Choosing the Right MCB Rating for Each Circuit

A row of MCBs of different current ratings in a distribution board, each protecting a labelled circuit

Every circuit in a home needs an MCB of the right rating — and "right" has a precise meaning that many cheap installations get wrong. The MCB's job is to protect the circuit's cable, so its rating must sit in a specific window: above the circuit's normal running current, and below what the cable can safely carry. Get it right and the breaker protects the wire from ever overheating; get it wrong — usually by fitting one too big — and the protection quietly disappears. This guide explains how the rating is chosen, and the common values for a home.

It builds on the MCB & MCCB guide and pairs with the MCB & RCCB selector and the wire size calculator.

The safety line. This guide explains how MCB ratings are chosen so you understand your installation and can ask the right questions. The actual selection must be done by a licensed electrician, coordinated with the real cable, load and installation conditions to IS 732 and IS/IEC 60898. Do not change breakers yourself.

The golden rule: the breaker protects the cable

The single principle that governs MCB selection:

Load current ≤ MCB rating ≤ cable's safe current-carrying capacity.

The MCB rating must be at least the circuit's normal load (or it nuisance-trips), and no more than the cable can safely carry (or the cable can overheat without tripping the breaker). The breaker and the cable are a matched pair — you never choose one without the other. This is exactly why fitting a bigger breaker to stop tripping is dangerous: it breaks the upper half of this rule and removes the cable's protection.

Common ratings for home circuits

These are the typical, indicative values an electrician works from — always confirmed against the actual cable and load:

Circuit	Typical cable (copper)	Typical MCB	Trip curve
Lighting / fans	1.0 – 1.5 sq mm	6 A	B or C
General 6 A sockets	2.5 sq mm	16 A	C
Kitchen / power points	4 sq mm	20 A	C
Geyser	4 sq mm	20 A	C
Air-conditioner (1.5 T)	4 sq mm	20 A	C
Larger AC / heavy point	6 sq mm	25 – 32 A	C
Main (single-phase home)	per load	40 – 63 A	C

Indicative for typical Indian homes. The correct rating depends on the exact cable, its length (voltage drop), the installation method and the appliance — set by a licensed electrician.

Choosing the trip curve

The trip curve (B, C or D) is chosen for how much the load surges at switch-on:

Type B (trips at ~3–5× rating) — lighting and simple resistive loads with little inrush.
Type C (trips at ~5–10×) — the common home choice: sockets, ACs, motors, mixed circuits that draw a brief surge at start-up.
Type D (trips at ~10–20×) — high-inrush industrial loads; rarely needed at home.

Choosing Type C for a motor circuit avoids the nuisance tripping a Type B would suffer on start-up inrush, while still protecting the cable. Match the curve to the load, not by guesswork.

Common mistakes to avoid

Oversizing the breaker to stop tripping. The cardinal error — it removes the cable's protection. Fix the overload or fault, or upgrade cable and breaker together.
One big breaker for everything. Defeats the point of separate circuits; a fault then kills the whole home and the cable sizing cannot match one rating.
Ignoring the trip curve. A Type B on an AC circuit nuisance-trips; a Type D on a lighting circuit is too slow to protect well.
Forgetting the RCCB. MCB rating is about overload; it does nothing for shock. Pair circuits with a 30 mA RCCB or RCBO.

The one-line answer

The right MCB rating sits in a window — at least the circuit's normal load current, and no more than the cable's safe capacity — because the breaker exists to protect the cable, and the two are always chosen as a matched pair. Use the common values (6 A lighting, 16 A sockets, 20 A geyser/AC, and so on) as a guide, pick Type C for most home circuits, never oversize a breaker to silence tripping, and pair everything with a 30 mA RCCB — with a licensed electrician making the final selection against your actual wiring.

Where to go next

The breaker basics: MCB & MCCB Guide.
Shock protection to pair with it: RCCB, RCBO & ELCB Guide.
Try it: MCB & RCCB Selector.
Size the cable: Wire Size Calculator.

References

IS/IEC 60898-1 : 2015, Circuit-Breakers for Overcurrent Protection for Household and Similar Installations (MCBs), Bureau of Indian Standards.
IS 732 : 2019, Code of Practice for Electrical Wiring Installations, BIS.
National Electrical Code of India, SP 30 : 2023, BIS: https://www.bis.gov.in/

All ratings and curves are indicative for typical Indian homes and must be set by a licensed electrician coordinated with the actual cable and load. Verify any standard's status via the BIS catalogue before relying on it.