DMX Wiring

Controlling lighting with low voltage signals

DMX leads are used to send low voltage control signals to DMX-equipped lighting units, such as dimmer packs, scanners, lighting effects, lasers, etc. Leads Direct carries a huges range of these cables from stock (in lengths from 1m to 30m); they can be custom-manufactured in any length up to 100m. Visit the DMX leads section to review the range and order ready-made cables, or the Connectors section to order the parts to make your own. If you need tools, you will find them in the Tools section.

DMX cables are most commonly made with 2-core shielded data cable terminated at either end with 3 or 5-pin XLR connectors (one male, one female). The DMX data itself requires only two of the cable cores plus the shield, so recent devices have moved to the 3-pin format. However, some older units still use the 5-pin connectors, with only three pins used.

Some specialist devices use a four-core plus shield cable, with five-pin XLR connectors. The two additional cores have no defined purpose, so manufacturers can use them for any purpose they deem appropriate. For example, the Pearl 2000 desk from Avolites uses the extra cores as a second DMX512 output; using an appropriate splitter takes you from a single 5-way XLR to two 3-way XLRs of DMX512.

DMX lines can be run an approximate maximum distance of 1500 metres, and each line can support a maximum of 32 devices. Transmitting devices and DMX out ports on devices should be female connectors, while DMX in ports should be male.

The last device on the DMX line must terminate the line to avoid serious signal degredation due to signal reflections and external electro-magnetic interference. Some modern devices have a switch on them to tell them that they are the last device on the line and that they should terminate rather than expect something to be plugged into their DMX out port. Other devices can sense an empty out port automatically and act according to terminate the line. There are some pieces of equipment which do not automatically terminate and do not feature built-in termination – and in these cases, termination must be supplied. The best way of doing this is connecting a resistor 120 ohms in size across Data + and Data –. Terminators (XLR connectors with the resistor already fitted) are available from our e-shop: order DMXT for the 3-pin version or DMX5T for the 5-pin.

The wiring of the XLR connectors in a DMX cable is shown below:

3 Pin XLR

Pin	Signal	Description
1	Signal Common	Earth / Ground / Shield
2	Data Minus	Negative signal
3	Data Plus	Positive signal

5 PIn XLR

Pin	Signal	Description
1	Signal Common	Earth / Ground / Shield
2	Data Minus	Negative signal
3	Data Plus	Positive signal
4	Not used	Originally intended for feeding diagnostic data back to the DMX512 controller, but never implemented Sometimes used to carry other data or power
5	Not used

If you are seeking information on DMX wiring but cannot find it here, please email info@leadsdirect.co.uk and we will try to both answer your question and make sure that the information is made available through these pages for future reference

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