This is a classic troubleshooting puzzle, and it sounds like you've done a good job of narrowing things down. Here's a breakdown of potential explanations and what to consider

Possible Explanations (Beyond the Obvious Ground Fault):
Loose Connection/High Resistance at the Original Outlet

Even if it looks tight, a slightly loose connection at the original outlet can cause increased resistance. Increased resistance translates to heat. This heat can, over time, affect the breaker (even a new one) making it more sensitive. It also creates a voltage drop. While not a ground fault or short circuit, this voltage drop and heat cycle can push a perfectly good pump motor (especially an older one) toward its amperage limit, eventually tripping the breaker. This is the

most likely explanation. Marginal Breaker (Even Though New)

While you replaced the breaker, it's possible you got another breaker that's on the weaker end of its tolerance range. Breakers are manufactured with tolerances. Two 20A breakers might not trip at exactly the same amperage. This is less likely, but shouldn't be ruled out

Voltage Fluctuation/Sag at the Original Outlet

The voltage at the original outlet might be subtly different than the voltage at the outlet you switched to. This could be due to other loads on the circuit, distance from the panel, or even a slight imbalance in the power coming into your house. A lower voltage can cause the motor to draw slightly more current to maintain the same power output, pushing it closer to the breaker's limit.

Minor Neutral Issue

While you've ruled out a ground fault, a subtle issue on the neutral side of the circuit could contribute. This is harder to diagnose without specialized equipment.

Harmonic Distortion (Less Likely, But Possible)

This is a more advanced concept. If other equipment on the same panel is creating harmonic distortion (distortions in the sine wave of the AC power), it can affect the current draw of the pump motor, even without causing a ground fault.

Things to Check & Further Investigate


Inspect the Original Outlet Extremely Carefully



Turn off the breaker! Remove the outlet from the box. Check for any signs of burning, discoloration, or melting on the wires or the outlet itself. Make sure the wires are tightly connected to the outlet terminals. Pigtail and use wire nuts if the existing wire is too short after cutting back any burned sections. If it's a back-wired outlet (where wires are inserted into holes in the back), switch to using the screw terminals on the sides. Back-wired connections are more prone to loosening. Consider replacing the original outlet entirely. It's a cheap part, and if it's been subjected to heat, it's a good idea.2. Voltage Measurements (While Pump is Running)

Use a multimeter to measure the voltage at the original outlet

while the pump is running. Compare this to the voltage at the outlet where it's currently working without tripping. A significant voltage drop at the original outlet is a clue.3. Amperage Measurements (While Pump is Running)

Use a clamp meter to measure the current draw of the pump at both outlets while it's running. This will tell you if the pump is genuinely drawing more current at the original outlet. Measure each leg separately, and compare.4.

Check Connections in the Panel



Turn off the main breaker! Inspect the connections of the wires for the original breaker at the panel itself. Make sure they are tight and show no signs of corrosion or overheating.5. Check the Wiring Run

If possible, try to trace the wiring run from the panel to the original outlet. Look for any signs of damage, splices in junction boxes, or anything that could indicate a problem with the wiring itself.6.

Breaker Type

Although you said the breaker is "regular", confirm that it is a standard thermal-magnetic breaker and not a Combination Arc Fault breaker (CAFCI). While arc fault breakers usually trip with a specific code or a distinct difference from a regular overload trip, misidentification is worth checking.

Important Considerations



Safety First

Always turn off the power before working on electrical circuits. If you're not comfortable working with electricity, hire a qualified electrician.

Permanent Fix

The fact that the pump is working on a different outlet doesn't mean the problem is solved. There's still a potential issue with the original circuit that needs to be addressed. Ignoring it could lead to more serious problems down the road.*

Document Everything

Keep detailed notes of everything you check, measure, and change. This will help you (or an electrician) track down the problem.

In Summary:

The most likely explanation is a loose/high-resistance connection at the original outlet, combined with a pump that's running close to its amperage limit anyway. Thoroughly inspect and replace the original outlet, check voltage and amperage readings, and consider having an electrician take a look if you're unsure or the problem persists. Flag for review