PVC has one flaw that must always be considered when using it for electrical conduit runs.  PVC has a very noticeable expansion rate when exposed to sunlight and heat.  Of course, when the ambient temperatures cool down, the PVC will shrink back.  However if the conduit is hung on the side of a wall when exposed to the sun, when it expands the conduit will droop down.  When it cools off the droop does not return to its original shape.  As long as PVC is installed in the shade or buried in earth or concrete it will not expand enough to be a problem.

One time, when I first began using PVC conduit, I installed a run on the side of a building, under an eave.  Where it remained in the shade, it would hold fine.  Where it was exposed to the afternoon sun it warped something terrible!  Another concern with the expanding PVC is that the wiring does not expand.  (at least not at the same rate.)  This can cause the longer conduit run to pull the wiring out of its connections.

About that time I discovered expansion joints.  Expansion joints are fittings you fasten at each end of the conduit with a sleeve in the middle.  The sleeve permits the conduit to expand and contract without harming the enclosed wiring.

On one occasion I was laying a long run of PVC conduit to be covered with cement.  The sun came out and bowed the conduit right up into the air above the limits of the forms.  I had to re-do the run and make sure the cement was poured before the sun became too hot.  An expansion joint would have worked very well there.

Recently there have been other advances in “plastic” conduit.  It is more expensive but it is also very useful.

Another aspect of PVC work I have learned the hard way is regarding the gluing of the PVC parts.  When gluing the PVC together, do not let the glue get inside the conduit itself.  That will produce two problems.

It can cause what you put into the conduit to become fastened to the inside wall of the conduit.  Things that can become glued in that manner are wire, fish tapes, etc.  That is annoying to say the least.  The second problem is that a buildup of glue on the inside of the conduit will reduce the available inside diameter.  Not only will that increase the resistance when pulling wire through the conduit, the reduced area can produce a wiring hot spot.  Wire-fill in conduit is predicated on enough air movement to reduce heat buildup.

Some things you have to “Learn by Doing” because they are not generally taught in classes, or the electricians that already have the knowledge forget to pass it on.

We still use steel conduit on large commercial and industrial jobs, but PVC has almost taken over most conduit work.

One time I was called down to a restaurant to determine why there was an electrical problem in the kitchen.  I determined that there was a short somewhere in one of the kitchen circuits.

This particular kitchen had a concrete floor and running along in the floor was a crack.  The wiring had been installed in metal conduit buried in the floor.  There was also a water leak that, for some indeterminate time in the past, had been running water down the crack to the floor below.  I determined that the short was in the conduit buried in the floor.  Therefore I needed to tear up the concrete floor, find the conduit that held the short and correct the problem.

We found the problematic conduit.  It had been completely rusted away for about 10 inches by the running water.  The wire insulation had also been eaten away, exposing the copper wiring to the water and metal.

At that time PVC conduit was not yet available.  I had to cut the metal conduit back to where there was clean pipe at either end, insert a short piece, re-pull the wire, and re-pour the concrete.  I had no idea how long the fix would last, because basically, I had just recreated the original circumstances.

I mention PVC because of its superior properties when it comes to using it as electrical conduit.  PVC is an acronym for Poly-Vinyl Chloride.  This is an ideal electrical conduit because it doesn’t produce condensation inside the pipe.  It has a certain amount of flexibility and stretch.

It does however have a few downsides to take into account.

PVC does not conduct electricity, so it cannot be used as a grounding element in an electrical system.  It does not bend as metal conduit does, so it is less convenient for use.

The way that we have overcome these failings is to carry a ground wire inside the PVC conduit and to carry manufactured, pre-bent, fittings.  It is also possible to bend PVC by heating it at the point of the bend, perform the bend, and then cool it quickly so that it comes out of its Delta and reforms with its original hardness.

Bending PVC by means of heat has two concerns; 1) the conduit wall may be slightly thinner and less able to withstand outside pressure.  2) it is very possible to overheat and thus burn the conduit beyond redemption.

Recently there have been some advances in PVC bending.  There is now available a spring insert that can be placed in a PVC conduit at the point of the bend.  The PVC is then bent as you would a piece of metal conduit and the spring insert is then withdrawn.

Here again there is the concern about the conduit wall thickness after performing such a bend.  The upside is that, as in the case of the concrete floor experience above, a PVC conduit would last much longer and resist the possibility of corrosion.

In fact the half-life of PVC has not yet been determined.  It has only been around for a short time.  Not long enough to determine its ultimate longevity.

I have some very vivid scenes in my mind from driving back and forth to Pullman for various jobs.  I remember when four of us were driving to Pullman before dawn.  When the sun came up on our left, we were all talking and visiting as the sun rose over the tops of the hills.  All at the same time we all stopped talking to look at the beautiful sight.

Another time I was driving alone on a wintery day.  It was January 1.  As I came up out of the valley by Spangle, the early morning sun just flashed before my eyes.  I realized that a cut in the hills south east of me had allowed the sun to flash through for a brief moment.  I was always curious about that cut in the hills, and wanted to drive down and find it, but I never found the time.

On a different wintery day, on another trip to Pullman, as I passed through the Spokane area on my way south, I noticed small patches of green and red in the snow, on and beside the highway.  I realized that it was anti-freeze from radiators that had been damaged in traffic accidents.

After I passed downtown Spokane there were no more colorful green and red patches.  After I passed Rosalia, there was no more pavement to be seen because the snow was packing as it fell.  After a short time I would notice a black patch on the white road.  That meant that some of the packed snow had kicked loose to reveal the black pavement.  Using the intermittent black patches, I was able to navigate my way to the job site in Pullman.

I worked all day on the college campus at Pullman.  All day long I wondered how I would make it home.  When it was time to go, I called my wife and told her that if I wasn’t home in 2 hours to come looking for me.  She knew what route I would be taking.

As I pulled up to the highway the night was lit by a full moon, … and the road was perfectly clear.  Apparently either the road crews or the wind had completely cleared the highway.  It was one of the easiest drives I ever made.  I think I met no more than 5 cars on the road on that trip home.