How to connect external PVC electrical conduit to interior box?

[plowhog]

I'm running two 1" schedule 40 underground conduits from a subpanel in my barn to a small adjacent garage, maybe 30 feet or so. One conduit for power, one for phone. Zinsco breakers, but that's another story ....

I will come up the side of the building using schedule 80 above ground, then use an LB to turn 90 degrees where I can penetrate the wood siding of the garage. The interior of the building is wood frame construction, unfinished with no insulation.

Once I get the LB routing in through the siding, what then? I looked at some 1" to 3/4" bushings, so I could then use a very short section of 3/4" pvc, fitted to a male adaptor, that pushes through and screws onto the back of a metal box using the 3/4" knockout hole. The metal box would be nailed/screwed to a stud.

Is this the right way to do this?

 

[dstig1]

Absolutely. Just a male thread on the end of the conduit poking into the box and secured with a conduit nut. Best to get a very large box so you have room to maneuver.

Edit: Of course, being an electrical thread, it will stretch to 7 pages by Sunday... But it is still the way to do it.

 

[RNeumann]

Once inside the wall you don’t need conduit- technically just protection.
Remember to separate the power and low voltage- standard would be 1’. Just separate them by putting one on each edge of the trench.
If the soil moves around (freeze thaw etc) add a slip fitting on the conduit between the ground and the wall penetrations.

 

[quicksandfarmer]

Once inside the wall you don’t need conduit- technically just protection.
Remember to separate the power and low voltage- standard would be 1’. Just separate them by putting one on each edge of the trench.
If the soil moves around (freeze thaw etc) add a slip fitting on the conduit between the ground and the wall penetrations.

Romex isn't allowed in conduit, so you have to transition from separate conductors to romex at the same time you transition out of the conduit. The transition needs to be in a junction box. PVC can be run into an interior junction box using a male terminal adapter and a conduit locknut.

I wouldn't use a reducing fitting, I'd just use a junction box with a 1" knock-out. If you can't find a box with the knock-out where you need it you can drill a 1-3/8" hole.

 

[RNeumann]

Their isn’t code or manufacture specs I have seen that limits NM or Romex in conduit. I’m just assuming he is using NM/Romex based on the description. If it’s individual wires- yes a box or back to back LBs.

 

[Tractor Seabee]

While I am here perusing TBN instead of counting sheep!

They make a 4 11/16 X 4 11/16 junction box with 1" knockouts or use a step drill and bore out the 3/4". Nipple out of your condulet into the back of the box, a chase nipple may work depending on wall thickness and exterior conduit stand off. Running Romex inside conduit may be code OK but is a waste of money. This assumes you come through the wall under the panel so a short piece of conduit up from the junction box. Put a 2 gang mud ring on the J box for a blank cover. I would use PVC conduit all the way. Why are you using schedule 80 conduit above ground? You don't say what size and type wire you are using.

Some pictures would help us design your solution.

Ron

 

[mbohuntr]

Life is easier if you run your power thru 1.5", or 2" conduit. Then you can run a "mouse" with jet line to make pulling a snap. Take a grocery bag, wad it up and tie it to jet line. Use a vacuum to pull it thru. Pull from LB to LB then push thru the lb later.

 

[plowhog]

My electrician asked what size conduit I would run. I said 2". He said: "oh gosh, one inch is fine." Hmmm.

I'm going to connect to a 30a breaker. Electrician said either #10 or #8 wire, with #8 preferred. He said get a roll of #8 black stranded and we can use phase tape.

btw, code around here requires any above grade electrical PVC to be schedule 80. And I believe schedule 80 is recommended also in any driveway situations where a vehicle will travel over it.

I looked at every box at Lowe's and only found 1/2" and 3/4" knockouts. Never thought about using a step drill and keeping it at 1" with no reducer. That would sure making pulling wire a lot easier. I need to go get a few 1" male adapters in place of the reducer and 3/4" male adapters I was going to use.

 

[s219]

1" conduit seems awful small to me. I normally do 1.5" minimum, or 2", but it actually depends on the wiring gauge, wiring jacket, and ampacity, so check the code/specs to be sure it's all correct. You always need to have a certain amount of air space in a conduit per code.

Depending on the wiring and how it may transition, I have run conduit into a building in a couple ways.

If you have access under the wall or under the footing, or can bust through the wall/footing below the soil level, just run the conduit directly into the building and up the interior wall. Easy to do prior to pouring a slab in barns, maybe not so easy in other scenarios.

For all other cases, I run conduit from ground up the side of the exterior wall and attach it (via threaded threaded adapter) to a junction box mounted on the exterior wall (and caulked/sealed to the siding to be protected from weather). There are various sizes of gray PVC junction boxes that you can use. For my generator shed I used a 12x12x8" box, in other cases I have used 6x6x4" box. You can cut holes in the box as needed to attach conduit.

Then from that junction box, run through the wall. If using jacketed wire rated for plenums, such as Romex, you can simply drill a hole. For single conductor wires, you need to have conduit. A short section of conduit with nuts on each end can join the exterior junction box with your interior box, be it a breaker panel, load center, other junction box, etc.

I attached a photo of one such arrangement where the box on an exterior wall was simply used as a transition and a place to contain a slack loop of cable (I love to have slack in strategic places for future work, if something needs to be repaired or swapped out). This is on my generator shed, and that is 1/0 aluminum XHHW wiring. That particular wiring was run continuous from home to load center in the generator shed -- on the other side of the junction box is a load center with a single 100A breaker. Past that, the wiring transitions to fine strand copper to properly handle vibrations when attaching to the generator.



If you happen to be joining different wire types, the exterior junction box is a good place to do that. For example, for my barn power line, I have #6 aluminum single conductor wires running underground, but it marries up with jacketed Romex copper to tie into my home's main breaker panel. The exterior junction box is the place where the two wire types meet up and connect. The box is a convenient, code-acceptable place to make the connection and gives you a lot of room to work. The box is sort of an intermediate meeting place where different types of wire (plenum rated Romex coming through the wall and single conductor XHHW coming from underground) can meet up and satisfy code in both ways. Even if using jacketed wire on both legs, say Romex for interior and UF from underground, the exterior junction box is a good place to tie them together.

A final benefit of the exterior junction box is that it lets you wire the project in stages -- just leave the unused ends of each leg of wire curled up in the junction box (and properly terminated as necessary) until you complete the wiring with other legs coming into the box.

 

[s219]

My electrician asked what size conduit I would run. I said 2". He said: "oh gosh, one inch is fine." Hmmm.

I'm going to connect to a 30a breaker. Electrician said either #10 or #8 wire, with #8 preferred. He said get a roll of #8 black stranded and we can use phase tape.

btw, code around here requires any above grade electrical PVC to be schedule 80. And I believe schedule 80 is recommended also in any driveway situations where a vehicle will travel over it.

I looked at every box at Lowe's and only found 1/2" and 3/4" knockouts. Never thought about using a step drill and keeping it at 1" with no reducer. That would sure making pulling wire a lot easier. I need to go get a few 1" male adapters in place of the reducer and 3/4" male adapters I was going to use.

For 30A run less than about 250' distance and only used as 240V AC, #10 is fine in many cases. #8 may be required to reduce voltage drop over longer distances with higher amp loads, and/or if you are using individual 120V legs (voltage drop is more severe on lower voltage). There are calculators online for voltage drop, so you can play with voltages, amp loads, and distances to see what works.

I ran #10 copper about 250' for my pier power line, mainly to power a boat lift with 240V. I do use one of the 120V legs to power a battery maintainer on the boat (very low amperage) and an occasional power tool and the voltage drop is still acceptable. For more extensive 120V use I would have run #8 copper. But at the time I spent over $300 on #10 copper and was more focused on keeping cost reasonable for the main intended 240V purpose of the boat lift.

I used 1.5" conduit for the #10 copper where the wire ran from underground up to my exterior junction box on my house, and where it ran from under my pier up a piling to a breaker box. I would not have wanted to go any smaller as the UF wire I was using was about 1" wide and not easy to push through the conduit. If using individual conductors you can go slightly smaller but I probably wouldn't go smaller than 1.25". 1" seems too small to me unless we're not on the same page as your electrician for some reason.