AC polarity is important for best performance. This is most important in countries like those in the EU not using polarised plugs, two prongs and lacking a ground pin, that can be easily rotated 180 degrees in the wall socket.

To check AC polarity, plug in and turn on the product. Then touch the tip of the polarity pen to the inside edge of the AC power cord plug where it connects to the AC socket in the product. The tip of the pen should light up, indicating you have correct polarity. If it does not light up on the inside edge, then you need to rotate the European power plug in the wall socket and test again.

In countries where a polarised two prong or three prong plug is used, like the UK and US the polarity the AC power coming from the wall should be correct. But, in case the AC wiring inside your home is not correct, it’s still a good idea to check this. If the test reveals incorrect polarity, you may need to switch the positive and negative leads in the wall socket itself.