Industrial Switchgear and Circuit Breakers in Pakistan

MCBs protect final circuits such as lighting, sockets and small control supplies, typically up to about 125 A. They combine thermal overload and magnetic short-circuit tripping in a DIN-rail module.

Trip curves define how fast the magnetic element operates: B curve for resistive loads, C curve for general and lighting loads, D curve for high inrush loads such as transformers and small motors.

MCCBs cover the middle ground, commonly from around 16 A up to 1600 A, protecting feeders, sub-main incomers and large motor circuits. Many offer adjustable thermal and magnetic settings, and electronic trip units add more precise protection and metering.

Accessories such as shunt trips, undervoltage releases, auxiliary contacts and motor operators are often required by the panel design and should be listed with the breaker.

ACBs are used as main incomers and bus couplers on LV main distribution boards, typically from around 630 A to 6300 A. They interrupt fault current in air and are often drawout, so they can be isolated and removed for maintenance.

Electronic protection units provide long-time, short-time, instantaneous and earth-fault settings, which allows discrimination with downstream MCCBs.

Contactors are electrically operated switches that start and stop motors, heaters, capacitor banks and lighting loads. A coil, energised by the control circuit, closes the main contacts.

Contactors are rated by utilisation category: AC-3 for squirrel-cage motor starting and stopping, AC-1 for resistive loads. Star-delta and reversing starters use combinations of contactors with mechanical interlocks.

Overload relays protect motors against sustained overcurrent and, in many models, phase loss. They are mounted directly on or near a contactor and trip the contactor coil circuit.

Thermal overloads use bimetal elements with an adjustable range; electronic overloads offer wider ranges, better accuracy and options like trip class selection for heavy-starting loads.