Twisted Pair Cable
The winding of the outgoing and returning conductors around each other at regular intervals. The twist shrinks the area enclosed by the pair and induces the same noise in both conductors, so the effect cancels itself out. It is the cheapest way to increase immunity on control signals.
The voltage a magnetic field produces in a cable is proportional to the area enclosed by the conductors. When two conductors run parallel and spaced apart this area is large; when they are twisted around each other each turn becomes the reversed counterpart of the previous one and the induced voltages largely cancel. In addition the noise appears on both conductors as common mode, which differential input circuits suppress.
- Application: run the control line going to the contactor coil, the limit switch line and the low-voltage supply pair as twisted pairs.
- Mistake: routing the outgoing and returning conductors along different paths. This zeroes out the gain of the twist and turns the cable into one large loop.
- Together with: a twisted pair is effective when used together with shielding and the separation-distance rule; on its own it may not solve high-level inverter noise.
This arrangement is among the first corrections to apply when intermittent response complaints originate from the cabling.
The context in which this term is used: Wireless remote control installation: pairing, relay, safety