I am wanting to change out my 4 light vanity light fixture with a new one that centers over the mirror. I know they all have backing plates but question is, is the hole universally the same behind the backing plate to screw it on? This is a newer home.
and also, can I just turn off light switch to bathroom light or do I need to turn off breaker switch before changing?
Some homes will have whats referred to as a junction box where the wires from the house connect to the wires from the fixture. It’s usually a small round our square box plastic or metal mounted to a wall stud or sometimes secured with clips to the drywall. They usually have several places where you can attach the mounting plate for a new fixture then mount the fixture to the mounting plate. Not all homes are built with a junction box, some homes have the fixtures screwed right into the wall and are hardwired. In this case you would install a junction box yourself, the are referred to as an "old work junction box" because the home isn’t "new work" or being built. They are cheap and very easy to install. Your home being new will most likely have a junction box. All fixtures come with instructions on how to install, follow them closely but be prepared to adapt to a unique situation with your particular home setup. All builders do different things so many homes are slightly different. As far as the power, you need to turn off the switch as well as the power at the power panel. I always flip the main switch and kill power to the whole house. An electrician will use a voltage meter to check the wire and make sure it’s dead, I am not an electrician but I use this same technique because getting shocked once is enough. Good luck.
You should turn off the circuit breaker. Turning off the light switch alone may, or may not, interrupt the "hot" wire, but you could still have voltage on the "neutral" from other devices on the same circuit.
There’s no way of knowing what’s behind the fixture without looking. In my house, the builder got away with just a hole in the drywall. (The inspector should not have passed it, in my opinion.)
yes it is. its just a junction box where the wires come from the breaker and they have been a standard for a long time. just turn off the light switch and the power will be off. if you want to be extra safe turn off the breaker, but there is no need to.