Blue/black/brown wire?

Brown -> Power/Positive

Blue -> Ground/Neutral/Negative

Black -> Output

You need to check the voltage of your device, and whether it is an AC or DC operated switch. If it is an AC switch, then the black wire will be hot when the switch is made. If the switch is DC it will either be PNP or NPN, on a PNP switch the black wire will have the same potential as the positive line you are powering the switch with. On an NPN sensor, the black wire will have the same potential as your negative line.

Having said that, I still agree that you should read the instructions. Especially when dealing with high voltage.

Edit:

If it is for a light then you should tie all of the neutrals (presumably all white wires and also the blue on your switch) together.The hot line coming from the breaker box should tie to one of the leads from your switch while the line powering the light should tie to the third.

The brown, blue, black color code is a European standard that is now used extensively worldwide, and most often on switches and sensors, the assignments are as I stated above, however, that does not necessarily mean that the manufacturer of your switch will use the same assignments. You should always check the manual or look for a connection diagram on the switch itself.

Your three wire device is intended for two-phase supplies not 3-phase. Usually the blue and black wires are for power and should be connected to the two-phase supply. The black wire is probably neutral or earth, but there is doubt here.

Before connecting the device to your domestic power you should try testing the device first with a battery and low voltage light bulb or an ohm meter, to see whether the blue and brown wires allow a current to flow. If this does not work then try to determine which combination of the three will cause current to flow before applying mains voltages.

It is not a 3 phase device. The motion sensor is a switch. It needs power, the black wire is the power. One of the other two is a common neutral wire and the third is for a switched load, say a light.

Just guessing, I'd say the grey wire is the common neutral.

Astrobuf

It is extremely unlikely that your mom bought a device meant for three phase power.

The best thing you could do is read the instructions, or look for manufacturer's identification on the device, and look it up on the manufacturer's web site.

If this device is intended to replace a wall switch, two of the connections will be for hot and neutral, and the third connection will go to the light fixture. But don't guess.

I would just go and buy a new nunchuk. Its sounds ruined. They're only $20. They also sell wireless nunchuk if you dont want to worry about it happening again. Hope it helps.