Safety of running Modified Sine Wave power through house wiring?

[Roadhawg]

Hi Guys, Looking for some safety advice here, and struggling to get 100% clarity.

 

We have a Generator at home, wired up with a full changeover switch, on a separate board with isolators for both the generator and Eskom sides. This seems overkill, but also maybe an extra safety layer. Male plug goes into the output of the Generator.  Works well.

Now we also have one of these Mecer UPS trolleys with 2 big batteries, modified sine wave..   For the shorter load shedding periods, I had the idea of plugging the UPS into the above wiring setup, just to run lights (I turn off geyser and all plug circuits at the board...Ok all except one circuit that seems to run some wall lights in our lounge for some reason). Keeps the lights on without the drone of the goddamn generator.

Is this acceptable?  It seems to work fine, done it 3 times now and nothing bad happened. I make sure no fridges or appliances are trying to run. The only reason I ask is that the UPS does kinda say in the manual not to do this (reason is that some appliances may be damaged...which I'm avoiding). But then on some google searching, I saw something about the Earth leakage possibly not working if Modified Sine Wave power is used?

If this is the case....Why?    Can someone explain to me like I'm 5yrs old?  I'm not an electrician and I don't understand too much about the angry pixies that come out of the wall sockets.

[Coulomb]

On 2022/04/28 at 5:34 PM, Roadhawg said:

just to run lights

That could be OK, depending on the lights.

IF the lights are low voltage (e.g. 12 V tungsten), then these likely use a 50 Hz transformer, and they won't like the non-sine wave from the inverter. It will overheat the transformer, with the attendant problems of premature failure, possible fire, etc.

Motors also usually don't like the square waves that a "modified sine wave" inverter produces. (They're extremely modified, like on or off versus smoothly changing). So don't be tempted to run the fridge or freezer, even though the temptation will be high (all that expensive food going off...)

The problem with manual changeovers like this is that one day you'll forget and leave something connected. Five minutes of that might be OK, but an hour won't be. Are you feeling lucky today? Tomorrow? Next month's storm?