2.4 Approach distances, signs, barricades and attendants
The boundary between qualified and unqualified is only useful if it exists in space. This chapter is the tape measure: the 10-foot rule and where it actually comes from, the shorter distances a qualified person may use, the rules for anything with a boom or a mast, and the three things 1910.335(b) allows an employer to use to make the line visible — signs, barricades and a person.
1 Start with the real requirement: deenergize the line
Approach distances are a fallback, and it is worth reading the paragraph they sit inside. 29 CFR 1910.333(c)(3): "If work is to be performed near overhead lines, the lines shall be deenergized and grounded, or other protective measures shall be provided before work is started." If the lines are to be deenergized, arrangements are made with the person or organization that operates the circuits. If protective measures — guarding, isolating or insulating — are used instead, those precautions must prevent employees from contacting the lines directly or indirectly through conductive materials, tools or equipment.
Distance is what remains when the utility has not been called and nothing has been guarded. It is the weakest control in the paragraph, and it is the one most sites rely on.
2 The 10-foot rule, precisely
1910.333(c)(3)(i)(A) covers unqualified persons in an elevated position near overhead lines: the location must be such that the person and the longest conductive object he or she may contact cannot come closer to any unguarded, energized overhead line than 10 feet for voltages to ground of 50 kV or below, and 10 feet plus 4 inches for every 10 kV above 50 kV. (B) applies the same distances to an unqualified person working on the ground: no conductive object closer than those distances.
Two details do the work. "The longest conductive object he or she may contact" means the measurement is not from your body — it is from the end of the level, the pipe, the gutter, the rebar, the tape on the aluminum pole. And a note to the paragraph closes the last loophole: "For voltages normally encountered with overhead power lines, objects which do not have an insulating rating for the voltage involved are considered to be conductive." A fiberglass ladder without a rating is, for this purpose, conductive.
3 Table S-5: the qualified person's distances
A qualified person working in the vicinity of overhead lines may not approach, or take any conductive object without an approved insulating handle closer to exposed energized parts than Table S-5 allows — unless the person is insulated from the energized part, the part is insulated from the person and from other conductive objects at a different potential, or the person is insulated from all conductive objects at a different potential (1910.333(c)(3)(ii)).
| Voltage range (phase to phase) | Minimum approach distance |
|---|---|
| 300 V and less | Avoid contact |
| Over 300 V, not over 750 V | 1 ft 0 in |
| Over 750 V, not over 2 kV | 1 ft 6 in |
| Over 2 kV, not over 15 kV | 2 ft 0 in |
| Over 15 kV, not over 37 kV | 3 ft 0 in |
| Over 37 kV, not over 87.5 kV | 3 ft 6 in |
| Over 87.5 kV, not over 121 kV | 4 ft 0 in |
| Over 121 kV, not over 140 kV | 4 ft 6 in |
Look at the top row. At 300 volts and less the standard does not give a number; it says avoid contact. That is not permission to work inches away casually — it is the recognition that at those voltages the injury mechanism is contact, and the control is insulation and technique rather than air gap. These are also the distances a qualified person must know by 1910.332(b)(3), together with the voltages they will be exposed to.
4 Anything with a boom, a mast or a bed
1910.333(c)(3)(iii)(A) covers any vehicle or mechanical equipment capable of having parts of its structure elevated near energized overhead lines: it is operated so that a clearance of 10 feet is maintained, increased 4 inches for every 10 kV above 50 kV. The clearance may be reduced only in three named situations.
- 1In transit, structure lowered — 4 feet. Still increased above 50 kV. Driving through with the boom down is not the same as working with it up.
- 2Insulating barriers installed. Rated for the voltage of the line being guarded, and not part of or attached to the vehicle or its raised structure. Then the clearance may be reduced to within the barrier's designed working dimensions.
- 3An aerial lift insulated for the voltage, worked by a qualified person. Only then does the clearance between the uninsulated portion of the lift and the line drop to Table S-5.
And there is a rule for everyone standing near that machine, which crews almost never hear: under (c)(3)(iii)(B), employees on the ground may not contact the vehicle, the equipment or any of its attachments unless they are using protective equipment rated for the voltage, or the equipment is positioned so that no uninsulated part of its structure can come closer to the line than allowed. If a boom contacts a line, the ground man holding the tag line is in the circuit.
5 Making the boundary visible: 1910.335(b)
Indoors there is no overhead-line distance to apply, so the standard reaches for alerting techniques instead. 1910.335(b) gives three, in escalating order.
| Technique | What the standard says |
|---|---|
| (b)(1) Safety signs and tags | Safety signs, safety symbols or accident prevention tags are used where necessary to warn employees about electrical hazards which may endanger them. |
| (b)(2) Barricades | Barricades are used with safety signs where it is necessary to prevent or limit employee access to work areas exposing employees to uninsulated energized conductors or circuit parts. Conductive barricades may not be used where they might cause an electrical contact hazard. |
| (b)(3) Attendants | Where signs and barricades do not provide sufficient warning and protection from electrical hazards, an attendant is stationed to warn and protect employees. |
The escalation is the point. A sign informs, a barricade obstructs, a person judges. When the qualified person on the job says "I need somebody on the door", that is (b)(3), not a favor.
6 The space in front of the panel
One last distance, and it is the one most often violated by people who never touch electricity. 1910.303(g)(1)(i)(B) sets the width of the working space in front of electric equipment at the width of the equipment or 30 inches, whichever is greater, and requires the space to permit at least a 90-degree opening of equipment doors or hinged panels. (g)(1)(ii) is blunt: "Working space required by this standard may not be used for storage." (g)(1)(v) requires illumination of the working space around service equipment, switchboards, panelboards and motor control centers installed indoors.
Pallets in front of a panel, a rack of material against a motor control center, a job box parked in an electrical room — those are not housekeeping complaints. They are the reason a qualified person cannot stand where they need to stand, or get out of the way when something goes wrong.
- The first requirement near overhead lines is to deenergize and ground them, or to guard, isolate or insulate — distance is the fallback (1910.333(c)(3)).
- Unqualified persons: 10 feet at 50 kV or below, plus 4 inches per 10 kV above, measured from the longest conductive object they may contact (1910.333(c)(3)(i)(A)).
- Unrated objects are treated as conductive for voltages normally found on overhead lines.
- Table S-5 gives qualified persons shorter distances, starting at "avoid contact" for 300 V and less — and 1910.332(b)(3) requires them to know it.
- Vehicles and booms keep 10 feet; the reduction to 4 feet applies only in transit with the structure lowered, and ground personnel may not touch the machine.
- Indoors the boundary is signs, then barricades, then an attendant (1910.335(b)) — and the working space in front of a panel is 30 inches minimum and may never be used for storage.
Free educational content — not OSHA-authorized training, no certificate or card issued. Follow your employer's program and the standards cited.