How to Wire a Low Voltage Transformer

Written by g.k. bayne
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Low voltage transformers can be used in control circuits that range from ringing the front door bell to sophisticated motor automation. Low voltage transformers are, for the most part, single phased units with a voltage range on the high side, primarily of 120 to 480 volts alternating current (VAC). The low-end voltage is generally 12 to 24 VAC. By following a basic process, you can wire a low voltage transformer in a matter of minutes.

Skill level:
Moderately Challenging

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Things you need

  • Low voltage transformer
  • Wire strippers
  • Screwdriver, Philips or slotted

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  1. 1

    Observe the nameplate tag on the low voltage transformer and the corresponding "high" side or primary connections. Typically. the high side terminals of the transformer are identified as H1, H2, H3 and H4 for 240 and 480 VAC inputs. The 120VAC inputs can simply be a two-screw connection for most low voltage transformers. Before any termination to a transformer, follow the nameplate schematic for all terminations.

  2. 2

    Connect the transformer for a 230 or 480VAC primary input. Interconnect terminals H2 and H3 with either the vendor provided metal jumper, or make a small wire jumper by stripping a short piece of wire with the wire strippers. Attach the jumper, using the screwdriver, and tighten the screw terminals to secure the wire jumper in place.

  3. 3

    Attach the input or high voltage wires to H1 and H2. The low voltage terminals will be identified by X1, X2, X3 and X4. The interconnection of the low voltage side, or secondary terminals, depends on the high side, or primary voltage.

  4. 4

    Terminate the low side of the transformer for a 480VAC primary inputs. As in step 2, interconnect terminals X4 and X2, and one of the low voltage output wires can be connected to one of these terminals. You must also interconnect X3 and X1 in the same manner. The other low voltage wire will connect to this combined terminal, as well.

  5. 5

    Wire the low voltage transformer for a 230VAC input on the primary. The interconnection of the secondary will use X2 and X3; tie these two terminals together with a jumper and tighten with the screwdriver. One output wire is connected to X1, and the other output wire is tied to X4.

  6. 6

    Attach a grounding wire from X4 of the low side terminations to the case ground, or metal frame of the transformer. This will ensure a proper grounding for the low voltage side of the transformer.

Tips and warnings

  • Follow all manufacturer's instructions for terminations on transformers. Various applications for step down transformers can be achieved with various interconnections.

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