Two 16 zone unit install

I am installing two 16 zones units and need some help/validation to make sure the install is correct. Here is the details of my wiring and how it was installed prior to rachios:

  • I have 4 x multi conductor wire bundles. (Two 12 wire, one six wire and one 5 wire). Each bundle includes a white common.
  • Originally 3 of these bundles (the two twelve and the 5 were wired into a 24 zone controller. All 3 the common wired were twisted together and wired to the common slot.
  • The fourth bundle (6 wire) was hooked to a separate controller.
    Before pictures:

    Here is how I wired the two new Rachio gen 2’s:
  • I wired one of the 12 wire bundles and the 6 wire bundle to one Rachio. Connected each of the common wires from the two bundles to two common connectors on the rachio.
  • I wired the other 12 wire bundle and the 5 wire bundle to the second rachio gen2. Again connecting each of the two common wires to two common connectors of the rachio.
    After pictures:

My question is whether this wiring is correct. I have read a number of threads and the support bulletin that clearly states you should not share a common wire across two rachios. I believe I am not sharing a common wire as I have separated the bundles across the two rachios.

Most of my zones are working just fine. I do have 3 zones that are not working and when I check the omhs reading on those they are all very high ( over 100 and into the 200s) so I am guessing something else is wrong with these zones. Note they did give me some trouble in the past with the previous controller as well.

Does the wiring look right or do I really need an isolator?

Installers will sometimes tie commons together out in the field. If any of them are tied together out there, you are sharing a common.

Thanks for the reply. What is the best way to know for sure? Also, since at least one set was on a separate controller before would that not mean it would have caused issues?

@joostesa - check the resistivity between the commons. If it is very high, then those two commons are not shared. Just test every common against the others and you’ll know.

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@joostesa Check each common as @DLane has suggested.

Using the voltmeter to ohm read, what happens when you touch the red leads to the common wires on one controller with the black lead to the commons on the other? Leave the commons in the terminal block.

Thanks for the replies and sorry for the delay in responding. I just got back in town and was able to do the measurement. When I measure the two commons across the boxes it does give me a reading. Starts at about 15 ohms and then keeps creeping higher slowly. This would confirm the commons are connected in the field somewhere. So I suppose my only option at this point is to install the isolators. Definitely not the most convenient and adds a bit to the cost of getting Rachios, ouch!

Out of curiosity. Would this not have been an issue before given I had two separate control boxes before?

I’m not so sure, my buddy’s fluke meter does this when there is no connection. Eventually it will error out, but when there is good connection,it steady states pretty quickly.

@joostesa It could have been an issue. I’ve never dealt with two shared commons in the field. I just know not to do it. I’m guessing the main issue is having both controllers activate at the same time if they share a common.

I’ve had a curious event happen to me several times in the past, though. Something I can’t explain. I’ve checked ohms across control wires to solenoids and had no ohm reading. Then, when I activate the zones and check ohms again, the readings are normal. I assume it’s loose wire connections, but I haven’t confirmed that.

Activate some zones on both controllers and recheck the ohms and see if the readings are the same.

@joostesa - are you using a digital or analog meter? Although it is a PITA, I would take the common leads out of the Rachio terminal block to do the testing. That way there is no phantom or ghost voltage due to pull-up current in the measurement. I think one reason not to share common wires is due to electricity seeking the path of least resistance and creating ground loops. One might be able to get away with shared common wires when using dumb mechanical controllers, but with the electronic smarts in Rachio it might cause problems.

If you have a single master valve shared between controllers, you need to use relays or the Isolator devices to prevent backflow of current to the non-active controller. I didn’t want to spend the money on the Isolator devices, so I ordered some relays off Amazon and used those instead. The relays are a lot more complicated on the wiring, but much less expensive. If I had it to do over again, I would probably spend the extra money for the isolators for the simplicity. See the following article.