We recently ran a 10-3 line from our house panel to a sub panel in our
barn, using a 30-amp GFCI circuit breaker.

I have since run two separate 12-2 cable lines from the barn's sub
panel to outdoor outlets.

I was planning on putting in two 15-amp GFCI circuit breakers to
protect the lines. I realize I could also use GFCI outlets (putting
them first in line), but went with the breakers instead.

1. Since the entire sub panel is protected, do I need any GFCI
protection in these two lines, or is the sub panel protection good
enough?

2. Is there any issue with using GFCI breakers in a panel protected by
a GFCI breaker? In other words, since the main line to the barn's sub
panel is protected, can I use GFCI breakers in the barn's sub panel?

THANKS in advance...

We recently ran a 10-3 line from our house panel to a sub panel in our
barn, using a 30-amp GFCI circuit breaker.

Years ago we did the same thing but everytime I tried to use a circular hand
saw it popped the breaker. We had to remove the gfci from the main panel and
used 20amp gfci's in the garage for each line with no problem.

According to Jim :

I was planning on putting in two 15-amp GFCI circuit breakers to
protect the lines. I realize I could also use GFCI outlets (putting
them first in line), but went with the breakers instead.

1. Since the entire sub panel is protected, do I need any GFCI
protection in these two lines, or is the sub panel protection good
enough?

The sub panel protection is good enough, you don't need extras.

2. Is there any issue with using GFCI breakers in a panel protected by
a GFCI breaker? In other words, since the main line to the barn's sub
panel is protected, can I use GFCI breakers in the barn's sub panel?

You _can_ have both "layers", but you don't have to.

They won't "interact". It should work fine. If you get tripping problems,
something is wrong (or miswired).
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Sub Panel protection is good enough. GFCI devices measure the current going
through the hot leg and returning on the neutral. If an imbalance exists, it
will trip.

Electric motors will cause some havoc with some GFCI devices, but I've
always found the breakers to be more reliable than outlet-based GFCI.

Jake

According to Jake :
Sub Panel protection is good enough. GFCI devices measure the current going
through the hot leg and returning on the neutral. If an imbalance exists, it
will trip.

Dual GFCI's (the subpanel feed breaker) aren't quite that simple.

They need to measure the two hots and neutral current. If the current flow
through the neutral isn't the difference in current flow between the two hots,
_then_ they trip.

It's probably also worthy of note that if a 4-wire supplied/GFCI'd subpanel
has the neutral-ground bond strap installed, the GFCI will always trip. If
the subpanel's neutral current has any other path back to the main panel other
than thru the GFCI neutral (eg: a ground wire in parallel), it won't stay
untripped (except when the subpanel isn't supplying anything).

Electric motors will cause some havoc with some GFCI devices, but I've
always found the breakers to be more reliable than outlet-based GFCI.

"Will sometimes cause". Under certain conditions electric motors can occasionally
cause nuisance trips. But if it's anything even remotely close to "consistently
causing trips", there's a problem with the motor (or, less likely, the GFCI).
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.