Wiring LED Products

These notes provide help and guidance with the specifics of wiring LED products. They are not a substitute for using a ‘competent person’ to do the installation. All electrical work can be dangerous.

Single Colour Products

Single colour lightstrips have two power terminals, a positive and a negative. Applying the relevant dc voltage (12 or 24, as required by the product), in the correct polarity, across these terminals is all that is needed.

Ropelight consists of two or three rows of LEDs. The positive wire is commoned inside the rope; there is a negative wire for each row. It is possible to control the rows separately to give a choice of brightness or flash them to give a rippling effect, in which case they can be treated as rgb products (see below). To use them as a single product the two or three negative wires must be joined and connected to the negative of the power supply.

Incorrect connection of Supply

In most cases the incorrect polarity will not cause a problem, the product simply will not light. However in a small number of cases the product can be destroyed by the reverse polarity. Applying the wrong voltage can be a bigger problem. If a too low voltage is applied then the product will glow faintly, or not light at all. Again this is not a problem, simply apply the correct voltage. However, if a too high voltage is applied then the product may well be permanently damaged.

Refreshing the power

If long lengths of product are used then the current for the whole length has to travel through the first piece, and also through the supply cable. To avoid this it is necessary to refresh the power every so often along the run. This is achieved by breaking the run of product at a suitable point and bringing another cable in from the power source. The length that can be powered with one connection is dependent on the current drawn by the product and the current capacity of the wires or tracks in the product. It is therefore different for each product.

Ending a run of LEDs

Most LED systems are not fitted with flying leads on each end. In this case nothing special needs to be done with the last section. Some, particularly waterproof products, are fitted with flying leads to allow daisy chaining, and these leads cannot be removed. The unused flying lead on the end of the run should be appropriately terminated, usually be snipping off any exposed wire ends and taping the wire out of the way. Do not connect the two cores together or back to the beginning.

Power Cables

Although LEDs are low energy devices, the voltage is also low so the current is relatively high, especially when there are a lot of LEDs on the same supply. One of the top questions is how long can the supply cable be. The answer is as long as you want it to be. As with normal electrical practice the current capacity of the cable must be correct for the load and the environment. Also, if the run is going to be long the capacity of the cable should be increased to compensate for volt drop, again as is normal practice.

If the power supply is some distance from a lot of LEDs then consider running a higher capacity cable to the locality of the LEDs, from where smaller cables are distributed to each individual run of LEDs.

Power Supplies

The voltage of the power supply must match that of the product. The current capacity of the power supply must be equal to or greater than the total requirement of everything that is to be powered. It cannot be too big, in electrical terms, but this will increase the size and cost.

Several products can be connected to one power supply, up to the rating of the power supply (see Fusing). Many products can be connected to one large power supply or several small power supplies as appropriate. Never connect more than one power supply to one product or common the outputs from more than one supply. The current drawn from each power supply will not balance and you will end up damaging at least one of the power supplies.

Fusing

A power supply will usually be self protected and limit the current it can supply to a little above its rating. A characteristic of overloading a psu is intermittent flashing as the unit shuts down and then recovers. However, care must be taken if a large power supply is used to run a number of separate items. If a fault developed then any individual connection could take the full capacity of the supply before it would shut down. So each cable run should be suitably protected, by either rating each run to the full capacity of the supply, or by fusing each run with its own fuse and rating the run to that fuse. Again, this is normal electrical practice.

Location of equipment

Sometimes power supplies and control equipment have to be located at a distance from the LEDs. This may be due to poor access to the lighting area or the requirement to house the equipment in a suitable location. Whenever possible put the power supplies as close as possible to the controllers, and all as close as possible to the LEDs. This makes the high current (low voltage) cables short and the mains cables as long as necessary. This reduces the cost of cables and installation and reduces the energy lost in the cables.

Protection in use

The majority of LED products are not inherently protected. You must ensure that they cannot come into contact with metal or moisture, and cannot be knocked or kicked accidentally. If such problems are likely then the product needs to be protected in some way; there are some products available that are already protected. No LEDs, whether protected or not, should be exposed to high temperatures such as steam from kettles.

RGB Products

RGB lightstrips have four power terminals, a single positive and a negative for each colour (known as common positive). Applying the relevant dc voltage (12 or 24, as required by the product), in the correct polarity, across the relevant pair of terminals is all that is needed to turn a colour full on.

RGB ropelight is simply the three row version with one row of each colour. In this case the four wires in the power lead are kept separate.

However, RGB products are usually used to produce blends of colours and so the three primary colours have to be controlled (dimmed) appropriately to end up with the required effect. If dimming or flashing of single colour products is required then the same techniques can be used. Equally colour effects can be created by controlling separate colour sources. Simply common the positive connection of each coloured product and treat it like an RGB product.

All of the points above, concerning powering and cabling, apply equally to RGB products, but there are some additional points to consider.

Controllers

A controller sits between the power supply and the product. It converts the steady dc output from the power supply to a pulse of power into the product. The size of the pulse determines the brightness. A single output controller is usually referred to as a dimmer. Three such devices together, or a triple output controller, is an RGB controller. The input that determines the brightness can be an internal preset programme, one set by buttons and a display, a DMX signal, a 0-10V signal, or a combination.

Because the controller sits in the low voltage power source to the products all of the points above apply to the cabling and location.

If different areas are to be controlled separately (different effects) then a controller is required for each area. However, if areas require the same pattern or there is more product than a single controller can handle then extension modules are required; a single controller must be used for the entire system to get the same effect everywhere. If the original source of the pattern is external (DMX or 0-10V) then it is possible to instruct several controllers to do the same thing so they can be used instead of extension modules.

Extension modules

An extension module can be considered as a power amplifier, boosting an RGB signal and driving more product. It takes its instructions from the main controller (or any RGB source), has a fresh power source, and supplies the extra product. It cannot operate without an external RGB input. It can also be used to operate product that requires a different voltage from that on the main controller or other extension modules.

In a complex system it is often arranged that the main controller is positioned in a suitable place for set-up and operation. It does not drive any product itself. In this case it only needs a small power supply and there is no need of thick cable to the area where the lighting is installed. The slaves are then positioned, with their power supplies, near to each section of product, so the runs of low voltage cable are kept to a minimum.

To connect the controller to the slaves only thin signal cable is required and long distances can be achieved. Alarm, telephone or CAT 5e cable can be used for the purpose.

RGB Power Cables

All the points above, under single colour products, apply, but RGB products need 4-core cable. It is also worth pointing out that, although each negative wire only carries a third of the total current, the common positive wire has to carry the total current of all three colours. The overall rating of the cable must be calculated with respect to this total. One way around this is to use a thicker cable for the positive wire or use more than one core.

4-core cable is not commonly available, especially in the higher current ranges. One solution is to obtain ‘twin & earth’ electrical installation cable with different colour sheaths (say grey and white) and use the two main cores of each cable. Alternatively cut two lengths and mark each end of one piece with a marker. Do not use the earth core as it is thinner than the main cores.