I'll try to give as much info as possible...
replacing 1HP pump with 1.5HP, did impeller and seal kit as well. 25K IG pool with 1.5" piping, Hayward 2600 series pump housing and S240 filter. Motor set and wired proper for 115V. New motor trips 20A breaker, another new motor sitting on ground never installed or wet also trips breaker after 3 seconds running.
25K gallon in-ground
Hayward S240 Sand Filter
Hayward 2600 series pump/filter housing
All original wiring done professionally. Inside 30A feeds box 10 feet away outside which has dedicated 20A dual pole for pump. Wiring from breaker to pump is maybe 6 feet long and 12AWG.
No timer (bought one to install when all this is sorted)
Old pump - 1HP Magnatek, 7.2/14.4A, 115V - bearings went bad and needed new pump. (very old - screws were all rusted and pump could not be disassembled) We have had the house 6 years with trouble free pool/pump operation, pool is about 14yrs old
I did some research measuring feet of head and all that and seemed 1.5HP would be a better fit, hoping this isn't the root of my problem.
Installed the new AO Smith UST1152 (1.5HP, 115V, 9.3/18.6A) after switching it to 115V. I turned it on and immediately the breaker tripped. I looked at the wiring and found the ground wire insulation was a little rough and it shorted on the screw at the black wire. Woops...
Decided to put new connectors on the hot and neutral and trimmed back the ground to good insulation. The connectors for the hot and neutral are female spade type and the wire at the motor is stranded type.
With everything tight (including external case ground) I reset the breakers and it fired up for about 3 seconds and tripped the outside 20A. I reset the breaker and tried again, and again ran for 3 seconds and tripped the breaker.
I learned somewhere along the way that a wrong size impeller could cause this so I replaced the impeller (with seal kit) with a Hayward SP2615X. It was definitely a little bigger and though I had it solved. Nope - turn on breaker, runs for 3 seconds and shuts off. When I look at the pool I can see the water is moving, pressure at the filter is around 15-18. The old pump also pumped fine it was just LOUD, so no obstructions.
The new pump seemed like it had a lot of vibration and was noisier than the old pump pre-bearing failure. I talked with the pump vendor and got a new one. Took the new one straight back to the pump area, and without it ever touching water or being installed (still had the rubber cone on impeller threads even) I wired it up (same as old pump, same as other new pump, switching it to 115V) and ran what should have been a bench test. Flip the breaker on, it ram for 3 seconds, maybe got 4 out of it, and it tripped. I. Am. Stumped.
The only thing I haven't done is replace the breaker. I bought one last night but in my hurry, got the wrong physical size.
I looked inside the outside CB box and checked all the connections and everything seemed fine. One thing I did notice - the wire to the pump starts in the box as solid wire, but where it comes out of the conduit, it's stranded. The stranded is good here as it's tight quarters and the stranded is more flexible. I tested resistance from pump to breaker and all was good. (although a multimeter tests that with little load) Also, tried measuring draw with my multimeter that is fused for 20A max and it blew that after a half second or so. I'm guessing it's not as robust as a household CB so not sure how much credibility it has. I'd like to get a clamp type ammeter but they're 60-70 bucks and up...
Going to try a new breaker but -
Is there anything I am missing?
Was my "bench test" OK or will the motor trip the breaker without a proper load on it?