Cart 0
UPDATED June 2016 - 12v Low Voltage Cables For Patio Lights and Outdoor Garden Lights?

UPDATED June 2016 - 12v Low Voltage Cables For Patio Lights and Outdoor Garden Lights?

The ability to self-install your own low voltage patio lights, decking lights and garden lights without the need for a qualified electrician is becoming more and more popular.  The lighting effects in the garden can be stunning and can make the gardens vibrant and an extension to the main home.

The safe, 12v low voltage outdoor lighting cabling is far more flexible than 230V mains electricity cabling and fitting the garden lights couldn't be easier.  

However, lots of people want to know more information about the cables that are needed and the overall length they can lay. 

So I thought I'd bring our previous blog up to date, giving our experience and views on the length of low voltage 12v cable runs for patio lights, decking lights and garden lights. 

We've installed Techmar's high quality 12v low voltage cables with Techmar garden light products as far as 65 metres and at the end of the cable used three 30 watt LED floodlights for up-lighting some large trees!  The layout was carefully considered so don't leap to a conclusion that a 65 metre run will work 'out of the box' for everyone.

We think we could have cabled a lot further, maybe up to 90 metres, especially if the high consuming LED floodlights had been low consuming spotlights (e.g. if the installed 3 x 30 watt LED floodlights that use 90 watts were replaced by say 10 x 4 watt LED spotlights that would use a total of 40 watts).

The cable run was supplying 11 fittings in total amounting to 122 watts consumption powered by a 150 watt transformer. 

(Further information about low voltage garden lighting cables can be found at . Techmar's cables for 12v garden lights are either classed as SPT-1 or SPT-3. More information about cabling up the light fittings is also given in our FAQ's page)

So can we give a simple and definitive answer on cabling for everyone?  Answer: No.

Each situation is different and it's a tricky one to answer as it involves a few variables that need to be looked at closely.

Low Voltage - Look Closely At The Variables ImageWe always try to understand the

  • total 'possible' cable length
  • LED fittings likely to be used and where sited on the run
  • overall cabling and fitting design to suit the layout of the garden or outdoor area and
  • the size of the transformer!


How do the 'VARIABLES' impact the garden lighting voltage cabling runs?    Well here's a short 'lay-mans' explanation!

It's not written to harmonise totally with the 'laws of electricity' but to try and give a picture in the minds eye. 
If it doesn't help then have a look at our web shop for further information ( or email and we'll be pleased to help.


1 Electricity Loss

All electricity loses power as it goes along a cable.  The longer the cable the more electricity it loses.  

The nearest analogy I can think of is a normal domestic hosepipe with a constant water pressure forcing the water through it.

You can imagine that if the hosepipe is short, the water would come out almost as quickly as it went in.  If the hosepipe is 200 metres long the water would probably trickle out. 

Electricity passing through cables is just the same.  As electricity passes down the cable it loses power.  It's called 'line loss' (not pressure loss).

So it's perfectly true to say that a 230v mains supply running through your garden has more power and therefore can reach further along a cable than a 12v supply (all matters being similar). However, it's also a potentially dangerous cable whereas a 12v cable is never dangerous!

2 What is being used by the LED's and where are they on the cable run?

The next main variable is what is being used along the garden lighting cable by each light bulb and where they are sited on the cable run.  If the fittings are using a lot of electricity, especially at the beginning of the cable run, then then the length of electricity supply will be shorter before the power runs out.  

Again, imagine a large sprinkler being used at the beginning of a hosepipe.  As it uses most of the water the end of the hosepipe will only trickle out what's left!

3 Minimum and constant supply

Thirdly, LED technology typically likes to have a constant AND 'minimum' voltage to ensure it works.  So if some fittings at the earlier part of the cable use more electricity and 'drain' the supply then others that may be downstream may not work at all.

4 Total electricity being used.

Then there is the total electricity being used.  The transformer must be able to supply sufficient electricity to power all the light fittings. This can be controlled to some degree by the transformer's output and how many 'watt's it can supply for consumption by the LED bulbs. However, if the total wattage of the LED's being powered is more than the transformer can provide then some LED's won't work.  Never have more 'watts' being used than the transformer can 'output

5 Conclusion

So two of the main 'variables' are easy to identify. The total electricity that is likely to be used (the total light bulb wattage) and the power you can put in at the beginning of the low voltage cable (the maximum transformer wattage output). 

However, the exact length of the low voltage garden lighting cable is still unknown.

Frankly, it will require a far deeper level of electrical calculations that become extremely difficult to work out.  The calculations would need a lot further information such as the precise type and purity of the copper core used in the wiring, other losses from fittings etc etc.  

So as we can't calculate each situation precisely, and as we have installed extremely long runs before, we conclude that a 65 metre run and maybe up to 90 metres for the low voltage garden lighting cable should normally be used as a typical maximum run length.  This should cover the installations for most patio lighting, decking lighting and garden lighting.

We also use various design techniques to split power supplies over more than one circuit and this enables a lot more lights to be used around a larger garden.  

We haven't been stumped to date, but if you are still puzzled or in any doubt feel free to contact me via email or just call me on 0121 416 0408 and I'll be pleased to help. 

Older Post Newer Post

Leave a comment

Please note, comments must be approved before they are published