Conduit pipe size for house wiring: 20mm or 25mm? Guide for homes in Siliguri, Jalpaiguri and Malda

For most house wiring, use 20 mm PVC conduit pipe for light and fan points and 25 mm conduit for socket, AC, geyser and kitchen runs. Use 32 mm for the main feeder from the meter to the DB or where many circuits share one route. Pick MMS (medium) grade pipe for walls and HMS (heavy) grade for pipes cast inside the roof slab, and buy only ISI-marked pipe made to IS 9537 Part 3.

This guide is for anyone building or renovating a house, flat or shop in Siliguri, Jalpaiguri, Malda and the rest of North Bengal, and the same advice works for homes across Bihar and Sikkim too. Getting the pipe size right costs very little at the start, but a pipe that is too small or too thin is almost impossible to fix once the plaster and tiles are done.

20mm or 25mm conduit pipe for house wiring?

Think of the pipe as a road for wires. A light or fan point carries only a few thin wires, so 20 mm is enough. A power circuit carries thicker wire (2.5, 4 or 6 sq mm), so it needs a wider road.

Where the pipe goes	Usual wire inside	Pipe size to ask for
Light and fan points, switch drops	1.5 sq mm phase, neutral, earth	20 mm
6A sockets in rooms	1.5 or 2.5 sq mm	20 mm or 25 mm
16A sockets, AC, geyser, kitchen	2.5 or 4 sq mm	25 mm
AC above 1.5 ton, 6 sq mm circuits, pump	4 or 6 sq mm	25 mm or 32 mm
Meter to main DB, floor-to-floor feeder	6 to 10 sq mm	32 mm
Several circuits sharing one route	Mixed	32 mm, or two separate pipes

This table is general trade practice, not a clause from a standard. Your electrician or the building’s drawing has the final word. One common tender specification, for example, asks for power wiring in conduit not smaller than 25 mm%20CONDUIT%20WIRING.pdf) and keeps lighting and power in separate pipes. That is a good habit for a house too.

If you are still deciding which wire goes on which circuit, see our house wire size guide.

How many wires can go in a 20mm conduit pipe?

Fewer than most people think. Wires must slide in and slide out later, so the pipe should never be packed tight. Different references give different counts, because some allow for bends and some do not:

Wire size	20 mm pipe	25 mm pipe	32 mm pipe
1.5 sq mm	3 (tender spec) to 8 (40% fill)	6 to 12	9 to 21
2.5 sq mm	2 to 5	4 to 9	8 to 15
4 sq mm	2 to 4	3 to 6	6 to 11
6 sq mm	– (tender spec) to 3	3 to 5	6 to 8

The lower numbers come from a conduit wiring tender specification%20CONDUIT%20WIRING.pdf) that cites IS 732. The higher numbers come from a pipe maker’s 40% fill chart for straight runs. In a real house, with bends and long pulls through walls, stay closer to the lower number. If you are near the limit, go one size up. The price difference between 20 mm and 25 mm pipe is small next to the cost of breaking a wall.

Remember to count the earth wire too. It also goes inside the pipe and takes space.

What is LMS, MMS and HMS conduit pipe?

These letters tell you how strong the pipe wall is. They are the light, medium and heavy mechanical stress grades of rigid PVC conduit under IS 9537 Part 3, as explained by a pipe maker here.

Grade	Wall	Where to use it at home
LMS (light)	Thinnest	Surface wiring on walls, false ceilings
MMS (medium)	Medium	Concealed wiring in wall chases and brick walls
HMS (heavy)	Thickest	Inside the RCC roof slab, under floors, underground

A common site mistake is thin LMS pipe laid in the roof slab. When concrete is poured and people walk over the steel, a thin pipe can crack or get flattened. Later the wire will not pull through, or it gets damaged on the way. For slab work, ask for HMS. For walls, MMS is the usual choice.

Which conduit pipe is best for a slab and concealed wiring?

For a new house, a few simple checks matter more than the brand name:

• ISI mark and IS 9537 Part 3 printed on the pipe.
• Right grade for the place: HMS in slab, MMS in walls.
• Matching bends, couplers and junction boxes of the same size and make, so joints are tight and concrete slurry cannot get in.
• FRLS or fire-retardant pipe where the drawing asks for it, for example in flats, shops, hotels and hospitals.
• Junction boxes at reasonable gaps. The tender spec above keeps inspection boxes no more than 12 m apart or after two 90-degree bends, which also makes later pulling easier.
• A fish wire (pulling wire) left inside every concealed pipe, so wires can be drawn in after plaster.

Why does conduit size matter in North Bengal homes?

Our weather is hard on wiring. Long, heavy monsoons and damp walls in Siliguri, Jalpaiguri and the Dooars mean wires sometimes need replacing after a leak or a short. Lightning season can also damage wiring and appliances. In a house where every circuit runs in its own properly sized pipe, an electrician can pull out the old wire and pull in new wire in a few hours. In a house with packed or crushed pipes, the same job means chiselling walls and redoing paint.

Also, many homes add ACs, geysers, inverters or an EV charger a few years after moving in. Laying a 25 mm pipe (or one spare pipe) to the bedroom and parking area today keeps that option open. If you are planning the DB too, read how many way DB for home so the number of pipes matches the number of circuits.

Please have a licensed electrician lay the pipes and do the wiring, keep the earth wire in every circuit, and never skip the MCB or RCCB to save money.

What decides the conduit pipe price?

People search “conduit pipe price” a lot, but the rate depends on several things:

• Size – 20, 25, 32 mm and above.
• Grade – LMS is cheapest, then MMS, then HMS.
• Type – plain PVC, FRLS, or metal (GI) conduit for industrial jobs.
• Brand and ISI marking.
• Quantity – pipes come in standard lengths, and bends, couplers, boxes and saddles add to the bill.

We do not publish rates because they move with PVC and steel prices. WhatsApp us your list for today’s rate.

How much conduit pipe do I need for a 2BHK?

There is no fixed number, because it depends on the layout and the number of points. A simple way is to ask your electrician to mark every point on the plan, measure the run from each point to the switchboard and from each board to the DB, then add about 10% for wastage and bends. Count bends, couplers, round boxes and junction boxes separately. Send that list to Shree Shyam Suppliers and we will check it with you before you order, so you do not run short in the middle of the slab work.

Buying everything from one local authorised dealer also helps. You get genuine stock, the same make of pipe and fittings, wire cut to length for each circuit, and one itemised quote for pipe, wire, boxes, switches, MCBs and the DB. Shree Shyam Suppliers has served contractors, builders and homeowners in Siliguri for over 25 years, and you can see our cables, wires and accessories here.

Ordering tip

Send us on WhatsApp: pipe sizes (20, 25, 32 mm) and grade (LMS, MMS or HMS), quantity in lengths or metres, number of bends, couplers and boxes, the wire sizes you need, any brand you prefer, and your site location. We will send an itemised quote for the full list.