Is This a Blown Capacitor?

Another view....Still think its the capacitor? Thank you for the input.

Yes I do. Where's the electrolyte? An electrolytic oil should be inside that vessel. It looks like the failure that popped the vent blew all of the failing electrolyte out, a common failure scenario. Regardless it looks like you need to replace that opened capacitor anyway.

If you are not lucky, a motor winding insulation is breaking down to the case thus still causing a ground fault.

I believe you're right. It looks like a non-polarized electrolytic start capacitor.

A typical motor start capacitor, as can be seen by its black colour and can shape

https://en.wikipedia.org/wiki/Motor_capacitor

The electrolyte (brown rusty looking stuff) is a conductor and when it leaked out could very likely have created the sneak path to ground causing the ground fault interrupter to trip.

I agree it's probably blown. Since it has four terminals, it's probably two capacitors in one case; a starting capacitor and a smaller running capacitor. They are pretty cheap, but make sure you get the correct unit: Same values of capacitance, and the same or a higher voltage rating as the original. If there is a temperature rating given, the replacement should have the same or a higher temperature rating.

Newer capacitors are commonly smaller in physical size than the originals. If that is the case, make sure to use some form of heat-resistant padding, so the capacitor can't vibrate when the motor is running.

When you reassemble the unit, make sure each of the four (or possibly three) wires goes to its correct terminal. Hopefully, you took a photo before disconnecting the wires. If not, study the motor's diagram on the plate. It should identify the correct terminals.

The ground fault essentially measures the difference between the current in the hot side and neutral side. If these are not equal, part of the current is returning to the source via the ground and the ground fault trips. A conduction path to the ground can be either on the hot or neutral side of the pump.

Take the plug for the pump and measure between both the hot and neutral to the ground prong. It should be an open circuit. Check it with the capacitor removed from the circuit. My guess is that the corrosion on the capacitor may be providing a ground path.

First test:Disconnect the pump with only the capacitor connected.(Motor disconnected from cap and circuit).

If it trips, the capacitor is bad,but there may be another issue involved.

Cap Testers do not use a high voltage for testing,so it may be breaking down under line voltage.

Be sure to ground the capacitor to the ground wire of the supply conductor when you remove it from the motor circuit.

Test# 2 If it trips,remove the capacitor from the circuit,and test the circuit with nothing connected at the pump end of the line.

If it trips,there is a nick in the wiring to the pump,or the wiring insulation is breaking down.

I suspect the capacitor is bad.

I have never seen a good capacitor with a leak outside of the case,in over 50 years of electrical work.

When I was younger (before going to college for electronics) I used to connect small electrolytic capacitors to 110VAC (US).

I'd stand back, watch them smoke then explode. I would find paper shrapnel from the internal wrapping - did you find any paper bits? Tell tale sign of bad electrolytic.

After working on medical equipment, they had electrolytic capacitors the size of a beer can - ALWAYS wanted to connect one of those to AC. Tried to act grown up tho……..

Most definitely blown so when you get a replacement capacitor make sure you test the capacitance with a capacitance meter and get one that is close as possible to the original value. You will find that they are quoted as +10% -20% but I have never found one that has been +10%. Just replaced one in a water pump and the value on the case of the new one was 10uF but tested at 8uF. I needed an 8uF so I used the one that measured 8uF. The 8uF I changed out was down to 4uF and the pump was having trouble getting started. This is a common failing as the quality goes out of the capacitor

Not being familiar with 120AC as 240 AC is the norm here but the replacement cap for 240VAC is 450vAC or 600VAC motor start duty.

Don't buy a metal can capacitor if you can help it as they fail more often as the motor heat is transferred to the internals from the motor heat and not the other way around and the plastic case insulates the internals should they fail.

Normally the Capacitors are not electrolytic but paper/mylar and the liquid is not electrolyte but insulating oil.

Don't think buying Brand Name capacitors guarantees you quality, sure you pay more but I have just had to change 75uF 450VAC capacitors out on a power correction filter in a welder. I pulled them apart and they all had a common connection problem where the connecting wire had arced the foil away. That is why I test every capacitor for value and Q factor, before installation, buyer beware

A blown capacitor essentially never has its original capacitance, so measuring it with a capacitance meter tells you very little about what value to buy.

Hopefully, NM can either read the values from the Cap or from the motor plate. Or possibly read a part number for direct replacement.

Any markings on the sides or top of the capacitor body?

yes... lots of data I do not understand.

After looking more closely at your first picture,you may have had water getting into your capacitor,evidenced by the rusty enclosure.The terminal looks very close to the metal fitting,and there may have been an arc at some time that shorted the capacitor,or there could be a path for leakage current to get to the ground,which will trip a G Fault breaker.

It only requires .005 amps to trip a GFCI, not even enough to create a visible arc.

Sometimes they will trip due to the arching of the plug when inserted into the receptacle.so a good practice is to plug in the load first with the breaker off,then turn on the breaker.

However,I am still betting that the capacitor is bad.

When you replace the capacitor,put a layer of clear silicone caulk around the terminals and the case seal to guard against water damage in the future.

Please let us know what you find.

OK.... Thank you all for the input.

I have a friend in the electrical supply business that says he has one that will work.

Thank you all for helping .

Remember the 7-up commercial where the athlete gives a kid a bottle of 7-up and says "here catch" while tossing him his dirty laundry?

That was my cousin growing up, but instead of soda and laundry it was charged capacitors.

.... Goats leave him alone too

ha ha ha ha

As these things are usually less than £10GBP including postage it is not worth arguing about it. Just replace it with a new one, and try again, perhaps?