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A single winding with a tap, not two separate coils.
Also known as: Auto transformer, Single-winding transformer, Variac, Tapped coil symbol
An autotransformer has one winding shared between primary and secondary rather than two isolated ones, which makes it smaller and cheaper — and removes the electrical isolation entirely. A fault can put the full input voltage on the output side, which is why it is barred from some applications.
Denotes an autotransformer: a transformer with a single winding tapped to provide the second voltage.
Contexts: Electrical equipment
Provides no galvanic isolation between input and output, unlike a two-winding transformer, because the windings are physically the same conductor.
Contexts: Electrical equipment
Is smaller and more efficient than an isolating transformer of the same rating, which is why it is used for voltage adjustment where isolation is not required.
Contexts: Electrical equipment
A single coil of loops or a rectangle with three connection points, one at each end and one partway along.