For lines rated over 50 kV, Washington State Legislature requires 10 feet plus 4/10 inch for each 1 kV over 50 kV.
Key takeaways
- The base distance for lines rated 50 kV or below is 10 feet, as stated in WAC 296-155-77100 according to Washington State Legislature.
- Once the line voltage exceeds 50 kV, the minimum clearance must be 10 feet plus 4/10 inch for each 1 kV over 50 kV, or twice the length of the line insulator, but never less than 10 feet, according to Washington State Legislature.
- For equipment in transit with no load and the boom lowered, the minimum clearance is 4 feet for voltages less than 50 kV, 10 feet for voltages over 50 kV up to and including 345 kV, and 16 feet for voltages up to and including 750 kV, according to Washington State Legislature.
- Write the line location, the clearance you marked, and which page you used before the boom moves.
How far equipment stays from an overhead line
For lines rated 50 kV or below, the minimum clearance between the lines and any part of the equipment or load must be 10 feet, according to Washington State Legislature. This distance applies to the space between the overhead line and any part of the equipment or load. When the line is rated over 50 kV, the minimum clearance is 10 feet plus 4/10 inch for each 1 kV over 50 kV, according to Washington State Legislature. The source also states this clearance can be twice the length of the line insulator, but never less than 10 feet. Write the specific voltage rating you were given for the line before calculating the extra distance. If the voltage is 51 kV, add 4/10 inch to the 10-foot base. Do not treat the portable-ladder rule in Portable ladder checks: 4 steps before climbing as this equipment rule. The numbers here apply to equipment or loads near overhead lines. Mark the clearance on your plan before the boom moves. Use the page you consulted to verify the voltage rating. Record the line location and the clearance you marked. This check belongs in your Construction Daily Log Checklist for Supervisors.
The base clearance up to 50 kilovolts
When the power line voltage is 50 kV or below, the restricted space around the line sets a specific minimum distance for any part of your equipment or load. You must mark this distance on your site plan before the boom or crane moves.
According to Washington State Legislature, for lines rated 50 kV or below, the minimum clearance between the lines and any part of the equipment or load must be 10 feet. You should write this 10-foot figure on your daily log to confirm the restricted area is understood by the crew. The quote specifies the minimum clearance directly between the line and the equipment or load.
Similarly, the Oregon Occupational Safety and Health Division states that for lines rated more than 600 V to 50 kV, restricted space extends 10 feet in all directions from the surface of the line or equipment. This definition establishes a spherical or cylindrical zone of protection around the line itself. The phrase "in all directions" indicates that the 10-foot distance applies horizontally and vertically from the line's surface.
Washington State Legislature prints 10 feet for lines rated 50 kV or below, and Oregon Occupational Safety and Health Division prints 10 feet for lines rated more than 600 V to 50 kV. However, you must keep the claim tied to the specific source you are using for your jurisdiction. Do not treat one publisher's number as every other publisher's number without checking the local text. The Washington State Legislature quote focuses on the minimum clearance between lines and equipment, while the Oregon Occupational Safety and Health Division quote describes the restricted space extending from the line surface.
The extra distance once the line is over 50 kilovolts
When the overhead line rating exceeds 50 kilovolts, the required clearance increases beyond the standard base distance. The Washington State Legislature specifies that for lines rated over 50 kV, the minimum clearance between the lines and any part of the equipment or load must be 10 feet plus 4/10 inch for each 1 kV over 50 kV, or twice the length of the line insulator, but never less than 10 feet, according to Washington State Legislature. This calculation requires adding the incremental distance for every kilovolt above the 50 kV threshold to the 10-foot baseline. The alternative measurement of twice the line insulator length provides a second way to determine the minimum space, with the 10-foot floor applying to both methods.
The Oregon Occupational Safety and Health Division presents a similar structure for its restricted space definition. For lines rated over 50 kV, the restricted space extends 10 feet plus 0.4 inch for each 1 kV over 50 kV, or twice the length of the insulator, but never less than 10 feet in all directions from the surface of the line or equipment, according to Oregon Occupational Safety and Health Division. Note that the Oregon rule uses the decimal value 0.4 inch for the incremental addition, whereas the Washington rule uses the fraction 4/10 inch. Both sources maintain the 10-foot minimum and the option to use twice the insulator length as the determining factor.
To mark the clearance for your specific job, identify the exact voltage of the line you are working near. If that voltage is above 50 kV, calculate the additional inches required by multiplying the amount over 50 kV by the specific incremental value printed in the source you are using. Write this calculated distance on your site plan. Do not assume the incremental value is identical across all jurisdictions; the specific number must come from the applicable rule text for your location. If you are using the Washington State Legislature text, use the 4/10 inch figure. If you are using the Oregon Occupational Safety and Health Division text, use the 0.4 inch figure. Record the source page you used so the number is traceable.
How to calculate the add-on
- Determine the voltage of the overhead line.
- Subtract 50 kV from that voltage to find the excess.
- Multiply the excess by the incremental value (4/10 inch or 0.4 inch) specified in your source.
- Add this result to the 10-foot base distance.
- Or use twice the length of the line insulator.
- Use either the 10-foot-plus-increment result or twice the insulator length, and do not use a distance under 10 feet.
Keep the calculation visible to the operator and the spotter.
Illustrative example of the add-on
Suppose the voltage you were given is 70 kV. Subtract 50 kV and the excess is 20 kV. Multiply 20 by 4/10 inch. The add-on in this illustration is 8 inches. Add that add-on to the 10-foot base, which gives 10 feet plus 8 inches. This illustration uses round figures only, and it does not apply twice the length of the line insulator. It is not a clearance for a real line. Check the page you consulted before you mark the plan.
Reference table of clearance numbers
The following table lists the specific clearance distances printed by each publisher for equipment near overhead lines. Each row is built strictly from the quoted facts for that specific source.
| publisher | base distance it prints | add-on above 50 kilovolts | any transit or watch rule it prints |
|---|---|---|---|
| Washington State Legislature | 10 feet for lines rated 50 kV or below | 4/10 inch for each 1 kV over 50 kV, or twice the length of the line insulator, but never less than 10 feet | 4 feet for voltages less than 50 kV; 10 feet for voltages over 50 kV up to and including 345 kV; 16 feet for voltages up to and including 750 kV |
| Oregon Occupational Safety and Health Division | 10 feet for lines rated more than 600 V to 50 kV | 0.4 inch for each 1 kV over 50 kV, or twice the length of the insulator, but never less than 10 feet | 4 feet for lines rated 50 kV or less; 10 feet for lines rated over 50 kV; 16 feet for lines rated over 345 kV up to and including 750 kV |
Washington State Legislature prints a base clearance of 10 feet for lines rated 50 kV or below, according to Washington State Legislature. For lines rated over 50 kV, that source requires 10 feet plus 4/10 inch for each 1 kV over 50 kV, or twice the length of the line insulator, but never less than 10 feet, according to Washington State Legislature. In transit with no load and boom lowered, the equipment clearance must be a minimum of 4 feet for voltages less than 50 kV, and 10 feet for voltages over 50 kV up to and including 345 kV, and 16 feet for voltages up to and including 750 kV, according to Washington State Legislature.
Transit distances and the person who watches the gap
When the boom is lowered and the equipment carries no load, the required separation changes. Washington State Legislature specifies that in transit, the minimum clearance is 4 feet for voltages less than 50 kV, 10 feet for voltages over 50 kV up to and including 345 kV, and 16 feet for voltages up to and including 750 kV, according to Washington State Legislature. Oregon Occupational Safety and Health Division defines restricted space for equipment or structures in transit on level surfaces as extending 4 feet in all directions from lines or equipment rated 50 kV or less, 10 feet in all directions for lines or equipment rated over 50 kV, and 16 feet in all directions for lines or equipment rated over 345 kV up to and including 750 kV, according to Oregon Occupational Safety and Health Division.
Visual confirmation is not always possible for the operator. Washington State Legislature requires designating a person to observe clearance of the equipment and give timely warning to insure that the required separation is maintained for all operators where it is difficult for the operator to maintain the desired clearance by visual means, according to Washington State Legislature. This observer role applies specifically when the operator cannot visually maintain the desired clearance. The transit distances and the observer requirement are distinct from the working clearance rules covered in other sections.
A blank line for today's line clearance check
Today, write the line location, the voltage you were given, the clearance you marked, and the page you used. The federal crane page prints a twenty-foot option for determining if equipment could get closer to a power line, according to Legal Information Institute. Use that page if your check involves a boom or load moving near the line.
FAQ about equipment near overhead lines
What distance applies up to 50 kilovolts?
For lines rated 50 kV or below, the minimum clearance between the lines and any part of the equipment or load must be 10 feet according to Washington State Legislature. This 10-foot requirement applies to the equipment and the load during operations within the work zone.
What is added above that voltage?
Over 50 kV, Washington State Legislature requires 10 feet plus 4/10 inch for each 1 kV over 50 kV, or twice the line insulator, but never less than 10 feet, and Oregon Occupational Safety and Health Division requires 10 feet plus 0.4 inch for each 1 kV over 50 kV, or twice the insulator, but never less than 10 feet.
How does transit differ?
In transit with no load and boom lowered, the equipment clearance must be a minimum of 4 feet for voltages less than 50 kV according to Washington State Legislature. For voltages over 50 kV up to and including 345 kV, the transit clearance is 10 feet, and for voltages up to and including 750 kV, it is 16 feet according to Washington State Legislature.
Who watches the gap?
You must designate a person to observe clearance of the equipment and give timely warning to insure that the required separation is maintained for all operators where it is difficult for the operator to maintain the desired clearance by visual means according to Washington State Legislature. This observer role is required when visual monitoring by the operator is insufficient.
What to write down today?
Write the line location, the voltage you were given, the clearance you marked, and the page you used.