I want to add an RV subpanel to our cabin, but the location where I want it is very close to the main service switch, but pretty far from the circuit panel inside the cabin. Currently, there is about 100' of underground wire (I think it's MCM 250 aluminum) feeding into the cabin. What I want to do is put in a subpanel, but connect it to the main supply feed (but after the service disconnect switch).

I was thinking that I could use a tap to pull a 6ga wire off of the MCM 250 inside the service disconnect and run that (through underground conduit) to the RV sub panel. I'm having trouble finding out if that is legal though. I was going to put a 4x4 pressure treated post in the ground and mount the sub panel to that, and run the 6ga wire underground through the conduit to it.

Here's a picture of what I have in mind:

Wiring Diagram

You can ignore the generator part of the diagram for now, unless you want to comment on what I have in mind (putting the ATS right below the service switch about 20-25' from the generator).

Is what I have in mind here kosher? Or do I need another main cutoff switch before the RV sub panel?

One of the main questions I have is if I can tap on the switched (after the main 200a breaker) side of the main service switch using something like a "Morris 97643 Multi-Cable Connector", then run the tapped wire off to a sub panel. Since the main service switch would switch off both the circuit breaker in the cabin as well as the sub panel, I'm wondering if that is ok.

  • Where is the meter located? If it's next to your 200A panel you probably won't have much choice in that regard
    – Machavity
    Jun 5, 2019 at 15:46
  • It's right above the 'main service switch' in my diagram.
    – kevin42
    Jun 5, 2019 at 15:47
  • Possible duplicate of How to split a 200 Amp main feed betweena cabin and workshop?
    – Machavity
    Jun 5, 2019 at 15:55
  • I updated the question to clarify what I think is different.
    – kevin42
    Jun 5, 2019 at 16:24
  • 1
    There is a 25’ tap rule look at section 240.21. The tap would have to be sized at a minimum of 1/3 the feeder and terminate in a breaker, not a problem there usually conduit or a gutter is also required. I have installed many RV power pedestals that have 50a 240 breakers but also have 30 a 120 and 20a 120 outlets in 1 box designed for just this case they run ~ 120$ with some close to 200$ So it can be done (just like the one in your picture), the question is how to make the tap. That depends on the disconnect some have multiple lugs, some times a 3 point Polaris connector is the way to go.
    – Ed Beal
    Jun 5, 2019 at 19:19

1 Answer 1


Yes, you can tap into the conductors in the cabinet. As long as it meets...Chapter 3, Article 312 cabinets and cutout boxes. ( Installation 312.8 ) Over current enclosures taps,and feed through conductors 75% fill. And taps may run up to 25 feet..240.21 wire is a least 1/3 the size of the conductor. your tapping into

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