sharing rs-485 data bus with ethernet on same cat6 cable

[mikefamig]

I am installing some elk expansion boards in my detached garage and need to pull about 250' of cable through a buried conduit to connect the boards to an Elk M1 controller at the house. I already have one cat6 cable between the buildings for ethernet access and was planning to pull a second cable when it occurred to me that ethernet is only using two of the four wire pairs on the existing cable.
 
So my question is, can I use the other two wire pairs for my Elk rs-485 data bus? Has anyone done this successfully?
 
Mike.

 

[tadr]

I am installing some elk expansion boards in my detached garage and need to pull about 250' of cable through a buried conduit to connect the boards to an Elk M1 controller at the house. I already have one cat6 cable between the buildings for ethernet access and was planning to pull a second cable when it occurred to me that ethernet is only using two of the four wire pairs on the existing cable.
 
So my question is, can I use the other two wire pairs for my Elk rs-485 data bus? Has anyone done this successfully?
 
Mike.

You're only running 100mbps ethernet?  gigabit uses all of the pairs.
 
I don't see why this wouldn't work - but it's hackish as hell.  I'd run the extra wire, if you already have a pull in the conduit.

 

[mikefamig]

You're only running 100mbps ethernet?  gigabit uses all of the pairs.
 
I don't see why this wouldn't work - but it's hackish as hell.  I'd run the extra wire, if you already have a pull in the conduit.

I have ATT Uverse which is gigabit but I did not know that it used all four pairs. Live and learn.
 
Mike.

 

[mikefamig]

You're only running 100mbps ethernet?  gigabit uses all of the pairs.
 
I don't see why this wouldn't work - but it's hackish as hell.  I'd run the extra wire, if you already have a pull in the conduit.

You say hackish, I say frugal. Space in a conduit gets used up fast and I don't see any need for the extra cost and effort if it's unecessary. But like I said, I didn't know that the gigabit used the four pairs. so I'll be pulling another cable or two. I guess I got behind the times.
 
Mike.

 

[snakevargas]

Well, technically you don't have to run gigabit to your garage, you could run 100 megabit. It doesn't have to match your ATT Uverse connection unless you really need that level of connectivity to the detached garage. I'd still pull the extra cable though. I've done some silly things before running other signals on unused pairs in cat5, and almost always wished I'd have been able to do it the right way and pull an additional cable. Cat5 is relatively cheap, time spent diagnosing cabling oddities is expensive!

 

[mikefamig]

Well, technically you don't have to run gigabit to your garage, you could run 100 megabit. It doesn't have to match your ATT Uverse connection unless you really need that level of connectivity to the detached garage. I'd still pull the extra cable though. I've done some silly things before running other signals on unused pairs in cat5, and almost always wished I'd have been able to do it the right way and pull an additional cable. Cat5 is relatively cheap, time spent diagnosing cabling oddities is expensive!

I just ordered 500' of cat6 gel filled cable to pull two more runs to the garage. My garage is a bit of a mancave with TV and internet access and I make good use of the bandwidth. I'm getting 1080p video on a 50" plasma TV with no problems at all.I'll pull two so that I can use one for the Elk and one as a replacement if one fails or for future use.
 
Mike.

 

[tmbrown97]

Just remember to use gel filled only for horizontal runs - not vertical - for instance, if it goes underground then drops down into a basement, in time that gel can flow to the lowest point creating a bit of a mess. 
 
I've done my share of hackery sharing wires in Cat5e usually out of laziness but when the option exists to home run more, it's always best. 
 
Also the Elk's DataBus uses 4-6 wires depending on the topology - you can run it as one of the legs off a DBH in which case it needs another pair for the data return, or you can terminate at the garage eliminating the need for that return pair.  It's a good idea to understand how RS485 works and how/where you'll be terminating each leg.

 

[mikefamig]

Just remember to use gel filled only for horizontal runs - not vertical - for instance, if it goes underground then drops down into a basement, in time that gel can flow to the lowest point creating a bit of a mess. 
 
I've done my share of hackery sharing wires in Cat5e usually out of laziness but when the option exists to home run more, it's always best. 
 
Also the Elk's DataBus uses 4-6 wires depending on the topology - you can run it as one of the legs off a DBH in which case it needs another pair for the data return, or you can terminate at the garage eliminating the need for that return pair.  It's a good idea to understand how RS485 works and how/where you'll be terminating each leg.

I have a single gang box J-box in my basement that I ran icky-pick to when the garage was built and it drops a few feet to get there. I'll have to go take the cover off and look at it later, I haven't been in there in a few years. It's a short distance so I'm not concerned.
 
I understand what you're saying about the A B data leads needing to be wired to the next device in the chain until the end of the line where you terminate with a resistor. I did some reading about EOL resistors and their function and see how they are used to make supervision of the line possible. I have also watched the Elk Basic Training webinar on youtube. For anyone that isn't aware of these you might want to check them out.  I found it very helpful.
 
http://www.elkproducts.com/webinars_recorded.html
 
I plan to run one cat6 from the controller to a DBH in the house which will supply all of the rs-485 devices in the house and a second cat6 from the controler to a second DBH in the garage to supply all of the rs-485 devices in the garage.
 
Mike.

 

[tmbrown97]

That works perfect - then you can have the terminating connector in each DBH.  In my garage I have 3 or 4 devices but I just adapted to regular RD485 wiring on one leg of the DBH - but mine's attached and actually pretty close to the M1 main panel.

 

[mikefamig]

That works perfect - then you can have the terminating connector in each DBH.  In my garage I have 3 or 4 devices but I just adapted to regular RD485 wiring on one leg of the DBH - but mine's attached and actually pretty close to the M1 main panel.

I went back and forth on using the hubs vs just splicing everything with wire nuts but I decided that the hubs will make it easy for me to change my mind and move things around both physically and logically in the early stages of installing. I figure that once everything is in place there will be no advantage to having hubs but I think it will make the installation easier for a first timer and much neater.
 
Mike.

 

[Del91574]

One word...crosstalk. Running 2 sources of data, even if on UTP, in the same cable can lead towards a lot of anomolies that can't be explained.
 
Copper is cheap. Troubleshooting and intermittents are not.

 

[mikefamig]

One word...crosstalk. Running 2 sources of data, even if on UTP, in the same cable can lead towards a lot of anomolies that can't be explained.
 
Copper is cheap. Troubleshooting and intermittents are not.

I've decided to pull two more cat 6 UTP gel filled cables. I considered getting shielded cable because the rs-485 is occupying the same conduit as the U-verse cable but I'm betting that I'll be ok. I will also be pulling a 16-4 direct burial wire for two audio feeds. When the garage was built I buried two separate conduits, one for data and one for high voltage supply.
 
Mike.