A friend is having trouble with a GFCI breaker tripping when he turns
on the swtich for his whirlpool tub. It's not a "new" problem as it's
been happening since he moved in 5 years ago.

(This is the GFCI breaker that I asked about yesterday when I wanted
to know if you could tell what caused it to trip - a fault or
overcurrent)

The main symptom is that when he first turns on the wall switch and
the breaker trips. He goes to the basement, resets the breaker, flips
the wall switch again and the tub powers up and runs fine. This is a
consistent symptom. He hasn't run any tests to see how long between
uses he has to let everything "rest" before the initial trip will
occur, so that is an unknown.

Here are some more details and a few questions.

The circuit in question is a dedicated 115V circuit on a 20A breaker
with what my friend believes is 10 gauge wire. I haven't looked at it,
but he said that he has both 12 and 14 gauge wire at home and the wire
to the tub is larger than both of them.

On the tub motor there is one label that gives the voltage and
amperage specs:

230V / 115V 8A / 16A

There is a another label that says:

"This device must be used with a switch sufficient for a 1 1/2 HP
motor. A 30 Amp electrical supply is required."

The wall switch is rated for 30A, but as noted earlier, the breaker is
a 20A GFCI.

So here are my questions:

Is the 20A breaker the (obvious) problem?

If so, why does it trip once and then work?

If the motor is rated at 16A @ 115V, why is a 30A circuit required? If
it's for startup surges, then isn't a 30A breaker too big for steady-
state operation? It seems to me that a lot can go wrong between the
16A the motor draws under steady-state operation and the 30A required
to trip the breaker.

Thanks!