The Ongoing Debate of Mic Cable for DMX

[gafftaper]

We had a show in January where we had mics farther from the console than we had mic cables. We also have made several cables from cat5e (3 pin xlr connectors) which we generally use for DMX, but I used them for the mics this time. Granted, it may work until it doesn't, but we had no issues with phantom powering mics on this cable.

My understanding is that cat5 is a low capacitance cable and although it doesn't technically meet the DMX 512 standard it can be used for long DMX runs without the worries of Mic cables. There are several old threads around here about making DMX cables from cat5. So, it should actually be superior to mic cable.

 

[mstaylor]

My understanding is that cat5 is a low capacitance cable and although it doesn't technically meet the DMX 512 standard it can be used for long DMX runs without the worries of Mic cables. There are several old threads around here about making DMX cables from cat5. So, it should actually be superior to mic cable.

I will leave it to somebody that knows more than me but I thought you could only use cat 5e for conduit runs so it is shielded.

 

[Van]

I will leave it to somebody that knows more than me but I thought you could only use cat 5e for conduit runs so it is shielded.

Speaking as a former Field Tech for Rosco/ET, We used Cat5 for in-wall aplications. Any permanent install was done with a Belkin # 65XXXXX Crap I can't remember the number now. But yes Cat5 was completely acceptabel for DMX runs. I would not use a solid wire Cate5 cable for Temporary runs, however, as the potential for breakage exists.

 

[sk8rsdad]

I will leave it to somebody that knows more than me but I thought you could only use cat 5e for conduit runs so it is shielded.

EIA-485-A, upon which DMX512 is based, does not specify the need for a shield. It uses differential signalling to minimize the impact of noise or interference. There are other reasons why conduit may be desirable, but being a shield is not one of them.

 

[headcrab]

Speaking as a former Field Tech for Rosco/ET, We used Cat5 for in-wall aplications. Any permanent install was done with a Belkin # 65XXXXX Crap I can't remember the number now. But yes Cat5 was completely acceptabel for DMX runs. I would not use a solid wire Cate5 cable for Temporary runs, however, as the potential for breakage exists.

Indeed. All the portable cable we have is stranded. I only use solid for permanent runs.

 

[gafftaper]

In fact, you can purchase some handy little adapters that go from RJ45 to XLR 3 or 5 pin (male or female) for around $15. Pop a Cat5 (or better) cable in any length on the other end and you are good to go with a long distance cable run, for a lot less than traditional DMX cables, without the risk of signal loss in a mic cable.

Here's a link to those adapters for $13.25 from Production Advantage. I designed a small permanent system that's been using them for about a year now with no problems. I ran Cat5e through the walls and installed RJ45 jacks where I needed them and then used short stranded cat5e cables from the jacks to the dimmers/console. Cheap and easy compared to hundreds of feet of standard DMX cable.

 

[KeeperoftheKeys]

True. Except that I typically don't have "long" cable runs. Event lighting is a different ballpark than, say, concerts or theater. It's very unusual for someone in my segment to make a cable run between fixtures of more than 50'. Most of the time I have 15' - 25' between the controller and the first fixture, if that. My total cable on most jobs, even with 36 - 48 fixtures, is less than 750' total. Stage work is obviously different. You may have 300 - 500' of run before you get to the first fixture.

Maybe I'm misreading you, but the way I'm understanding you it sounds like you think a long cable run is determined by distance to first fixture.

The distance is from console until the end of the run or until the booster/signal splitter on the line (and from there it is again until the end of the run), the fixtrures are supposed to just pass the signal through without boosting, splitting or anything else.
You could almost see them as very expensive cable couplers (that happen to not really be needed), a 750' (250m) run, though not yet being at the absolute limits of the DMX standard is still quite a long run....

As far as CAT 5e goes I believe the recommended practise said that the standard recommends to stick to the same specs as "normal" cat 5e runs, ie. no more then 90m in walls and no more then 100m total cable run, this partially to make sure that a decision to upgrade to an ethernet-based network will not involve having to redo cables.
Other then that there is even a recommended pinout for rj45 connectors.

 

[avery]

The fact is you can do it thousands of times and it will be fine, then one night it will go south.

You also just described a normal 5 pin DMX run scenario.

I use DMX over mic cable for the simple reason of not having to worry about the audio guys taking my cable.