The National Electric Code governs the standards for installation of residential electric devices, and it has little to say about the standard height for light switches. The Americans with Disabilities Act is more specific about placing switches, and most electricians follow its guidelines, especially for new installations. If you're making renovations, it's wise to comply with ADA requirements to ensure universal accessibility.
Article 404 of the NEC
The only location requirements specified in Article 404 -- the section of the NEC that elucidates standards for switch installation -- are that switches must be in readily accessible locations and can be no higher above the floor than 6 feet, 7 inches, almost the height of a standard door frame. You can mount a switch higher than that if it's next to the equipment it controls and you have have a portable means of accessing it. The NEC sets no minimum height requirement for switches.
As far as the ADA is concerned, switches must be accessible to people in wheelchairs. The Fair Housing Accessibility Guidelines, which are based on ADA guidelines, set these requirements for switch locations:
- The height from the floor to the middle of the switch plate should not exceed 48 inches, and the minimum height should not be less than 15 inches.
- When the switch is over a counter that has a knee space, and the counter depth exceeds 20 inches, the maximum height of a switch is reduced to 44 inches.
- If the counter has no knee space, the counter width shouldn't exceed 24 inches, and the maximum height of the switch is 46 inches.
The ADA guidelines are written to make switches accessible to everyone, including children and people in wheelchairs, so most electricians conform to them. When measuring for the switch box, which has a height of 4 inches, it's acceptable to measure the distance from the top or center of the box to the floor, but not the bottom, since that places the actual switch higher than the ADA recommendations.
In the case of switches in a workshop or garage where conformity with ADA guidelines isn't an issue, many woodworkers prefer to set them 52 inches above the floor so a sheet of plywood leaning against the wall fits underneath the switch.