Handbook of Electrical Engineering

376 HANDBOOK OF ELECTRICAL ENGINEERING

Figure 13.14 Interference and screening circuit of cables that are run in parallel with each other.

Ls is the self-inductance of the cable core.

Msc is the mutual inductance between the screen and the core.

For the couplings between the cables

M 3 s is the mutual inductance between the interference cable and the screen of the

signal cable.

M 3 c is the mutual inductance between the interference cable and the core of the

signal cable.

For the components connected to the cables

Rin is the internal resistance of the signal source.

Ro is the output or load resistance on the signal source.

Re is the resistance of the common earth path of the signal cable.

Consider two cases, firstly a cable without a screen and secondly one with a screen. The two
cases will then be compared.

Case A. Signal cable without a screen.
The summation of voltages and emfs in the signal cable is:-

Vin=(Rin+Rc+jωLc)Ic+jωM 3 cI 3 +(Ro+Re)Ic