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I have a Zoeller M-53 sump pump and I'm considering using a float switch to stop the pump from cycling too frequently. Here's the situation...

The water level is pretty high where I live. The sump pit is really an old, rather shallow brick-lined pit. The pump is working fine, but there are many times of the year that the pump just goes off too much. I'm afraid that the pump's life will be limited by this constant cycling. There are times that I know the water level won't climb out of the pit, but the pump's built-in switch triggers the pump anyway. I don't need the water to be that low.

Note: I cannot raise the pump higher than it is because of how shallow the pit is already. Plus, I have a battery backup pump that is on top of this that just sits at the absolute top of the pit.

Is it ok to do this to my pump, or would the pump being covered in water cause more damage?

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  • I have the same pump and the same situation. Did you follow their advice, and if so how did it work out? If you did buy a secondary float switch, which model did you buy?
    – user12945
    May 10, 2013 at 20:31

3 Answers 3

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As kkeilman points out, your pump is fully submersible, so that part should be no problem.

You can easily just piggy-back a float switch like this one on your existing pump. It has a special plug that you plug the existing sump pump into (no wiring necessary), and this one in particular handles up to 1/2 HP, which is more than enough for your 0.3 HP Zoeller.

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The nice thing about these tether floats is you can adjust the heights depending on where you attach it, and how much tether you give it. Just be sure to test it manually moving up and down to be sure it's at the right heights, and it's not going to get hung up on anything (causing it to either stay on, or not turn on when needed). I highly recommend you secure all the wires going into the pit with zip ties or electrical tape to be sure they're not going to fall down in the future.

You can leave the existing float working, which is fine - it will act as an extra safety to shut it off if the pit is dry, but also be sure this one doesn't get hung up - because both floats will have to be "on" to make the pump turn on -- if either is off, the pump is off.

If you don't want to use the existing float, there may be a way to bypass it internally by rewiring the pump, or you can simply zip tie it "up" so it is in the on position all the time.

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Looks to me like the pump can be fully submerged so there shouldn't be any issue allowing the sump level to raise up a little higher.

I would use the float switch much as an 'enable' on a relay powering your sump pump. Get a RIB (or any relay capable of the amperage your sump pump needs and use the float switch for your switching input.

Also highly recommend putting some kind of water high level alarm for a backup.

I made a quick and dirty drawing for you - top picture is your current situation. Bottom image is using a relay to control power to the pump motor, using the float switch as the relay enable. FYI - "RIB" is a brand name for Relay In a Box (I used them all the time back in my industrial automation days - handily packaged, reliable and easy to use).

As a best practice, you shouldn't use a switch to control large cycling loads (anything more than a few amps really). The arcing and sparking caused by opening/closing that switch under load will significantly shorten switch life.

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  • Thanks kkeilman. This is probably a stupid question, but I can't seem to figure out what this RIB relay is/does. Won't the float switch handle the cycling of the pump?
    – user980
    Jan 4, 2011 at 12:37
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    Check out my revised post - you can see how I would use a relay in this scenario.
    – kkeilman
    Jan 5, 2011 at 0:25
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    You don't need a relay if you have the correct float switch. They're designed for switching pumps in these situations.
    – gregmac
    Jan 5, 2011 at 6:07
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Resurrecting an old thread here. The M53 contains an integrated float. I’m not a plumber but my understanding is that the M-series pumps fail at the integrated mechanical float most frequently. Why not upgrade to an N53 (which is an always on pump), and then use one tether-float or solid-state float, to control the pump? IMHO, again, not a plumber, adding a tether float to the pump induces two sources of potential failure such that if either float failed, the pump wouldn’t kick on and the basement would flood. Thoughts?

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