As wiring materials improve, the ducting used for previous generations of wiring can still be useful, but adaptation is necessary. For example, copper wiring has a larger diameter than fiber optic cabling, and as copper wiring gives way to fiberoptic cables, the larger diameter conduit used for copper wiring can be used to house fiber optic cables if inner-ducting is used. To choose the right inner-ducting material, it is important to know what characteristics are desirable.
What is Inner-Ducting?
If you pass a smaller diameter pipe inside of a larger diameter conduit, the smaller pipe on the inside of the larger pipe is called inner-ducting. Inner-ducting helps to separate the delicate cables that are run through the conduit, so that they don't rub against and damage each other. Choosing an inner-ducting material can be complicated.
HDPE vs. PVC
Pipes made from polyvinyl chloride, or PVC, used to be widely used for conduit, but PVC does have some drawbacks. For one, it is not flexible and will break if you try to bend it. For another, as temperatures fall, PVC gets even more brittle. High density polyethylene, or HDPE, on the other hand, is more flexible and more weather resistant than PVC. Thus, it is easy to bend your conduit around corners, and you don't have to worry as much about it breaking when under stress.
Smooth Walls vs. Corrugated
If you use a smooth-walled HDPE conduit, it will have some memory. This is significant because HDPE conduit often comes in rolls, so when you try to pass it through a straight PVC pipe, it can rub against the walls of the PVC. Corrugated pipe, on the other hand, does not have a memory and is more bendable than its smooth-walled counterpart. Thus, if you have the choice between smooth-walled or corrugated pipe for inner-ducting, go with corrugated.
A final term to keep in mind is plenum. Plenum materials are designed to be fire retardant. If you have a material that you have to pass through the ceiling of a building or in any area where the risk of fire is real and present, choosing plenum will help you to mitigate the risk of combustion.
If you need to retrofit a building, you do not necessarily have to rip out all of your old ducting and replace it. As long as the diameter of your old conduit is large enough, you should look into inner-ducting. Check out a company like Cabletec for more information.