Isolator Switch: Which Pole Count, Which Rating, and What It Costs

What is an isolator switch?

An isolator switch is a DIN rail switch that cuts the supply to a board or a machine so that it can be worked on safely. It looks like an MCB, sits in the same distribution board, and has a lever that opens all its poles at once. The difference is that it never trips by itself. It does not protect anything against overload or short circuit; it only gives a clear, deliberate OFF.

We make isolators in 40A and 63A, in double pole, three pole and four pole, under our VIYONA brand at our works in Marol, Andheri East, Mumbai. That is six codes, from ₹230 to ₹530 MRP.

Double, three and four pole isolators

Drawn by us, not to scale. Contacts shown open. Codes are our VIYONA isolators: 40A first, then 63A.

Our isolator switches: all six codes

Every isolator we make comes in two current ratings, 40A and 63A, and three pole counts. These are printed MRPs from our current catalogue:

Going from 40A to 63A costs only ₹30 to ₹60 more at the same pole count. The full range is on our VIYONA isolator product page and the VIYONA MCBs and isolators page.

Isolator vs MCB: the one-line difference

An MCB switches and protects: it trips on overload and short circuit. An isolator only switches. That is why they appear together in a DB: the isolator as the main OFF for the whole board, the MCBs below it protecting each circuit.

The price reflects it. Our 40A double pole isolator (442) is ₹230; our 40A double pole MCB (VIYONA 412) is ₹435. The two do different jobs, so the isolator is not a cheaper MCB. It belongs as the main only where the cable feeding the board is already protected upstream, by the electricity company’s cut-out or a breaker at the meter, and every circuit below has its own MCB. Where the main itself must protect that cable, fit a DP MCB.

The full comparison, with symbols and how to tell them apart on the rail, is in our isolator vs MCB guide.

Double pole isolator: single phase homes and shops

A double pole isolator switches phase and neutral together. It is a common main switch for a single phase flat, shop or office DB where the incoming cable is protected at the meter, sitting at the incoming end with an RCCB and the outgoing MCBs below it.

Choose 442 (40A, ₹230) or 443 (63A, ₹290). The isolator rating should be at least that of the protective device feeding it, which for a home is usually the electricity company’s cut-out or a breaker at the meter.

Double pole isolators also make good local switches for a sub-board in a kitchen, a terrace room or a shop at the front of a house: the person working on that board can cut it without walking to the main DB. Our SPN MCB box page covers the boxes they fit.

Three pole isolator: three phase machines

A three pole isolator switches the three phases, R, Y and B, and leaves the neutral alone. It suits three phase loads that have no neutral connection at all, such as a three phase motor for a borewell, a lift, a compressor or a workshop machine.

Our three pole isolators are 452 (40A, ₹370) and 453 (63A, ₹400). Mounted beside the machine or at its starter, the isolator lets a mechanic make the machine dead right where he is working.

A motor also needs its own protection, normally an MCB of the right curve or a motor starter; our motor starter guide covers pumps.

Fit the isolator where the person working on the machine can see it. A switch two floors away in a locked room does not stop a colleague from closing it while a pump is being opened.

Four pole isolator: three phase boards (TPN)

A four pole isolator switches all three phases and the neutral. It is the main switch for a three phase distribution board, the TPN board found in larger homes, bungalows, shops and offices on a three phase supply.

Our four pole isolators are 461 (40A, ₹480) and 462 (63A, ₹530). Both fit at the incoming end of our TPN double door boards, from the 4 way TPN at ₹2,620.

The TPN MCB box page sizes the board, and our 3 pole vs 4 pole guide explains why a TPN main isolates the neutral.

40A or 63A: which rating?

The isolator’s rating is the current it can carry continuously while closed. It must be at least the rating of the fuse or breaker that protects the cable feeding it, so that the isolator is never the weakest part of the path.

• 40A: most single phase flats, small shops and sub-boards
• 63A: larger single phase homes, three phase boards, and any board fed through a 63A breaker

Two worked examples. A 2BHK on a single phase supply, with a 32A double pole MCB at the meter, takes a 40A double pole isolator in the flat’s DB: 40 is above 32, so the isolator is never the weak point. A bungalow on three phase, fed through a 63A four pole breaker, takes a 63A four pole isolator in its TPN board, because a 40A isolator there would be smaller than the breaker protecting it.

Because the step costs so little, from ₹30 at three pole to ₹60 at double pole, many electricians fit 63A as standard on a new board. Our MCB for home guide shows where the main sits in a typical flat.

How to use an isolator safely

An isolator is built to make a circuit dead, not to break a heavy running load as a matter of routine. The safe order of work:

1. Switch off the loads or their MCBs first
2. Open the isolator: one lever, every pole
3. Prove the circuit dead with a tester before touching anything
4. Tag the isolator with a clear notice so no one closes it while you work

The last step matters most in shops, offices and housing societies, where someone else may walk up to the board.

Our home electrical maintenance checklist covers the routine checks on a DB.

Mistakes people make with isolators

Most isolator mistakes come from treating it as a breaker, or from choosing the wrong pole count:

• Isolator, no MCB: nothing trips on a fault.
• 3 pole on a TPN board: the neutral stays connected.
• 40A behind a 63A breaker: the isolator becomes the weakest link.
• Switching heavy load off: switch loads off first.

If a board trips and the main is an isolator, the trip came from an MCB or an RCCB below it, never from the isolator. Our RCCB tripping guide and the MCB tripping guide trace the cause.

Isolator price and boxes

Our isolators run from ₹230 (442, 40A double pole) to ₹530 (462, 63A four pole). They are packed 6 per box for double pole, 4 for three pole and 3 for four pole, and sold in full boxes only through dealers. A box of six 442s is ₹1,380 at MRP.

Size the box as outgoing circuits + 2 ways for the isolator + 2 for the RCCB + 2 spare. For a 1BHK with five outgoing circuits that is 11 ways: a 10–12 way SPN box (373, ₹620) if its printed way count includes the main. With a 442 isolator that comes to ₹850 at MRP before the RCCB and MCBs. Every isolator and breaker we make is in our MCB price list.

Where the isolator sits in the board

In a home or shop DB the isolator is the first device after the incoming cable. Reading the rail from the incoming end, a typical single phase board runs:

1. Isolator, double pole: the main OFF
2. RCCB: trips on leakage to earth, protecting people
3. MCBs: one per circuit, protecting the wires
4. Neutral link and earth bar

Each pole of an isolator usually takes one way of the rail, so a double pole isolator takes two ways and a four pole isolator four. Count them when ordering the box, along with the RCCB and two spare ways, and check whether the box’s printed way count includes the main, or the last outgoing circuit has nowhere to go.

Our DB box vs MCB box guide explains the parts of a board, and the double door MCB box page covers the double door boards that suit a shop or office.

Where we supply

Everything on this page is made at our works in Marol, Andheri East, Mumbai, and sold through dealers across Maharashtra and in many other states. See where we supply in Maharashtra and how we supply the rest of India. Orders placed through our office are delivered all over India, in full boxes only.