NFPA 70E (Standard for Electrical Safety in the
Workplace), Study Questions 2025 Exam
Questions and Corresponding Answers with
Surety of 100% Pass Mark
1. **What is an arc flash?**
**Answer:** A release of radiant energy in the form of heat
and light.
**Explanation:** An arc flash is a dangerous electrical
explosion caused by a fault (e.g., short circuit or ground fault)
that ionizes the air, releasing intense heat, light, pressure, and
sound. It can cause severe burns, blindness, hearing damage, or
fatalities. NFPA 70E emphasizes assessing and mitigating this
hazard through risk assessments and proper PPE.
2. **What is the primary cause of an arc flash?**
**Answer:** A major short circuit or ground fault.
**Explanation:** Arc flashes typically occur when there's
unintended contact between energized conductors (e.g., due to
tool drops, dust accumulation, or corrosion), creating a low-
,impedance path. This leads to rapid energy release. NFPA 70E
requires de-energizing equipment whenever possible to
eliminate this risk, as it's the safest approach.
3. **What is an arc blast?**
**Answer:** An explosive event that accompanies an arc
flash.
**Explanation:** The arc blast is the pressure wave, shrapnel,
and sound from superheated air expanding rapidly during an
arc flash (temperatures can exceed 35,000°F). It can cause
traumatic injuries like ruptured eardrums or being thrown.
NFPA 70E addresses this in arc flash hazard analysis, requiring
boundaries and PPE rated for both thermal and pressure
effects.
4. **What is the best way to avoid electrical hazards according
to NFPA 70E?**
**Answer:** Create an electrically safe work condition (de-
energize the equipment).
**Explanation:** NFPA 70E prioritizes establishing an
electrically safe work condition by locking out/tagging out and
verifying absence of voltage. Energized work is only permitted if
it creates greater hazards (e.g., interrupting life support) or is
, infeasible, and it requires justification via an energized work
permit.
5. **What does the arc flash boundary represent?**
**Answer:** The distance from a prospective arc source
where a person could receive a second-degree burn (typically at
1.2 cal/cm² incident energy).
**Explanation:** This boundary is calculated based on
available fault current, clearing time, and system voltage.
Beyond it, no special arc-rated PPE is needed for arc flash
(though shock protection may still apply). Inside, qualified
persons must wear appropriate arc-rated clothing. NFPA 70E
provides tables or calculation methods (e.g., IEEE 1584) for
determining it.
6. **What is incident energy, and how is it measured?**
**Answer:** The amount of thermal energy released during
an arc flash event, measured in cal/cm² (calories per square
centimeter).
**Explanation:** Incident energy quantifies the heat
exposure at a working distance. At 1.2 cal/cm², unprotected
skin can suffer a second-degree burn in about 0.1 seconds.
NFPA 70E uses this to select PPE arc ratings (e.g., Category 2
Workplace), Study Questions 2025 Exam
Questions and Corresponding Answers with
Surety of 100% Pass Mark
1. **What is an arc flash?**
**Answer:** A release of radiant energy in the form of heat
and light.
**Explanation:** An arc flash is a dangerous electrical
explosion caused by a fault (e.g., short circuit or ground fault)
that ionizes the air, releasing intense heat, light, pressure, and
sound. It can cause severe burns, blindness, hearing damage, or
fatalities. NFPA 70E emphasizes assessing and mitigating this
hazard through risk assessments and proper PPE.
2. **What is the primary cause of an arc flash?**
**Answer:** A major short circuit or ground fault.
**Explanation:** Arc flashes typically occur when there's
unintended contact between energized conductors (e.g., due to
tool drops, dust accumulation, or corrosion), creating a low-
,impedance path. This leads to rapid energy release. NFPA 70E
requires de-energizing equipment whenever possible to
eliminate this risk, as it's the safest approach.
3. **What is an arc blast?**
**Answer:** An explosive event that accompanies an arc
flash.
**Explanation:** The arc blast is the pressure wave, shrapnel,
and sound from superheated air expanding rapidly during an
arc flash (temperatures can exceed 35,000°F). It can cause
traumatic injuries like ruptured eardrums or being thrown.
NFPA 70E addresses this in arc flash hazard analysis, requiring
boundaries and PPE rated for both thermal and pressure
effects.
4. **What is the best way to avoid electrical hazards according
to NFPA 70E?**
**Answer:** Create an electrically safe work condition (de-
energize the equipment).
**Explanation:** NFPA 70E prioritizes establishing an
electrically safe work condition by locking out/tagging out and
verifying absence of voltage. Energized work is only permitted if
it creates greater hazards (e.g., interrupting life support) or is
, infeasible, and it requires justification via an energized work
permit.
5. **What does the arc flash boundary represent?**
**Answer:** The distance from a prospective arc source
where a person could receive a second-degree burn (typically at
1.2 cal/cm² incident energy).
**Explanation:** This boundary is calculated based on
available fault current, clearing time, and system voltage.
Beyond it, no special arc-rated PPE is needed for arc flash
(though shock protection may still apply). Inside, qualified
persons must wear appropriate arc-rated clothing. NFPA 70E
provides tables or calculation methods (e.g., IEEE 1584) for
determining it.
6. **What is incident energy, and how is it measured?**
**Answer:** The amount of thermal energy released during
an arc flash event, measured in cal/cm² (calories per square
centimeter).
**Explanation:** Incident energy quantifies the heat
exposure at a working distance. At 1.2 cal/cm², unprotected
skin can suffer a second-degree burn in about 0.1 seconds.
NFPA 70E uses this to select PPE arc ratings (e.g., Category 2
