Transformer: labelled reference, US style

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Transformer: labelled reference, US style, sheet 1 of 1

  1. Fig. 1

    P1P2S1S2

    Transformer

    The separate-winding transformer shown here transfers energy magnetically between windings without an internal conducting connection between them. This description excludes an autotransformer, whose windings share a conducting connection.

  2. Fig. 2

    P1P2S1S2CT

    Centre-tapped transformer

    A centre tap is an electrical connection at the midpoint of a winding, shown as an extra lead from that winding.

  3. Fig. 3

    P1P2S1S2

    Air-core transformer

    In the transformer drawings here, parallel lines between windings indicate a magnetic core, drawn as iron-core examples. The air-core example omits these lines; another drawing's legend may use a plain coil more generally.

Terminal key
Fig.TerminalsWhat the terminal is
1–3P1, P2The primary winding is the one driven by the source.
1–3S1, S2The secondary winding is the one that delivers power to the load.
2CTA centre tap is an electrical connection at the midpoint of a winding, shown as an extra lead from that winding.

Sources

  1. ModEL — Transformers, §§4.1, 4.3–4.4 (windings, centre taps, autotransformers and dots), Tony R. Kuphaldt, retrieved 2026-09-22
  2. ModEL — Components and Symbols, §§3.13–3.14 (inductors and transformers, pp. 24–26), Tony R. Kuphaldt, retrieved 2026-09-22
  3. Lessons In Electric Circuits, Vol. V — §9, Circuit Schematic Symbols (pp. 130–139), Tony R. Kuphaldt, retrieved 2026-09-22
Name
Class
Date
Sheet
1 of 1
Drawing
Transformer Labelled reference
Style
US style
From
circuitsymbols.com
Licence
CC BY 4.0