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:

  1. Are there any exposed energized parts?
  2. Is the equipment in good condition?
  3. 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 Phase4Exposed Movable ConductorFixes Circuit PartRestricted Approach Boundaryb; Includes Inadvertent Movement AdderProhibited 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 Phase4Exposed Movable ConductorFixes Circuit PartRestricted Approach Boundaryb; Includes Inadvertent Movement AdderProhibited 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.)
a All dimensions are distance from exposed energized electrical conductors or circuit parts to worker.
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:

  1. Nominal System Voltage
  2. Arc Flash Boundary
  3. 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:

WARNING
Arc Flash and Shock Hazard Appropriate PPE Required
24 inchFlash Hazard Boundary
3cal/cm 2 Flash Hazard at 18 inches
1PPE Level, 1 layer 6 oz. Nomex,
Leather Gloves Faceshield
480 VACShock Hazard when Cover is removed
42 inchLimited Approach
12 inchRestricted Approach 500 V Class 00 Gloves
1 inchProhibited Approach 500 V Class 00 Gloves
 
WARNING
Arc Flash and Shock Hazard Appropriate PPE Required
FLASH PROTECTION Flash Hazard Category: 4 Min. Arc Rating (cal/cm2): 40 Flash Proctection Boundary: 36
PPE: [x] Cotton Underwear
[x] FR Shirt and Pants (or FR coverall)
[ ] Full Flash Suit and Hood
[x] Hard Hat
[x] Safety Glasses or Goggles
[ ] Hearing Protection
[x] Leather Gloves and Shoes
SHOCK PROTECTION220 Vac Shock Hazard When: Cover Is RemovedLimited Approach Boundary: 42 Restricted Approach Boundary: 12 Prohibited Approach Boundary: 1
PPE: [x] Class 4
[x] V-Rating
[ ]

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.

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Article Author

Chris Grainger

Engineering & Services Manager – Carolina’s

Chris Grainger is Engineering & Services Manager at EECO. He is driven by understanding client needs and developing solutions to assist them in achieving their goals. Chris provides oversight for the Solution Architecture and Product Manager teams in the Carolina’s at EECO, Chris thinks outside the box to change the experience and expectations clients should have about their motor service providers. Chris was an engineering co-op student at EECO and joined the team full time after graduating from Old Dominion University in 2003.