Landscape Lighting

Low-voltage landscape lighting fails in exactly one way: the fixtures at the far end are dimmer than the ones at the start. It is always voltage drop, and it is always discovered after the cable is buried.

Three numbers, worked out together

Fixture count from run length and spacing. Transformer rating from total load — never run one above 80% of its nameplate, because a transformer at full rating runs hot and heat is what kills them. Cable gauge from voltage drop over the run.

Get any one of the three wrong and the system underperforms in a way that looks like a faulty fixture.

Current is halved, and that is correct

With fixtures spread evenly along a run, the full load current only flows in the first section of cable. By the far end almost nothing is left. Calculating as though the whole load ran the whole distance doubles the apparent drop and sells you twice the copper.

The window is narrow

12 V LED fixtures want 10.5–15 V. Below that they visibly dim and some flicker; above it they fail early. Ten percent drop is the practical ceiling, and it is tighter than the 3% branch-circuit convention would suggest is necessary — because there is no headroom to spare at 12 volts.

Two fixes that cost nothing

Feed from the middle rather than one end. That halves the effective distance and roughly quarters the drop, for the price of a different trench route.

Leave headroom on the transformer. Landscape lighting always grows — one more fixture at the new tree, two more along the path. Sizing to exactly today's load means buying a second transformer next spring.

Multi-tap is compensation, not a substitute

Transformers with 13, 14 and 15 V terminals exist to compensate a long run. They work. But raising the voltage at the source to fix undersized cable also raises it at the near fixtures, which then run hot.