I am in the middle of a kitchen remodel. I originally thought there were (2) 120v circuits into the kitchen, so I thought I'd only have to add a couple more, but that is not the case. The two circuits ended up being multi wire branch circuits that connected to the living room and garage. Therefore I need to add a circuit (each) for lighting, 2 circuits for counter space outlets, fridge, dishwasher/disposal and microwave.

Anyway, the panel is an outdoor surface mount on the back of the house. The house is slab on grade with an attic. I am planning to run the "home run" through the attic and protecting the wires close to the attic access. My current problem resides around dropping the wires from the attic to the breaker box.

I originally just thought about dropping a conduit from the attic to the box just like the one coming out of the top left of the box (see picture: this contains the wires for a 50 amp and 20 amp 220v circuits) to the right side of the box. Then just dropping the NM romex through that. But...as I have read about this, I think the requirements are a little more nuanced than this.

So here are my questions:

1.Can I run the conduit to the right top of the panel and have the conduit just terminate in the box on one and and in the attic on the other end? To do this I will have to cut a hole in the top of the panel with a hole saw. It is 25.5 inches from the top of the top of the conduit body to the top of the breaker box.

2.There is a pop out toward of the bottom right side of the panel. Could I use that pop out and run the conduit a little further to avoid cutting and potentially dropping the waste metal on the live nut inside the panel?

I would use raintight conduit connectors for either of these options.

  1. If either of these are not a problem, can I simply continue the NM romex into the conduit from the attic into the box, or do I need to transition to NM-b or UF romex before entering the conduit?

  2. If I have to transition to UF, can it be in one junction box for the 5 romex cables or do they need to be separate?

  3. Although I am not running a combination of 12 awg and 14 awg (separate circuits for each size of course) depending on the circuit, is a 1-1/4" conduit sufficient for (5) 12/2 romex NM or UF (whichever is required?

  4. Is there anything else I am missing or that I should consider?

Thank you in advance for any advice you can give me.

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2 Answers 2


You run individual THHN wires in conduit, not NM or UF cables

The first mistake most DIYers make when they first approach conduit is trying to stuff NM or UF down it. Instead, what you're supposed to use in conduit is individual wires of a type called THHN. These are usually stranded, making them much more flexible than NM or UF cable, and also take up much less space than a cable since they don't twist around awkwardly during pulling.

You're better off running conduit all the way for that many circuits (no, it's not as hard as it sounds)

Furthermore, you're far better off putting a large junction box (a 6" by 6" by 4" NEMA 1 pull box would do quite fine for this) in your attic or kitchen at some convenient point and running all your NM cables to it, then taking two lengths of ¾ ENT ("smurf tube") and running them from said box out to the LB conduit bodies you'll need to use to make the turn down outside. This lets you run quite a bit more power (in the form of up to 8 circuits normally, or 16 if you go whole-hog on MWBCs) to your kitchen without getting bit by ampacity adjustments that knock down the carrying capacity of wires once you stuff too many (more than 9 for wires 10AWG or smaller) wires down a conduit. This solution also removes the need to provide working space for a subpanel in the kitchen, which isn't always the most practical thing in the world.

And finally...

Last but not least, from the aforementioned LBs, you'll want to run rigid PVC conduit down the side of the panel then turn into the panel with LL bodies fitted with weep holes, in the fashion of your Option 2. This way, you won't need the special three-piece hub ("Myers hub") fittings that are required to come into the top of an outdoor breaker box or electrical cabinet at a location not factory-designated for a hub fitting.

Note that you may need to field punch knockouts in the side of the breaker box to do this; this is fine, as long as the KOs don't overlap factory KOs and don't extend above the lowest live part in the box.

  • For clarity, the Myers hub is only required for entering the top of an outdoor/wet location box, not something that's inside a structure. Correct?
    – FreeMan
    Jan 27, 2021 at 13:04
  • It is required for wet locations. Outside it would be required because it is wet out there. I think it depends inside, but in most applications inside where water is not a normal possibility they are not required. That is my limited, perhaps flawed, knowledge.
    – Quinn
    Jan 27, 2021 at 17:33
  • 1
    @FreeMan -- it's required when entering a NEMA 3R (rainproof) box/cabinet through a KO above the lowest energized part (the idea with NEMA 3R boxes is that water that gets in gets out before it ever gets to the zappy bits); they're more commonly used with NEMA 4X or 12 enclosures that are actually sealed against the harsher elements found in industrial situations, though Jan 27, 2021 at 23:35
  • Thanks! Of course, in my limited experience I'm only thinking residential and fail to see the commercial/industrial side of things.
    – FreeMan
    Jan 28, 2021 at 12:06

The number of NM cables you need won't fit in a sanely sized pipe... and UF cable makes the situation much worse because it is even wider and flatter than NM. (unfortunately this is outdoors, and "liquidtight" conduit isn't). When going through conduit, cable counts same as a round wire of the large dimension. You're not allowed to piece the conduit together over the wires - they must be pulled only after the conduit is complete - so that really matters.

A subpanel makes a lot of sense, if you can locate it

When I see an outdoor panel like this, usually 2 things are true: #1 getting numerous circuits out to it is hard, and #2 such panels are notoriously short on breaker spaces.

The trick with a subpanel is the working space. There must be a space 30" wide x 6'6" tall x 36" deep in front of the panel and kept clear at all times. This is best set up in an entryway or hallway which will remain naturally clear.

If you have to run a bunch of wires in conduit pipe(s), just know the rules.

First, as ThreePhaseEel discusses at length, you are better off using THWN individual wires, and stranded is ideal since you won't be trying to terminate it on any receptacle screws. There are limits to how many circuits can be in a conduit, but you can work around them. Not least, you can simply run dual conduits!

No more than four in a conduit without derate.

This assumes you are not in New York City nor an urban high-rise, and therefore your power is 120/240V split-phase. By happy happenstance of the derating rules, every type of circuit you can punch down into a 120/240V split-phase panel counts as 2 wires for conduit derate purposes. You're allowed 9 wires before derates come to bear on 10-20A circuits, so that means 4 circuits.

A Multi-Wire Branch Circuit (2 hots + a shared neutral) counts as 1 circuit, so that means 8 "half-circuits" if they are all MWBC.

However, MWBCs are increasingly difficult to work with, because they don't play all that well with AFCI and GFCI, necessitating expensive breakers instead of cheap receptacles for protection of the initial run from panel to where the MWBC splits off. On the upside, if the route from service panel to first receptacle is entirely metal conduit or metal jacketed cable, then an AFCI can be at the first receptacle instead of the breaker!

Ten per conduit if you derate by "bumping" a wire size.

You can install up to 10 circuits in 1 conduit if you are willing to "pay for it" by bumping all the wires 1 wire size. So a 20A circuit now uses 10 AWG wire and a 15A circuit now uses 12 AWG wire. That means up to 20 MWBC "half-circuits".

However 10 AWG wire is fairly expensive and you may be better off simply running 2 conduit pipes.

A 1/2" conduit can hold nine #12 wires. One must be ground (unless it's non-flexible metal conduit) so that means just 4 simple circuits. There's no shame in running 3 or 4 1/2" conduits; I see it all the time.

A 3/4" conduit is a good choice for four MWBCs/8 half-circuits (12 wires + 1 ground). However 3/4" is a lost cause if you're opting to "upsize" your wires: it can hold only twelve #10 wires and one is ground, leaving a maximum of 5 simple circuits or 3-1/2 MWBCs - and that's not any better than the four-MWBC option, is it?

A 1" or larger conduit is a better choice if you are serious about doing the wire upsize. 1" will support 19 #10 wires, one being ground, leaving 18 wires for circuits.

I for one find 1/2" conduit easiest to work with, so I'd prefer a multitude of small conduits, myself. It can be covered with a fascia board if looks are a concern.

  • So.....as I suspected, there is a lot that goes into adding just a little bit of conduit to the outside of the house. Would it just be easier to just cut a hole in the inside wall of the house behind the panel and run it through a hole in the back of the panel then up to the attic like the rest of the electrical work in the house? Then patch the hole in the drywall?
    – Quinn
    Jan 27, 2021 at 15:16
  • 1
    Sure, if you don't mind busting up drywall everytime you add a wire. I realize wires-in-conduit seems bewildering but that 's only because it's new to you. Also I forgot to add one more option, if you use a large enough conduit, fill derate goes out the window. Jan 27, 2021 at 17:59
  • BTW: you need to go to a wireway (trough/gutter) to get that 20% rule to work, round conduit is still held to the normal ampacity adjustments Jan 28, 2021 at 0:18
  • I am assuming the "wireway (trough/gutter)" would be to protect the wires once they enter the attic as a protective sleeve, right? A replacement for the smurf tube you mention in your answer to the original question? @ThreePhaseEel
    – Quinn
    Jan 28, 2021 at 18:28
  • @Quinn -- a wireway is a rectangular trough that one can run wires through; thing is, they're like really long junction boxes in that you can't bury them in walls, which is the main difference between a wireway and a conduit aside from the obvious one of shape Jan 28, 2021 at 23:44

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