Planning for Wiring Outdoor Privacy Wall/Retaining Walls

16 years ago

Over the coming months I will be constructing two concrete block 5' or 6' high walls with stone veneer, each about 35' long running my property perimeter. Also, I will be constructing three concrete block 3' high retaining walls, each 30' long, for a total of 5 walls. Each wall will have 120v light fixtures at or near the top (shining down the wall) spaced about 8' to 10' apart, or about 4 fixtures per wall total. The bulbs will be very low wattage, more decorative but also mildly functional (For reasons not relevant to my question, low voltage lighting isn't a consideration - or desire - here).

An electrician will be doing ALL the wiring and connections down the road, but I need to get a handle on the wiring plan prior to pouring the concrete footings for each wall, as I intend to have a buried PVC conduit that comes up through the concrete footing, and into the inside of the wall to each fixture, then back down inside the wall, back through the concrete footing, into the main trench, and onto the next fixture where it repeats the process.

While all will be subject to the advice of my electrician, let's assume each wall will have its own circuit, say 20amp, #12 Type TW conductor in its own 1" Sched 40 or 80 pvc conduit, buried 18" deep directly in front of each wall, all running from a newly-installed outdoor panel.

Question #1: Will I need to have the PVC conduit make an elbow turn from the main trench at the location of each fixture and go up through the concrete footing and the wall to the fixture, and then back down in an adjacent pvc conduit leading back to the main trench, make an elbow turn and continue... OR can the conductor go up the wall and back down in the same conduit, thereby only requiring a PVC Tee fitting. I would hate to pour the concrete with only one conduit embedded only to find out I should have had two.

Question #2: If I can use a Tee fitting, could I also include in the same conduit the conductors for a different circuit leading to a wall further out?

Question #3: Is the proximity of the conduit to the rebar in the concrete wall an issue of which to be aware?

Question #4: Can a conduit with speaker wire, ethernet cable, and coax cable share the same trench (not conduit) as the 120v conduit? Is there a minimum distance requirement?

Again, I won't be doing any of the wiring but I'd like to have as much planned out before a walk-though with the electrician.

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Comments (5)

joed
16 years ago
#1 If you use a T fitting you will never be able to properly fish the wires. Two conduits with sweeps should be used.
#2 the conductor for several circuits can be contained in the same conduit. Perhaps a waterproof junction box at the bottom of each fixture so that only one conduit is required up the wall and then you can bypass with conductors for other circuits without going up/down the wall.
#3 proximity to rebar is no concern. You could use the rebar to hold the conduit in place by tieing the conduit to the rebar.
#4 Share the same trench no problem. Interference could be an issue if they are too close.
spencer_electrician
16 years ago
One circuit per wall is kind of overkill unless you're putting in receptacles as well. Even 2 20 amp circuits sharring a neutral would be enough. Not much need for 1 inch conduit, 3/4 would be an easy pull.
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It's difficult to predict the life span of your wall. A major unknown is how the fence upright supports are integrated into the wall and if they extend into the footer or below. If I understand your first post, the block cavities were originally filled with dirt. I have a hard time believing the contractor removed all that dirt and replaced it with concrete unless I saw him do it. I would probably dig down behind the wall and drill through the block to see what was in the cavities near the footer. With all the unkowns, here is my best guess. There is no steel tie from wall to footer and a major weakness is at this junction. The soil will exert a force against the wall that would over many years cause the wall to tip over. The fence will have an added force that at times will be in the same direction as that of the soil force and at other times the fence force will counter the soil force, but only in the area of the fence supports. The effect of the live load from the fence will cause hairline cracks between wall and footer beginning at the fence support and then elongating. The fluctuating forces will also lead to vertical cracks through the wall somewhere between the fence supports and the mid point between fence spans. When the cracking reaches a critical point the wall will begin to move. If the failure occurs in the spans between fence supports, it will likely be a slow failure. Failure at the fence supports in a wind storm where the wall blocks separate near the supports could be sudden. Expect the cracks. Watch for any shift or movement from vertical or any irregularity in the wall face. Be prepared to make repairs. One to two years for beginning cracks. Two to eight years to first wall movement.
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gilshultz
16 years ago
Sounds like a fun project. My personal preference would be to put conduit in the wall and connect one end to a box for the fixture and the other to a common junction box in the wall. Note this box must be accessible from the surface when the wall is finished as must the others. Adding a few plugs would be good. The reason for doing it this way? Later if I change my mind the wire becomes accessible and changeable. Plastic conduit is cheep and easy to work with. Talk to your electrician as to what to put in and what the local code is. You can use pieces of wire to attach the conduit to the re-bar before the cement is poured.
jeffnickc
Original Author
16 years ago
Thanks for the tips; at least one of the walls will have receptacles, but for those that don't perhaps two walls on one circuit makes more sense (and will be easier as well).
gilshultz
16 years ago
Sorry I was not very clear, I was just referring to the walls proper. You can run each wall conduit back to the house or from wall to wall then the house, depends on what is convenient. Just be sure to size the conduct properly (larger is ok) for the number of wires required. Your local building inspector can tell you what he will accept. Add one wire for the earth ground, it must be connected to your panel.

I would suggest you get some landscape wire and run one to each wall, then you can connect speakers to it (the purest s will complain) but it works. 5 amp at 8 ohms will give you about 200 watts. Remember to check the voltage drop in the wire so you can size it properly.

Planning for Wiring Outdoor Privacy Wall/Retaining Walls

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