Yes you need circuit protection. You also need to be able to turn this off. If you get a circuit breaker you can use it for both purposes.The max cable size this inverter can accept is 4 awg. The nominal power consumption is 67 amps (800 Watts = 12 volts x Amps) but because of surges you might like to go for an 80 amp circuit breaker to avoid nuisance tripping. If you use 4 awg wire that is marine grade with 105 deg C insulation the ampacity (from the Ampacity Tables) is 160 amps.
Uses for the VE.Direct communication port