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Old 01-05-2010, 07:11 PM   #146
Ran D. St. Clair
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Join Date: Apr 2009
Posts: 212
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I Conduit (and so can you)

I have pretty much completed the installation of the electrical boxes and conduit. The next step is to pull the wires. I should mention that I used plastic “handy boxes” for most things. When building a wall inside of existing FRP with 1.5” x 1.5” studs and using ½” plywood, you need a box that is no more than 2” deep. Handy boxes are perfect at 2”. They are also readily available everywhere, made of sturdy grey plastic, and have 7/8” knockouts on 3 sides. They are a bit small, and only contain a single outlet, but they can be screwed directly to the FRP with self tapping screws so they can easily be placed anywhere.

I used ½” water tight flexible conduit for most everything, even the relatively straight runs. It has thinner walls than the rigid grey plastic ½” conduit which allows for a little more room to pull the wires through. It also bends easily around corners at any reasonable radius, which means you can keep the runs as short as reasonably possible. It also avoids the need for a lot of individual pieces, 90 degree bends, offset pieces, couplers, etc. and just generally makes life easier. The conduit fits nicely into the 7/8” holes in the boxes. I did not use any clamps or fasteners at the boxes, just ran the conduit through the holes and clamped it to the walls.

I did run a bead of “Amazing Goop” (http://www.eclecticproducts.com/ag_adhesives.htm) around the joint where the conduit enters the boxes to seal the entrance and make a tough flexible joint. Goop is a great glue for things like this. It grabs onto shiny smooth plastic better than most things, but if you have to you can rip it apart and peel the glue off to fix a mistake. In this case I wasn’t really trying to make a watertight seal, but I did want to make sure that the conduit didn’t slide around or pull out of position when I was (will be) pulling the wires through. There will also be quite a bit of the canned spray foam injected around the conduit to fill spaces around the Max-R insulation panels, and I didn’t want it finding its way into the electrical boxes.

I don’t know if this technique is per code, or if there is even a code that applies to what I am doing. I am an electronics engineer, not an electrician. I will make things that work, and are hopefully safe, but I have no idea if they meet code (and I really don’t care).

Some of the corners I have to go around were a bit of a challenge. The bend from the wall to the ceiling was a little tight as the inner plywood box has sharp corners while the outer FRP box has aluminum extrusions that are somewhat in the way. One technique that opens up the radius when going around a 90 degree corner is to approach the corner on a 45 degree bias. In other words, you don’t go straight up the wall and straight across the ceiling. Instead you go up the wall at up to 45 degrees near the ceiling, and then you exit into the ceiling at 45 degrees as well. It’s hard to explain with words, so check out some of the pictures if you need an example. They are located as always under keyword “Stealth”. By using this technique you can open a 90 degree bend to about 130 degrees, which opens up the radius and makes the wires easier to pull through the conduit.

I did as much planning on paper as I could in an effort to avoid conduit crossing in the walls. The conduit is 7/8” diameter, so at the point of crossing it is 1 ¾” thick. Considering that the studs are only 1 ½” thick it won’t fit by ¼” of an inch. I experimented with notching the conduit slightly to make it fit, but ultimately I decided on a simpler method. I just run the conduit where it crosses and then afterwards heat it with a heat gun and smash it down a little. The conduit becomes a little oval at the point of crossing but each side only looses an 1/8” of an inch or less, so it’s not much.

You may note from the pictures that the walls are rather densely packed with conduit. I might have gone a bit overboard, but my thinking was to accommodate every wire I could think of, and a few that might never be used. I not only used conduit for the AC wiring, and the 12V DC wiring, but also for things like antenna wires, to the TV’s and computers, Ethernet wires between the computer and the PS3, video and audio wires between the PS3 and the TV’s, and USB wires between the computer and the Wi-Fi amplifier. It may well turn out that I forgot something, and it will have to be tacked along the wall on the inside, but at least I tried.

All that conduit will negatively impact the R value of the insulation in my walls. It will also mean that I have to cut lots of little oddly shaped pieces of R-MAX insulation to fit around it. That, and I already mentioned the canned foam to fill in all the gaps that will be created. It’s going to be tedious installing the insulation when the time comes, and I am sure I will end up wasting a bit in the process. The ceiling insulation, on the other hand, is 4 ½” to 5 1/2” thick so the loss of R value there should not be significant. Also the right side wall has more insulation as an unintended consequence of the side doors which became awnings so insulation and crossing conduit on that side is no problem.

Running conduit through the studs required lots of drilling, but nothing difficult, just a standard 7/8” spade bit. Some of the electrical boxes required additional holes not supported by existing knockouts. A 7/8” hole saw made quick work of those. You do need to be a bit careful though. That hole saw will grab into plastic and like to rip your hand off if you aren’t careful.

To be continued…
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