There are two the easiest way to distinguish between ground and zero. The first method, which, however, does not give you 100% guarantee correct results is to look at the color of your three wire cable. Usually, if electricians who did the wiring in you house, know the standards, they leave the ground on the yellow-green wire. Let's see if you have one, this is most likely a ground.
For the second method get a working cartridge and a light bulb at 220 volts. A screwdriver-indicator to find the wire phase and connect it to one of the contacts of the cartridge. The second contact holder alternately connect the remaining two wires. If the bulb glows, the wire is zero. Accordingly, the third wire (the rest is not connected to the cartridge) to the ground.
If the bulb does not light, the wire that is connected to the cartridge is grounded. Be careful, if after this procedure, you have lost the light in the apartment, but it can occur after connecting to the cartridge ground wire, so you have RCD (residual current device). If so, find it (it is similar to circuit breaker but it has a test button, button "T") and put the lever in the topmost position.
Because the cartridge is under tension when performing all operations, be extremely careful that you are not electrocuted. If you are far from electricians, call a professional and let you will do everything you need.