EMT routing question

[Mancino]

I plan on doing EMT throughout my garage. I know the general layout of where I want my outlets, but I've run into a dilemma when I thought about how I wanted to run the tubing.

My problem is, I have windows on the sidewalls and the bottom of them are about 40" from the floor. In my mind I thought I would have my outlets around 48-50" height to be able to stand sheets of plywood, parts, etc and not cover any outlets.

So, the question is, how should I route the tubing around the garage? Do I stick to my 48-50" height and run the tubing around the windows? Or would it be smarter to run the main EMT trunks above the windows (say 8' or so) and drop down to where I want my outlets?

 

[LXCam]

I would go over the window. Going below might interfere with a bench at some point. You're other potential option would be to run the conduit around the upper perimeter , install a 4s box at each drop location then of course your drop down to the receptacle. That way if you changed your mind at a later date it's a simple move without a bunch of wiring to deal with.

 

[sberry]

The garage looks empty now, soon there will not be a place to lean sheets up against the wall but I also favor a run around the top and drop where needed, it may be easy to change or add as you go.

 

[Hot Rod Grampa]

3rd on upper perimeter. In bigger shops run 1" emt with 4 11/16 boxes, give the wires a loop in the box even if you are not branching there. No problem running an outlet of whatever voltage anywhere you want. It also makes it easy to surface run conduit to lights on ceiling or wall. Good luck

 

[rjn2649]

Yeah I would go above the windows. I also like sberry's answer wish I did mine that way now that I'm moving stuff around...

 

[alfredeneuman]

In bigger shops run 1" emt with 4 11/16 boxes, No problem running an outlet of whatever voltage anywhere you want.

There's a good possibility of derating (of over 3 conductors), especially with small wires.
ie: You can run up to 9 #12s and still put it on a 20amp breaker, 10 #12s and you have to switch to a 15A breaker.
If you want to keep the breaker size of 20A you'll need to run #10s.

 

[PoorOwner]

There's a good possibility of derating (of over 3 conductors), especially with small wires.
ie: You can run up to 9 #12s and still put it on a 20amp breaker, 10 #12s and you have to switch to a 15A breaker.
If you want to keep the breaker size of 20A you'll need to run #10s.

Curious how you came up with that, according to this chart it can fit 26 12 awg wires in 1” emt. That maybe physical percentage max Before derating I suppose

http://www.elliottelectric.com/Stat...nces/ElectricalTables/Conduit_Fill_Table.aspx

 

[AA7483]

I'm wiring my shop the same way this weekend. I plan to go all the way to the top and drop as needed

 

[alfredeneuman]

Curious how you came up with that, according to this chart it can fit 26 12 awg wires in 1” emt. That maybe physical percentage max Before derating I suppose

Table 310.15(B)(3)(a) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable

Number of Conductors
4–6................80%
7–9................70%
10–20.............50%
21–30.............45%
31–40.............40%
41 and above...35%

That's from the 90°C rating.

 

[sberry]

Just to add,,,, the fill and the current carrying conductors may be a different number. Its just a habit but I really like a single circuit in pipe for just welders. I don't really care for inch either, nothing technically wrong with it but find ZI just don't really need it especially if the welding in most cases is in another pipe.

 

[alfredeneuman]

Thanks, sberry
Single phase neutrals on a multiwire circuit aren't considered as current carrying unless they're supplying non-linear loads. (like motors and computer power supplies)
Neutrals of non multiwire circuits are considered as current carrying

EDIT: I should add to the non linear load list electronic ballast transformers of any kind.

 

[PoorOwner]

I am trying to fit 6 12awg wires in 3/4 and one ground wire
So 80% of 16 wire max filll?
Thanks.

 

[alfredeneuman]

No. 80% of the amps, so you're good with 6-#12s (up to 9 before it's derated from 20 amps)
Ground wires don't count because they're not current carrying conductors.

 

[mm08822]

I am trying to fit 6 12awg wires in 3/4 and one ground wire
So 80% of 16 wire max filll?
Thanks.

NO. You are intermixing the intent and results of two completely different tables.

The conduit fill table is based upon the size, number of conductors and insulation type within a conduit to not exceed 40% cross sectional area of the conduit.. Tables typically provide a conductor count using all same size conductors/insulation types. If there are two or more sizes/insulation types, then calculations are required to determine if intended fill exceeds 40% of conduit cross-sectional area.

The adjustment factors table that Alfred is referring to is used to adjust the maximum ocp of the conductors in the conduit when more than 3 current carrying conductors are installed. This is required to limit the heat build-up within the conduit when all conductors are in use to prevent insulation breakdown. This is an adjustment to the stated ampacities provided in table 310.15.

To provide headroom in derating #12 thhn for your example, the 90c column ampacities are used for derating calculations. Even though #12 thhn has a max continuous load ocp rating of 20A.
3 ccc’s >>> 100% x 30A = 30 a>>>> max ocp =20a
6 ccc’s >>> 80% x 30A = 24 a>>>> max ocp =20a
9 ccc’s >>> 70% x 30A = 21 a>>>> max ocp =20a
10ccc’s >>> 50% x 30A = 15 a>>>> max ocp =15a

So your 7 conductors will be well below the 40% max fill of 16 and the 6 current carrying conductors can be ocp’d at 20A.

 

[PoorOwner]

Thanks alfred and mm,

I kept everything at 20A to be simple,

but what it was 4x 12 AWG, + 2x 14AWG <-15A breaker intended
how do you derate a combination of wires?

PS. sorry OP for derailing the question, hopefully give you idea of which size conduit to use

 

[sberry]

I did one of my own a while back, technically it would have had 10 wires all current carrying and in practice it wouldn't mean squat as they were all intermittent and lightly loaded. To meet the letter of it all I used a multi wire on one of them to make it 9 current conductors. If I hadn't needed gfci on a couple would have reduced another one but it was so much easier to finish running another wire and giving them their own white.

 

[mm08822]

Thanks alfred and mm,

I kept everything at 20A to be simple,

but what it was 4x 12 AWG, + 2x 14AWG <-15A breaker intended
how do you derate a combination of wires?

PS. sorry OP for derailing the question, hopefully give you idea of which size conduit to use

Apply the specific ampacity for each conductor size. Total current carrying conductor count (and %) stays the same.

So the 2-14's.......
6 ccc’s >>> 80% x 25A = 20 a>>>> max ocp =15a

A 10th (or more) CCC's would force you to upsize the 14's to 12's or use a separate conduit to keep the count low.

 

[sberry]

Alfred, yes my helper was running a couple garage door openers, not that it mattered due to count and load but I had him run a pipe just for them. He used a multi wire nd even if he didn't it would have been legal but sometimes its worth it to me to add 1 extra pipe where all that is in it is the openers, not a bunch of snot to sort thru or wonder about.
Well worth it on occasions for welders, nothing beats a single circuit in pipe right smack to the recept.