Most led garden lighting works at 12 volts, so you need to locate transformers or dc power supplies in the garden and use flexible low voltage cable from the transformer to the garden lights themselves. Cable loses voltage according to its length and the number & power of garden lights you connect to it; this is rarely a problem with led garden lighting as it consumes much less power than halogen lighting, but it is good practice to keep low voltage cable runs as short as possible to optimise the performance of your garden lights. The best ground burial low voltage cable to use is a round, double-insulated rubber type with a tough outer sheath impervious to moisture and salts in the soil to suit most garden lighting applications. The round shape seals well through cable glands or membranes into junction boxes to avoid moisture getting in. The cable is usually run under bark or gravel mulch to aid flexibility in locating garden lights, but we recommend the same cable for use under decking and over pergolas to resist condensation as well as rain. Protective conduit may be used where cable might be vulnerable, for example where it crosses under a grass path where lawn edging during maintenance might damage the cable. Black clips (T9950 Box 50) are used for neat clipping of cable over pergolas and along deck joists. You will rarely need the thicker 4mm2 cable to overcome voltage drop to led lights, for which we suggest 2 sizes of ground burial low voltage cable as standard; 2.5mm2 (T9912 - 50m; T9913 - 25m) used for longer cable runs and higher power led lights and 1.5mm2 (T9918 - 50m) ground burial low voltage cable for low power applications such as wiring up led lights around a deck.
What length of cable can I use from the power supply to a garden light?
"Cable voltage drop" occurs in all electric cables, but in a 12 volt garden lighting system care must be taken to limit this to avoid loss of light output resulting from voltage reduction at the lamp. If you cable up too many led lights on one cable run, or along a cable run that is too long for that number of lights, then you may find that lights at the far end of the cable run are dimmer, flicker or go out. The table below gives the maximum length of cable run for typical garden lighting wiring requirements for halogen lamps - stick to these cable lengths to get full brightness from your outdoor lighting system. L.e.d.s consume a lot less power than incandescent lamps and are generally less sensitive to small voltage reductions, so cable runs can also be a lot longer. Remember, when working out your cable runs, higher power led lights (those from 1 watt upwards) take more power than their nominal rating as they incorporate a voltage driver which converts the constant current characteristic of an led to 12 volt constant voltage operation for easy installations in gardens; for example 1w Navigators actually consume 2w of power.
Tips on power supply location and low voltage cabling:
- Locate a power supply centrally amongst a group of garden lights it is to power
- To run 2 sets of garden lights operated by separate switches, you must provide 2 separate power supplies & circuits.
- If the distance exceeds the maximum cable length recommended for a single garden light, revise the layout, increasing the number of garden lighting power supplies to reduce the low voltage cable runs, or use thicker cable.
- If the run for multiple lights connected to one cable exceeds the maximum, divide the led garden lights onto individual cables
- In gardens with garden lighting or irrigation, garden with a fork rather than a spade until you are sure there are no garden lighting cables or irrigation pipes where you want to plant your new shrub!
- Clip cables neatly along deck joists, pergolas etc wherever possible to reduce the likelihood of damage as a result of gardening, children’s games, pet activity or animal nesting.
Copyright 2014; Information based on products supplied by Lighting for Gardens Limited and is advisory only. The company accepts no responsibility for incorrect use or application of information given. Light fittings can become hot in use; exercise appropriate precautions. Exterior electrical installations should be undertaken by a qualified electrician.