When are a cable duct and spiral conduit used?
A duct and conduit protect the cable against mechanical wear, UV and liquids and organise the route. A duct is preferred in a closed panel, and split conduit on vehicles and in moving areas. An important rule: do not carry power and signal cables inside the same conduit; in practice leave at least 15 cm between them.
The choice is made according to the harshness of the environment and the need for access.
- Cable duct: used inside panels and enclosures where a tidy route that allows cables to be added later is required. Do not overdo the fill ratio; a tightly packed harness heats up and its current carrying capacity falls.
- Spiral conduit: preferred on vehicles and work machines, in vibrating and dirty environments. The split type makes adding cables later easy, the closed type protects better.
- Environmental suitability: choose a UV-resistant type outdoors and a heat-resistant type in the engine bay. Standard PVC conduit hardens and cracks in a short time near an exhaust.
Application rules:
- Separate conduit for power and signal; 90 degrees if a crossing is necessary.
- Conduit alone is not enough where cables pass through holes in sheet metal; also use a rubber grommet.
- Before the conduit end enters the enclosure it is routed with a downward loop, that is, a drip loop; the water drips at the lowest point of the loop.
- Conduit can carry water inside itself; make sure both ends are positioned so as to allow drainage.
- Close unused enclosure holes with blanking plugs and choose the gland to suit the cable diameter.
The full topic: Installation, redundancy and field continuity