Topic 2 of 5
Conduit, trunking and tray
Containment holds and protects cables, and makes it easier to add or replace them later.
| System | Features | Typical use |
|---|---|---|
| PVC conduit | Light, cheap, doesn't rust, easy to cut and bend | Domestic and commercial, surface or in walls |
| Steel conduit | Strong protection against damage. Black enamel for indoors, galvanised for outdoors or damp | Industrial, workshops, plant rooms |
| Trunking (PVC or steel) | A channel with a removable lid, so cables can be laid in | Many cables along the same route, offices, dado trunking |
| Mini trunking | Small PVC trunking | Neat surface runs in homes |
| Cable tray | Perforated metal tray that cables are tied to | SWA and other sheathed cables in industrial buildings |
| Cable ladder | Ladder-shaped, very strong | Large, heavy cables over long spans |
| Cable basket | Wire mesh, light and quick to fit | Data and small power cables in ceilings |
Will the cables fit?
Too many cables in conduit or trunking makes them hard to pull in, can damage the insulation, and stops heat escaping. The cable factor method checks this: add up the factor for every cable and make sure the total is no more than the conduit or trunking factor. Try the conduit fill calculator.
Good practice
- Remove sharp edges and burrs from cut ends so they can't cut the cables.
- Fit bushes or grommets where cables enter boxes and enclosures.
- Steel conduit and trunking can act as the CPC only if every joint is tight and electrically continuous. Many designers run a separate CPC anyway.
- Fit fire barriers inside trunking where it passes through fire-rated walls and floors.
Exam tip: galvanised steel conduit is for outdoor and damp areas. Black enamel conduit is for dry indoor areas.
Try it: Conduit fill calculator
Mini test
6 questions. Pick an answer to see if you're right and why.