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I have a 240v 50amp service circuit and I would like to split it into 2x 120v circuits, something like the image below.

How would I do that, junction box of some sort? And specifically, how would I "split into 2" the ground and the neutral? Just throw some Marrettes on them and pigtail it or use some sort of bus bar or junction box?

Please provide specifics on the parts if you can (i.e.: this type of junction box, etc.)

I'll keep the gauge wire the same (6 AWG in the 240v I think) for the 240v and 120v, as they will both be rated for 50amps.

enter image description here

This is for my RV. It has 240v 50amp service. I am installing 2 inverter, charger, solar controllers, both rated for 120v, 3000 watts each. Each has a 120v input (ground, neutral, line) and a 120v output (neutral and line, grounded to chassis), not including the PV in and battery in. So essentially, I need to split that 240v input that goes into my breaker panel, into 2x 120v (one for each inverter) and then the 120v output of each inverter will go to each side of the panel. The panel has a dual pole 50amp breaker.

Considering the 3000 watts of the inverters, I'll probably switch that 50amp to a 30 amp breaker. The inverters will peak at +10% for 20 seconds and cut out if needed, but a breaker will add extra protection.

This is so that when I am connected to "shore power" I can use the utility power, the inverters will balance the load between solar, battery and utility as needed.

Here is an image of the breaker panel:

Breaker Panel

and here is an image of the 120v inputs and outputs on the inverter (there will be 2 of these) - also, not my wiring, this is a stock footage off the internet of my model of inverter. I haven't hooked mine up yet.

Inverter inputs

We might be getting closer to the answer, maybe it was pretty simple. I think maybe a power distribution block is what I was looking for?

How about just 2 of these?

PDB

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3 Answers 3

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Basically for what you ask just wire connectors rated for #6 in a junction box is good.

Thinkin #6 is too big for marrettes, you probably need polaris or NSI inslated connector like this IPL4-3C.

enter image description here

In jurisdictions regulated by adoption of the NEC you need a box 5 in³ per conductor, your grounds will count as one, so a 50 in³ box.

The big concern is if you're feeding devices that draw less than +/-40A that 50A breaker might not trip before a fire is started, so more details are needed to determine if what you propose is safe.

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  • 3-6 AWG is indeed too much. 2-6AWG they do make wirenuts for, but that won't work here, and you need to be a very confident brute to use them at all for that.
    – Ecnerwal
    Commented Nov 16, 2023 at 2:48
  • @Ecnerwal I get a little thrown off with the term "marretes". I understand the term is mostly interchangable with "wirenuts", but not being from an area where the term is used I don't know how far the term is stretched. Commented Nov 16, 2023 at 2:52
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    William P. Marr is the Scottish-born Canadian that invented the wirenut, but his brand is of course Marrette. As with several other Canadian inventions, the US seems to like disrespecting the inventor by using a different name for the product than Canadians and Britons do. "Twist-on wire connector" seems to be the most generic description.
    – Ecnerwal
    Commented Nov 16, 2023 at 3:00
  • This is the best answer I've seen. Based on this information I found some power distribution blocks that I will use. Thanks for the input! Commented Nov 21, 2023 at 16:22
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The correct method for almost all conceivable uses of 50A at 120V is to use a sub-panel to power a number of 15 and/or 20 or in a few rare cases 30A single-pole breakers to supply the 120V loads on separate, properly overload protected circuits.

No cord-and-plug connected 120V load goes larger than 30A. Normal cord and plug connected 120V loads are allowed to run from 20A circuits, and you could run 6 of those (though you could manage to trip the 50A feed if all 6 are fully loaded.) You could in fact run many more circuits, so long as the total load at any given time remains below 50A per phase - it's quite normal for branch circuit breakers to exceed the feed or main breaker size.

So, barring a real unicorn you haven't revealed, I'm betting that a subpanel is the correct method to turn your 240V 50A circuit into (a total of) 100A of 120V loads.

Edit, update: It's a Uni...nope, horse with a horn taped to its forehead.

The manual for your horse does not show it to be a unicorn. On Page 10 it clearly states that the separate input/output breakers (off the inverter, from the language) are to be 30A. So, your 50A RV hookup would connect to a subpanel with 30A breakers to feed the inverter inputs, and you could also have (if you wanted) some 20A breakers fed from "shore power" that were not fed by the inverter offboard output breakers (also 30A.) The 50A breaker you are proposing to replace with a 30A dual pole would be the inverter output breaker, per your description of the inverters being between shore power and the RV systems. You appear not to intend to provide an input breaker at all, or to depend on the RV-park-stand 50A breaker, rather than the required 30A input breaker.

Connecting it straight to a 50A plug (as proposed) appears to be against the instructions.

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  • No, I'll be using the provided (in the box) 30amp breaker on the input side, as per the instructions. Again, a little off track from the original question, but appreciate the input. Commented Nov 21, 2023 at 1:36
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I am leaving this answer here because it applies to what I thought was the question - something like "I have an old 50A range circuit and I put in a gas range so now I don't need it but I'd like to have more 120V circuits in my kitchen for small appliances". But it turns out the actual question has to with (a) an RV (so yes a panel, but not a regular residential service), (b) inverters and (c) solar. Which is an entirely different set of issues. But leaving this in case somebody need an answer to the originally stated (as I understood it) question.


50A 120V is pretty much non-existent for a bunch of reasons. There are some 30A 120V receptacles for certain RV connections, but far more common (and I suspect the case here) are 15A and 20A 120V receptacles.

There are two basic solutions to "split" a 50A 240V circuit into 2 x 120V circuits:

Subpanel

This is well-covered in another answer. It is the most flexible solution, but not a trivial solution. One big concern is that while an ordinary junction box just needs to accessible, an actual subpanel requires a 30" x 36" open space in front of it - no shelves, appliances, etc., which is often a problem when adding a subpanel in an existing building. If you have the space then a subpanel is definitely the best long-term solution.

MWBC

A Multi-Wire Branch Circuit uses the two hots and the neutral of a 240V circuit to power two connected 120V circuit. This used to be quite common for kitchens as a way to provide for the required 2 20A countertop circuits with a single /3 cable, saving a little bit on cable/wire costs.

In this case, you could:

  • Replace the 50A double-breaker with a smaller double-breaker (20A for ordinary 15A/20A receptacle circuits, 30A for a pair of RV receptacles if that's the goal)
  • Use Ideal 454 Blue or equivalent wire nuts to connect each hot 6 AWG wire with a matching 12 AWG (20A) or 10 AWG (30A) wire in a junction box
  • Use Ideal 454 Blue or equivalent wire nuts to connect the neutral 6 AWG wire with two matching 12 AWG (20A) or 10 AWG (30A) wires in a junction box
  • All grounds together and connect to the metal box (you are using metal, right?)
  • Run wires in conduit or appropriate cable from this junction box to each receptacle box (they can be together or any distance apart, doesn't matter)
  • Install an appropriate receptacle in each box

There is one other thing you need to watch out for here: GFCI and/or AFCI.

Until recently 240V circuits were exempt from GFCI and AFCI requirements in most areas. They are still exempt in some areas. However, newly installed (i.e., new circuits, not replacements) 15A/20A receptacles almost always require GFCI (kitchen, basement, outside, laundry, etc.) or AFCI (most other rooms). 30A RV receptacles are normally garage or outside, so they also require GFCI. For 15A/20A receptacles that is easy as you can put the protection at point of use, at least for GFCI (AFCI gets a bit more complicated unless you have metal conduit). For 30A receptacles that is a bit of a problem as 30A GFCI receptacles are not generally (if at all) available. The alternative solution is a 20A or 30A GFCI and/or AFCI (whatever is required) double-breaker - those are available for most modern panels but are relatively expensive.

For straight replacements you normally don't trigger GFCI and AFCI requirements. But turning a 50A 240V circuit into two smaller 120V circuits is arguably the same as running entirely new circuits with respect to code compliance/grandfathering.

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    Note that, while AFCI & GFCI are both Good Ideas™, they may not be required by code depending on where you live. My state is still on NEC 2008 and GFCI is not required in many locations (yet still a good idea).
    – FreeMan
    Commented Nov 16, 2023 at 16:22
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    I've updated the original post with additional details as to what it's for and where it is Commented Nov 16, 2023 at 23:01

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