So the bottom line is don't use a 20A rated circuit breaker in a 6V circuit that had a 30A circuit breaker in it, as it would be under-protected and might cause a fire.
If you replace a 30a breaker with a 20a breaker, all that is going to happen is that you may trip the breaker a lot. it will not cause a fire. It may be so over protected that it can not function because the breaker keeps opening.
Sorry, but I grow tired of all the math formulas, and equations. I try not to confuse other people with my prattle. Thought I could help, but you will figure it out.
