I'm trying to connect a 4/3 nm feeder cable into to my exterior mounted service entry / main panel.

There is already what looks like a 1 1/2" rigid conduit from the crawlspace through the rim joist up into the bottom of the panel that all of the houses wiring currently uses: conduit

There are only 9 single pole circuits (so 18 conductors?) going through the conduit already so I believe im way under the fill capacity for a 1 1/2" conduit. However, it still is pretty tight to physically run my 4/3 cable through it: box entry

I'm worried if I run the 4/3 through the existing conduit I will be over capacity or the inspector will complain im jamming too many wires through it. Should I be worried or just put the cable through it anyways?

My next thought was to just run another conduit turn next to the existing one to put the feeder through. The first problem I ran into was that my box only has 1" knockouts left on the bottom. I tried to bend the 4/3 cable through a 1" LB fitting and, although the fitting itself said it could handle 4 #4 conductors, it felt like cramming it in there was not going to work. If I upsize to 1 1/4" it seems like it will fit, but then how do I connect the 1 1/4" conduit to the 1" hole in the box? Do they make "reducing" hubs? What kind of fitting(s) would let me do this?

  • 2
    A bit of lube may make it easier to pull the cable through the existing conduit. Or depending on the panel, you may be able to drill the knockout hole to make it bigger using a step drill bit. You may also be able to make a your own hole, using a punch
    – Tester101
    May 9, 2013 at 12:09

1 Answer 1


The NEC wants you to avoid overfilling a conduit so that the conductors can dissipate heat, and so you can remove a conductor without damaging it. See NEC 300.17.

There are only 9 single pole circuits (so 18 conductors?)

Ground conductors count for equipment fill, so you have more than 18 -- maybe 23?

Ironically, when you get close to a fill limit, the NEC actually wants you to increase conductor size, because that reduces heat.

Should I be worried or just put the cable through it anyways?

If this was my house, I would want to add a new conduit, if only because pulling the new conductor will be so much easier.

Do they make "reducing" hubs?

Yes. Here are some examples: http://www.thomasbetts.com/ps/endeca/index.cgi?a=nav&N=3819+598+4294951140&Ntt=

I've always found I needed 6" of conduit to make the transition between the reducer and the male fitting that connects to the box. Luckily my local hardware store will sell PVC conduit by the foot, so I don't have to buy a full stick for this.

As @Tester101 mentions, you can also make the hole bigger. A step bit is a nice tool, but 1 1/4" conduit requires a knockout that's actually ~1 3/4". The one he linked to only goes to 1 3/8", and I haven't seen bigger.

The professional way to make a larger knockout is to use a punch. They're a little expensive. Maybe you can find an electrician who will punch the hole for you in exchange for beer or a favor. Or maybe a tool rental place will have a bunch for you.

You don't have to bring the conduit in through an existing knockout - you could punch a hole on the side in a blank area, if that's more convenient for you. Alternately, if there's a good spot with 2 small knockouts, you can consume that whole area.

In your existing installation, I think the lock washer is upside-down. There are sharp edges that are intended to bit in to the metal, so it won't come loose. Unfortunately fixing this means undoing a lot of wiring.

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Also, I think you should use a bushing to protect the conductor from the end of the conduit. Whether your inspector will require it is difficult to guess, but it's seems like cheap insurance. Something like this:

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Also, I hope that if you're going through the trouble of pulling a big conductor to a new location, you're installing a subpanel at the other end. Because subpanels are awesome.

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