SPN MCB Box: Which Size of Single Phase DB, and What It Costs

What is an SPN MCB box?

An SPN MCB box is a distribution board for a single phase supply. SPN stands for single pole and neutral: inside, one phase busbar feeds a row of single pole MCBs, and a neutral link and an earth bar take the return and earth wires of each circuit. It is the board in almost every Indian flat, shop and small office.

We make the VIYONA SPN white line MCB box in four sizes, from 2–4 way at ₹380 to 16–18 way at ₹950 MRP, and small PVC surface boxes from ₹40, at our works in Marol, Andheri East, Mumbai.

What sits inside an SPN box

Drawn by us, not to scale. A typical layout; the exact parts supplied with each box are listed by your dealer.

SPN MCB box sizes and prices

The SPN white line MCB box comes in four sizes. Each is listed as a span of ways:

The biggest jump is at the top: 16–18 way costs ₹330 more than 10–12 way. If a flat’s count, spares included, fits in 12 ways, the 373 is the better buy. Full photos are on the SPN white line MCB box product page.

What does “way” mean in an MCB box?

One way is the space one single pole MCB takes on the rail. A double pole device, such as a DP main breaker, a DP isolator or a two pole RCCB, takes two ways. An 8 way box therefore holds eight single pole MCBs, or a DP main plus six single pole MCBs, and so on.

The catch is the incomer. Whether the main switch and the RCCB sit within the stated ways or in space of their own varies by design, and it decides how many outgoing circuits you really get. Ask your dealer for the layout of the exact box before ordering, and count every device: main, RCCB and each outgoing MCB.

The rule we use: outgoing circuits + 2 ways for a DP main + 2 for an RCCB + 2 spare. A worked count for a small flat: a double pole main (2 ways), a two pole RCCB (2 ways), six single pole outgoing MCBs (6 ways) and two spare make 12 ways in all. If the box’s printed ways cover only the outgoing breakers, a 6–8 way box takes the six circuits and two spares; if they include the main and RCCB, a 10–12 way box is the right size.

Our MCB box size list lists every box we make in one table.

Which size SPN box for a 1BHK, 2BHK or 3BHK?

Count circuits, not rooms. A typical list, with each item one single pole MCB unless noted:

• 1BHK: 1 lighting, 1 room, 1 kitchen, 1 geyser, 1 AC = 5 outgoing, plus DP main and RCCB
• 2BHK: 2 lighting, 2 room, 1 kitchen, 1 washing machine, 2 geyser, 2 AC = 10 outgoing (8 to 10 is typical)
• 3BHK: 3 lighting, 3 room, 2 kitchen, 3 geyser, 3 AC, 1 washing machine = 15 outgoing

Add 2 ways for the DP main, 2 for the RCCB and 2 spare: 11 ways for the 1BHK, 16 for the 2BHK and 21 for the 3BHK. Then check whether the box’s printed way count includes the main and RCCB. If it does, that points to 373 (10–12 way) for a 1BHK and 374 (16–18 way) for a 2BHK, while a 3BHK needs more than our largest SPN box: split it over two boards. If the main and RCCB have their own incomer space, a 1BHK fits 372 (6–8 way), a 2BHK 373 and a 3BHK 374. The circuit list itself comes from our MCB for home guide; the ratings are explained on the 16 amp and 6 amp MCB pages.

Small jobs: PVC surface MCB boxes

For one or two breakers on a wall, a full DB is more than you need. Our PVC surface MCB boxes take one to four DIN rail devices:

• 375: 1 & 2 way PVC surface MCB box, ₹40
• 377: 1 & 2 way PVC Royal surface MCB box, ₹66
• 376: 3 & 4 way PVC surface MCB box, ₹90

Typical uses: a separate breaker for a water pump in a covered pump room, a sub-feed to a servant room, a breaker for an outdoor light circuit mounted indoors, or a local double pole switch-off beside a shop signboard. Our catalogue gives these boxes no weather rating, so fit them indoors or under cover, and give pump and outdoor circuits a 30 mA RCCB.

The 1 & 2 way box takes a single pole MCB, two single pole MCBs, or one double pole device such as a DP isolator. The 3 & 4 way box takes up to four ways, enough for a four pole isolator on a three phase motor or a small group of breakers in a terrace room.

The Royal version is on our 1 and 2 way PVC Royal MCB box page.

SPN white line or double door?

The white line SPN box is the straightforward choice for a flat. Our double door distribution boards cost more but add an outer door over the inner cover, which keeps dust and curious hands away from the breakers. They suit shops, offices and housing society common areas where many people pass the board.

The price gap at similar sizes: a 10–12 way white line box is ₹620; a 12 way double door board is ₹1,210. Our double door MCB box page covers that range.

SPN or TPN: which board do you need?

Your supply decides. A single phase connection, two wires from the meter, takes an SPN board. A three phase connection, four wires, takes a TPN board with three busbars. Most flats in Mumbai and across India are single phase; larger bungalows, some shops and most factories are three phase.

Check the meter or the electricity bill. A three phase supply fed into an SPN box will not work; a single phase supply in a TPN box wastes money and space.

The full comparison is in our SPN vs TPN distribution board guide, and the TPN MCB box page covers the three phase boards.

What goes inside, and what it costs

An empty box is only part of the bill. For a 2BHK with a 16–18 way box, a 40A double pole main and ten single pole MCBs, our parts at MRP come to:

• 374 16–18 way SPN box: ₹950
• VIYONA 412 40A double pole main: ₹435
• 10 × VIYONA 401 single pole MCBs: ₹1,450

That is ₹2,835 before the RCCB, wire and labour. A 442 40A double pole isolator (₹230) can take the main’s place only where the cable from the meter is already protected upstream; it switches, it does not trip. The VIYONA 401 to 433 range is made to IS/IEC 60898-1 under BIS licence CM/L-2544151; see our VIYONA 10 kA MCB page.

Mistakes people make with SPN boxes

Most problems with a home DB start on the day the box is ordered:

• Box sized to today: no spare ways for the next AC.
• Forgetting the RCCB: two ways nobody counted.
• Neutrals on one screw: every circuit needs its own neutral link terminal.
• No earth bar used: earth wires twisted together behind the cover.
• No labels: nobody knows which breaker is the geyser.

On the labels: write each circuit on the cover at the time of wiring. It costs nothing and saves the next electrician an hour. Our how to replace an MCB guide shows how a labelled board makes later work safe.

SPN MCB box price and packing

Our SPN white line boxes run from ₹380 (371, 2–4 way) to ₹950 (374, 16–18 way). PVC surface boxes run from ₹40 (375) to ₹90 (376). All are packed 10 per box and sold in full boxes only through dealers, so a box of ten 373s is ₹6,200 at MRP.

Electricians and contractors buy by the box; homeowners buy one from a dealer who has opened it. Every box and breaker we make is in our MCB price list.

Where to fit the SPN box

The DB belongs near the entrance, close to where the supply cable from the meter enters the flat, at a height an adult can reach without a stool and a child cannot. A passage wall just inside the main door is the usual spot. It should be dry, away from the bathroom and kitchen sink, and never inside a wardrobe or behind a fridge.

Leave the area in front of it clear. In an emergency someone has to reach the main switch in seconds, often in the dark. A torch hook or a small night lamp nearby is a sensible extra.

Plan the conduits into the box before the walls are plastered: each outgoing circuit needs its own route out, and a 12 way board can have a dozen conduits converging on it. Our house electrical layout guide places the DB in a 2BHK plan.

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.