Diagnosing issue with an appliance - blown fuse and tripped breaker

Thread Starter


Joined Mar 28, 2018
Hi all,

Hoping someone may be able to shed some light on what might be going on based on the following results:

1. Have an appliance with universal power supply, attempting to run it on 240v mains (Australia)
2. Upon plugging into live socket (before switching on appliance), after several seconds, fuse in appliance blows and circuit breaker trips (combined MCD and RCB breaker)
3. Above has happened multiple times in a row with different units of same appliance, different sockets on different circuits and replacement fuses

Manufacturer points to oversupply or poor grounding in my mains - seems unlikely as no issues with other appliances

I point to faulty appliance - but seems unlikely as manufacturer plausibly claims that numerous units are running successfully on 240v mains elsewhere, and I've had the same issue with the original unit and a replacement.

Who do you think is right and why?


Joined Jul 18, 2013
Is the appliance fed from 2 wire or 3 wire (GND).
If it is 3 wire, you could try it with the earth wire open circuit and see if it trips, (earth leakage).
Just ensure you do not touch the metal parts of the appliance when testing this.
Some SMPS power supplies have suppression components connected to earth gnd.


Joined Feb 8, 2018
The fact that the internal fuse blows leads me to suspect that there may be a transient suppressor, typically a metal oxide varistor (MOV), across the line and either it is rated for insufficient continuous RMS voltage or your line voltage is unusually high.

"Accepted practice" for universal input switchers is to design for nominal AC voltage of 100 to 240 RMS with limits of 85 and 264 volts.

As max wrote, if a switcher has a ground wire it is nearly universal that radio frequency interference suppression capacitors will be connected from each side of the line to ground, but I would expect a breaker that detected ground current to trip nearly instantly, since they are rather useless if they don't. Normally the capacitance is limited by safety regulations to a value that will not cause lethal shock if the ground connection is broken and replaced with a human.


Joined Jan 23, 2018
The obvious question that is missing is about a voltage selector switch. If there is one then it must be set correctly. Then the next question is does the motor turn freely? A bound up motor will certainly trip the protection system.