Molded Case Switch And Circuit Breakers

A Molded Case Switch is an MCCB without the protective release. Just an on-load isolator. It is used to isolate certain circuits for maintenance. Protection is available in the MCCB anyway. Another way is to use a Plug-in CB, which can be withdrawn for (a) maintenance on itself and (b) isolation of the downstream circuit for maintenance. Such a CB will replace both the MCS and MCCB in this situation.

i did not know that the MCS is rated higher than the downstream MCCB. Possibly so that it will stay on when there is a short-circuit till the MCCB clears. Or maybe it is a code-related thing.

Your question doesn't make a lot of sense. Re difference in feeder protection against board protection. Quite normal in HV systems, but not in a situation where LV MCCB's would be used.

Even though an MCS is an MCCB "without the trip elements", it's not really true. They still have magnetic trips, they're just not adjustable; usually fixed at 10X the frame size rating of the breaker. This is in order to prevent the breaker from exceeding it's interrupt capacity and having someone try to open it manually in that occurrence. If a high magnetude fault occurs, the MCS will still open IF the fault is not interrupted at a lower level (closer to the fault). So if your purpose for having an MCS in a peice of switchgear is STRICTLY as an isolator for maintenance, to avoid confusion after an even, you size it one frame size ABOVE the main breaker so that in the case of a fault, it's the main breaker that trips, not the isolator.

Yes, the MCS does have high-set magnetic trips usually for self protection, no use to the customer though. That is why i ignored it. But your answer is more complete.

Thank you. I really appreciate it.

Thank you. I reallay appreciate it.