Timer to control two loads at different voltage

[Patmac0020]

I am trying to find a setup to ensure my chlorinator pump only turns on when my pool pump is running. If the power goes out, I can see a scenario where the timers are out of sync.

Currently, I use a Woods digital timer for the chlorinator pump and a GM40AV mechanical timer for the pool pump. I would like my GM40AV pool pump timer to control both the pool pump and the control whether the chlorinator pump can be activated when the digital timer's program activates.

Here is my setup.
I have a GM40AV timer in my pool panel. Currently it switches both legs of my 220v pool pump as shown below.



I may be mistaken, but I understand that you can wire it to switch one leg instead of both (without additional current draw). In theory this would free a switch for a 120v circuit (powering my stenner chlorinator pump). I've attached my proposed wiring diagram below.


My main questions: Can you see any reason not to do this? Has anyone else done this before?

Thank you,
Patrick

 

[kimkats]

I have a pm into someone that may know. Hold on a bit and lets see what they have to say.

 

[JoyfulNoise]

I'm not an electrical expert but I think what you're proposing is dangerous from an electrical safety standpoint. Based on your 2nd diagram, one leg of the pumps windings would be energized with AC power all the time. That's a hazard as someone might inadvertently think that, when the pump is off, it's not energized. Sticking a screwdriver in the wrong spot could be a life-threatening decision. I don't know this for sure, but energizing half the pump circuit would seem to me to put unnecessary electrical stress on pump components like the start and run capacitors which would lead to shortened pump life.

 

[JohnT]

It will work, and is done fairly often. I don't care a lot for it though. The downside is that the pumps are still hot even when the timer turns them off. You should never rely on an automatic switching device like a timer to safely remove power from a load whether it switches both lines or just one, but it still makes me a bit nervous to have a load with power even when it appears to be off.

An alternative is a cycle timer with a 240V clock fed by the same leads as the pool pump to turn your chlorinator on and off only while the pool pump is powered.

 

[CJadamec]

I'm with John on this one as well, yea it will work but it really not an ideal way of doing things. I would certainly never wire a pump that way, just because it will work doesn't mean its the right way to do it.

As for controlling the stenner with the pump timer you could use a 220vAC relay powered off the pump leads to switch the stenner pump on and off with the pool pump. You can get a timed relay to further control how long the stenner would run if you run the pump longer than the stenner needs to run.

 

[Bama Rambler]

Well, let me just throw my 2¢ in with the others.

It is a very common practice and it's not against code.

Having said that, I agree with the others. I always like breaking all the hot legs to a load. To me it just makes it a little safer.

 

[ps0303]

"I am trying to find a setup to ensure my chlorinator pump only turns on when my pool pump is running."

Put your chlorinator on the same timer clock as the pool pump. Problem solved.

Why do you have a separate timer just for the chlorinator? At no time should your stenner be allowed to be powered up when the pump is not working. The stenner will continue to pump chlorine into the system when the pool pump is off and then when the pump kicks on, you'll have a very high dose of chlorine pumped into the pool. That is not good. We had a case here in Florida where a swim school had the pumps on one circuit and the stenners on another. A storm came thru and something happened where the pump breaker kicked off but the stenner didn't. When the breaker was finally reset, I believe it was off for around an hour, all of the chlorine that was held up pumped into the pool and kids were overcome by chlorine gas. Luckily no one was seriously hurt.

 

[dfahrion]

I agree with what everyone has said. I assume you have the digital timer because you don't have any way to throttle down the stenner and don't want it running as much as your pool pump.

As to how to wire it, does your digital timer keep time and programming without power? If so you could power it from half the pump power (120v) and be on the same circuit and still be breaking both legs of the pump power when off as well. If the timers get out of sync you would not run the stenner without the pump, the failure mode would be the stenner wouldn't run or would run as much as you had it programmed for.

I'm not a certified electrician so don't take my word alone, but the way I would wire it is leave the pump wired as is from the existing timer breaking both legs, then take a new wire from either NO or NO2 for your 120V power to power the digital timer which then powers the stenner. Use neutral to make the other half of that circuit to make the 120V your digital timer and stenner needs.

 

[Patmac0020]

Thank you for all the advice. The main issue is that my 120v chlorinator pump is on a battery powered timer and the 220v pump runs on a mechanical timer without a battery. So I'm trying to account for the fact that the timers could get off with a large power outage.

I emailed an electrical engineer too. If I understand him correctly, he said that it will work but it may cause an issue with the breaker tripping if there is an issue when it is turned off. In short, it's not a best practice for multiple reasons and I don't plan to do it this way. I am more likely to use a relay or a flow sensor. I'll post more about it when I figure out what I'm using.

I'm thinking an AC-AC relay would make the most sense in the short term, but a flow sensor feeding a relay may be the safest because it ensures that the pump is functional despite power being applied to it.