Elk m1 rs485: unused wire after terminator

[snakevargas]

I've wired my keypad with cat5 as suggested in the manual (two cat5 wires to each rs485 wire). I did this so it would be easy to home run and add the data us hub should I want to run more rs485 devices in the future.

However, since I don't need the capability now, I'm wondering if I can just install the terminating resistor jumper at the keypad and ignore those extra return wires. Will this cause signal quality issues? If its a problem, then I can always install the terminator on the return wires; it's only a little more work.

 

[Big517]

Pretty sure the data bus hub eliminated the need for the return. Just plug the the terminating rj45 Jack in the next port and you are done. Make sure you still enroll devices and yes it's normal when the keypad says it lost connection during enroll process.

 

[jpmargis]

If by ignore you mean disconnect, then yes the terminator can be at the keypad.  Otherwise, the terminator needs to be at the location where the hub will be installed.  Any 120 ohm resistor will do.  You can't leave the physical end of the data bus unterminated.

 

[apostolakisl]

I'm a little confused by your post. "two cat5 wires to each rs485 wire".
 
The Elk databus hub uses a single cat5 to do it all.  The rs485 signal goes out one pair, then returns on a second pair within the same cat5.  The databus hub is simply doing all the connections for you, you could do the same thing by manually splicing the wires (but its totally worth it to buy the databus hub and just plug it in).  The databus hub comes with an rj45 jack with a resistor installed jumpering the proper pair, but you don't have to do it that way.  You can jumper the proper pair manually at the last device in the series or you can do it the end of the cat5 where you have it home runned back to the Elk.  I have done it this way because I had filled every jack on the databus hub so the rj45 with the jumper had no where to plug in.

 

[snakevargas]

I meant two wires within the cat5 cable. Orange + Green to keypad Green. Wht/Org + Wht/Grn to keypad white. My question was whether or not I could install the terminating jumper at the keypad and leave the green pair unconnected back at the panel (until such time as I do buy a databus hub).
 
It sounds like I cannot, and the best solution is to terminate the green pair with a 120 ohm resistor.
 

I'm a little confused by your post. "two cat5 wires to each rs485 wire".
 
The Elk databus hub uses a single cat5 to do it all.  The rs485 signal goes out one pair, then returns on a second pair within the same cat5.  The databus hub is simply doing all the connections for you, you could do the same thing by manually splicing the wires (but its totally worth it to buy the databus hub and just plug it in).  The databus hub comes with an rj45 jack with a resistor installed jumpering the proper pair, but you don't have to do it that way.  You can jumper the proper pair manually at the last device in the series or you can do it the end of the cat5 where you have it home runned back to the Elk.  I have done it this way because I had filled every jack on the databus hub so the rj45 with the jumper had no where to plug in.

 

[apostolakisl]

I meant two wires within the cat5 cable. Orange + Green to keypad Green. Wht/Org + Wht/Grn to keypad white. My question was whether or not I could install the terminating jumper at the keypad and leave the green pair unconnected back at the panel (until such time as I do buy a databus hub).
 
It sounds like I cannot, and the best solution is to terminate the green pair with a 120 ohm resistor.

 
 
No, you misunderstood me.  You can terminate it at the device, provided that it is the final device in that set of daisy chained devices.  Like if you have 3 keypads daisy chained together, you can put your resistor at the last device.  The deal is that the rs-485 signal will "reflect" off of an open wire at the end of the line, you need the resistor to basically "eat" the signal and the length of wire between the last device and that resistor isn't important.
 
However, in my opinion you should put it back at the panel.  The reason being that if you ever want to add another device to the end of that series of daisy chained devices, you won't have to physically take the keypad off the wall and redo the wiring, it will all be right there at the main panel.

 

[sda]

Agree with Lou.  Putting the resistor at the keypad in your current setup, even though the bus would seem to be properly terminated at the keypad, would leave two long "attenna" wires going back to the panel that could pick up noise.

 

[jpmargis]

In no way is a data bus with the termination in the middle of the bus "properly terminated".  The two long wires going back to the panel are not antennas; they are very much a part of the data bus and must be treated as such.  And, they don't "pick up noise"; they generate reflections which corrupt the RS-485 waveform.

 

[apostolakisl]

In no way is a data bus with the termination in the middle of the bus "properly terminated".  The two long wires going back to the panel are not antennas; they are very much a part of the data bus and must be treated as such.  And, they don't "pick up noise"; they generate reflections which corrupt the RS-485 waveform.

 
 
Not sure what you mean by "in the middle of the bus".  The termination is always after the last device, but I don't think it makes a hoot of difference if you terminate 1mm past the last device or 100m past the last device.  The Elk manual has you terminate the last device at the device when doing a direct device to device daisy chain.  If you are using cat5/6 and doing the dbh route, they have you terminate at the panel/dbh.   The reason for that is simplicity, not that it is electrically better or worse.

 

[Del91574]

It doesn't necessarily make a difference where the termination exists on RS-485, however in Elk's case, it does need to be at the last connected device, as I doubt many are installing their own 120 ohm resistors on the bus.
 
I've installed plenty of hardware that runs 485 and put a "termination resistor" directly on the 485 port with no ill effects, and many times recommended by the manufacturer to help load down the bus if there's only a single leg/branch.