/diy/ - Do It Yourself

>>1143566
>pic here

The water heater is wired for 230V
RED is Line
BLACK is Line
GREEN in earth
(230V water heaters don't use neutral)

Your romex is for 115V
BLACK is line
WHITE is neurtal
BARE is earth
It's technically not allowed but still common to use this romex for 230V water heaters
BLACK romex from one side of dual 30A breaker to BLACK on water heater.
WHITE romex from other side of dual breaker to RED on water heater.
BARE in romex from bonding/neurtal in breaker box to water heater cabinet.
The ground/earth on the romex at the water heater usually goes to the screw on top of the cover plate which is made it two pieces.

From looking at the damage pic, >>1143584
you had a bare wire on either RED or BLACK where the wires were stripped back at the sheath.
The bare line wire touched the bare earth wire.
If you examine them with the breaker off you will see the problem.
Pic related - shows pinched/cut insulation