Electrical – Can you wire a 30A 2P standard circuit breaker “downstream” from a 60A GFCI 2p circuit breaker

You should never chain two GFCI circuits together. When you install a GFCI circuit, you should only ever chain standard outlets off of them. Multiple GFCI on the same circuit can cause each other to trip.

So yes, what you want to do is actually what you should do.

What you do need to do, however, is make sure you connect the new outlet to the LOAD terminals on the GFCI outlet. That will put the new outlet on GFCI protection.

You should also sticker the new outlets as GFCI protected.

See in the above how the duplex (standard) outlet is fed from the GFCI, NOT the main line.

And in case it's unclear- the 3 gfci in the pic are not chained - they are connected in parallel. Only the standard outlet is "chained" - or connected in serial.

Since it's a Ground Fault Circuit Interrupter (GFCI) breaker, it's very likely that you have a ground fault.

GFCIs work by detecting an imbalance in current between the ungrounded (hot), and grounded (neutral) conductors. This is why you only see the trip when the circuit is under load. If there is 0 current flow, the current is balanced.

I'd start by inspecting the receptacle. Turn off the breaker, then open up the box where the receptacle is installed. Look for damage to the receptacle itself, or water/moisture in the box.

For outdoor installations you should always have a weatherproof box, and a cover that is weatherproof even when the receptacle is in use.