TPN main switch (switch fuse unit), 16A to 200A at 415 V — switches the three phases of a three-phase + neutral supply, with a rewireable fuse in each.
- Triple pole and neutral (TPN): switches all three phases together, with the neutral on a link.
- A rewireable fuse carrier in each phase — the only protection the unit gives.
- Rated 415 V; choose 16A, 32A, 63A, 100A or 200A.
- Side handle outside the box — ON up, OFF down, as marked on the label.
- Three switch blades on one bar, moved by a spring-loaded mechanism.
- White metal enclosure with a hinged, screw-fixed door.
- No trip and no earth-leakage protection — add an RCCB for shock protection.
A TPN main switch — also called a switch fuse unit, SFU or TPN switch — is the on/off switch and fuse protection of a three-phase + neutral supply in one enclosure. The side handle switches all three phases together, and a rewireable fuse carrier in each phase blows on a heavy overload or short circuit.
The fuse wire is its only protection, so it must match the load and the cable, and it gives no protection against earth leakage or electric shock. Pair it with an RCCB, and use MCBs for the outgoing circuits.
Ratings in this listing: 16A, 32A, 63A, 100A and 200A at 415 V — choose from the options.
Which rating do I need
- 16A: small three-phase loads — a pump, motor or small home.
- 32A: three-phase homes, shops and motor feeders.
- 63A: larger homes, shops, offices and machine feeders.
- 100A: building incomers, workshops and panels.
- 200A: commercial and industrial incomers and panels.
Typical uses only — the switch must suit the incoming supply and cable, and the fuse wire the actual load, as sized by your electrician.
Where to use it
- Incoming main switch of three-phase homes, shops and offices.
- Motor, pump and machine feeders in workshops and small factories.
- Sub-main switch for three-phase distribution boards and panels.
- Construction sites and temporary three-phase supplies.
How to install
- Isolate the incoming supply (the supply company's cut-out or the upstream switch) before working.
- Fix the unit upright on a wall or panel, with room for the side handle to move.
- Bring the incoming cable to the line terminals and the outgoing cable to the load terminals, with the neutral on the neutral link.
- Fit fuse wire of the correct rating in each phase carrier, earth the enclosure and close the door before switching on.
Electrical work should be done by a licensed electrician. Re-wire a blown fuse only with the supply off, using fuse wire of the correct rating — never thicker wire or copper strip.
Frequently asked questions
- What does TPN mean?
- Triple pole and neutral: the three phases are switched and fused, and the neutral runs through a link. It is used on three-phase four-wire supplies, 415 V between phases.
- Why must the fuse wire match the rating?
- The fuse wire is the only thing protecting the cable. Wire that is too thick, doubled up or replaced by a copper strip will not blow on a fault, and the cable can overheat and catch fire.
- Should the neutral have a fuse?
- No. Indian safety regulations do not allow a fuse in the neutral conductor — the neutral goes through the solid neutral link.
- Main switch or MCB — which is better?
- An MCB trips on overload and short circuit and simply resets; a switch fuse unit needs its fuse wire replaced after a fault. Both are used as main switches; many installations keep a switch fuse unit as the incomer and MCBs for the circuits.
Buy TPN main switches online from Electric Market, Chennai. For site, contractor or bulk quantities, contact us for a quote.