Bad Inverter WZRELB.

I just purchased a new 12 volt 1500 watt power inverter. It's a WZRELB inverter. I tested this on my 700 watt microwave and it started to smoke. I then checked the fuses and they were melting. There was also a frayed exposed wire. This has brand new 40 amp fuses and I just did another test to see if it could carry a small 270 watt heater. I also had my 400 watt inverter going that did run the heater.