Circuit Protection Devices

MCB, MCCB, Fuses – Selection Tables & Practical Guidelines

Circuit protection devices safeguard electrical systems from overloads, short circuits and equipment failures. Proper selection ensures safe operation, prevents cable overheating and protects motors, control panels and distribution boards. This section provides practical reference tables for miniature circuit breakers (MCB), molded‑case circuit breakers (MCCB) and industrial fuses.


1. MCB (Miniature Circuit Breakers) – Typical Ratings

MCB – Typical Ratings and Cable Sizes
MCB Rating (A) Cable Size (Cu) Typical Use
6 1.5 mm² Lighting circuits, control circuits
10 1.5–2.5 mm² Small loads, control power
13 2.5 mm² Sockets (UK), small appliances
16 2.5 mm² Sockets, small motors
20 2.5–4 mm² Industrial sockets, small feeders
25 4 mm² Motors 4–5.5 kW
32 6 mm² Motors 7.5 kW, small distribution
40 10 mm² Motors 11 kW, feeders
50 10–16 mm² Industrial loads
63 16 mm² Heavy circuits, sub‑distribution

2. MCCB (Molded‑Case Circuit Breakers) – Typical Applications

MCCB – Typical Ratings and Cable Sizes
MCCB Rating (A) Cable Size (Cu) Typical Use
63 16 mm² Small distribution boards
80 16–25 mm² Industrial feeders
100 25 mm² Main supply lines
125 35 mm² Large feeders
160 50 mm² Heavy industrial loads
200 70 mm² Main distribution
250 95 mm² High‑power circuits
315 120 mm² Large industrial systems
400 150–185 mm² Main switchboards

3. Industrial Fuses – gG / aM Types

Fuse Types – gG / aM
Fuse Type Purpose Typical Use
gG General protection Cables, distribution, general loads
aM Motor protection Motors, heavy starting loads

Typical Fuse Ratings for Motors (400 V)

Motor Fuse Ratings (aM) – 400 V Motors
Motor Power (kW) Fuse Rating (aM)
0.75 6 A
1.1 10 A
1.5 10 A
2.2 16 A
3 20 A
4 20–25 A
5.5 25 A
7.5 32 A
11 40 A
15 50 A
18.5 63 A
22 80 A
30 100 A

4. Practical Notes

• MCBs are used for small circuits; MCCBs for higher currents.

• aM fuses are designed specifically for motors (high inrush current).

• Cable size must always match breaker rating.

• Breakers must be selected according to short‑circuit capacity (kA).

• Always follow local electrical standards and manufacturer datasheets.