Determining Safe Distances from Electrical Hazards
How Close Can I Get To My Gear?
The first and most important thing to consider when being around electrical systems is to determine if a hazard is present.
A hazard is defined by the NFPA 70E as “A source of possible injury or damage to health”. There are two major hazards associated with electrical systems; Arc Flash and Electric Shock.
Electrical Shock
An Electric Shock Hazard is a “source of possible injury or damage to health associated with current through the body caused by contact or approach to energized electrical conductors or circuits”.
There are a couple considerations to make:
- Are there any exposed energized parts?
- Is the equipment in good condition?
- Has the equipment been routinely tested and had continuous maintenance?
If the equipment has no exposed energized parts, is in good condition and has had routine testing and maintenance then the equipment if most likely safe to approach by a qualified person. Who is a qualified person? A qualified person is defined by the NFPA 70E as a person “trained and knowledgeable in the construction and operation of equipment or a specific work method” and “trained to identify and avoid electrical hazards that might be present with respect to that equipment or work method. Only an employer can determine if someone is qualified.
50V or Less
For systems less than 50V, the NFPA 70E recognizes NO shock hazard.
50V – 750V
For systems that are 50V – 750V, there are two major shock boundaries when qualified people are working on or near exposed energized equipment.
- Limited Approach Boundary - The Limited Approach Boundary (LAB) is identified as the “distance from an exposed energized electrical conductor or circuit part within which a shock hazard exists”. Best practice if for any unqualified person to stay 42” (3’ 6”) or more away from the hazard. A qualified person should use protective shields and barriers to protect employees working within the LAB. Barriers should be used to help unqualified persons recognize a hazard is present and keep them from entering the LAB without being escorted by a qualified person.
- Restricted Approach Boundary - The Restricted Approach Boundary (RAB) is identified as the “distance from an exposed energized electrical conductor or circuit part within which there is an increased likelihood of electrical shock, due to arc-over combined with inadvertent movement”. Best practice is to stay 12” or more away from the hazard. This area should only be entered by qualified persons and the qualified person should be wearing Personal protective Equipment (PPE). Any work done within the 12” is considered energized work and requires an Energized Electrical Work Permit.
750V - <50kV
The LAB and RAB vary depending on voltage present. Best practice is to keep any unqualified person 10’ or more away from the hazard. Please see the chart below to determine these distances for the above identified voltages and greater:
NFPA 70E Table 130.4 (C) (a)
Approach Boundaries to Energized Electrical Conductors or Circuit Parts for Shock Protection for Alternating Current Systems (all dimensions are distances from energized electrical conductor or circuit parts to employee)
| (1) | (2) | (3) | (4) | (5) |
| Limited Approach Boundary b | ||||
| Nominal System Voltage Range, Phase to Phase4 | Exposed Movable Conductor | Fixes Circuit Part | Restricted Approach Boundaryb; Includes Inadvertent Movement Adder | Prohibited Approach Boundaryb |
| 50 V | Not Specified | Not Specified | Not Specified | Not Specified |
| 50 V — 300 V | 3.0 m (10 ft. 0 in.) | 1.0 m (3 ft. 6 in.) | Avoid Contact | Avoid Contact |
| 301 V — 750 V | 3.0 m (10 ft. 0 in.) | 1.0 m (3 ft. 6 in.) | 0.3 m (1 ft. 0 in.) | 25 mm (0 ft. 1 in.) |
| 751 V — 15 kV | 3.0 m (10 ft. 0 in.) | 1.5 m (5 ft. 0 in.) | 0.7 m (2 ft. 2 in.) | 0.2 m (0 ft. 7 in.) |
| 15.1 kV — 36 kV | 3.0 m (10 ft. 0 in.) | 1.8 m (6 ft. 0 in.) | 0.8 m (2 ft. 7 in.) | 0.3 m (0 ft. 10 in.) |
| 36.1 kV — 46 kV | 3.0 m (10 ft. 0 in.) | 2.5 m (8 ft. 0 in.) | 0.8 m (2 ft. 9 in.) | 0.4 m (1 ft. 5 in.) |
| 46.1 kV — 72.5 kV | 3.0 m (10 ft. 0 in.) | 2.5 m (8 ft. 0 in.) | 1.0 m (3 ft. 3 in.) | 0.7 m (2 ft. 2 in.) |
| 72.6 kV — 121 kV | 3.3 m (10 ft. 8 in.) | 2.5 m (8 ft. 0 in.) | 1.0 m (3 ft. 3 in.) | 0.8 m (2 ft. 9 in.) |
| 138 kV — 145 kV | 3.4 m (10 ft. 0 in.) | 3.0 m (10 ft. 0 in.) | 1.2 m (3 ft. 10 in.) | 1.0 m (1 ft. 4 in.) |
| 161 kV — 169 kV | 3.6 m (11 ft. 8 in.) | 3.6 m (11 ft. 8 in.) | 1.3 m (4 ft. 3 in.) | 1.1 m (3 ft. 9 in.) |
| 230 kV — 242 kV | 4.0 m (13 ft. 0 in.) | 4.0 m (13 ft. 0 in.) | 1.3 m (4 ft. 3 in.) | 1.6 m (5 ft. 2 in.) |
| 345 kV — 363 kV | 4.7 m (15 ft. 4 in.) | 4.7 m (15 ft. 4 in.) | 2.8 m (9 ft. 2 in.) | 2.6 m (8 ft. 8 in.) |
| 500 kV — 550 kV | 5.8 m (19 ft. 0 in.) | 5.8 m (19 ft. 0 in.) | 3.6 m (11 ft. 10 in.) | 3.5 m (11 ft. 4 in.) |
| 765 kV — 800 kV | 7.2 m (23 ft. 9 in.) | 7.2 m (23 ft. 9 in.) | 4.9 m (15 ft. 11 in.) | 4.7 m (15 ft. 5 in.) |
NFPA 70E Table 130.4 (C) (a)
Approach Boundaries to Energized Electrical Conductors or Circuit Parts for Shock Protection for Direct Current Voltage Systems
| (1) | (2) | (3) | (4) | (5) |
| Limited Approach Boundary b | ||||
| Nominal System Voltage Range, Phase to Phase4 | Exposed Movable Conductor | Fixes Circuit Part | Restricted Approach Boundaryb; Includes Inadvertent Movement Adder | Prohibited Approach Boundaryb |
| <100 V | Not Specified | Not Specified | Not Specified | Not Specified |
| 100 V — 300 V | 3.0 m (10 ft. 0 in.) | 1.0 m (3 ft. 6 in.) | Avoid Contact | Avoid Contact |
| 301 V — 1 kV | 3.0 m (10 ft. 0 in.) | 1.0 m (3 ft. 6 in.) | 0.3 m (1 ft. 0 in.) | 25 mm (0 ft. 1 in.) |
| 1.1 kV — 5 kV | 3.0 m (10 ft. 0 in.) | 1.5 m (5 ft. 0 in.) | 0.5 m (1 ft.5 in.) | 0.1 m (0 ft. 4 in.) |
| 5.1 kV — 15 kV | 3.0 m (10 ft. 0 in.) | 1.5 m (5 ft. 0 in.) | 0.7 m (2 ft. 2 in.) | 0.2 m (0 ft. 7 in.) |
| 15.1 kV — 45 kV | 3.0 m (10 ft. 0 in.) | 2.5 m (8 ft. 0 in.) | 0.8 m (2 ft. 9 in.) | 0.4 m (1 ft. 5 in.) |
| 45.1 kV — 75 kV | 3.0 m (10 ft. 0 in.) | 2.5 m (8 ft. 0 in.) | 1.0 m (3 ft. 3 in.) | 0.7 m (2 ft. 2 in.) |
| 75.1 kV — 150 kV | 3.3 m (10 ft. 8 in.) | 3.0 m (10 ft. 0 in.) | 1.2 m (4 ft. 0 in.) | 1.0 m (3 ft. 2 in.) |
| 150.1 kV — 250 kV | 3.6 m (11 ft. 8 in.) | 3.6 m (11 ft. 8 in.) | 1.6 m (5 ft. 3 in.) | 1.5 m (5 ft. 0 in.) |
| 250.1 kV — 500 kV | 6.0 m (20 ft. 0 in.) | 6.0 m (20 ft. 0 in.) | 3.5 m (11 ft. 6 in.) | 3.3 m (10 ft. 10 in.) |
| 500.1 kV — 800 kV | 8.0 m (26 ft. 0 in.) | 8.0 m (26 ft. 0 in.) | 5.0 m (16 ft. 5 in.) | 5.0 m (16 ft. 5 in.) |
b This term describes a condition in which the distance between the conductor and a person is not under the control of the person. The term normally is applied to overhead line conductors supported by poles.
Appropriate PPE, Limited Approach Boundary, Restricted Approach Boundary, and Arc Flash Hazard can be identified with the appropriate Arc Flash and Shock Hazard Label.
Arc Flash
An Arc Flash Hazard is “a source of possible injury or damage to health associated with the release of energy caused by an electric arc”.
An arc flash study and coordination study will be the best sources for appropriate arc flash identification. Hiring a company to do these studies is best practice. These studies will help to estimate the incident energy present at specific electrical equipment. From there, the appropriate Arc Flash Boundary will be identified, and the appropriate PPE needed when qualified persons are working within this boundary.
Per the NFPA 70E, the label is required to have the following information:
- Nominal System Voltage
- Arc Flash Boundary
- At least one of the following items
- Incident energy and working distance OR required PPE Category
- Minimum arc rating of clothing
- Site specific PPE level
Examples:
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Other methods of determining the Arc Flash boundary are:
- Use of NFPA 70E Table 130.7(C)(15)(a)/(b)
Knowledge Eliminates Risk
Having knowledge of when it is safe and what the appropriate boundaries are can help mitigate risk associate with electrical hazards. The elimination of risk will help to prevent injury or bodily harm cause by electrical shock and arc flash incidents. Ensure your company has the appropriate studies completed and have labeled all electrical equipment with the correct Hazard Warning Labels.
