That Rule 1500 that froze, I had a 20 amp breaker on the wire. When I got to boat I noticed the breaker had opened and the aft bilge was frozen. I had to wait a week for it to thaw. I pushed in the breaker and the pump pumped out the water. Pump seems ok to me. A few years later I upgraded with a Rule 2000 pump pulled out from forward bilges. I upgraded forward bilges with two Rule 3700 pumps just in case something happens. They were a great deal on Ebay. The seller was selling a bunch of them. I bought one, it arrived smashed? Looking at it, the steel motor is so heavy, if it is dropped it will crack the inner plastic ABS and outer PVC housing.
So he ships another one , it was good. I did not think I could fix that smashed pump, but I did, so now have two 3700 pumps. For both 3700, I have a single 40 amp breaker with a 10 gauge wire. I also designed the circuit so each pump switch turns on its associated pump, yet with one manual switch, I can simultaneously turn both on together. For that I used 2 relays.
The FS is float switch. Diagram shows relay as one, but I used 2 40 amp cube relays.
Instead of a relay, you can use a diode schottky which has a lower voltage drop.
Or a standard diode. Diodes do have a slight forward volt drop.
So anyway, I now have 6 bilge pumps in the boat, two rule 3700, a rule 2000, a rule 300 in the forward bilge. And rule 500, and rule 2000 in the aft bilge. Each bilge is separated from the other water tight by a sealed bulkhead.