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LED String Wiring

A page describing shop-bought LED Christmas light strings


Most low voltage LED strings are made with the LEDs wired into in sections. Each section usually contains 10 to 12 LEDs wired in series and also has a current limiting resistor as shown below. As the LEDs in a given section are all wired in series, the current through each will be the same.

Most common LEDs are rated for operation at a maximum continuous current of 20mA. As the LEDs in Christmas light strings are of unknown origin with no defined current rating, a cautious approach of only running them at 10mA seems prudent. This also means they are less likely to fail prematurely in hotter conditions. The lower current will also bring about less voltage drop (losses) in the wiring.

The overall string will have many of these sections wired in parallel. For example, a 200 LED string will usually have 20 sections, each with 10 LEDs. The more sections an LED string has, the more current it requires to operate. The working voltage however remains the same, as that is determined by the number of LEDs in each section and the value of the resistor.


LED strings with more than one channel still have the LEDs wired in sections. The only difference is that the sections for one channel are physically offset to the other(s).

An LED string with more than one channel will have n + 1 wires at the input, where n is the number of channels. So, a 2 channel string has 3 wires, a 4 channel string has 5 wires, etc. Most low voltage LED strings these days tend to be 2 channel (3 wires).

The string polarity is almost always arranged to that the channel wires are negative and the common wire is positive. This suits 99% of the DC controllers out there.

Big W 2 Channel Strings

Here's the schematic (circuit diagram) of one section (approx 2 metres) in a 2 channel Big W multicolour LED string.

The common +ve wire goes from one end to the other and carries the current for the entire string (both channels).

Each channel wire connects to the start of each section as well as continuing on to the next section.

A 200 LED count string is made up of 10 of these sections, wired end to end. The end of the last section goes to a female 3 pin socket, which is where the next (extension) string plugs in.

You can cut these strings every two metres, at the point where the number of wires drops to 3. This could be useful for cutting strings down to a more suitable length or extending them.

Each section has a current limiting resistor for each channel. The value shown above is indicative only and may vary by string LED colour(s).

The other Big W LED strings are wired exactly the same, except the LEDs are all the same colour.

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