Mounting for an exterior main panel?

What’s the best way to mount a sensor unit when the main electric panel is on the outside of the house? My panel (150A) is a metal box that’s in the wall and has the door on the exterior wall of a stucco coated house. The sides of the panel are in the wall so they’re not easy to access. I’m in Southern California so the weather isn’t a big issue. I don’t think that I can legally put low voltage electronics in the main enclosure. The only solution I’ve come up with is to mount a weather proof box on the outside of the stucco, drill a hole through the back of it into the wall and fish the sensor lines through that and into the side/top/bottom of the main panel box through one of the knock out holes. Is there some other way to get the sensor lines into a main panel enclosure that I’m overlooking?


Hi TD,

You’re correct in your assumption.
The NEC says no Low Voltage Electronics in a Load Center. (breaker box)
Your existing Load Center should have knockouts on the top and bottom walls.
There may be one or two on the side walls.

All of the Load Center boxes that I’ve seen have knockouts on the rear wall as well as the top and bottom walls, so you shouldn’t have to drill any holes in the new box.

As you’ve surmised, surface mounting a new box next to the existing box (called a flush mount) and fishing wires is what you’ll need to do.

The NEC says the low voltage wires i.e. the CT leads, need to be run separately from any high voltage wiring. I.e. not in the same conduit.

@Bill.Thomson, would he be OK putting the l.v. electronics inside a grounded metal box inside the load centre, or is it a ‘catch-all’ rule with no discretion allowed? (In the UK, anything is allowed provided that you can establish that it is as good or better than what the rules specify.)

But of course, power still has to get in, and the signal in whatever form still has to get out some way or another, so there’s little to gain with a box inside the box.

Unfortunately, the electrical code makes allowance for CTs, but not for the electronics. :disappointed:
On top of that, the typical residential load center usually has little, if any, extra room inside it. I’d have to look at the NEC itself, but I’d say any kind of metal box inside a load center would be a code violation.
I emphasized usually because some LCs actually do have a fair bit of extra room in them, but that’s the exception rather than the rule.

It was but a thought.

Every time, I’d go for cable entry in the back of the box and straight through the wall if at all possible (but then I don’t need approval from “the management”).

A load center “can” similar to the one pictured below will make that a little easier.


Thanks - but I don’t think my wife would approve of tearing up the kitchen just for this. I’m going to have to hope there is an empty knock out I can use and fish it behind the stucco wall.