GFCI nuisance tripping

[geddy]

Both my bathroom are on the same circuit, which is protected by a 15 amp GFCI circuit breaker.

In the past few months the breaker has been tripping ever week or so, seemingly at random (ie it doesn't happen when someone is using a hairdryer, etc).

Possible causes
1) A few months ago I added a couple of light fixtures, circuit could now be too long.
2) 25-year-old GFCI breaker could have worn out. How to test? Replacements are $40-$50!
3) Short in the wiring. With the breaker tripped, I get a reading of 4 ohms resistance between ground and hot where the wiring enters the bathroom (and the wiring within the bathrooms disconnected). Is this normal? Shouldn't it be infinity? In general, what resistance should I be getting between ground/hot/neutral? Does it matter if the circuit is energized or not? Or if there is a GFCI breaker as opposed to a regular breaker?

Thanks for any help!

[kactuskid]

Well, first off it's not allowed to add any lighting on that bathroom circuit. Since this dedicated circuit supplies power to BOTH bathroom receptacels, no lighting in these bathrooms or anywhere else is allowed to be on this same circuit.

Sometimes ligting on a GFCI protected circuit can cause leakage current which will trip a GFCI. Remove the lighting loads and I bet your problem goes away.

Here's a link to the codes that are involved concerning bathrooms. Scroll to the last part of the page for the info.

http://www.selfhelpandmore.com/homewiringusa/2002/maindwelling/newdwel/index.htm

[geddy]

Thanks for the reply.

What about the pre-existing lighting and fans, all of which are on the same 15 amp circuit with the receptacles? Is this OK because it was grandfathered in? But if I want to add a single new light fixture, I'm going to have to install a new circuit?

Also how can I test the leakage current with a simple multimeter?