Conduit is any system designed to protect electrical cabling.
Various sizes of conduit is available to accommodate multiple cable runs. Conduit of a flexible tubular design is a popular choice for protecting cable.
We tend to use the term trunking for rectangular section conduit that has a removable lid designed for easy access.
During the first fix is the time to consider conduit. On many older canal boat conversions the fitters simply ran the PVC cased wiring underneath the panel work in direct contact with the polystyrene sheet insulation. It’s only years later that we see the negative effects of the cable insulation reacting with the polystyrene. This happens because compounds called plasticisers are used in the manufacture of PVC. They impart desirable physical properties to the PVC such as flexibility and strength. During the manufacturing process these plasticisers are not fully bonded to the PVC compound and therefore under certain conditions they can become “detached” or “extracted”. The problem is that commonly used plasticisers in PVC manufacture are soluble, can be dissolved, by polystyrene and polyurethane insulation. This plasticiser migration will cause PVC insulation on cables to become brittle with the associated risk of exposing the conducting wire underneath to short circuit.
So, on older boats with styrene or PU insulation that is in direct contact with the PVC insulation of electric cable it is advisable to conduit or trunk as much of the cable as you have access to.
For modern craft and new builds, current electrical practise will probably ensure a future proof job is being done. If you are unsure, it’s worth asking your boat builder how they run cables. They will not be offended if doing the job correctly and after all it’s your money!
It’s our nature that at some stage we will find the need for adding an extra socket or light into the circuit. As we’ve kept records of how the cables run (link to keeping a record) we know whether or not can safely tap into the system.
Future proof your wiring by adding the facility to run extra cable in the conduit by adding a pull string. Just in case the current carrying capacity of the existing wiring is exceeded by any modifications you may need to make, a pull string will make adding cable to the existing conduit a whole lot easier.
If running conduit side by side for separate systems, identify the conduit by spiral wrapping different coloured electrical tape along the length. Add this colour coding to your records to make it easier to identify circuits for future additions or maintenance.
The Boat Safety Scheme states that cables should be run as high as possible and ideally 125mm away from potential sources of impact and that conduits must be firmly fixed at 900mm intervals.
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