SF6 circuit breakers have higher short circuit withstand capability compared to vacuum circuit breakers. This is because SF6 has much higher dielectric strength than air or any other insulating medium.

The rated short circuit making current of a circuit breaker is usually 1.5 to 2.5 times higher than its rated short circuit-breaking current. This is because the peak value of the current during closing is higher than the RMS value during opening.

No, using an MCCB with a higher ampere rating than the distribution board is not allowed as it may not coordinate properly with upstream protection or overload the distribution wiring. The MCCB rating should always be lower than or equal to the distribution board's current rating.

As per standards, the short time current rating of MCCB should be a minimum of 3 times its nominal current rating. Therefore, for a 400A MCCB, the short time current rating needed is a minimum of 1200A.

Numerical relays have advantages like the flexibility of setting, self-diagnosis, communication capability, continuous monitoring, and fault recording. They offer more dependable, versatile, and secure protection compared to electro-mechanical relays.