I'm running 3 circuits from a panel mounted on the outside of a backyard studio shed to the inside of the shed, and am not sure how to best do this. The shed is stud construction with 1/2" zip sheathing and James Hardie lap siding. Panel is screwed to the outside of the siding, through the sheathing and into 2x4 backing. I'm running NM cable through the stud walls to outlets, lights, and heater.

UPDATE My plan is to run 1-1/4" PVC conduit from panel to LB box, then to the inside of the shed in a stud bay. I'm planning on using the pictured clamp to attach the conduit from the LB to the panel. I bought a separate O-ring (from the plumbing section) to help make the connection water tight.

Is this ok? Or is there a better way to make a watertight connection to the panel? I'd love to go straight through the back, but not sure how to make that watertight.

Can I use an O-ring to make it watertight? enter image description here

Can I discard the metal ring and just use the PVC directly against the washer? enter image description here

This is the panel enter image description here

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    You can't and don't need to use a clamp this way. Where cables need clamping they need proper clamping, to the building, boxes, etc. They don't need to be clamped to enter or exit a conduit, and if you're using a conduit just to help guide them through a wall that's fine but not with a big clamp like that. It's A little unclear what you're doing. Are you using NM cable? Is the shed stud construction? Are you running the cables inside the walls? Can't you go directly into the back of the panel?
    – jay613
    Feb 7 at 22:54
  • @jay613 thank you! I kind of figured that out on my way home, that the clamp needs to be inside the panel. The panel is mounted to the siding, so I'm not sure how to drill through the back and through the siding and keep it watertight. Definitely open to suggestions! The shed is stud construction with 1/2" zip sheathing and James Hardie lap siding. Running NM cable through stud walls to outlets, lights, and heater. I'll update the question with those details, too.
    – Rufus L
    Feb 7 at 23:44
  • @jay613 Also, I'm sorry I have changed the question a bit since your comment.
    – Rufus L
    Feb 7 at 23:51
  • 8 space panel. 2 spaces for a backfed double breaker as a disconnect. 3 spaces for your circuits. Only leaves 3 spares. Feb 8 at 1:01
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    All outdoor/buried conduit is, by code definition, wet at all times. Therefore, the conduit itself will be wet inside. The only waterproofing you need to do is to keep water from getting behind the panel and running through openings into the stud bays of the shed. THAT part should be waterproofed.
    – FreeMan
    Feb 8 at 13:10

1 Answer 1


You don't need the clamp on the conduit connector. Your cables will enter the house, and they need to be clamped to the framing just inside. They don't need to be clamped at the conduit and they shouldn't be clamped that way all in a bundle.

You don't need the LB. Use one of those knockouts on the back wall of the panel to get into the house directly.

You don't need to invent your own PVC fittings for electrical boxes. They exist, go buy one. You will pat yourself on the back for what a good job you did inventing your own. Really. But don't use it. PVC pipe through the wall straight into the breaker panel using a store-bought electrical PVC connector. Pass the cables through that, no clamp, staple them to the framing just inside the shed, and take it from there.

May as well use a larger one than 1-1/4 since you're passing whole NM through it. Y

Why don't you put this panel inside the shed where it will be better protected from the elements, spiders, etc? How are you running your feeder? That could go directly indoors too.

  • Thanks! I thought for sure they had to be clamped as they passed into the panel. That's a relief. I'm helping my neighbor build this and he wanted the panel outside. Feeder is coming from house underground in conduit and up through the bottom of the panel. For the wall-side of the short PVC coming from the panel, do I just cut it flush with the inside of the sheathing? Nothing needed on the end?
    – Rufus L
    Feb 8 at 1:12
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    Ya. You probably don't even need any conduit. The PVC connector will probably go all the way through the siding and into the stud bay.
    – jay613
    Feb 8 at 1:32
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    The strict way is a big junction box inside, with normal cable clamps for all the NM, connected to the outside box with nipple and connectors at both ends, and outside-rated loose wires between the two boxes. There isn't to my knowledge an exception saying you can staple the NM cables to the framing inside and pass them directly into the panel through a conduit. But it's unlikely an inspector would fail that and make you build a spaghetti box! And that would REALLY beg the question of why not put the panel inside.
    – jay613
    Feb 8 at 1:43

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