Clearance Between Generator and GCB

This sort of thing tends to depend on local or regional regulations. You didn't specify your locale, and not too many of us may just so happen to have a copy of your local rules, anyway.

1. No specs, just half way between generator and transformer

2. Sure, but is it half way?

3. My experience is that anyone that would design a multimillion dollar generator/transformer installation based upon information from anonymous strangers on the web should definitely be fired ASAP.

<...GCB...>?

Generator Circuit Breaker, usually only found on smaller machines since the interrupting current capacities are very high as are the short circuit duties and mechanical withstand forces.

There is no thumb rule, the clearance is dependent upon the voltage level and the standards of clearance depends onthe country. For 13.58kV 3 meters clearance is sufficient.