Hello ,an AC light bolp has needs two wires , while AC power in the wall has three wires.
So how am i supposed to connect the lightbolp in the power in the wall?
Thanks.

 

The short answer is - get it done by someone who knows what they are doing, so it's safe.

In more detail, the brown supplies power through to the blue, and the green is connected to the framework of the light fitting for safety.

https://en.wikipedia.org/wiki/Single-phase_electric_power

 

Agreed.. if you don't even know how to wire a light bulb to a standard power supply wire... don't even try.

 

Connect the Live (L) wire from the wall (brown) to one terminal of the light bulb socket.
Connect the Neutral (N) wire from the wall (blue) to the other terminal of the light bulb socket.
Do not connect the Protective Earth (PE) wire to the light bulb socket, as standard light bulbs do not require it.

 

Connect the Live (L) wire from the wall (brown) to one terminal of the light bulb socket.
Connect the Neutral (N) wire from the wall (blue) to the other terminal of the light bulb socket.
Do not connect the Protective Earth (PE) wire to the light bulb socket, as standard light bulbs do not require it.

This is incorrect, and potentially dangerous.

The connections of live and neutral are not arbitrary and reversible them can lead to painful—or worse—shocks. A lamp socket is only safe if the neutral, and not the live, is connected to the terminal with continuity go exposed metal parts of the socket which the user may contact.

The screws of the socket with be color coded, like this one:

​

The neutral goes to the silver screw and the live to the gold (brass). And, many—though not all—lamp sockets provide a terminal for the safety ground, and it must be connected if there is one in the line cord. In the case of a two pin plug, the same applies and for the US Edison connector, a polarized type must be used (larger blade is neutral).

 

The connections of live and neutral are not arbitrary and reversible

It depends on the type of bulb socket. True for an Edison Screw type, but not necessarily so for a Bayonet Cap type.

 

It depends on the type of bulb socket. True for an Edison Screw type, but not necessarily so for a Bayonet Cap type.

It's true that a typical modern phenolic B22 socket, which is entire insulated has no preferred polarization, but there are older B22 sockets with metal shells, and these must be wired with the correct arrangement. This is an example of of a UK-made B22 socket with brass shell:

​

 

Even the type shown above makes no distinction between Line and Neutral connections, but the socket does need a correct Earth connection.

 

Even the type shown above makes no distinction between Line and Neutral connections, but the socket does need a correct Earth connection.

You could e right about that, I was under the impression that the neutral appeared on the shell, but It is earthed and the neutral is isolated, that also works.

Of course my original point is you can't just ignore the L and N in many cases, and the ground in others. So many lamps are miswired in the US, but the 120V is somewhat mitigating. The 240V of the UK/EU is probably the reason for the fulliy insulated B22 socket.

 

As I pointed out here recently, https://forum.allaboutcircuits.com/...-contact-in-the-bottom-of-lamp-socket.203720/
Post #10.
The UK style is safer when a lamp is in the socket, the NA type it is possible to have the outer thread connected to live !

 

Well, this discussion has certainly reinforced my original comment - even a light socket is not simple to connect safely!

 

What is certified as unsafe is to put one's finger into a light socket. And nobody asked the TS what type of socket. Worse yet, the sample held up was a power cord, not suitable for permanent wiring in a building, at least not in the US. In other parts of the world, rules may differ. AND A QUESTION: what color are the line (hot) and neutral of permanent wires in the UK? That is, not in ortable cords, but in wires hidden inside the walls.

 

what color are the line (hot) and neutral of permanent wires in the UK? That is, not in ortable cords, but in wires hidden inside the walls.

Line=brown, Neutral=blue, both in wall wiring and in appliance cords, in both UK and Europe.

 

OK, much different than here in the USA, Line=Black, Neutral=White, Line2=Red (sometimes)

 

One recent change in enclosure wiring colours by N.A. (NFPA79) to conform to Europe standard, was wiring inside enclosures that remained powered live from a different source when the local enclosure disconnect was OFF, was the N.A. custom of using colour Yellow in place of the now E.U. standard of Orange.

 

One recent change in enclosure wiring colours by N.A. (NFPA79) to conform to Europe standard, was wiring inside enclosures that remained powered live from a different source when the local enclosure disconnect was OFF, was the N.A. custom of using colour Yellow in place of the now E.U. standard of Orange.

Interesting indeed, Max, since orange may be easy to mistake for faded RED, while any of the shades of Yellow clearly stand out as not at all red or orange. I wonder what explanation was provided as to how the change improves safety.
"Yellow MAY STILL BE HOT" was so very easy to understand.