In a distribution board, what is the typical role of MCCBs and fuses?

• A. MCCBs provide adjustable overcurrent protection; fuses provide overcurrent protection and isolation where required; both must be correctly rated
• B. MCCBs provide short-circuit protection only; fuses provide isolation for maintenance
• C. MCCBs are for high voltage; fuses are for DC circuits
• D. MCCBs and fuses perform the same function; only one is needed

Answer: (A)

The main idea is that a distribution board uses two types of protective devices to cover different needs: adjustable protection and reliable isolation. MCCBs are designed to provide adjustable overcurrent protection—they let you set the trip current to match the cable size and load, and they respond to both overloads and short circuits with a thermal-magnetic trip. They can be reset after a fault, so you don’t need to replace anything to restore power.

Fuses also protect against overcurrents, but they do it with a fusible element that melts when the current is too high. That gives fast protection for faults, but after a fault you must replace the fuse rather than reset it. Fuses can be used in locations or circuits where simple, inexpensive protection and clear isolation on fault are desired.

Both devices must be correctly rated for the circuit—matching voltage, current, and the desired coordination between protections—so the nearest device to a fault trips first and there’s a safe, reliable way to isolate the circuit for maintenance. That combination—MCCBs for adjustable protection and fuses for protection plus selective isolation where needed—fits typical practice in distribution boards.