Cat 5 for DMX in the wall wiring

[Johnparmalee]

Greetings, John here, lights and backdrop guy for Faithbridge in Spring (NW Houston), TX

Will Cat 5 work for in the wall wiring for DMX? I understand the 120 ohm situation. I can't find the impedance and for sure understand the no mic cable situation.
If not Cat 5 in the wall what is a good cable to put in the wall?

JP

[Esoteric]

I use CAT5 for all my permanent installs where there not going to be a lot of electrical interference.

Mike

[derekleffew]

Category 5 cable is an excellent alternative to traditional DMX cable for in-wall applications (provided it is inside conduit) and the practice is actually recommended in Nick Mobsby's book, Practical DMX.

See also ANSI E1.27-2 - 2009:Entertainment Technology - Recommended Practice for Permanently Installed Control Cables for Use with ANSI E1.11 (DMX512-A) and USITT DMX512/1990 Products from ESTA's Technical Standards Program.


Outside the wall and for Portable Control Cables? Not so much. Some reasons: Most RJ-45 connectors are delicate and not designed for repeated mating cycles, 22 AWG solid cable is fragile, and kinks easily when coiled. Most A/V companies that use long runs of it for video purposes test it before every use. There's no cost-benefit to shielded, stranded, ruggedized UTP cable over say a Belden 9842 (pdf). From Belden's document:

A third cable alternative is Category cables, such as Category 5e, or 6. These are most often UTP, unshielded twisted pairs. Their impedance (100Ω) puts them reasonably close to the 120Ω of RS-485. Further, while they can run DMX-512 today, there is a lot of work being done to use the Ethernet® networking protocol for DMX-512. That would mean that Category data cables installed today to run DMX-512 could also run Ethernet tomorrow. It also means that the same cable type could be used for both Ethernet and DMX-512 applications. There are dozens and dozens of UTP Category cables that might be considered for DMX-512.

[Johnparmalee]

Thanks

JP
Faithbridge

[STEVETERRY]

Originally Posted by Johnparmalee

Thanks

JP
Faithbridge

Don't forget that category cables with solid conductors can only be reliably terminated into insulation-displacement (vampire tap) wiring devices intended for the purpose.

Don't strip the cable and terminate to compression screw terminals, crimps or solder joints--that will cause big reliability issues!

ST

[derekleffew]

Originally Posted by STEVETERRY

Don't strip the cable and terminate to compression screw terminals, crimps or solder joints--that will cause big reliability issues!

The dickens you say? Works fine with every phone jack in my house. What about P-nuts?

[JD]

Cat 5 is 8 conductors in four pairs. When using it for DMX, one pair is connected to pins 2 & 3. If you are using 5 pin DMX, the second pair should go to pins 4 & 5. The other two pairs (all 4 wires) should all go to pin 1. Keep your polarity consistent. Never parallel a pair! Only one wire each on pins 2,3,4,5. If you one of those crazy rebels using 3 pin, all unused wires should go to pin 1.

When used in building wiring, the conduit itself serves as a shield. Never run it in a conduit that contains building power!

Now, on to the "Opinion" section :

1) The Cat line should be the ONLY wire in the conduit.

2) You may have problems finding XLR wall mount connectors with insulation displacement terminals. I have not run into issues using the solder type connectors. Just remember, you are making a connection that runs at RF frequencies, workmanship is important.

3) Now, my most controversial point: Outside of the wall, don't use Cat cable. Not only is it fragile, it's not shielded. This post will probably be followed by a half dozen posts from people who have no problem with it. I'm glad for them! I, however, will never do it.

[Esoteric]

I am with you JD. I only use the recommended Belkin cable outside of walls (unless I run in conduit then I will use CAT5 even outside the wall).

Mike

[STEVETERRY]

Originally Posted by derekleffew

The dickens you say? Works fine with every phone jack in my house. What about P-nuts?

How lucky do you feel?

When there's an unplanned blackout, I'll give the audience your number. Oh wait, your phone might not be working due to broken wires.

Seriously, the problem is with stripping the Cat5 without nicking it, making it subject to future fracture. Might work, might not. Why take the chance? Be conservative. The audience will like you for it.

FYI, ETC makes a CAT5 insulation displacement XLR-5 wall mount, and perhaps others do as well.


ST

[cdub260]

Originally Posted by STEVETERRY

The audience will like you for it.

But I don't want the audience to like me. As a matter of fact, most of the time I don't want them to even know I exist.