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Calculating transformer ratings

A frequently asked question is “how many lights can I run from one transformer”? In fact, transformers are available in a wide range of wattage ratings, so we need to look at the question in reverse: “what size of transformer do I need to power a group of lights”?

Exterior & Ground Burial Transformers

A transformer is an electrical or electronic device which changes voltage from one level to another; in garden lighting this is usually from 240 volts to 12 volts. From the transformer to the luminaries (light fittings), the wiring is low voltage cable which typically runs under mulch and over garden structures. To minimise cable voltage drop to the luminaires, identify groups of lights which can be supplied from one central transformer.

Filters and Lenses

Installation of low voltage step/wall lights

Installation materials

Low voltage cabling layout

Most good garden lighting works at 12 volts, so you need to locate transformers in the garden and use flexible low voltage cable from the transformer to the lights themselves. Cable loses voltage according to its length and the number & power of lights you connect to it, so keep low voltage cable runs as short as possible to optimise the performance of your lights.

Low voltage lamp choice

Recessing brass uplights in paving

If you need to install recessed uplights in paving, you will want to ensure a flush, level fit and prewire the light positions without risk of damage to the lights during installation or cement spill etc spoiling the finish or making final installation difficult.