Looking to see if I'm wiring a multiwire branch circuit correctly

Question

Currently working on running power from my house out to my shed.  Planning on running four THWN conductors (B,W,G,R) for two 20A circuits with no subpanel, which is my understanding of the maximum of what is allowed without doing a panel (and will be plenty for me).
The electrician I was using to help me kept telling me things that didn't match the code so I've been trying to do the necessary research to complete the project by myself.  I have very little electrical experience prior to this.
Here's an expertly drawn diagram of what I think I need to do:

Just in case my stellar art skills aren't enough, I'll try to explain my plan/questions:
I do know I need a disconnect in the shed. I plan to use a double pole switch right after the junction box but didn't draw it to make things a little less confusing.
Power coming into the shed via THWN conductors will transition to 12/3 cable running to a three-way switch, as well as 12/2 cable running to a single pole switch, both in the same location.  Again I didn't draw the separate ground/neutrals from the JB to reduce clutter.
I understand that anything in this circuit needs to be GFCI protected so I plan on making (at least) the first receptacle in each leg GFCI.  The shed is split into two parts, so essentially each side will have a total of 4 outlets, each with a 20A feed. I plan to run everything I need, including lights out of these outlets.  Each separate circuit has the first GFCI feeding a regular receptacle off of its "LOAD" terminals.
My questions are:
Since there is only one neutral wire coming in, is it essentially connected together throughout the whole circuit?  Will running it in different directions from where everything is connected at the two switches cause any faults with the GFCI receptacles?
Also I know that on shared ground systems that the neutrals have to be pigtailed to receptacles down the line.  If that is the case and the neutral is considered shared, do I instead need to use all GFCI outlets and pigtail the connections to the "LINE" side of each pair?

Harper - Reinstate Monica · Accepted Answer

They aren't two separate circuits.  They are one multi-(hot)-wire branch circuit.
You will need to feed it from either 2 breakers handle-tied, or a 2-pole breaker.  This can be a GFCI breaker.  Unfortunately because it is 2-pole, using a GFCI breaker does not qualify you for 12” cover of burial depth so you must still be at the usual 18” for PVC conduit or 24” direct burial.
You could throw another gray wire into the pipe and make them 2 plain circuits, but that would mean 2 circuits to an outbuilding, and that is not allowed.
Unless the second circuit has a different voltage or form of control, for instance if it was switched from the house because you keep forgetting to turn off the shed lights.
A 3-way switch as a disconnect doesn't work, since there is no definitive "off" position which firemen can rely on to de-energize the structure, and further, 3-ways don't de-energize the structure at all. They simply exchange which of the 2 travelers is hot.
Other than that, your wiring is correct; you are using LINE and LOAD correctly.  The rule of thumb with GFCIs is that for any given cable, if any wire comes off the LOAD terminals, all wires must do so. Except for safety ground, obviously.
Your approach of splitting an MWBC into two simple sub-circuits is a common approach, and makes GFCI a lot easier to deal with.  When you make this split, after the split, GFCIs will work as in a simple circuit, and there is no further need to pigtail neutrals.   You must pigtail them in the switch box but not receptacle boxes.

Looking to see if I'm wiring a multiwire branch circuit correctly

One Answer

Add your own answers!

Ask a Question