Miniature Circuit Breakers (MCB)

MCB’s are ‘overload protection devices’ commonly found in Electrical Switchboards, especially any sub-boards in a residential situation, and other power distribution devices. Often ‘MCB’ is short-hand for any overload-protecting device (or circuit breaker) thats mounts on a DIN rail, though this is not always the case.

While there are other variations available, we typically use ‘Thermal-magnetic’ and ‘Hydraulic-magnetic’ MCB’s in our PDUs.

With an MCB mounted vertically (typical mounting style), the toggle will always be ‘up’ for “On” or ‘down’ for “OFF”. This is also indicated on the front panel of the MCB.

An MCB will typically have the following information printed on the front, easily accesible without dismantling a product or switchboard:

• Manufacturer/OEM Identification
• Product Family/Code
• Current Rating (often Cxx, where xx is the current rating of the breaker)
• Fault Rating (4.5 & 6kA are typical in residential situations, 10kA is more typical in industrial applications)
• a Fault rating of 6kA means that if the breaker receives a current of over 6000Amps, it will typically fail either by fusing “closed” (no longer able to ‘trip’) or by exploding.
• Circuits are designed so that the above failures should never happen.

Thermal-magnetic breakers use a combination of heat buildup within the breaker and ‘changes in the magnetic field’ inside the breaker to monitor both instantaneous high overload situations (such as a short circuit) as well as more gradual continuous low-level overload situations.

Hydraulic-magnetic breakers use a solenoid in fluid, rather than ‘heat buildup method’ used in Thermal-magnetic breakers. The advantage is that an operator can remove any faulty device and immediately close the circuit of the breaker (turn back to the ‘on’ position) without having to wait for the internal temperature to reduce to acceptable levels.