Electrical – What could be causing the main breaker to continually trip

Some surge protectors work by "redirecting" surges to the equipment ground, which is pretty much the definition of a ground fault. In this case, it's definitely possible that surge suppressors could be tripping GFCI receptacles/breakers (given a large enough surge).

As for the AFCIs... When electrical contacts separate, they often create an arc between the contacts. This arc spans the gap until the contacts are too far apart, and the arc can no longer be sustained. It's possible (in theory) that the GFCI tripping could create a large enough arc, for long enough to cause the AFCI to trip. It's not likely that a properly functioning GFCI would do this, but if the GFCI was old and worn it could be opening the contacts slow enough that a detectable arc is being produced.

Determining if the GFCI tripping is causing the AFCI to trip, is a simple test. Simply press the test button on the GFCI. If the AFCI trips, you'll have figured out half the problem. If the ACFI does not trip, you could repeat the test using a receptacle tester with a GFCI test function.

If it's determined that the GFCI is causing the AFCI breaker to trip, replacing the GFCI receptacle may resolve that part of the issue.

Figuring out if the surge suppressor is tripping the GFCI, is a more difficult proposition. It will likely require you to monitor the supply voltage over some time, to identify and document possible surges.

I don't think this indicates a problem.

Circuit breakers have at least 2 different triggers for cutting the power:

1. Thermal mechanism for small over-current protection, e.g. trying to draw 20 amps from a 15 amp circuit. This may take several seconds or even more than a minute, depending on how much over the rated capacity you are.
2. Magnetic mechanism for short-circuit protection, which should kick in around 20x the rated ampacity. This should trip the breaker virtually instantly.

You can look up the time-current curve for your breakers if you're curious how long it takes them to trip under different conditions.

(There may be additional features that cause the breaker to trip, such as arcing or ground fault detection.)

If your circuit had tripped because of a slight over current, such as too many appliances running at the same time, only the breaker for that individual circuit should have tripped.

However, for a short-circuit condition (which I assume you had with your dimmer), either one could go. It's a little surprising that both tripped, but there is a slight delay in response time so it's not inconceivable.

(Actually, you could have had 3 different breakers trip: the breaker for the circuit, the breaker for the sub panel feed, and the main breaker).