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I'm installing a NEMA 14-50 in the garage with a dedicated 50amp breaker. I have run the 6/3 romex through the attic and am at the point where I'd exit the attic to the exterior of the house and down to the main panel. I am realizing that I'm not 100% sure how to enter our main breaker panel.

I had planned to use a short run of EMT from inside the attic to exterion, LB conduit body to transition down the exterior wall and then into the top of the panel. My understanding is that code allows me to run romex in the conduit (up to 10ft) and that I must enter the top of the panel. (reference: Can Romex (NM-B) be run through conduit?)

My panel has a ~2x2 square plate on the top. I don't know how to terminate the EMT in a rain tight method. Here's a picture of the top of the panel and general overview of the setup before I've done anything. How can I terminate the EMT in the panel and ensure it's watertight?

Panel Panel Top

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You can't run NM in an outdoor conduit

NM is not rated for wet locations. Any exterior conduit is a wet location, so NM can't go there. Besides, getting NM to go down conduit is more of a pain than you want or need.

Running into the top of the panel is unwise

Running a conduit into the hub at the top isn't the wisest idea, to say the least -- that hub is intended to be used for a service mast with its attendant weatherhead to keep the rain out, not a conduit going up into a LB, and you can't have any other openings in the top, or else the box loses its NEMA 3R weathertightness rating.

Instead of that, I would use a box to transition to 6AWG THWN in 3/4" EMT in the attic, then run the EMT out of the house and LB the run down to a LR body that goes into the right side of the box, right above where the service wires go in. Also, put a 1/8" hole in the bottom of the LR to make sure that water can get out of it instead of building up and then going off into your panel.

Having the meter pulled for at least parts of this is a good idea.

I'd have the meter pulled for this on two occasions:

  1. Making the KO in the panel and attaching the EMT fitting to it
  2. Making the final pull and hookup of the wires from the LR to the breaker.

If you leave the cover off the LR, you can do the rest of the pull with the power still on. If any of this makes you uncomfortable, of course, simply poke your favorite electrician.

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Yes you can run the 6/3 into a piece of EMT, but you have to meet the 40% fill rule which I believe is a 2" conduit. You can instal a threaded hub where the 4" square is, but it must match the Panelboard Type (Sq D, GE, etc.). You will attach it with a Water type compression connector to the hub and, where the cable enters the EMT it must be bushed (they make a plastic ring for that or you can just use another connector with an insulated throat). You should also strap it within 2' of both sides of the conduit. I would use a small piece if 7/8" unistrut and 2" unistrut conduit clamps.

Note: Be very careful around the Panelboard since you are going to have to work around exposed live conductors. I would advise you to turn off all of the breakers in order including the main and pull the meter to ensure safety while working on the panel. This usually requires notification of your Utility Company that you are cutting their seal. Otherwise you may be subject to fines. Also you might be subject to permitting the project before they allow you to reconnect. Of course when you plug in the meter turn on the Main the each breaker slowly and deliberately.

If any breaker trips while you are installing the new feeder or turning on the breakers, stop work immediately, turn off all power, and rectify the problem before continuing. If this makes you feel uncomfortable I would seek out a trusted contractor.

Good Luck and be safe.

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