Linking 4 rachios 3s to common well pump relay

Hi everyone. We’re starting landscaping on a new house on a big lot with 39 zones of irrigation. I’d like to make sure the watering can occur offpeak from PGE (my (bankrupt) utility) to reduce the price of running the pump due to PGE’s rapacious pricing in the daytime. The irrigation is fed from well that can simultaneously pump enough water to support 5+ zones running at once.

When I do the math of what has to run in the summer to accomplish keeping things running offpeak, I need a minimum of 3 zones running at once, and 4 would make it really easy. I am planning to use 4 Rachio 3 12 zone units (from costco). I want to wire them up so that any one of the Rachios can turn the pump on. I explicitly want them to be able to all run at the same time, and the piping is set up to be able to make all that work.

The issue with using Rachio here is common pump control, and of the various smart irrigation controllers, only Rachio directs the use of the TSR isolators: There are no examples on how to wire them for use with more than 2 controllers.

I am an engineer, but there are no schematics on the website to tell exactly what the isolator is doing. Obviously, if the 4 24VAC transfomers for the 4 Rachio 3’s are not wired from the same 120VAC circuit, or the hots and neutral get confused, you can have a big problem. In my case they will all be co-located, and fed from the same breaker. However, the safest bet might be to use a common much larger 24VAC power supply and feed all the Rachios from the same source. This prevents them from potentially causing a problem, and should result all the commons being tied together. It’s easy to find one of these and wire them together in this way (and neater too)

Does this resolve the need for the isolators? If needed, I can also wire up 4 relays to the master well relay in a way that the commons on the pump controls are not shared, but would like to know the best way to handle this configuration.

Hunter does make a large controller that can handle all these valves and simultaneous running of 4+ zones, but its a commercial unity and has no smarts, app control, etc…

Would love some advice from folks on solving this problem. I guess I could take one of the Rachios apart and see how the power is routed from the 24VAC line around the circuit boards, but I don’t think I should have to do that to figure out this configuration!


@fresnoboy - one option would be to grab three SPST 24 VAC relays. Then I’d run the relay coils for Rachio 2 - 4 from the M terminal on the respective Rachio with the return wire from the coil going to the respective Rachio’s C terminal. I’d connect Rachio 1’s 24 VAC + line to one side of each of the relay’s pole, with the other side of the relay’s pole going to a pump start relay. These three relays would we wired in parallel. The common wire for the pump start relay would return to Rachio 1’s C terminal. With Rachio 1’s M terminal also being wired to the pump start relay.

In this configuration Rachio 1’s power and common would be controlling the pump start relay and no commons would be interconnect. It would so be cheaper than buying all the isolators. This assumes the 39 zones will be wired with a dedicated common to the Rachio that is controlling them.

Yes, if one wanted a consistent configuration there could be a relay on Rachio 1’s M terminal just like the other three.

My concern with one larger 24 VAC power supply, say 4 Amp (4 x 1 Amp), is in the event of a short somewhere that is a lot more current flowing down that wire trace and components on the board that they are probably not designed to handle.

Let me know if you need me to hack together a schematic or if the above description is good enough.

Welcome to the community.


DLane, thanks for the explanation - makes total sense to me, and easy for me to wire.

One thing though - Rachio seems to advise using isolators to avoid a “common” common between multiple units. I was trying to understand why they require this if the Rachios are all on a common circuit. They said this is a violation of the NEC, but I don’t quite understand why this is the case. That’s why I was suggesting using a single bigger power supply.

However if using the 4 separate supplies and a common common is not an issue, then the relay wiring for the well control is easy to do and this will be less complicated than I had thought.

One question, what is exactly inside these isolators and what problem is it trying to address with 2 rachios who don’t have a well pump or master valve?


@fresnoboy - I’m not an electrical engineer nor an electrician nor familiar with the National Electrical Code.

I have no idea what is inside the isolators. My guesses on the potential issues are: ground loops, different phases or reversed power/neutral. Since connecting two devices with different power supplies isn’t foolproof, then put some protection in there.

Ok, but using the normal power supplies with multiple units and a common common between them should be ok?


@fresnoboy - I would use dedicated, isolated commons for all the devices attached to each controller. The relays would go back to their controller and the pump start relay to the Rachio that is powering it for every relay. The same for the zones in the field. If needed, a second wire in the field bundle could act as a common for a second set of valves off the same field wire, but going to a different Rachio.

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Electrical issues aside, what raises concern for me is how you will be able to maintain consistent flow rate so your pump will be “happy” all the time. If only one zone is running, I would think your would wind up short cycling because the flow through the single zone wouldn’t be enough flow. Are you running individual pressure regulators on each zone to prevent the pressure differences from 1 zone to 5 zones running on the same pump? It sounds like a scheduling nightmare with 4 separate controllers.

Yes, I too am an engineer.

Well, I am hoping have the 4 separate controllers run roughly all at the same time, when PG&E’s energy is the cheapest, which is after 9 PM, and try and get about equal times (the time is dominated by the drip systems). That said, some of them will be running when others are not.

It’s hard to run individual pressure regulators because the 4 areas are not plumbed from a master manifold - that’s not how the landscapers laid them out. There is a master feed, and it’s split off from a main line in a few places. I guess I could try and put regulators on each tributary, but that seems a little overkill.

Is the pressure variation that high? There is a main pressure regulator on the well to keep things in certain limits.


It is more an issue of flow rate and pressure. Your pump has an associated pump curve showing flow and pressure. At wide open, lots of flow with no pressure. That’s the bottom right of the curve. The upper left of the curve is max developed pressure with zero flow. In between shows how your pump supplies water at different pressures, or “feet of head”.

When you look at all the possibilities of which zones could be running at the same time, if you have 4 large zones all open at the same, you will have a whole lot less pressure at the sprinkler heads than if only one zone is running. This means the performance of the sprinklers will be much different in those two scenarios.

In normal sprinkler design, all zones are sized based on available flow, which is normally considered a fixed value. I definitely understand your predicament with the utility, but don’t see an easy solution with 4 separate controllers running off of one pump.

I would suggest visiting and pay special attention to the Country Bumkin Water section where he talks about flow and pressure from a pump.

Good luck.