I have a 240v radial arm saw powered by a 240v outlet installed by a licensed electrician. This outlet is powered by 2 20 amp breakers ganged at the panel. The wire to the 240v outlet only has 3 wires. 2 are insulated (white and grey) and the third is a bare ground wire. There are 120v between each insulated wire and the bare ground wire. Can I add a 120v outlet by splicing it to one of the insulated wires and the bare ground wire or is this unsafe because I actually need an insulated neutral wire plus the bare copper ground wire?
Welcome to the community.
No. you need another insulated neutral wire. You should not use a ground wire as neutral, and you should not use bare wire as a current carrying conductor.