Electrical – getting nuisance trips with the GFCI breaker

Any load trips a new GFCI breaker:

Conditions:

• Brand new construction.

• New 75' 4wire feed to new subpanel from a long working and reliable main subpanel.

• One GFCI breaker feeding 4 outlets from new subpanel.

• ANY load on any outlet trips a new GFCI or new Arc-Fault GFI breaker,including one new and one old vacuum cleaner, and even a simple 40 WATT LIGHT BULB!

None of the other 10 individually GFI fitted outlets anywhere else on the property has tripped for any reason except a water splash on the actual outlet.

• I have lifted each new outlet one at a time from the GFCI breaker and tested circuits individually.

• I have removed all outlet wires from the GFCI breaker and directly wired just one new outlet hanging out of the new panel.

• I measured a little voltage from ground to neutral (typically this is normal on a sub-panel) so I tried bonding the neutral to ground at the new panel.

• I have used a Megger on all branch and neutral wires looking for shorts, and everything measures good. I even used the Megger on the lamp and vacuums and no problems found.

• I have read troubleshooting sugestions from at least 30 different sites (all say essentially the same things) and none of the typical wiring or equipment faults that could cause a false trip are present in this case, or simply do not apply.

Nothing stops the breaker from tripping as soon as any load is applied.

I am an electronic engineer and have a lot of experience as an apprentice electrician. I have brought out all my troubleshooting skills and test gear to no avail … so this one is twisting my brain.

Should I tear into the main panel, megger the new subpanel feed wires, check the main house ground, Sink a local ground wire at the new subpanel?

Any ideas out there?