Installing Separate Switches for a Bathroom Exhaust Fan/Light Combo and a Vanity Light
February 16, 2007
We get called out a lot and receive numerous emails for this type of project. This is a pretty simple project to complete.
The first thing you need to do is check with your local building codes department to ensure you are able to do this work legally. Some areas allow homeowners to complete electrical wiring projects on their own homes and others areas have restrictions.
The next step is to turn off the power to this circuit and verify the power is off with a voltage tester.
There are a few ways you can do this. The first depends on your existing switch box’s cubic inch size and amount of wires currently in the box. There are numerous different single box sizes. If you are unsure if your box is full, look at the back of your box and you will find a cubic inch rating. You may submit this information along with the number and size of your wires that are currently in this box in the comment section of this post and I will calculate this for you.
Typically, the power is run from the switch to the vanity light and then to the exhaust fan. If the switch box is not full, I would remove the 2 conductor cable going to the vanity light and install a new 3 conductor cable with a ground. If there is attic space above or an unfinished basement or crawl space below, you can fish the wires. If not, then you need to open up some sheetrock.
Terminating these wires depends on your existing wiring. If the power originates in the switch box, splice the grounds (bare copper wires) together and leave a pigtail to attach to the switch. Next splice the neutrals (white wires) together. Now connect the red wire to the switch that will operate your vanity light and the black wire to the new switch for your exhaust fan. Use the existing hot wire to supply power to both switches.
In the vanity light box, splice the grounds together and attach to the ground wire on the light fixture. Splice all of the neutrals together and connect to the neutral wire on the light fixture. The black wires will splice together and tuck back into the box. Finally, connect the red wire to the vanity light.
If the power originates in the vanity light box, then you need to mark the white wire as a hot and use it to supply power to both switches. The easiest way to mark the white wire as a hot is with a black permanent marker or black electrical tape. This wire needs to be marked in both boxes or on both ends. The red wire will terminate to the switch for the vanity light and the black wire will terminate to the new switch for the exhaust fan.
In the vanity light box, the grounds splice together and connect to the ground wire on the light fixture. The neutral from your power supply cable and to the fan splice together and connect to the neutral on the light fixture. The black from the 3 conductor cable will splice to the black wire going to the fan and tuck back into the box. The red wire from the 3 conductor cable connects to the light. Finally, the white wire from the 3 conductor, that you marked as a hot will splice to the black power supply wire.
If you existing switch box is full, you need to remove it and install a larger box. Now just run either a 2 conductor or 3 conductor cable to the exhaust fan/light combo. If you run a 2 conductor cable, your fan and light will come on at the same time. If you run a 3 conductor cable, you can switch the fan and light separately. I recommend the 3 conductor cable. You don’t need to switch the fan and light separately, but this gives you the option to do so at a later date.
As for the switch, I recommend a spring wound timer or other type of fan rated timer switch. The timer switch will allow you to turn it on to remove odors or steam and it will automatically turn off after a set period of time.
If you need further assistance with this project, please submit your questions in the comment section of this post.
Do you need assistance with your electrical wiring project? Please visit my DIY Electrical Wiring Help from a Master Electrician page. Where I provide electrical wiring tips, expert electrical advice, answers to your electrical questions and electrical consulting & design services over the phone, via instant messenger or via email.
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