I have a older home that I just purchased. The bathroom has a light that is controlled by a switch. I need to add an gfci outlet. How can I do this to make the switch operate the light without effecting the new gfci outlet? There is one wire going to the switch (black, white and Ground).

Stratmando

It is possible that a constant hot, neutral and ground is at light fixture. The one cable to switch comes from power to switch,and back to light.
You may be able to fish wire from light to new recepticle.

icecream

i would start there.

donf

Russ,

A word about safety here. Please do not be fooled by the wire from the overhead to the switch. A switch ONLY carries load voltages, therefor both the black and the white wires are hot. (There should be a small wrap of black, red or blue tape around the white wire to signify that it is a load carrying wire not a neutral return. If there isn't any marking, put one there. It's for your safety.) In general, the overhead light will be on a 15 Amp Circuit. What is the amperage rating of the GFCI outlet that you want to install?

The reason I ask is if it is 20 Amp, then you may want to consider having an licensed electrician pull a permit, if required, and pull a 20 Amp line from the panel box to the where you want the GFCI.

Typically outlets and lights are on different circuits with power brought to the ceiling and a switch loop brings the load from the ceiling to the switch and then to the overhead light.
You may want to consult with an Electrical Inspector or a licensed electrician about whether or not you would be violating the NEC code if you pigtail the GFCI outlet to the 15 Amp source in the ceiling.

Stratmando

We can't use #14/15 Amp down here. To do so would be code violation. It is possible that it is #14. If bath light on circuit with other lighting, You may consider trying to get #12
to new bath recpticle. A Hair dryer will not trip circuit.