I have a 240V 2 speed Magnetek 1081 motor/pump connected to an Intermatic RC2491RT mechanical timer on my swim spa, everything 20+ years old. I want to add a 240V ozonator powered on LO only. When I test Line2 terminal and the Timer/Lo terminal I get "0"V when the pump is OFF, 240V when the pump is LO, and 5V when the pump is HI. I expected the HI reading to be "0"V (Line1 is 240V on HI, OFF; "0"V on ON). Where is this 5V possibly coming from, and would it harm the ozonator if I connected it? All other voltage combinations seem normal.

I can't find anything on the model you listed, so I can't really help except to say you're probably reading some induced voltage back through the low speed windings when the pump is running on high. 5 volts shouldn't be enough to affect the ozonator.

Why do you want to add an ozonator? Are you having issues?

Thanks for your input. I didn't think the problem was in the timer because the reading was "0"V when I disconnected the pump loads. That leaves the pump with a short somewhere (tripped breaker or a 240V reading???), or induced voltage as you mentioned (the 5V reading appears on both the Line2 and Load2 terminal and the timer terminal at hi speed). I'm adding the ozonator to hopefully greatly reduce my maintenance requirements/consequences. I'm a senior citizen, had some back problems, and sometimes become immobile/disinterested while the wife continues to use the spa routinely.

An ozone system won't have any visible impact on a typical residential pool unless you have a major swim party. Chlorine alone is more than enough unless you have a number of people swimming at the same time. With enough swimmers chlorine can't completely keep up and when that happens ozone can help out with the extra oxidation load.

The grandkids pushed me over. After 4 hours in the swim spa one day of a few (they love it while visiting us), the water just went cloudy. I tell them not to.......yeah, right.

That just means you need to bump up the chlorine a bit before and after they are there. I do not think the ozone will help as much as you think it will ... especially for the cost ... and if the kids are only there on rare occasions.

What are you using to maintain chlorine levels? How are you testing it?

Not sure of you background, but have you read Pool School (button at the upper right of the page) to get an understanding of the chemistry?