Will this N2 wiring work

[techservices]

Have to run a RS-485 Wire for a New UNT controller from the main N-2 Risercontrol

[billcontrols]

That is exactly how not to do it. Pull two cables the 67 feet and maintain the daisy chain. Up from the NAE to the UNT. Then Up from the UNT to the Upper floors. Do not put Tees in RS485 networks.

Plus the Red and black in your diagram should be a twisted pair. And the cable needs a third conductor for the Ref connection. We usually use a 2 pair cable and use both of the second pair as the Ref.

[desert guy]

"T-Tap" can give you some grief and as Bill said you need a third wire for the REF. I always use a shielded 18/3. Admittedly, I have seen two seperate N2 Buss segments each with a nominal amount of controllers on each one landed on the terminals at an NCM, NAE or JACE with no ill effects but I would not do a 67' T-Tap.

[Cagey57]

techservices,
To answer your question, "I would be really suprised if it did "! (short answer No!)

Suggest you use 18/3 Shielded cable and make the connection for the UNT on the same terminals as the existing N2 Bus. Make sure you get Reference, N2- and N2+ correct.

Using 2 conductor on N2 bus can create a whole myriad of problems especially if you have DX-9100's and UNT-1100's on the same trunk.

I have never gotten a "T-Tap" of more than 10' to work. Bad practice unless there is no other choice, and there usually is.

[JCIYorkDude]

All good answers above, make sure it is plenum rated cable if you are running through an open plenum.

[Right Control]

No T-TAPS!! Have seen some bad problems with that. One was where the maintenance staff ran N2 to new drives. In T-TAP form some over 50 feet. And there was lot a drives. I want to say like 40. I had all kinds of issue's with the bus!!

[steves4]

The N2 bus is electrically a RS-485 network. So, you cannot look at one device in isolation. Definitely, the "T" tap is a problem. As several people mentioned the N2 bus needs to be strictly daisy chained. In addition, make sure that the entire N2 bus is properly terminated and add repeaters wherever required. You didn't mention what supervisory controller you were using. Some devices are more tolerant of wiring problems than others so this might also come into play in answering the question "will it work"?

[929rc51]

Trying to learn controlls here not thread jack, why won't that work and what do you mean by daisy chain? Series instead of parallel?

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[steves4]

Go to the JCI site and search for a document called N2 Communications Bus. It is ancient but all of the concepts about the N2 bus are still valid. It shows lots a good examples of how to set up a N2 bus and what to avoid. It is document number 636018. Every time you have a "T" or "Y" connection in the N2 bus the power can drop because you have to support multiple legs on the bus. You can think of it as all devices on the N2 bus have to be in series. However, the daisy chain is just through the connector, not electrically through each device. Another good resource is the B&B Electronics web site technical reference documents. The N2 bus is electrically RS-485 and they have a number of documents that dig into the standard itself and why the technology works.

[929rc51]

Thank you.

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[hvacfisch]

I have seen successful installs where the t-tap is made at a repeater. Acromag (repeater manufacturer) website shows this and I have seen it work. Problem is if you have comm issues, that t-tap will always cause a doubt in your mind even if not the cause. Sometimes piece of mind is worth some extra wire pulling.


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[billcontrols]

I have seen successful installs where the t-tap is made at a repeater. Acromag (repeater manufacturer) website shows this and I have seen it work. Problem is if you have comm issues, that t-tap will always cause a doubt in your mind even if not the cause. Sometimes piece of mind is worth some extra wire pulling.

I don't think the diagram you are thinking of is really a T-tap. Yes a repeater can be used to create a T, but that is because the repeater actually splits a network into two separate segments that have to be looked at as two networks electrically. The repeater does not have to be at the end of a network. It can be installed in the middle of each network is is repeating. The effect can be 4 network cables leaving the repeater. Kind of looks like a T-tap, but is really a repeater in the middle of two separate networks.