[Mike Betts]

Originally Posted by Eldarion

... I still wonder, though, about the 40 amp breakers and the main 120 amp breaker? Wouldn't they prevent the 800-amp meltdown? ...

Check the data sheets that come as an appendix to the robot rules.

All circuit breakers (and fuses for that matter) have an "inverse time" curve. They have an extremely small but accurate internal resistance which heats up via the power dissipated in this small resistance (P=I*I*R). The actual trip mechanism is thermal.

In the data sheet for the 120A CB, find the plot labeled "TIME VS PERCENT OF RATED CURRENT". Note that the CB will allow rated current (120A) to flow nearly forever. At 200% (240A), it will trip in about 20 seconds. At 400% (480A), it will trip in about 4 seconds.

While I'm on the subject...

Be warned that the internal heat does not dissipate quickly. If you run at 480A for 2 seconds and then try running at 240A, you will trip in a lot less time than the quoted 20 seconds (more like 10).

This warning also applies to self resetting 20, 30 and 40A circuit breakers. Once they start tripping, they will re-trip in a very short time at the same amperage.

Lastly, these are not "precision" devices. Variations of +/- 30% are not uncommon. Plan accordingly.

Mike