Circuit Breaker/Isolator

To what end?

As far as I know, it's not something you would get away with under UK M&Q regs. But it's 10 years since I had anything to do with M&Q

Oops-missed the main point. This is when isolating the equipment for maintenance works.

If the circuit breaker can be isolated from the busbars and circuit, IE racked out of the service position and locked, it would be acceptable.

I've worked on many MV systems where this is the only method of isolation.

• Only when it is permitted by the electrical codes applicable to the country of installation, and
• Only when its use in this way is covered by the Authorised Person raising a Permit To Work to cover the maintenance activity.

Some circuit breakers are rated for switching duty, meaning they can be manually operated repeatedly. If code permits (and requirements such as sight/distance are met), then it could be allowed. Please consult local authorities.

Vacuum circuit breakers, if not provided with a rack-out system (i.e. Metal Enclosed Switch Gear), are NOT considered safe isolation for maintenance purposes. Air circuit breakers are, but hardly anyone uses ACBs on MV equipment any more.

If you are referring to Low Voltage (600V and below), then Molded case Circuit Breakers (MCCBs) are considered safe circuit isolation for service work, as long as they are provided with locking mechanisms.

MCBs in particular, if they have a lock out facility fitted, will usually only accept small shackle locks. You need to check that any lock that fits the MCB is also compatible with the safety enforcement standards in place at the mine of factory where you are working. Mines in the UK have regulations on the type of lock that can be used.

Just wondering why do you want to use a circuit breaker for this???

Regardless of the atmosphere it is installed in you should use a disconnect switch for lock-out of equipment, (much cheaper also).

Depending on what state you are working in the installation codes vary, consult a local lic electrician for this. They would be able to tell you what NEMA rating you would need to satisfy the local inspectors and also to be safe.