If the power supply enters through the hole at the bottom of the junction box, a cable connector is not required.
Power Baseboard heaters generally use between 400 and 2,000 watts of power.
With its steel construction and a powder-coated finish, this heater can endure abuse without denting or scratching.
Connect one supply wire to one thermostat wire marked L1.
I found a "Quadplex" double 15A 2-pole breaker.
a 120 V heater can be a little different as some units just plug straight into the wall.