How To: Cable Sizing for 12v LED Garden Lighting

Garden Lighting Cable is available in a number of thicknesses, otherwise known as gauges or sizes. Because the conducting material is copper, the price increases significantly as the thickness increases. It can be tempting to use a smaller sized cable to save a little money, but making sure you have the right sized garden lighting cable is all about safety & minimising voltage drop.

Think About Distance & Wattage

The demand on a cable is all dependent on the wattage on the circuit & the distance the cable has to run between that wattage & the power source. So when someone asks “What size cable do I need for 6 lights?” the next question from us would be “What wattage globes are you using & how far is each light from the power source?” The higher the wattage of each light & the longer the cable has to run, the thicker the cable needs to be.

Cable Sizing Table

The table below is our best guide to sizing the cable on your lighting system. We must emphasise the word “guide” as there are a few conditions that can increase & decrease these limits. The following is a good guide for lighting systems where:

  1. All the light fittings on the run use the same wattage

  2. The first light is, at most, positioned halfway along the cable run

  3. The lights are evenly spaced after that.


Total Wattage

Cable Run Distance (m)

Cable Size

4.0mm

6.0mm

10mm

20W

65

97

164

40W

32

48

81

50W

25

38

65

60W

20

32

54

70W

18

27

46

80W

16

24

40

90W

14

21

35

100W

13

19

33

120W

10

16

27

150W

8.3

13

21

200W

6.5

10

16

250W

5

8

12.6

300W

4.2

6.7

10.7


Systems With Higher Load

If, like in some cases, your light fittings are a greater distance from the power source your cable will be under a greater load & needs to be sized accordingly. Likewise systems with a large number of light fittings & therefore higher wattage, the load is increased & the cable needs to be able to cope. So there are a few ways around it, which are listed below.

Up The Cable Size

If you’re cutting it fine with what’s specified, the safest thing to do is err on the side of the larger cable size. Although this may mean extra expense, if there’s a problem it will be far more costly.

Use Multiple Cable Runs

If you’ve got a large number of lights, split the load of the system by running multiple cable runs from, or from close to, the power source. In this case, refer to the table & calculate using the wattage of each cable run individually.

Run Thicker Cable to the First Light

If you’ve got a bunch of lights spaced similarly, but are a far greater distance from the power source, you can run thicker gauge cable to the first light & step down the cable size to the remaining lights. To work out the cable size in this situation; First, halve all of the distance values in our Cable Sizing Table. Second, use these new value to work out the cable size to the first light. Third, use the new values to calculate the cable size for the remaining lights.

Add an Extra Power Source

If the load is too great on the cable, consider separating the lighting system into two or more with individual drivers/transformers.



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