"Intelligent" circuit breakers?

[jbelectrical]

I have a client with some very unusual design requirements.

We're going to have a 1200A service entrance panel, which we'll call panel "A." Panel A supplies a 1200A automatic transfer switch. Panel "B" is a 1200A main distribution panel supplying all the buildings at the site.

The client wants panel B to be fed from two different paths: one set of feeders directly from panel A, and another set of feeders via the automatic transfer switch. He wants to essentially "isolate" the transfer switch while still keeping panel B energized in an event that maintenance staff may need to work on it.

If one 1200A circuit breaker at panel A is in the "on" postion, then the other 1200A circuit breaker must be in the "off" position, and vice-versa. How can this possibly be accomplished?

 

[davidbeach]

Why not just use bypass and isolation switch on the ATS? But yes, it is possible to provide interlocks for the breakers. Easier to do if the only control of the breakers is electric, but there are mechanical interlocking devices available, a kirk key set being the easiest.

 

[jraef]

You could also put a Shunt Trip coil in each breaker so that if one is on, it shunt trips the other. One problem I immediately see in your description is that A is feeding into B, so the ST in A would always trip if you simply wired it off the the load side of B and vice versa. You will need a little extra logic to accomplish what you need after you sort out all the possibilities of when you want this to happen and when you don't. You may also need a "maintenance switch" that enables this system only when someone wants to work on it. There are neat little inexpensive programmable relays that could do this simple task.

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[ScottyUK]

A No-volt release or "dead man's handle" would be a better choice than a shunt trip, but to my mind only as a back up a primary interlock like a Kirk or Castell key, or a Bowden cable interlock. The latter devices usually are directly linked into the breaker mechanism and are less likely to give a false indication.

Is there a requirement to maintain power to the load while transfer is effected? That is trickier - most likely it would be controlled through procedural means unless you are looking for additional cost and complexity to implement a high integrity automatic system.

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[Electic]

Use power circuit breakers and a control wiring to accomplish what you desire. What you propose should not be unusual wiring for Power Circuit Breakers.

If you need to automate the voltage sensing and transfer of power, a relay such as Eaton "IQ Transfer" may be employed as part of the control wiring.