The Definition of Minimum Approach Distance (MAD)

Definition of Minimum Approach Distance (MAD)

Minimum approach distance (MAD) is the closest distance that a worker, along with any tool, conductive object or piece of equipment they are using, may come to an exposed energized electrical conductor or circuit part. Staying outside the MAD prevents electricity from arcing across the air gap to the worker, which can cause severe burns, electrocution or an arc flash.

The MAD increases with voltage. Higher voltages can jump across larger air gaps, so the required distance grows as the system voltage rises. Elevation above sea level, transient overvoltages and the type of work being done can also affect the distance.

In the United States, OSHA sets minimum approach distances for qualified electrical workers in 29 CFR 1910.269 (electric power generation, transmission and distribution) and 29 CFR 1926 Subpart V (construction). NFPA 70E uses related concepts called the limited and restricted approach boundaries. For cranes and other equipment working near power lines, OSHA's crane standard sets separate minimum clearance distances, such as 20 feet for lines up to 350 kV, unless specific procedures are followed.

Who MAD Applies To

Qualified electrical workers

Only qualified workers, who have training in recognizing and controlling electrical hazards, may approach energized parts closer than the general clearance distances. They must still stay outside the MAD unless they are protected by insulating gloves and sleeves, insulated barriers or other approved methods, or the line is de-energized and grounded.

Unqualified workers and equipment operators

Workers who are not electrically qualified must stay well back, typically at least 10 feet from overhead lines up to 50 kV, with greater distances for higher voltages. Crane, excavator, dump truck, MEWP and boom operators must plan work so that no part of the machine, load or rigging can come closer than the required distance.

Controlling Risks Near Energized Lines

• Identify: locate and identify overhead and underground lines and their voltages before work begins. See underground utility locate.
• De-energize: where possible, have the utility de-energize and ground the lines.
• Maintain distance: mark the MAD or clearance zone with flags, tape or range limiters.
• Use spotters: assign a dedicated observer to watch clearances when equipment works near lines.
• Use insulating equipment: qualified workers use rated gloves, sleeves, line hoses and covers.
• Plan the job: include MAD in the job briefing and job hazard analysis.

Example of Minimum Approach Distance

A tree care crew was hired to trim branches near a 13.8 kV distribution line. The crew lead checked the voltage with the utility and confirmed that the crew's tree workers were not line-clearance qualified. The required clearance for unqualified workers was at least 10 feet.

Because some branches were within that distance, the crew lead arranged for a line-clearance qualified crew from the utility to handle those limbs. The rest of the work was done with a spotter watching the bucket truck's boom and a marked limit on how close it could approach the line.

Frequently Asked Questions: Minimum Approach Distance

Does MAD include tools and equipment?

Yes. The distance applies to the worker and anything they are holding or operating, including tools, ladders, booms and loads.

Is MAD the same for all voltages?

No. The minimum approach distance increases as voltage increases. OSHA tables list distances for different voltage ranges.

Can an unqualified worker work inside the MAD?

No. Only qualified electrical workers using approved protective methods may work closer than the required distances.