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Old 10-30-2016, 01:50 PM   #1
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Running underground electrical advice/considerations


Guys/Ladies...

To preface, I'm almost completely unknowledgeable/inexperienced in running and knowing my options in exterior wiring.

We did run my son's lateral service in Dana Point, but had the POCO directions. ( The few instances that I've encountered I subbed out.)

Objective: My son wants to run/bury a 20A line out to his soon to be gate opener.

He'll be coming off an existing 20A garage circuit (either fishing down the wall from an interior recep and exiting the garage) or somehow tying into a recessed exterior weatherproof recep and scraping the receptical).

Exiting the garage, there is a sidewalk (which we will cut out) but he would like to make the run out the garage as unobtrusive/minimal as possible for aesthetics.

The run will be 30-40 feet, depending on the circuit feed location choosen.

Questions and/or your advice:

1) We plan to pull 3 THHN/THWN stranded thru 1/2 (I'd rather use 3/4) Schedule 40 burried 18". Is schedule 40 ok for our exposed conduit...both exiting the exterior garage wall and coming out of the ground at the opener termination... or does it need to be 80. I'm assuming 40 is fine for burrial?

2) If we come off an interior recep, can we just transition from romex to Thhn in a LB box mounted on the exterior.

3) Is there an available coverplate for the existing recessed exterior recep, that would allow us to tie in a lb at that point... should we decide/choose that option.

4) As an alternative to 2 and 3.... should we go with an exterior mounted weatherproof J box when starting the conduit run. (It would be a little more obtrusive along the sidewalk.)

5) Or is there a better/neater/cleaner recomendation for transitioning to our conduit.

6)Should we put in a slip/expansion joint in a 30-40 foot run... southern california location.

7) Should be a simple pull... but do I recall that conduit joints should not be glued up with wire run in it allready.

Any/all recommendations advice is much appreciated. Thanks

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Old 10-30-2016, 02:25 PM   #2
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Re: Running underground electrical advice/considerations


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"...Is schedule 40 ok?..." = Yes. Schedule 40 is standard PVC conduit. Do not use DBII. PVC conduit is just fine.

"...I'm assuming 40 is fine for burial?..." = Absolutely, yes.

"...2) If we come off an interior recep, can we just transition from romex to Thhn in a LB box mounted on the exterior..." = There are mixed opinions on the acceptability of splicing in a conduit body (such as an LB). Some guys are hell-bent on no, some say its ok. As risk management, I would use a JB, if you can.

"...Is there an available coverplate for the existing recessed exterior recep, that would allow us to tie in a lb at that point... should we decide/choose that option..." = The cover would have to be fastened to it's wall box (with it's 6/32 screws) after the wire is pulled and terminated in the box.....pretty hard to do, mechanically speaking. I suspect that mounting a 1/2" FSU box directly on the existing recept's wall box might be all you can do. Of course, you'd have to bush the center rear hole with a chase nipple and install a bonding jumper from the 1104 wall box to the 1/2" FSU.

"...As an alternative to 2 and 3.... should we go with an exterior mounted weatherproof J box when starting the conduit run. (It would be a little more obtrusive along the sidewalk.)..." = Whoops, yes. I just answered that.

"...Should we put in a slip/expansion joint in a 30-40 foot run... southern california location..." = No. Of course, you can if you want.....but I wouldn't bother.

"...7) Should be a simple pull... but do I recall that conduit joints should not be glued up with wire run in it already..." = Unless you have a ton of 90deg turns in this, just glue the fittings now. However, if you can, pull the wire (or at least a pullstring) before you backfill and tamp.
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Old 10-30-2016, 03:04 PM   #3
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Re: Running underground electrical advice/considerations


An LB most often does not have enough space to allow for box fill when splicing.
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Old 10-30-2016, 03:56 PM   #4
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Re: Running underground electrical advice/considerations


Put an extension box on the exterior receptacle and drop conduit down. Keep the existing GFCI and run off the load terminals. Unless you have GFCI 18" is not deep enough. Sch 40 is fine unless subject to damage. You can't splice in an LB unless it is marked with cubic inches; and I have never seen a 1\2" LB marked.
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Old 10-31-2016, 07:59 AM   #5
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Re: Running underground electrical advice/considerations


Quote:
Originally Posted by Power- View Post
@MTN REMODEL

"...Is schedule 40 ok?..." = Yes. Schedule 40 is standard PVC conduit. Do not use DBII. PVC conduit is just fine.

"...I'm assuming 40 is fine for burial?..." = Absolutely, yes.

"...2) If we come off an interior recep, can we just transition from romex to Thhn in a LB box mounted on the exterior..." = There are mixed opinions on the acceptability of splicing in a conduit body (such as an LB). Some guys are hell-bent on no, some say its ok. As risk management, I would use a JB, if you can.

"...Is there an available coverplate for the existing recessed exterior recep, that would allow us to tie in a lb at that point... should we decide/choose that option..." = The cover would have to be fastened to it's wall box (with it's 6/32 screws) after the wire is pulled and terminated in the box.....pretty hard to do, mechanically speaking. I suspect that mounting a 1/2" FSU box directly on the existing recept's wall box might be all you can do. Of course, you'd have to bush the center rear hole with a chase nipple and install a bonding jumper from the 1104 wall box to the 1/2" FSU.

"...As an alternative to 2 and 3.... should we go with an exterior mounted weatherproof J box when starting the conduit run. (It would be a little more obtrusive along the sidewalk.)..." = Whoops, yes. I just answered that.

"...Should we put in a slip/expansion joint in a 30-40 foot run... southern california location..." = No. Of course, you can if you want.....but I wouldn't bother.

"...7) Should be a simple pull... but do I recall that conduit joints should not be glued up with wire run in it already..." = Unless you have a ton of 90deg turns in this, just glue the fittings now. However, if you can, pull the wire (or at least a pullstring) before you backfill and tamp.
It's completely fine to splice in an conduit body (LB, etc), as long as the conduit body has a cubic inch capacity marked by the manufacturer and the fill does not exceed the marked capacity.
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Old 10-31-2016, 10:03 AM   #6
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Re: Running underground electrical advice/considerations


Quote:
Originally Posted by Power- View Post
@MTN REMODEL

"...Is schedule 40 ok?..." = Yes. Schedule 40 is standard PVC conduit. Do not use DBII. PVC conduit is just fine.

"...I'm assuming 40 is fine for burial?..." = Absolutely, yes.

"...2) If we come off an interior recep, can we just transition from romex to Thhn in a LB box mounted on the exterior..." = There are mixed opinions on the acceptability of splicing in a conduit body (such as an LB). Some guys are hell-bent on no, some say its ok. As risk management, I would use a JB, if you can.

"...Is there an available coverplate for the existing recessed exterior recep, that would allow us to tie in a lb at that point... should we decide/choose that option..." = The cover would have to be fastened to it's wall box (with it's 6/32 screws) after the wire is pulled and terminated in the box.....pretty hard to do, mechanically speaking. I suspect that mounting a 1/2" FSU box directly on the existing recept's wall box might be all you can do. Of course, you'd have to bush the center rear hole with a chase nipple and install a bonding jumper from the 1104 wall box to the 1/2" FSU.

"...As an alternative to 2 and 3.... should we go with an exterior mounted weatherproof J box when starting the conduit run. (It would be a little more obtrusive along the sidewalk.)..." = Whoops, yes. I just answered that.

"...Should we put in a slip/expansion joint in a 30-40 foot run... southern california location..." = No. Of course, you can if you want.....but I wouldn't bother.

"...7) Should be a simple pull... but do I recall that conduit joints should not be glued up with wire run in it already..." = Unless you have a ton of 90deg turns in this, just glue the fittings now. However, if you can, pull the wire (or at least a pullstring) before you backfill and tamp.
Power and RJ and everyone... Thanks for the advice and confirmations ....

Just for my understanding... as I'm not familiar with the term FSU box (and not near an electrical supply)...

Is FSU a reference to what I call a weatherproof outside JB (cast aluminum with watertight screw-in knockouts and a couple of mounting ears)..?

If so... will I find a model as a box extender that will bolt/screw onto an existing 1104 (metal JB...?) and have a 1/2 "knockout" for starting the PVC conduit...

or is your reference to just mounting a full weatherproof box over the existing JB cutout and I guess caulking around that mount... and running a nippel out the back into the existing 1104 JB.

(I guess it's not feasable to somehow faceplate the existing recep box and drop just a plastic LB off the faceplate ...)

Thanks again
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Last edited by MTN REMODEL LLC; 10-31-2016 at 10:09 AM.
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Old 10-31-2016, 07:57 PM   #7
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Re: Running underground electrical advice/considerations


"...Is FSU a reference to what I call a weatherproof outside JB (cast aluminum with watertight screw-in knockouts and a couple of mounting ears)..?..." = Yes, it is.

"...If so... will I find a model as a box extender that will bolt/screw onto an existing 1104 (metal JB...?) and have a 1/2 "knockout" for starting the PVC conduit..." = FSU boxes are not extension rings....and you won't likely find an "extension ring" for this application as it needs to be Nema3R rated (weatherproof).

Another option you might want to try:

Remove the 1104 wall box completely (from it's own hole). This might be tedious and slow, but I suspect it can be done if your resolved. Do not damage the NM. Run the NM cable/s into the back of a PVC 4x4x2 box. This box must be mounted surface, and some siding/stucco would have to be trimmed/cut to permit space the box. The bottom of the box can be used for your 3/4" PVC from the gate.
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