I have 3 bathrooms with 9 lights. Can I use one 15A breaker for 3 bathrooms?
What you can do and what you should do are two different things.
I would put each bathroom on its own circuit. Follow Robert's advice and call an EC for a consult.
Datawise Solutions Inc
On any renovation my firm completes or build outs, I always run a separate circuit for each bathroom. A separate circuit for a wet bar. And one circuit for outlets in a kitchen on counters. As well as separate ones for appliances. Aside from separate amperage.
Better safe than sorry.
Plus if you are ever doing any reno or electrical work in one of the bathrooms in the future you will still have power in the other bathrooms.
The Short answer is yes. In most new build construction you will find 3 bathroom outlets all fed from one GFCI outlet located at the start of the line usually in the powder room. Builders use this technique to save having spend money on multiple GFCI's (which cost around $20 per outlet as compared to 89 cents for a regular outlet)
The only problem with this is that if you do trip the GFI, and you are in a different bathroom, you will have to go downstairs to the powder room and reset the outlet to get the power back on. Also the majority of home owners (and alot of contractors) don't realize the house is wired this way and end up calling a professional because they can't figure out why the power is off in there bathroom. I also see alot of homeowner installed GFCI outlets in these bathrooms where the circuit was already protected from the powder room.
Now to really answer your question, unless you are wiring the bathrooms as a money saving technique to only use one GFCI outlet to protect all 3 bathrooms, than this doesn't make a whole lot of sense to do it this way to me.
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