Electrical minimum safe approach distances, sometimes referred to as MAD, are used to ensure workers do not approach or bring any conductive items too close to energized machines or energized parts. It is a central element of OSHA’s standard for Electric Power Generation, Transmission and Distribution and employers have the responsibility to establish minimum approach distances based on OSHA’s formula for voltages over 72.6 kilovolts (29 CFR 1910.269).
This easy-to-use calculator will help you determine that distance in three simple steps:
First, select your units of measurement: meters or feet. Next, enter the maximum phase-to-phase system voltage (the max. transient overvoltage can be found by using the table below or conducting an engineering analysis) and the altitude of the worksite. Finally, check the last two boxes accordingly to get your results.
(1) Enter the maximum anticipated per-unit transient overvoltage, phase-to-ground, determined through an engineering analysis or assume a maximum anticipated per-unit transient overvoltage, phase-to-ground, by the following table:
Phase-to-ground Distance: (in meters)
Phase-to-phase Distance (in meters)
|Voltage range (kV)||Assumed maximum per-unit transient overvoltage|
|72.6 to 420.0||3.5|
|420.1 to 550.0||3.0|
|550.1 to 800.0||2.5|
* Accessibility Assistance: Contact OSHA's Directorate of Standards and Guidance at (202) 693-1950 for assistance accessing this content.
The calculator will output the minimum approach distance for both phase-to-ground and phase-to-phase exposures. This is the closest distance a worker can approach an energized or grounded object and the closest distance a Qualified Electrical Worker can perform job tasks unprotected.
Qualified employees are allowed to complete work past the minimum approach distance and must be trained on the skills and techniques to maintain the distance. Additionally, they will need to be prepared for working closely around energized equipment. Employers must provide workers with the necessary personal protective equipment which typically includes insulated gloves, insulated work boots, and insulated coveralls.
When reducing electrical hazards, remember:
- All other workers, whether they’re a manager or an operator, are required to keep a distance of 10 feet for energized conductors 50 kilovolts or less.
- Without insulated tools and PPE, qualified personnel must maintain minimum approach distances.
- Work sites at a higher elevation will likely have reduced air pressure. This means minimum approach distances will need to be increased accordingly.