120V to 12V AC Transformer Wiring Question

Discussion in 'Electrical Forum discussion & Blog' started by Doug Parsons, Oct 30, 2008.

  1. Doug Parsons

    Doug Parsons New Member

    Messages:
    1
    I'm trying to replace old defective transformer for under counter lighting. Purchased a replacement type with same input/output specs--120V AC to 12V AC 150W. New transformer has typical incoming Black/White leads but output only has two red leads. Question is: How to wire for proper operation. The incoming power line is operated by wall toggle switch which comes to transformer. There are two sections of under counter lights operated by the same transformer. However, the pair of wires for each under counter light system are both white. Not sure how to properly wire both sides with only two 12V hot leads.

    Thanks for suggestions.

    Doug
  2. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Light set #1 leads can be labelled a & b.
    Light set #2 leads can be labelled c & d.
    Transformer output leads can be labelled 1 & 2.
    Hook #1 to a and c.
    Hook #2 to b and d.
    If the transformer secondary is not short circuit proof or fused, you may want to add a fast-blow fuse to the primary winding.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,932
    Location:
    New England
    Assuming that the black and white are the primary (probably smaller gauge wire but should be identified somewhere), you want one wire from each bank to go to one red wire from the secondary , and those left over to the other red wire.
  4. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    Black and white = 120V

    Reds = 12V

    Blk to Blk, Wht to Wht,

    red to 2 whites (one from each set of lights)

    Other red to other whites.
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