I would still use 2 for redundancy.
I have DIY'ed a similar one but bought the float switches off ebay and the rest were stuff I had lying around. It has been a little over a year and so far so good no failures yet nor has it ever tripped the second float switch.

"Redundany" in this case that means dry floors! I like that word :lol:

Do you have 2 "max water" switches? Or is it like the BWI/Autotopoff one with 1 fail safe float?

The Double Switch Controller at autotopoff.com has a main float switch and then an emergency float switch set a little higher in the event that the first one fails. Not a bad set up for $50.

Either way one float has to be higher than the other and they both have to be wired to the pump to tell it when to turn on/off. If you set both floats at exactly the same height how would you know if one wasn't working?

Yup this is the way I have it set up.

LOL Jeff! I ment having 3 with each on top of each other. Which thinking more about it would be overkill :redface:

I don't see any disadvantage of having 3 switches there. I guess the biggest issue with adding so many failsafes are space and cost but switches costs only roughly $2.00 each so if it helps you sleep better and not worry about flooding your floor adding a third level of safety does not hurt.

ATO
 

Wayne, I use this one. It has never failed me yet.

http://www.aquariumsupplies.ca/tsuna...tem-p-840.html

Along with a Aqua lifter Pump, and a water container of some type, and some hose.

http://www.aquariumsupplies.ca/aqua-...ump-p-844.html

http://www.bluelineaquatics.com/prod...tem/index.html

Just another option. Doug

those are the units we carry!

we have the Dual and single sump mount switchs.. and also the 1/4" solenoids

I have the autotopoff.com (or BWI) ATO with an aqua lifter pump and it works great. With the aqua lifter pump you can have a small fresh water container and if you run the pump dry it shouldn't wreck the pump.

This is my second saftey the way I look at it I would rather burn out a pump then flood my floor.