Do I need junction boxes at house and detached garage for designated outlet

Question

I am running a designated 6/3 UF-B wire on its own breaker at my house to my detached garage to supply a designated nema 14-50 outlet. Will I need to split the wire and add junction boxes at each entry and exit point only to continue the wiring to the designated outlet?

Answer 1

Don't use 6/3 UF if you can avoid it. There are better choices at a fraction of the price.

Save money and sidestep a big Code mess

You need a disconnect switch at the garage. It can be indoors. But more than that, all circuits coming into the garage must have disconnect switches that are together. (NEC 230.72(A)).

So not only will you need a disconnect, you'll need to reroute the existing circuit(s) to add disconnects right next to the larger disconnect. Ugh! What a mess!

Also, nobody wants to spend $5 a foot on wire if they can avoid it. I propose $1.00 to $1.40/foot wire that has a great deal more capacity.

A subpanel solves all these problems.

It ticks every problem off the list: provides a disconnect, allows better wire, and can support the existing circuits right out of it, eliminating the need for a second disconnect. You use a main-lug subpanel:

• Any common 6-space or larger panel will be fine. You'll have a 50A breaker to feed the NEMA 14-50 recep, and 15A or 20A breaker(s) to feed the existing circuits in the garage.

• Yet even simpler -- no harder than what you originally planned, actually -- is to choose an "RV Subpanel" This is a combo subpanel + 2 receptacles: NEMA 14-50, and a 20A GFCI.

The breakers in the subpanel are the mandatory disconnect switches. It is OK for the disconnects to be indoors.

A subpanel allows terminating large wires. That gives us the liberty to use the wires I recommend -- #4 or #2 aluminum (it's OK) depending on what's readily available right now in your market. #4 provides 65A; #2 provides 90A.

There's nothing wrong with aluminum wire in heavy feeder. The subpanel lugs are themselves aluminum.

The existing garage circuits get served out of the subpanel

So the burial runs from the house get disconnected and abandoned. Leave their ends usable in case there's ever a reason to use them.

If you chose the (easy mode) RV subpanel, then you simply attach the receptacle circuit to the "LOAD" terminals on the GFCI that's already installed in the subpanel. That GFCI recep is fed by a plain 20A breaker. You'll need to change that to a plain 15A breaker ($6) if your receptacle circuit has any #14 wire. Add another breaker to feed the lighting circuit.

If you don't have an RV subpanel, then just stick appropriate breakers in the panel -- 50A for the NEMA 14-50 socket, 15A or 20A for the receptacle and lighting circuits.

Back at the main panel, you can use a 60A breaker to feed the #2/#4 feeder. That will suffice, and it's the cheapest ($12-ish).

• However #4 Al can be breakered up to 70A
• #2 Al can be breakered up to 90A

Cable type

Finding cables fit for both direct burial and interior use is tricky.

If you're running in conduit inside the buildings, you can use "MH feeder". That stuff is a commodity in #2 size.

If the entire run is conduit, you can use XHHW or THWN individual conductors also - and you can select a #8 copper or #6 aluminum ground wire. You need 4 wires.

For what it's worth, Rigid conduit is hella expensive, but only requires 8" burial depth (6" cover). If you don't have far to go, this is fantastic stuff because you can trench it with a garden trowel. Be sure to choose at least one threadless fitting, because it's normally pipe threaded like iron pipe.

6-3 UF requires 2" conduit, so it's a bad choice for conduit.

Answer 2

Since we're dealing with a 240V circuit vs a 120V, you can have the two feeds

Since the existing feed to the garage is 120V-only, you are permitted to add a 240V feed by NEC 225.30(D):

(D) Different Characteristics. Additional feeders or branch circuits shall be permitted for different voltages, frequencies, or phases, or for different uses such as control of outside lighting from multiple locations.

As to the boxes...

While you don't necessarily need junction boxes at each end, you will probably need a LB conduit body at the house end to transition the cable down into the protective conduit required by NEC 300.5(D)(1)/(D)(2):

(D) Protection from Damage. Direct-buried conductors and cables shall be protected from damage in accordance with 300.5(D)(1) through (D)(4).

(1) Emerging from Grade. Direct-buried conductors and cables emerging from grade and specified in columns 1 and 4 of Table 300.5 shall be protected by enclosures or raceways extending from the minimum cover distance below grade required by 300.5(A) to a point at least 2.5 m (8 ft) above finished grade. In no case shall the protection be required to exceed 450 mm (18 in.) below finished grade.

(2) Conductors Entering Buildings. Conductors entering a building shall be protected to the point of entrance.

This can be done using 1¼" PVC Schedule 80 conduit and a matching PVC LB, although you can use 1½" instead if you wish, as Note 2 in Chapter 9 of the NEC exempts your situation from having to meet fill requirements:

(2) Table 1 applies only to complete conduit or tubing systems and is not intended to apply to sections of conduit or tubing used to protect exposed wiring from physical damage.

Along the way, you'll need to make sure that you get down to 24" from the finished grade in order to provide adequate burial depth for your cable. The conduit can terminate (in a bell-end) at 18" below grade though, and you also need to use a bell-end where the LB discharges into the wall cavity (this protects the cable from abrasion).

At the garage end, we do something similar, only instead of a LB, we use a 60A non-fusible AC pullout disconnect box mounted on the outside of the garage, near the existing garage disconnect. This provides the disconnect required by NEC 225.31, and also serves as a convenient terminating point for the garage-side conduit protection, with NM or more UF connecting the disconnect box to the EV charger itself. Finally, you'll need to provide a 50A GFCI breaker at the head of the run as EVSE require external GFCI protection under the NEC.