questions about underground work & putting a cristy box in the ground

[zappy]

I got a few 90's coming up, and I was going to place a cristy box over them. Should the cristy box be slightly above grade? I think it would sink a little after a while, and if someone steps on it once in a while. The 90's inside, should I put duct seal inside them after I splice, so no water gets in them? This is a apt. building in the front yard, where i'm putting lights. Thank you for your advice.

 

[masterinbama]

I always bed mine in 6" of pea gravel and make sure the splices are watertight. We have one engineer in our area that wants them surrounded with a 12" concrete apron.

 

[iwire]

If you have splices in there they are required to be rated for wet locations.

 

[zappy]

Yes I was going to use waterproof wirenuts. So put gravel underneath for drainage I take it? What about placing cristy box above grade a little for settling good idea? And putting duct seal in the conduit so water doesn't get in? I just want to pass inspection. Don't do much underground work. So any advice all take it. Thanks.

 

[iwire]

I have never bothered with duct seal excpet on the runs heading into the buildings.

I do use bell ends on the PVCs

If I had my way I would set them high but most customers want them at grade.

Rock is great and we use it when its around but not always.

 

[Power Tech]

I always bring all conduits grouped up on one side of the hand hole.

This is important if the conductors are large.

This gives you space to neatly terminate and bend the conductors over.

Don't forget some 3/4" rock inside too for drainage.

I frame it 6" with 3/4" rock and 1" above planter grade.

 

[jckenner]

The major problems I see with underground is people stub conduits up either too high or not high enough into the box. Keep them down low enough that the wires can gently exit the conduits. I normally use a pipe reamer on smaller PVC to achieve a rounded edge on them. Keep them up high enough that dirt or gravel won't be getting back in them. This is what I use duct seal for: it's to keep crap from getting down your conduits. You needn't worry about water getting down the pipes -- it will often seep into your pipes just from being underground. They don't always manufacture electrical PVC and fittings to tolerances that keep out groundwater so it can sometimes take more attention to joints in PVC than most electricians make. Since you're using W rated conductors, this isn't an issue unless you're running them into a below grade structure. I like to pour a 1" or 2" layer of sackcrete in the bottom of a Christy to keep gophers and other ground critters from filling it up with dirt. You're left with a primo box interior. Of course the Cadillac install includes the concrete apron that Mr bama mentioned. That's what Caltrans makes you do, and of course those boxes don't settle at all. Otherwise, it's nice to keep them up at least an inch in landscaping, as long as it's not a trip hazard, otherwise (like in a lawn) you'll need to pay more attention to compacting under the box.

 

[wawireguy]

I'd make the box flush grade or someone will eat it up with a lawn mower.

 

[hardworkingstiff]

When I prep manholes for a concrete pour at gas stations, I install pressure treated lumber (turned flat) under the skirt of the manhole. This keeps it from pushing down in the sand or gravel when the concrete finishers are working and step on the manhole while finishing the concrete.

I believe this same methodology would keep your box stable for many years (provided the ground under the wood is well compacted).

 

[220/221]

I've been using Carlon PVC boxes for the splicing and installing the Christy box over that. Install the Christy box so it end up flush with the turf or 1/2" above dirt/gravel grade. High enough where it won't pool water and/or end up buried and low enought not to be a trip hazard.