Tom B writes:
Thanks. I'm a CS. I shut the mains down, checked voltage across the
bus bars, replaced 20 amp with a 30 amp, backed off and reset the
mains. All done, no sparks.

Note that putting a 30 amp breaker on wire that isn't rated for 30
amps is, at least in most (if not all) US cities, illegal. Make sure
the wire is able to carry the current, else it poses a fire hazard.
(the breaker protects the wire, not your tool)