I want to add an exhaust fan to my bathroom. Do I run power from the light switch to power the fan or do I run power from the light box. Thanks as of now there is a single pole do i use a double pole switch?![enter image d)
Answer from the UK but the principles should apply wherever.
You usually want switched live, permanent live and neutral (+ earth) going to the fan via a three-pole isolating switch. The permanent live is optional but lets you use a fan with a timer or humidistat that runs even when the light is off. The switch allows you to work safely on the fan without turning off power to the entire house and lets you turn it off temporarily if the fan ever breaks while still being able to use the light. The isolator would typically be located high up on a wall or in the ceiling, out of reach of bumps and splashes, and less intrusive visually.