Running EMT on Corrugated metal building

[tycoon]

Hello all,

I have found a few tips and tricks on here cruzing around on here, but wanted to get some better details. I plan on wiring all my wiring using external EMT, the building is a polebarn, and the floor is not yet poured. I think I will run a larger conduit sub floor, and install a sub panel on the adjacent corner as the load center. I seen some boxes that are built for Corrugated metal that have deep, and shallow punchouts, is this what most people are running? I would like to see some pictures of EMT runs on corrugated metal interiors, and see if any one has any tips and tricks for planning, and running all my circuits.

Thanks in advance.

 

[ycgoat]

Is this interior or exterior. I am running EMT in my metal building now, but it has steel ribs (rafters and posts) every 5'. I am running 3/4 EMT across the front and rear. Where I put junction boxes I used 10' metal studs cut in 1/2 and trimmed to fit between the studs how I wanted them (flush with the posts or tight up against the metal siding). This is all up high above the garage doors. For the outside lights I put the metal studs trimmed to fit tight up against the metal siding inside the building, and put a round pancake box outside screwed through the siding and metal stud.

 

[Walkers]

Bending all those hickeys to match the corrugated can sure be a buger!

 

[sparky 1971]

I wire a lot of pole barns with corrugated steel inside and out. The boxes that are made for the steel is a Raco product. Part # 232CS. Of the five supply houses I have accounts with, only one stocks those boxes, and they don't keep very many. That may be something you want to check on before the time comes and you can't get them.

Sorry, I have yet to think to take a picture of any work I've ever done. It would help if I wasn't so stuck on still using a flip phone.

I'm sure I'll think of more things and add as this goes along.

Even though the 232cs boxes are available, I usually run the conduits at the top of the wall and drop down to each receptacle, sometimes if a couple are close together, I will set a couple of 232cs's and tie them together. Running at the top of the wall is easy for me since I have a scissor lift. If you have to do it from a ladder, that makes things different.

I use those boxes more on the ceiling going across the ribs. Set one for each row of lights, the door openers, car lifts, etc.

Try to get an idea of the height you want your boxes to be so you can ensure there is framing to screw to. I did one building and all the boxes were about 5' off the floor because the next vertical framing member was about 24" high. I did another building and everything was about 36" aff. You don't want to just screw to the metal, at least I won't do that because I feel the metal isn't thick enough for the screws to hold.

This may seem trivial, but if the metal isn't up yet, make sure the inside and outside ribs line up with each other. I've only been that lucky once, but it sure was nice to be able to run a hole saw all the way through the wall from outside to inside and know that it wasn't going to come right through a rib when it got inside.

 

[sparky 1971]

I found one thing out today. When using the 232cs boxes and running horizontal conduit in and out of the raised knockouts, if you are putting two devices in the box and one of those devices is a gfci, it ain't gonna work. I had a 3/4" emt in one side and out the other and tried to install two gfci's in the box. The side of the gfci's hit the connector about 1/8 tp 3/16" before it was seated. I'm going to have to install another box above to it and have one gfci in each box. it will work fine using the regular knockouts and it MIGHT work using 1/2" emt, but I can't be sure of that. It will also work if the conduit comes in one side, but does not leave the other and there is only one gfci along with a switch or a duplex. You will just have to install the gfci on the side where the conduit isn't.

 

[ycgoat]

I found one thing out today. When using the 232cs boxes and running horizontal conduit in and out of the raised knockouts, if you are putting two devices in the box and one of those devices is a gfci, it ain't gonna work. I had a 3/4" emt in one side and out the other and tried to install two gfci's in the box. The side of the gfci's hit the connector about 1/8 tp 3/16" before it was seated. I'm going to have to install another box above to it and have one gfci in each box. it will work fine using the regular knockouts and it MIGHT work using 1/2" emt, but I can't be sure of that. It will also work if the conduit comes in one side, but does not leave the other and there is only one gfci along with a switch or a duplex. You will just have to install the gfci on the side where the conduit isn't.

Nice to know, but couldn't you use a double gang plaster ring, or is this an outlet box that they mount directly to.

 

[sparky 1971]

Nice to know, but couldn't you use a double gang plaster ring, or is this an outlet box that they mount directly to.

Plaster rings are for flush mount and look like **** when used for surface mounted boxes. The 232 CS is made specially for running conduit across the ribs of corrugated metal. For less than 1.5 seconds I considered using an extension box, but quickly came to my senses and decided on two separate boxes, but I didn't have two single gfci covers. I was trying to use a cover like this.

 

[sparky 1971]

And this is the 232CS. See how the knockouts on the sides are punched a little further out than the knockouts on the top and bottom, which are the standard ko's. That allows the conduit to lay on top of the ribs without any offsets. Unfortunately, it prevents a gfci from fitting unless it's the only thing in the box which means it's right in the center.

 

[dscheidt]

And this is the 232CS. See how the knockouts on the sides are punched a little further out than the knockouts on the top and bottom, which are the standard ko's. That allows the conduit to lay on top of the ribs without any offsets. Unfortunately, it prevents a gfci from fitting unless it's the only thing in the box which means it's right in the center.

will compact gfci devices work?

 

[sparky 1971]

I can't say the I've ever used a compact gfci, so all I can say for sure is maybe. If it's 1/4" or more shallower, it should, but won't promise it. The threads of the 3/4" connector stick quite a ways into the box, so if a compact is just as deep, but narrower, it will be a no go. I'm not going to try for three reasons. 1) this place is in the sticks, I'm not going to make an 80 mile round trip drive to get any compacts when I have the covers I need at my shop 2) if they do work, a few years down the road when one quits, it will have to be replaced with a compact and the odds of someone knowing that and supplying another compact in one trip aren't very good and 3) I try to use nothing but P&S devices and I don't think they make a compact, I just went to the Legrand website and skimmed through four pages of gfci's, didn't see one.

 

[Entropy]

Depending on Code in your area, you can do the GFCI using a breaker at the box. This obviously, would do the entire circuit and not the individual receptacle. I’ve done both.

The offset RACO boxes are a godsend and once planned and layed out, minimizes the amount of offset bends required.