MCB Rating Selector
Select a circuit type to see the typical MCB rating and curve used for Indian home wiring.
What MCB for a geyser?
A domestic geyser runs well on a dedicated 16 A C-curve MCB with 4 sq mm copper wire. The C-curve handles the initial heating surge without nuisance tripping.
How this works
An MCB protects the wire, so its rating must match the circuit's cable and load. B-curve MCBs trip faster and suit lights and sockets; C-curve MCBs tolerate the brief inrush of motors and are used for ACs, geysers and kitchen appliances.
Rating vs curve — two different things
An MCB has two numbers that matter. The rating (amps) must match the cable so the breaker trips before the wire overheats. The curve (B, C or D) sets how fast it trips on a surge. A B-curve trips quickly and suits resistive loads like lights and sockets; a C-curve tolerates the brief inrush of motors and is used for ACs, geysers and kitchen appliances.
Match the MCB to the cable, not the appliance
The golden rule: size the cable for the load first, then fit the largest MCB that cable can safely carry. Fitting a bigger breaker to stop nuisance tripping leaves the wire unprotected — if a circuit keeps tripping, the real cause is an overload, the wrong curve, or a genuine fault, not a breaker that is too small.
| Circuit | MCB | Curve | Cable |
|---|---|---|---|
| Lighting | 6 A | B | 1.5 sq mm |
| Power sockets | 16 A | B | 2.5 sq mm |
| Geyser | 16 A | C | 4 sq mm |
| Air conditioner (1.5T) | 20 A | C | 4 sq mm |
| Kitchen (heavy) | 20 A | C | 4 sq mm |
| Main isolator (2-3 BHK) | 40-63 A | C | 10-16 sq mm |
Frequently asked questions
What MCB for a geyser?
A domestic geyser runs well on a dedicated 16 A C-curve MCB with 4 sq mm copper wire. The C-curve handles the initial heating surge without nuisance tripping.
What is the difference between B and C curve?
A B-curve trips at 3-5 times its rating and suits lights and sockets. A C-curve trips at 5-10 times and suits motor loads like ACs, pumps and geysers that surge at start-up.
Why does my MCB keep tripping?
Usually an overloaded circuit, the wrong curve for the load, or a genuine fault. Fitting a larger MCB hides the problem and removes the cable's protection — find the cause instead.
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