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A 'coil tap' is a wiring feature found on some electrical transformers, inductors and coil pickups, all of which are sets of wire coils. The coil tap(s) are points in a wire coil where a conductive patch has been exposed (usually on a loop of wire that extends out of the main coil body).
When the coil taps are disconnected, the coil operates as normal (see transformer). When a coil tap is connected to one end of the coil (or the end disconnected and reconnected to the tap), the section of coil between the tap and its connected end is bypassed - effectively reducing the number of turns in the coil.

Contents

Uses

Transformers

Inductors

Coil Pickups

Telephone tapping

Uses

Transformers

In a transformer, coil taps are often used on both the input and output coils.

★ On the input coils, the taps are usually connected by switches to compensate for differing supply potential - for example, between 110 V and 230 V for American and European mains electricity.

★ On the output coils, taps are used to provide a range of output potentials. Prototyping transformers are often supplied in cases which have spring-loaded contact traps - one common and several taps (for example, Common; 3 V; 5 V; 10 V.)

Inductors

Coil taps on inductors are quite rare, but are sometimes used for band switching in tuning circuits.

Coil Pickups

Coil pickups used with 'measuring instruments' often feature coil taps to compensate for band rejection or equipment input impedance.
Magnetic coil pickups used in 'musical instruments' (such as electric guitars) use coil taps so that the output from a pickup can be lowered to the tapped value and allow higher frequencies to be heard more clearly.

Telephone tapping

Coil taps can be used as a rudimentary method for recording telephone conversations. See Telephone tapping.