Building own DMX cable

[impedious]

Hi I keep reading about making your own DMX cable but no one mentions what type of cable. I saw a thread about using Cat-5 but overall it sounded to risky to me. Our sound board is dying and the money will probably be coming out of the lighting budget so I am trying to get the price down even more.

Tim

[waynehoskins]

Cat-5 cable is a well-accepted alternative, and it's substantially less expensive than the other recommended cable types, cents a foot rather than a dollar a foot or more.

There are a handful of recommended cables. Since DMX is a moderately-high-speed serial data signal, line loss and reflections can be problematic. A proper cable has two twisted pairs of low capacitance and a controlled impedance. Any cable specified for RS-485 serial data would be suitable, one or two 120-ohm pairs with a shield. There are a few Belden, Alpha, etc. models of cables that have become standard, but I don't recall them off the top of my head. Any of them are significantly more expensive than Cat-5 cable.

You can build your own cable, and it may be less expensive, but I wouldn't count on it being substantially less expensive in the bigger picture, enough cost savings to offset replacing a console.

[Johnnycat]

I personally have never used Cat5 for DMX control and I wouldn't, there is an impedance difference that can cause communication problems. DMX cable is 120 Ohm while Cat5 cable is 100 Ohm.

You didn't mention how many cables you need to make and what length...it might be less in the long run to just buy the cables.

[cw4u]

I always use Cat5 for Dmx. No issues so far.

[waynehoskins]

I was skeptical at first about Cat-5, but I gave it a try after reading that it was an officially adopted ESTA and/or USITT standard. Works very well so far.

[impedious]

Our media person just told me she bought a 1000 ft of Cat-5 for networking stuff so I would have enough to use for my DMX-512 and keeping the wiring out of my budget and in hers

[daver2]

If you are making up your own DMX cable - don't forget to make up your own terminator plug and use it at the end of the DMX chain to prevent reflections.

Dave

[Steve Vanciel]

Originally Posted by impedious

Our media person just told me she bought a 1000 ft of Cat-5 for networking stuff so I would have enough to use for my DMX-512 and keeping the wiring out of my budget and in hers

Caution: most network cable uses a solid conductor wire intended for a permanent installation and it is not well suited for portable usage. It will breakdown quickly. It is possible to get a stranded conductor Cat-5 cable, with a heavier and flexible outer jacket but it will cost a bit more. Also, any RJ-45 connectors must also be specifically made for stranded wire, not solid.
The ANSI standard E1.27 (created by the ESTA now PLASA Technical Standards Program) spells out many of these details, including a standard wiring configuration between an RJ45 and 5 pin XLR.

SteveV
Orlando, FL

[JeffM]

What are the wiring connections using CAT 5?

[Gracetech]

I've used Cat5 for DMX for years. I generally only use it for installs but i've slapped a Cat5 DMX cable together to make temporary runs before. I've thought about using Gepco's 504HD for temporary cable runs but even it isn't all that flexible. I've run into ton's of other "Big" installs using it as well.

crt

[waynehoskins]

The convention calls for using the Orange pair for Data1, Green pair for Data2, and both wires of Brown pair for Common.

XLR pinout:
1 - Bn + BnWh - Common
2 - Or - Data1 Complement
3 - OrWh - Data1 True
4 - Gn - Data2 Complement
5 - GnWh - Data2 True

The 8P8C is pinned per T568B, standard for Ethernet wiring.

The Blue pair is intentionally avoided, as it would carry DC if a DMX 8P8C were inadvertently plugged into some network or telephone equipment.

[Steve Vanciel]

Originally Posted by Gracetech

I've run into ton's of other "Big" installs using it as well.

Some big events will use regular Cat-5 cable as a one-time-use disposable item to cut their costs while billing the client for the cable. Cheaper than renting or stocking standard DMX data cables. Most of us are not in that position.

SteveV