallic conduit may be used as the safety ground in many cases, however I don't trust this approach. Conduit rusts and the ground just 'fades away'. I recommend using an insulated green wire for the ground. You will have to bond this ground to each junction box.

-Jon
 
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