We are always asked what the difference between the different types of low voltage cables we offer. A very good question, but to answer it fully we need to explain a little about the history of 12 volt garden lighting systems.
Pre the onset of energy saving LED light sources we had the high wattage halogen bulbs. These would range from 10 watts up to 50 watts and therefore not only needed larger transformers, but also larger cables. Therefore, the SPT3 cable was generally used more as it would take a loading of 150 watts through it. The SPT1 (120w max wattage loading), lighter duty cable was always used towards the end of the run as it would be very unusual to have more than 120 watts of loading at the end of the system.
With Led light sources being much lower loading and up to 90% energy saving, the need for the larger SPT3 is not so important in most garden lighting plans. Therefore, the SPT1 is more than adequate for over 90% of systems now. I would say that most of the orders we supply don't even get to 40-50 watts. This equates to approximately 15x 3w spotlights, which is quite a lot for most average sized gardens.
If you are planning a large lighting scheme in your garden or for a client of over 50mtr in length and intend to use a mixture of SPT3 & SPT1 cables, we would always suggest you start with the heavier SPT3 towards the transformer and follow on with the lighter SPT1 cables. This is to avoid the chance of Volt Drop.
What is Volt Drop you ask? Well is where the voltage going through the light system drops the further it goes. This means that you could have a light or two, furthest away from the transformer, looking a little dimmer than the rest. If you tested the voltage at the furthest point of a big system. It would not be 12 volt, it could be 9 or 10 volts. Therefore, the reduced voltage may produce less light from the fittings towards the end. This was a much bigger problem in the old days for Halogen systems. To rectify this the manufacturer tests and produces LEDs that are designed to operate at full output with a reduced voltage input, thus eliminating Volt Drop on much bigger systems. This is not guaranteed as various things lead to Volt Drop, i.e system loading, transformer sizing and whether Techmar manufactured LEDs are being used.
If you are in any doubt, please call us as we have many years' experience in designing and supplying systems.
Please also see our blog regarding LEDs
SPT3 is approximately 10mm x 5mm (15mtr Main cable and 10m Extension cable)
SPT2 is approximately 7mm x 3.5mm (Cable on 3 way dividers, Deluxe Bundles and 1 & 3mtr extension cables)
SPT1 is approximately 5mm x 2.5mm (8, 10, 15 & 25mtr main cable plus 2mtr and 6mtr extension cables)
We now offer a SPT2 plain cable system (available on our Deluxe Bundles). This is a great new system that is even easier to install as the cable is plain and can easily be feed through ducting, in between paving stone gaps and laid across lawns. Once the cable is laid, it can be cut to length, capped off and a heavy-duty female connector clamped on where you want a light to plug in. Available in 10, 25 & 50mtr drums with male and female connectors. It is fully interchangeable with the standard Garden lights range of lights, and accessories.
Please call us on 01276 903 228 or send an email to
When you subscribe to the blog, we will send you an e-mail when there are new updates on the site so you wouldn't miss them.