Hint: A terrible tap
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This was a terrible attempt to tap power from this 800A circuit breaker. The installer simply took a 12 AWG wire and shoved it into the same terminal with the 350kcmil conductor. This created a very poor connection, which resulted in some arcing and sparking. The heat from this arcing ultimately damaged this 800A breaker to the point where it needed to be replaced because the terminals were so badly damaged. The conductors were also damaged. Thankfully, this did not start a fire.
Jamming two conductors into a terminal designed for only one is a violation of Sec. 110.14(A) and can result in damaged equipment, or even worse. There is one open terminal remaining for each pole of the breaker, but the terminal is much too big to accommodate the 12 AWG wire. If this installer was trying to make a feeder tap, there are splicing devices that could have been used to make a connection directly onto the conductors instead of jamming wires into the terminals. Of course, the installer could have put the 12 AWG wires on their own breaker too.
