# Why Do We Use Twist In Twisted Pair Cable?

The "why do we twist" question is best answered in the full context of wire selection.
There are three key properties to consider in the design of electrical circuits:
Resistance, capacitance, and inductance.

Resistance.  How do we ensure that a wire will not overheat, when we apply voltage and current to it? By selecting a wire gauge that is sufficiently large.  Don't use 22 AWG telephone wire to power a room air conditioner.

There are two kinds of electromagnetic induction: Capacitive coupling (electrostatic), and magnetic coupling (electrodynamic).

Capacitance.  How do we ensure that the signal transmitted over a wire, will not be degraded by excessive noise, when we place the wire into an environment, that has ambient electrical fields which tend to capacitively couple with the active signal-carrying wires? By covering the wires with a continuous metallic shield or foil, which is grounded at one or both ends. The ambient electrical fields capacitively couple with the shield instead of the active signal-carrying wires.  This helps prevent your wires from playing the role of a capacitor anode or cathode.

Inductance.  How do we ensure that the signal transmitted over a wire, will not be degraded by excessive noise, when we place the wire into an environment, that has ambient electromagnetic fields which tend to inductively couple with the active signal-carrying wires? By twisting the wires continuously, from end to end. The ambient electromagnetic fields magnetically couple with thousands of very small twisted coils, instead of the entire untwisted "single-loop" signal-carrying wires (a transformer with a 1:10000000 ratio induces infinitely less noise than one with a 1:1 ratio; it's called lowering your effective loop area, ELA).  Also, each adjacent pair of twists consists of one oppositely-wrapped loop, so each pair is self-cancelling.  This helps prevent the wires from playing the role of a transformer primary or secondary coil.
thanked the writer.