seeking advice about data bus configuration

rexwilson

Member
I'm installing an M1 system with 11 items on the data bus: 3 input expanders, 2 output expenders, and 6 keypads.
I want to use the M1DBH (data bus hub with RJ45 connectors) for a cleaner install and easier termination.
I would need to use two hubs to fit 11 devices, since each has 8 ports.
Each device will be home-run wired to the panel with new 22 gauge 6-conductor copper cable.
Grand total of all the wire lengths is well under 2,000 feet.
The Elk documentation says that I can have two data bus runs from the main panel.
It's also possible to chain together two of the M1DBH units by putting a short RJ45 patch cable between the last port from first M1DBH, to the 1st port of the second M1DBH.
Which would be better?
a. use one data bus feed, and patch the two M1DBH's together.
b. use two data bus feeds, and have a separate feed go to each M1DBH.
Does it matter??
Thanks in advance.
 
That would depend on the location of the DBH's and the length of the cables. If the first DBH is far from the panel then it would be best to connect the second DBH directly to the panel rather than to the first DBH.
 
The goal is to keep the length of the longest run (as measured from the panel to the farthest device on the bus) as short as possible. Don't forget that when using a DBH the cable goes out to the first device on the bus and then returns to the DBH before going out to the second device on the bus so the  cable length is doubled.
 
Mike.
 
Mike, Thanks for that guidance. Both DBH's are going to be in the same can as the panel, and all devices will be home-run wired to the same can.
 
Also make sure that your cable is cat5e or better. Do not use ordinary 22/6 cable. The windings in CAT cable rejects interference and reduces signal loss.
 
Mike.
 
EDIT
 
I want to add - If the 22/6 cable is already installed then I would hook it up and see if it works before pulling all new cable. I think that you might get away with it depending on the length of the runs. Maybe someone who has more experience and knowledge than me can chime in here.
 
jpmargis said:
If your expanders are in the can with the M1, then you only need one DBH.
For the sake of an elegant install, and consistent wiring, i'm running short pieces of cat6 cable with RJ45 connectors from each  M1XIN zone expander and M1XOVR output expanders. These, plus the keypads, add up to more connections than a single DBH can handle. That's the reason for the 2 DBH's.
 
I like the DBH because it makes it easy to visually see what is what on the data bus. Five years from now when I don't remember what I did I'll be able to figure it out easier than if it was just a bundle of wires spliced together. Easier for the next guy that works on it too.
 
Mike.
 
Yes, Mike, I agree 100%, which is why I'm going for 2 DHB's. That still leaves me unsure about my original question:
whether to have each DBH run to the main panel,  meaning there will be two data bus runs, one to each DBH;
or whether to chain together the two DBH's, and have only the first DBH go to the main panel.
(if it even matters?).
 
I would connect each DBH directly to the panel Remove the terminating jumper from the panel and terminate each leg at the DBH's.
 
After connecting each DBH to the panel I would balance the number of devices and power consumption evenly between the two. In addition to counting the number of devices on each DBH you should consider the power consumption of each device on each. There will be voltage drop on each leg and some devices draw more current than others so also consider the length of the run regarding power.
 
Mike.
 
rexwilson said:
Yes, Mike, I agree 100%, which is why I'm going for 2 DHB's. That still leaves me unsure about my original question:
whether to have each DBH run to the main panel,  meaning there will be two data bus runs, one to each DBH;
or whether to chain together the two DBH's, and have only the first DBH go to the main panel.
(if it even matters?).
 
you questioned whether it matters....
 
I would expect it to matter more to voltage drop over long lengths of cable before to the data signal strength. the data bus specs say that 4000' is the max length if I recall and I think that you are more likely to run into voltage drop problems over a distance before you lose signal strength.
 
In my house I have an XIN at the end of a 250' run and had some bad behavior when I powered it over the cat6 cable. I ended up running 18/2 cable to carry the 12vdc power source for the XIN and devices connected to it.
 
Mike.
 
I want to add that in a profeesional install there would be no DBH used. It adds several points of failure and adds cost to the job. Not only the cost of the two DBH's but the labor to add all of those terminating plugs on your cable ends. Splice the wires together properly and it will last as long as the cable lasts. All of those plugs in the DBH will collect moisture and fail at some point. Whenever my system is powered down I take the plugs in and out a few times to clean them up a little. A little electrical contact cleaner now and then is good too. But you can't beat a good splice for dependability.
 
Mike.
 
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