In article ,
bob haller wrote:

On Thursday, March 10, 2016 at 9:40:36 AM UTC-5, Wade Garrett wrote:
1979-built house, two bathrooms sharing a common wall, one plain
electrical outlet in each bathroom. Both outlets are on the same
circuit; i.e., one circuit breaker kills them both.

I want to install GFCI protection. Do I need to install one in each
bathroom?

Or is the downstream one protected by its upstream brother? If yes, how
do I determine which one is first in the circuit?

--
Wise men speak because they have something to say; fools because they
have to say something.
? Plato

its best to install a GFCI outlet at each location.

if just one feeds both bathrooms, in a failure mode your stuck.

no hair dryer for you

I agree. My downstairs GFCI feeds the upstairs bathroom.

To determine which feeds the other, look to see which outlet has two
pairs of wires. One comes from the breaker, the other goes to the
second outlet. Then you need to determine which pair comes from the
breaker, so you don't connect the GFCI backwards.

But what if both outlets have two sets of wires? In that case you have
additional outlets, and would have to disconnect one and see if the
other is dead when the breaker is restored.

Fred