How to splice into existing underground rigid metal conduit below ground and hide junction box?

Question

I have an existing rigid metal conduit run from the service panel to a junction box location that was previously powering an outdoor appliance. The circuit is 20A and running 12 guage wire. The RMC is buried 6" deep (i believe).

The junction box at the end of the run is a 90 that comes straight out of the ground approximately 6" up in the middle of the lawn.

The owner wants to power a shed/garage ~10 ft away from the current J-box, and wants to BURY the current junction site.

• What are my options to HIDE this splice/junction point? If I dig deeper to 12" or 18" (from the j-box to the shed) can I splice into the current RMC with waterproof splices and run UF wire to where the wire needs to enter the shed?
• If first option is not feasible -- how else can I hide the splice or can I hide the splice whether I can run UF in or out of more RMC? Outdoor waterproof junction box or maybe something like the sprinkler boxes that you can see in the ground? I see 4x4 direct burial j-boxes on HD website -- but would like to know code for this and whether owner has to live with this being visible in the lawn!

Answer 1

314.29 exception allows listed boxes and handhole enclosures shall be permitted where covered by gravel, light aggregate or noncohesive granulated soil if there location is identified and accessible for excavation. I have used landscape border at the ground level to identify the buried location. This has passed inspection just make sure to use a quality listed splice kit as this will be in water at times. Also get some thwn (most thhn is dual listed thhn / thwn) and put it in conduit 1 stick of pipe will get you there.

Answer 2

You can't bury a junction box - it has to remain accessible. The usual thing to use is a handhole - like a box where the lid is flush with the ground. You could get a handhole as small as 12" x 12".

You can bury a splice in a direct burial cable; the problem here would be transitioning from wires in conduit to a direct burial cable. You'd need to make the transition in a box, and the box would have to be accessible.

You could replace the wires in the conduit with a direct burial cable, and consider the conduit just a protective sleeve; this way it doesn't have to terminate in a box. However, the depth is an issue; the direct burial cable has to be at 24" and the existing conduit is at only 6" depth. So the transition from 6" depth to 24" depth would be an issue. I guess you could add an elbow down to 24" on the end of the RMC.

But would that even be compliant? If the pipe doesn't terminate in a box, and isn't really a conduit but just a protective sleeve, is it still allowed to be buried only 6"? That would be a gray area, an inspector may go either way.

Answer 3

There are no scenarios that allow you to reuse any of the THWN wire that is in the conduit now. It is just too short, since as you say it is spliced immediately upon entering the house.

Trying to establish a splice point at the old location will be rather difficult and not worth doing given the low cost of wire. Since you want to go the last 10 feet in direct burial wire, you will need to bury at 24" which means actually 14', and the descent to 2' depth at both ends also needs to be in conduit solely as wire physical protection. To say this is ungainly is an understatement and I think will cost you more than a new wire pull the entire way.

The easy way

This won't seem like the easy way. But that is only because it involves crafts you are unfamiliar or uncomfortable with.

This involves not wasting the long length of Rigid conduit and extending it the extra distance to the garage. Enter the garage in the normal way (up the building side then through an LB conduit body). Then run new THWN wire through it; easy peasy.

Dig up the area under the old junction box. Go as deep as you need to in order to expose the old Rigid conduit. Remove the old 90 degree that takes the pipe upwards, and if there's an elbow there you can cut much of it off rather than dig more dirt to swing it. Leave enough meat on it to get a pipe wrench to unscrew it from the coupler.

From there, trench a little the direction you think the conduit is going, and if the wires are gone you can stick a bit of re-rod in there to confirm direction. Plot out where to put a 45 or 90 bend (45 is better) to get over to the garage. This is metal pipe plumbing and will require you cut and thread pipe, but you only have to trench 8" (to give 6" cover).

You'll need one 10' stick of Rigid, one 90 elbow and possibly one 45. Possibly a nipple or another stick. Rigid is expensive but this little of it is cheap. It'll allow you to use 2xTHWN-2 instead of expensive UF.

It's good to either have a pipe vise and a RiDgid threader, or make a couple runs to the hardware store to have pipe threaded to length... The last one will be somewhat critical, though if you approach the wall at an angle that will make it much less critical, don't select the thru-wall location until the piping has reached it. And don't line up on a joist.

It's a lot of work but its also 90% of the work. Terminate indoors in a steel junction box. Now you pull a black and white THWN-2 and you're done. Very easy pull especially with stranded THWN. Pull the ground off the metal box.

And you have expansion room to blow it out to a MWBC (one more wire) or even pull bigger wire for a subpanel.

The hard way

You can use the Rigid conduit essentially as a wire guard (not as proper conduit) but this will mean running continuous UF all the way from house to garage, and worse, pulling Cable through long conduit, which is the mark of the amateur. You cannot reuse whatever THWN wire is in the conduit now.

You will need to extend the Rigid downward to the 25" depth so the direct burial cable can exit the conduit at a depth that is legal for it. You can

• back-trench the 10-20 feet of existing Rigid conduit so you can bend it downwards so its exit is at 25" depth for 24" cover.
• add two 90's and a nipple to drop the Rigid straight down, but this will mean at least three 90’s in this pull, which will make it a challenge.
• add two 45’s and a longer nipple, which will solve the pull problem but put you much closer to the garage, almost defeating the purpose of not just doing it the easy way (what is that purpose anyway?)

Then you trench at 25" to the garage, where you must use more conduit (90 and stick and LB) as a guard/shield to protect the UF as it rises from 25" depth, then come up the side of the garage to an LB conduit body and on into the garage.

So you still need a whole bunch of conduit, and more of the weird parts... and you only get to run in open dirt for a few feet. You must really like trenching to use this option.

And worse, you have left the customer much worse off than the other option. This provides only for a single #12 circuit and it can never be upgraded. If he ever wants more power in the garage, he's likely to be unaware he could just dig up in the right place and insert the missing 6-7 feet of conduit and have proper conduit the whole way. Not knowing that, he'd just trench a completely new cable.

Honestly this option just seems dumb.