The conduit is the part of a house wiring job that nobody sees after the plaster goes on, and it decides whether the wire inside can ever be replaced. A conduit that is crushed during casting, filled beyond its capacity, or run without a pull wire turns a rewire into a demolition job. Choosing the right type for each location is the first step; installing it so that wires can still be drawn through it twenty years later is the second.
Rigid PVC conduit: the default for concealed wiring
Heavy-gauge rigid PVC conduit is what almost all concealed wiring in Indian homes uses today. It does not corrode, it is a non-conductor so it never becomes a shock path, and it is cheap. It is available in light, medium and heavy grades; for casting into slabs and chasing into walls the heavy grade is the correct one, because the lighter grades flatten under wet concrete and the chaser’s hammer. Use ISI-marked conduit to IS 9537 Part 3, with matching bends and junction boxes solvent-welded, not pushed together. Sizes of 20 mm and 25 mm cover most domestic circuits, with 32 mm for the runs from the meter to the distribution board. The conduit fill chart shows how many wires of each size fit a given conduit without jamming.
Galvanised steel conduit: where mechanical protection or fire matter
GI conduit is heavier, dearer and slower to install, and it needs earthing along its length because it is metal. In return it cannot be crushed, it does not burn and it gives a degree of screening. It belongs in surface-run wiring in garages, workshops, plant rooms and exposed external walls, in any run that could be struck by a vehicle or a trolley, and wherever a local fire code asks for metal containment. It is rarely justified inside a modern apartment, where the wire itself now supplies the fire performance: a low-smoke grade such as Shakti FR LSH in PVC conduit is the normal specification for corridors and stairwells.
Flexible conduit: for the last metre only
Corrugated flexible PVC conduit is for short connections that cannot be made with rigid pipe: the drop from a false ceiling to a light fitting, the link to a motor or a pump that vibrates, the run into a modular kitchen where the route bends around cabinets. It should not be used for whole circuits. Its inside is ribbed, so wires are hard to pull and harder to replace, and it kinks and collapses where a rigid conduit would not. Where a longer flexible run is unavoidable, use the larger size and keep bends generous.
Installation rules that matter more than the type
Whatever the conduit, keep fill low enough that the wires slide; a conduit that has to be filled by force will never be re-wired. Leave a nylon or GI pull wire in every concealed run and label both ends. Provide a draw box at each change of direction beyond two bends, because wires cannot be pulled round three 90 degree bends in a slab. Seal open ends during construction so mortar does not fill the pipe. Keep power and communication conduits separate, as the shared conduit guide explains. And run each circuit’s phase, neutral and earth together in the same conduit, never split across two, or the cables will heat and the RCCB may trip for no visible reason.
Finally, an outdoor conduit run in sunlight needs UV-stabilised black or grey pipe, not the white indoor grade, which becomes brittle in a few summers. Inside it, use a heat-resistant wire such as Anushakti HR FR LSH for circuits that feed outdoor pumps, gate motors and terrace equipment where the conduit surface runs hot in the afternoon.