daisy-chaining the data bus...visual guide?

[eufreka]

Okay, this may seem obvious to others, but I may be too visual to understand the "simple" instructions...

Exactly *HOW* do you daisy-chain a row of devices on the data bus of the M1? The M1 installation manual has a handy dandy illustration FROM THE FRONT, but nothing that shows the actual wire connections.

In particular, the keypad has a wiring harness, so I can't really visualize how you would daisy-chain it in the middle of a run.

My specific situation:

I have 2 branches running from the main panel:

1) four-wire direct to a keypad (with termination on the keypad).
2) four-wire to a M1XRF2G (which I can't recall but assume has termination on the board).

So now I need to add in an M1XSP for thermostats. Is it really simply a 3-way splice of each wire? If so, does it matter how long a run I splice into the middle, as long as the total amount is less than the limit?

Or do I basically cut the existing wires, and insert both ends into the terminal block on the M1XSP?

Does it matter?

Thanks!

 

[Steve]

Kind of depends a bit on your physical layout (where the components are) and how neat you want things. I usually recommend using the data bus hubs (M1DBH and M1DBHR). If you have Cat5 run to the devices then the M1DBH is nice and neat - just homerun your cat5 from each device to where the hub is and each device plus into the hub via RJ45. The hub itself will handle the daisy chaining for you. If you are retrofitting and have just 22/4 run, the DBHR allows you to have 4 separate managed busses. If you have or care to switch to Cat5, the DBH is a nice neat solution.

Other than that, yes you can cut a wire and 'insert' the XSP into the chain. Make sure to align + A B - and take off the terminator jumper. The databus should measure around 65 ohms +- 10 or so if properly terminated.

 

[rocco]

. . . Is it really simply a 3-way splice of each wire?

If I understand what you mean by a 3-way splice, than no, you shouldn't have any of those. It won't cause much harm if the splice is no more than a few inches long, but it will still go against the data-bus specification. The bus is meant to be one long chain.

One way to picture it is that the RS485 bus should begin at one terminator, travel along a pair of wires from device to device, with the M1 somewhere in the middle (though it can be at the beginning or the end, as it is just another device), and end at the other terminator. There should be no "branches" along the way.

As Steve pointed out, the data-bus hubs do this for you, but use four wires to each device in order to maintain a single chain.

 

[eufreka]

Thanks for the responses! I will follow your direction, Steve on inserting the M1XSP...

A little additional discussion:

I understand that the Hubs "resolve" all this...but that is often overkill. Why spend $40+ on a new part AND pull new wire to "correct" something that is working (and to spec, according to the installation manual).

As I said, I already have 4-wire; so clearly it would be cheaper and easier to simply pull the keypad's 4-wire off the control, and insert the M1XSP "in the middle", running 4-sire from the M1XSP to the control. (The keypad is already terminated; and basically, I can pull back it's 4-wire to any point along its current path to insert the M1XSP--if I have enough service loop, I can just cut in as discussed above.)

My issue was (and is) understanding the actual mechanics of the wiring connections. And I must say that I am somewhat surprised to see that page 7 of the M1 installation manual shows this type of hookup without any explanation. The illustration actually shows a keypad in the middle of a 4-wire run, so I would still appreciate an explanation of the proper wiring for this specific connection--as described in the manual.

Maybe Spanky could help?

 

[Steve]

My issue was (and is) understanding the actual mechanics of the wiring connections. And I must say that I am somewhat surprised to see that page 7 of the M1 installation manual shows this type of hookup without any explanation. The illustration actually shows a keypad in the middle of a 4-wire run, so I would still appreciate an explanation of the proper wiring for this specific connection--as described in the manual.

Don't overthink/overcomplicate it. It is just as simple as you said earlier "Or do I basically cut the existing wires, and insert both ends into the terminal block on the M1XSP?". Yes, just tie the +, A, B, and - from the control and to the kpd together and insert into the appropriate position on the xsp.

 

[eufreka]

My issue was (and is) understanding the actual mechanics of the wiring connections. And I must say that I am somewhat surprised to see that page 7 of the M1 installation manual shows this type of hookup without any explanation. The illustration actually shows a keypad in the middle of a 4-wire run, so I would still appreciate an explanation of the proper wiring for this specific connection--as described in the manual.

Don't overthink/overcomplicate it. It is just as simple as you said earlier "Or do I basically cut the existing wires, and insert both ends into the terminal block on the M1XSP?". Yes, just tie the +, A, B, and - from the control and to the kpd together and insert into the appropriate position on the xsp.

Sorry, you misunderstood me. I fully understood and appreciate that explanation.

I was referring to the "keypad in the middle" example specifically...because as I recall, it uses a wiring harness, not a terminal block. That's why I originally asked about 3-way splices...which rocco says is "against the specification."

So...what is the "correct" way to wire a keypad into the middle of a 4-wire run?

 

[brotsten]

My issue was (and is) understanding the actual mechanics of the wiring connections. And I must say that I am somewhat surprised to see that page 7 of the M1 installation manual shows this type of hookup without any explanation. The illustration actually shows a keypad in the middle of a 4-wire run, so I would still appreciate an explanation of the proper wiring for this specific connection--as described in the manual.

Don't overthink/overcomplicate it. It is just as simple as you said earlier "Or do I basically cut the existing wires, and insert both ends into the terminal block on the M1XSP?". Yes, just tie the +, A, B, and - from the control and to the kpd together and insert into the appropriate position on the xsp.

Sorry, you misunderstood me. I fully understood and appreciate that explanation.

I was referring to the "keypad in the middle" example specifically...because as I recall, it uses a wiring harness, not a terminal block. That's why I originally asked about 3-way splices...which rocco says is "against the specification."

So...what is the "correct" way to wire a keypad into the middle of a 4-wire run?

It's the same with the keypad harness. FYI, I bought two M1DBH's, used Cat5 for my keypads and found it far eaiser and cleaner to do the chaining on a 66 block.

Brian

 

[Steve]

You don't have any choice. Treat the kpd harness the same as the block and simply tie the 3 wires together. I think Rocco was talking about a whole branch coming off the middle, like say instead of the short keypad harness you spliced in another line to run to other devices. That should be avoided but you should be fine with the 3 way splice just on the kpd harness. You will need to take the termination off the kpd and move it to the last device on the line.

 

[rocco]

Yes, I'm talking about a branch sprouting from the chain. I guess I really don't understand what you mean by a 3-way splice.

Normally, I picture a pair of wires coming to a device, and attaching to the A and B screw terminals (I have been ignoring + and -, as they are only power and can be safely wired a dozen different ways). Then, if it is not the last device in the chain, another pair of wires also connect to those terminals to continue on to the next device.

You can consider that a 3-way splice, in that you have two sets of wires and one set of terminals. If, instead of terminals you had a pigtail, then that may be the 3-way splice that you are referring to. That would be fine, as long as the pigtail was measured in inches, and not feet. The maximum length of the "stub" is a function of the baud rate, which I don't know.