Pardon Me, but Your Short is Exposed

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.