Need to bury a junction box and don't know if the ones at Home Depot
etc are watertight or could be made watertight. Essentially, need to
take a 12/3 line off the outside of my house, into conduit and into
the J box, then split into 3 seperate 12/3 lines in conduit (down the
driveway, along the driveway and to a flagpole).
Just be sure it is listed as a wet location box (usually grey). Nothing
underground us really "waterproof", that's why everything has to be listed "wet
location". Use wet location splices!
You are really better off if you can "homerun" all of your current carrying
conductors or splice them above ground.
Ask electricians who do old work and they will tell you virtually every
underground raceway system collects a certain amount of water.
Thanks for the info. Unfortunately, I have no choice but to bury this
thing otherwise, I'd have to dig 3 extra trenches out into the yard
about 200 feet. Good to know about wet location splices though.
In reality there is no such animal. There are some designs that will keep
water from entering if you were to bury the box with no penetrations for
conduit, or cable entry. As soon as the box has penetrations cut into it all
bets are off. If the installer takes great pains, is very careful with the
installation, and uses connectors designed for the purpose, water entry can
be kept to a minimum, but if there is any moisture available underground
(high water table, or consistent rain, water collecting on the ground above
the box, etc.) there will be water in the conduits, and boxes.
If you use an approved underground box, appropriate connectors, and good
workmanship, to keep the water entry to a minimum, chances are you wont
experience too much difficulty. If water conditions exist as mentioned
above, have your electrician use epoxy filled splice pouches (made by 3M and
others) to seal the wire nuts in the box (leaving the wires stripped out of
the cable a bit longer in case they need to be cut loose, and reconnected
later), and don't worry about the water.
Remove the two fish in address to respond
Have you considered some kind of access hatch? (perhaps one of the ones
sprinkler systems use) The last thing you want is that splice failing
underground, and having to dig again. I myself would look for ways to keep
the splices above ground.
Two things generally determine 'legality'. 1. the item is listed (usually
UL), which means 'approved' for the location in question, and 2. the AHJ,
that is the "authority having jurisdiction".
Number 2 is especially important. Usually, if you call the local
"authority" (read "Electrical Inspector") and ask him what to do, maybe even
ask if this or that will work, you will get his pre-approval for what you
want to do. Doing this may even allow him to bend the rules a little for an
unusual installation. If you blindly stumble on, you can wind up ripping
things out and starting over, thus justifying the cost of using a real
electrician in the first place.
In forty plus years in this business, number 2 has never failed me, tho NOT
using number 2 has cost me a couple of times. (slow learner)
oh yeah....I would ask if your two part epoxy is UL listed as an insulating
medium for the voltage at which the splice will operate?
It's not rocket science but probably more involved that you thought -
Telecoms systems use underground junction boxes all the time, and the phone
The standard method we use is to sink a small concrete pit (appropriately
sized), with a lid, with the conduits entering and leaving through holes
punched in the pit walls. The pit has holes in the bottom to allow
stormwater buildup to drain away. Once the cables are pulled, you seal the
conduits with expanding foam to prevent the conduits becoming part of your
The jointing is done with 3M epoxy splices (as mentioned in other posts) or
by using a more expensive "openable joint" (OJ) if you need to change things
later (Google search).
Once the jointing is done, the whole pit is filled with sand or weak-mix
cement to keep (most of) the water out.
The other responders have given you good input. I would try to find a way to
locate an outdoor-listed box above ground, and run the conduits up into the
bottom of it. You can buy them with various threaded hub arrangements, and
you might be able to hide it in the landscaping somewhere.
Actually, even when the cable is buried, the junctions and cable splices are
usually above ground around here (Virginia).
When a underground telephone subscriber "drop" is damaged (by construction,
lightning, trees, or whatever) "they" do make an undergrond splice. The
splice is protected by a mess (I use the word deliberately) of silicone
The silocone jelly approach is also used to keep water out of splices for
high voltage power (19.8 kV) splices. For low voltage power they keep the
water out with a layer or two of special tape.
Most places would consider what you described to be an underground "vault."
It's equivalent to pulling the splices in a basement.
Where is that done?
Not over here. It's extremely common to find telephone, fibre and cable
services below street level - all terminated in concrete pits using Openable
Things that require regular access, like multiple consumer connections, are
run to above-ground pillars, but if we are talking about cable splicing and
jointing - yep, that's what the pull-pits are for. (and BTW, the pits are
usually full of water :-( )
Industrial sites.. Petrochemical plants.. Factories.. Airports.. all kinds
of places. The need to go to this extreme would depend on the service you
are running, the need for regular access and the voltage involved. *All* HV underground cable-jointing I've seen (and I've seen a few) have
used the weak-mix method and several LV ones also - particularly where you
have a low water table problem or a flammable liquids site. I have also
used sand-filling with optic fibre cabling to protect the cable against
potential pit failure in high traffic areas.
The idea is to "bury" the cable in a water-excluding mix to keep the splices
as dry as possible. (The sand used is the really fine stuff - and it's
amazing how well it works - but for larger pits, weak mix is better)
Thanks everyone for the great feedback. After much thinking and such,
we actually ended up not needing a J box. We're running out of the
house from the existing outside box to 1 lamp, then on to the other
and then to the final lamp. To get over to the other side of the yard
and the flag pole, we're going to run an entirely new circuit out the
side of the house and up to a switch in the foyer.....