nmos fault

A wiring error? Confusing drain and source?

Often mosfets fail with drain-gate shorts. The applied supply voltage then turns on the gate, so the mosfet is permanently ON, continuously conducting from drain to source at its full capability, shorting the supply at Vgo(on), or about 6 volts or so. In contrast, a gate-to-source short would defeat any gate drive, preventing the mosfet from turning on.

Overdrive voltage between drain and source can kill the MOSFET.

Gate source voltage in excess of +/-20V can also do the same thing.

Over heating due to excessive load or high ON time also kills MOSFET.

Higher voltage to driver circuit will also force higher voltage to gate.

Figure out which one in above may be the cause of trouble. Place your schematic here and I will try to explain. Measure the voltage and also list the load type and control type in use.

Restrict the gate voltage to +/-15V or use 0-15V unipolar. Bipolar shuts the MOSFET faster as it removes charge from gate. Push-pull driver can deliver bipolar or unipolar depending on how you power the device.