blown starting capacitor... X2 [RE-wrenches]

[Todd Cory, Bald Mtn. Solar]

I have a submersible pump question for the group. I have a customer with
a buried water storage tank fed with water from a DC well pump. In this
tank is a 120 VAC 1/2 HP (fed via Trace SW2512) submersible pump for
pressurizing the domestic water delivery system's plumbing. All has been
fine with this system until the customer got a bean in her bonnet last
week about cleaning out the storage tank. She drained the tank until the
pump stopped via the low water float switch, then totally emptied the
rest of the water out with a sump pump. After cleaning and refilling,
the 120 VAC pump blew the starting capacitor when energized (this pump
has a mechanical relay starter on it too). I trouble shot the system
over the telephone and all was fine after the capacitor (clearly blown)
was replaced... until today when she decided she didn't like the
residual chlorine in the water from the previous weeks cleaning so
repeated the whole scenario, and just like before the starting capacitor
blew again... sigh.

Questions...
What would make this happen? The only thing I can see that was different
with the pump is that it no doubt had air in it when starting after the
cleaning. The pump is only about 4 years old, and has seen low use
levels, so I would suspect it is fine, especially since after the
capacitor was replaced everything operated fine again.

Do people familiar with these capacitor start motors think a bit of air
in the pump could cause this to happen?

I am not clear on what conditions blow starting capacitors anyway?

Maybe running on a "sine wave" inverter is causing this and the
capacitor's size needs to be changed to accommodate Trace's less than
perfect replication of a sine wave?

Any help or feedback from you pump experts is welcome and appreciated.

Thanks,

Todd

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