Joint???

[Badar]

Hi.
An electrical joint causes problem during data transmission
I have two questions:
1. Why it produces noise in a telephone line while it is twisted enough to make sufficient contact with other wire.

2. Does it causes problem with even power transmission(i.e. transmitting power for home appliances.240V 50-60Hz.)

 

[JimB]

1. Why it produces noise in a telephone line while it is twisted enough to make sufficient contact with other wire.

Initially, when the wires are clean, there will be good contact between the two wires - no problem.
After some time, the wires will oxidise and there will be a high resistance contact between them. As the wires move, the resistance may change causing a variable volt drop across the joint, and so the telephone signal will be noisy.

2. Does it causes problem with even power transmission(i.e. transmitting power for home appliances.240V 50-60Hz.)

At higher power, there is sufficient voltage to "burn through" the high resistance joint.
The joint will get hot, there could be a large volt drop across the joint, but unless the resistance becomes very high, you may not notice the problem.

JimB

 

[Hero999]

Capacitive coupling, is the answer, the two wires with an insulator between them form a capacitor which can pass AC signals and result in crosstalk.

 

[TheVictim]

Wires you want to keep connected for any length of time should be soldered or at least taped to keep them from oxidizing.