Cat5 Over Ceiling

[Synchronize]

Before I dig through the NEC for hours upon hours, I figured I would ask here. For a permanent installation of plenum rated Cat5 above a plaster and/or drop ceiling with data and 12VDC running through the cable in a commercial building, can the cable be left exposed? Am I correct in assuming that because it it low voltage it doesn't need to run through conduit?

 

[FMEng]

Yes, the cable can be left exposed. It should not be left laying on the drop tile ceiling. Support it by other means without kinking it. If the ceiling space is not used as a plenum (air return for HVAC), then you do not need more expensive, plenum rated cable.

 

[RickR]

You would never make these basic errors but, for reference:

An often overlooked issue is getting the cable into and out of the ceiling. NEC specifically forbids poking holes in the wall or ceiling to run cable.

I've also seen several issues with running DMX on cat5. Yes it works, but only if it's in conduit or is shielded cable!

A local site just broke both these rules running cable in now enclosed ceiling space. Expensive mistake!

 

[FMEng]

Shielded Cat 5 exists, although there may not be much savings over using DMX cable. Penetrations through walls should not be a problem if the hole gets sealed with fire rated caulking.

 

[JD]

Of course, we are all assuming you are running DMX over Cat5. If not..... never-mind

(except for that "poking holes" thing.)

 

[Wood4321]

I disagree with the assumption that shielded cable is required when running dmx over ethernet.
While ANSI E1.27-2 deals with this, and recommends ethernet when being used for DMX, all of the experts I have seen quoted say that it is not necessary.
Almost all of the noise immunity in Cat5 cable comes from the twisted pair.

In any case, Here is a link for the Plasa DMX over ethernet cable working group from 2001.
I run dmx over ethernet on a regular basis, and have never had any issues that were not related to poor connector termination, or a lack of proper signal termination.

 

[Goph704]

I"m with josh, on this. I run DMX on unshielded Cat-5 on a regular basis, with little to no issues. Rick, I would be willing to believe that you might be dealing with an issue of distance rather then of shielding. If that's the case, and You still have access to the space, then what might not be a bad idea is either putting a switch in line somewhere between point A and Point B just to boost the signal. It's usually under 20 bucks at radio shack. I think you may find that will help a lot. To my knowledge the only reason to shield Cat-5 would require shielding is to protect the cable. Cat-5 also doesn't care if it's in a conduit or not.

As for drilling holes in walls, we did it all the time when I was working low voltage stuff. First we would drill a hole, then we would cut a piece of conduit at about a 2ft' length and then shoot it through the hole, on each side we would put flame proofed caulk. Then we would suspend the Cat-5 in the ceiling with zip ties wherever needed. I'm not familiar with that regulation in regards to drilling holes in walls. Could you tell us more about the rules that these guys broke, because the things that they are getting called out for are pretty...... Odd. We may be Looking at some differences due to local regulations as opposed to National.

 

[tdrga]

Of course, we are all assuming you are running DMX over Cat5.

I believe the OP said 12vDC, which is the upper limit of the EIA-485 spec (which defines the DMX512-A electrical interface specs). I hope that DMX data is not being driven at that voltage. If the "data" is DMX and it is being combined with 12v power conductors in the same cable, then that is also asking for trouble and definitely not allowed by the ANSI DMX512-A spec.

So perhaps the DMX over CAT-5 cable is a red herring in this discussion?

-Todd

 

[tdrga]

I"m with josh, on this. I run DMX on unshielded Cat-5 on a regular basis, with little to no issues. Rick, I would be willing to believe that you might be dealing with an issue of distance rather then of shielding. If that's the case, and You still have access to the space, then what might not be a bad idea is either putting a switch in line somewhere between point A and Point B just to boost the signal. It's usually under 20 bucks at radio shack.

Just to post a point of clarification here: DMX over Ethernet is not the same as DMX over CAT5 cable.

DMX over Ethernet requires a active device at each end of the cable to change DMX data to one of many types of Ethernet protocols, which can then be distributed using regular computer networking hardware. That hardware, more often than not, uses CAT5 cables to transmit the Ethernet protocols.

DMX over CAT5 cable is simply using the CAT5 cable to transport DMX data. No active devices are needed, just the correct pinout for the connection on each end to make sure that the twisted pairs are maintained. This will not work with regular computer networking hardware as the physical layer electrical specs are completely different for DMX and Ethernet.

-Todd

 

[NZM]

I disagree with the assumption that shielded cable is required when running dmx over ethernet.
While ANSI E1.27-2 deals with this, and recommends ethernet when being used for DMX, all of the experts I have seen quoted say that it is not necessary.
Almost all of the noise immunity in Cat5 cable comes from the twisted pair.

In any case, Here is a link for the Plasa DMX over ethernet cable working group from 2001.
I run dmx over ethernet on a regular basis, and have never had any issues that were not related to poor connector termination, or a lack of proper signal termination.

There are two very different things being discussed now. DMX over Cat 5 cable and DMX over ethernet are not the same thing.

DMX over Cat 5 cable means they are terminating the Cat 5 cable directly in a 3 or 5 pin XLR connector and connecting directly into the DMX fixture. While DMX uses a "balanced" serial transmission, the choice of which conductors connect to which pins on the XLR will very much determine the "quality" of the DMX signal run. If runing DMX over Cat 5, then its important to use a single twisted pair of the 4 pairs in the Cat 5 cable for the DMX signal (pins 2 and 3 on a 3-pin XLR). If running 5-pin XLR for DMX, then you can optionally connect a second twisted pair of the Cat 5 cable to pins 4 and 5. For the DMX ground (pin 1 on both 3 and 5 pin XLR) should, I would connect both conductors of another twisted pair of the Cat 5 cable. So one pair just for DMX ground (pin 1) one pair for the DMX signal (pins 2&3) and optionally one pair for pins 4&5 is using 5-pin XLR.

DMX over ethernet requires that the Cat 5 cables are terminated with suitable RJ45 and connected to an ethernet switch at one end and an ethernet-DMX converter or device running ARTnet at the other end. So these would be running IEEE802.3 type ethernet protocol and obviously must conform to the cabling requirements (i.e. termination, cable type ad distance) for the appropriate ethernet type being used (IEEE802.3u - 100Base-TX, IEEE802,3ab - 1000Base-T etc).

 

[Wood4321]

Absolutely correct,
I should have been much clearer in my original response.
I am speaking of dmx over cat5 not Ethernet.

 

[JD]

Absolutely correct,
I should have been much clearer in my original response.
I am speaking of dmx over cat5 not Ethernet.

Will probably work just fine until the day it doesn't.....
Best to run in conduit, use shielded, or "install" grade DXM (usually pretty cheap) rather then pull all your hair out some day in the distant future when everything is going whack-o right as a show opens.

 

[Wood4321]

Incorrect, did you look at the plasa study? Almost all of the noise rejection in Cat 5 comes from the twisted pair, not the shield.
Many dmx experts have spoken about this, including Scott Blair.

Here is a quote from the summary,

Conclusion
Data obtained from all three of these test sessions confirms that, in most respects, UTP and STP Category 5 cable can be expected to perform at least as well as EIA-485 rated data cable for DMX512 applications.

 

[JD]

For "Best Practices" see- KnowledgeBase: DMX Over CAT 5 - Electronic Theatre Controls

"For DMX over CAT 5, there are several things to note. ESTA says Cat 5 UTP and STP is acceptable, however they do not note specific installation parameters. ETC prefers to have UTP, STP and FTP installed in grounded metal conduit for purposes of additional data integrity and physical protection. This is not to say that running outside of conduit will give you a problem, it may be fine. In fact, there are rarely issues -- but it is still our recommendation. "

 

[RickR]

I"m with josh, on this. I run DMX on unshielded Cat-5 on a regular basis, with little to no issues. Rick, I would be willing to believe that you might be dealing with an issue of distance rather then of shielding. If that's the case, and You still have access to the space, then what might not be a bad idea is either putting a switch in line somewhere between point A and Point B just to boost the signal. It's usually under 20 bucks at radio shack. I think you may find that will help a lot. To my knowledge the only reason to shield Cat-5 would require shielding is to protect the cable. Cat-5 also doesn't care if it's in a conduit or not.

As for drilling holes in walls, we did it all the time when I was working low voltage stuff. First we would drill a hole, then we would cut a piece of conduit at about a 2ft' length and then shoot it through the hole, on each side we would put flame proofed caulk. Then we would suspend the Cat-5 in the ceiling with zip ties wherever needed. I'm not familiar with that regulation in regards to drilling holes in walls. Could you tell us more about the rules that these guys broke, because the things that they are getting called out for are pretty...... Odd. We may be Looking at some differences due to local regulations as opposed to National.

This place had 2 30' runs between devices. (Real DMX no ethernet involved.) I consider that well within the distance limits no matter how you look at it. Interestingly we tried 3 consoles, one worked two did not. Go figure!

The cable just poked out from sheet rock with some mud and paint. I doubt they were cited, and I certainly didn't raise a stink but the rules seem pretty clear, though I claim no special knowledge. A snip from the 2011 NEC:
I am more than happy to learn of other sections that would allow it.

Many practices have long history and tradition, that doesn't mean the inspector won't site you! Local inspectors tell us they are under tremendous pressure to write as many citations as possible, to justify their job.

 

[Synchronize]

It is, in fact, DMX and 12vdc that I will be running through the Cat5 for an architectural control system.

I'm not sure about the poking holes thing... I see it happen all the time. I was planning on taking wiremold up through the hole and caulking it up. And it's not an enclosed ceiling space considering it is an auditorium with lighting coves, so maybe that makes a difference?

 

[FMEng]

The cable just poked out from sheet rock with some mud and paint. I doubt they were cited, and I certainly didn't raise a stink but the rules seem pretty clear, though I claim no special knowledge. A snip from the 2011 NEC:

I believe that section of the code is referring to line voltage wiring, not low voltage communications wiring. Two different animals. The latter is class 2.

 

[derekleffew]

Ignore if this has been said already...

I"m with josh, on this. I run DMX on unshielded Cat-5 on a regular basis, with little to no issues. Rick, I would be willing to believe that you might be dealing with an issue of distance rather then of shielding. If that's the case, and You still have access to the space, then what might not be a bad idea is either putting a switch in line somewhere between point A and Point B just to boost the signal. It's usually under 20 bucks at radio shack. I think you may find that will help a lot. ...

If DMX-over-CAT5, can't run though a switch or any other computer networking gear; see below. Further, the 100m limit of CAT5 between Ethernet switches is significantly less than the limit of DMX over CAT5: http://tsp.plasa.org/tsp/working_groups/CP/docs/DMXoverCat5_P1.pdf tested a 300m UTP run with positive results.

...
From Pathway Connectivity Inc. - Cat5 Pinout for DMX :

This chart is intended for DMX512 cabling only - NOT DMX-over-Ethernet cabling. Great care must be taken to prevent the accidental connection of DMX equipment to non-DMX equipment. The connection of DMX equipment to non-DMX equipment such as Ethernet switches or telephone equipment may result in serious equipment damage and/or personal injury, as pins 4 and 5 may carry voltages of up to 48VDC or greater.

...

Or from http://www.etcconnect.com/Community/wikis/products/knowledgebase-dmx-over-cat-5.aspx :

Warning: Accidental connection to non-DMX512 equipment likely to be encountered (e.g., an Ethernet Hub at a patch bay) may result in damage to equipment. Pins 4 and 5 may carry voltages outside the EIA-485 range in telecom applications (e.g., telephone ringing). Pins 4 and 7 may carry voltages outside the EIA-485 range in other applications (e.g., some manufacturers whose distributed DMX512 buffering products require low voltage DC power may use these wires for this purpose). Because of these various uses, misplugging unlike systems could cause serious damage.

-----

...DMX over Cat 5 cable means they are terminating the Cat 5 cable directly in a 3 or 5 pin XLR connector and connecting directly into the DMX fixture. While DMX uses a "balanced" serial transmission, the choice of which conductors connect to which pins on the XLR will very much determine the "quality" of the DMX signal run. If runing DMX over Cat 5, then its important to use a single twisted pair of the 4 pairs in the Cat 5 cable for the DMX signal (pins 2 and 3 on a 3-pin XLR). If running 5-pin XLR for DMX, then you can optionally connect a second twisted pair of the Cat 5 cable to pins 4 and 5. For the DMX ground (pin 1 on both 3 and 5 pin XLR) should, I would connect both conductors of another twisted pair of the Cat 5 cable. So one pair just for DMX ground (pin 1) one pair for the DMX signal (pins 2&3) and optionally one pair for pins 4&5 is using 5-pin XLR.

Too many things wrong in the above to correct, but
1. See the ETC KnowledgeBase linked above regarding the issues when terminating CAT5 to XLR connectors.
2. For Dog's sake, follow the industry-accepted pin-out (also at above); don't make up your own.

-----

As for mixing power and data over CAT5, see this post by ETC's DavidNorth.

 

[tdrga]

It is, in fact, DMX and 12vdc that I will be running through the Cat5 for an architectural control system.

Adam,

Is the architectural system designed to run DMX data and 12vDC in the same cable? I would be concerned about voltage drop on the 12v lines if you use CAT5, which typically has 24 gauge conductors. Scroller manufacturers run data and power together in the same cable, but the power conductors are typically 14 gauge.

If CAT5 does meet electrical specs, please don't label the cable as "DMX"- carrying 12v on any of the conductor pairs is not in compliance with the DMX spec. This will cause problems if someone later assumes that the wiring is done to DMX spec and connects a DMX device.

-Todd

 

[Goph704]

Rick,
Thanks, that makes a lot more sense. Section 400.6 lists the markings on all flexible cords and cables and I usually assume that is what 400.8 is making reference to. And please forgive my suggestion of a network switch, I was also confused about the difference between CAT-5 and Ethernet.

Synch
I think the running through an open ceiling might make this a slightly different beast. You really would want some means of protecting the cable from outside elements.

I'm going to Bow out of this conversation, But I'm really interested in hearing how it progresses.