Should a salve socket have a capacitor

Hi
In my house we have a telephone socket in every bedroom, dinning and living room. There are three cables going to the master socket next to the front door. I believe the electrician has seperate wires for the living/ dinning room then another for the bedrooms upstairs. I've found that many of sockets have a capacitor at the top. I thought only the master socket should have one. Am I not correct in saying that?

Edited by deleted (Wed 29-Jun-11 14:32:40)

Should not be there. A slave normally has nothing fitted .

What potential issues could it cause?

each capacitor can potentially introduce interference into the A/B pair from ring (bell) wires connected to that socket.