How is the unit supposed to be wired to prevent overheating at connect

I had the unit installed by someone claiming to be knowledgeable, but began having issues with the unit cutting out and turning on and off after about 6 months, randomly at first. But progressively, it became a more frequent problem until we'd get 5 minutes of tepid (not hot) water before having to reset the breaker (it did not trip on its own) to get a another minute of warm-ish water... Before it finally quit working at all.I turned it off at the breaker when I noticed a smell of overheating just before I was to leave for a weekend. I returned and went looking for the source, I took the cover off the unit and the terminal block had melted the insulator off and the coating from the wires had dripped a bit, but no other damage.

The BLACK and WHITE wires were connected inside the unit and the RED WAS CUT (but not wrapped or capped, just CUT just outside the unit) and I am not sure if it was that way from the beginning, or if it was sabotaged later, but it worked well at first, and doesn't work w/o using white

The control panel wouldn't power on without the white wire and black wires connected (White to L1 and BLK to L2) which got me back to barely tepid water despite setting it at 138°F. The unit still is off and on when it should just be ON. The unit has been thoroughly flushed and the PSI is in normal range.

*Should I also connect the RED wire to the L1 terminal? * I would say it's as if it's not getting enough power... But I don't want to overload it and fry the whole thing...

@davecarl64477

You would have to check how the 60A breaker was wired.

This is a 240V heater so it relies on two x 120V AC power feeds.

Standard wiring practice is that white wire is the Neutral, the black wire is the 1st 120V supply and the red wire is the 2nd 120V supply and green is earth.

The 60A breaker is supposed to be a 2 throw breaker so presumably there are two separate power feeds being switched through it i.e. 1st and 2nd power supplies.

If you have a DMM (digital multimeter) if you set it to measure AC volts (scale greater than 240VAC) and then connect the meter leads to the red and black wires at the unit you should measure 240V.

If you don't, connect the meter between the red wire and earth and check what voltage is shown. Then do the same with the Black wire and Earth. Each wire should have 120V on it

Looking at the wiring diagram, the red and the black are connected as is the green Earth but there's no mention of the White as no doubt it's not required.

@davecarl64477

Normally there shouldn't be 120V on the white wire. There may be a smaller feedback voltage as the Neutral is multipled to a lot of other appliances etc in the premises as well and they're still powered so the voltage is fed on the Neutral wire through them, but this is catered for in the design of each appliance and doesn't affect their operation..