25 multiple-choice questions for the OSHA Electrical Safety (Subpart S) Practice Test. Pick an answer to see the rule behind it, quoted from the official source.
1. An electrician is installing new branch circuit conductors in a junction box that already contains photovoltaic (PV) source circuit conductors. According to OSHA rules for solar photovoltaic systems, what condition must be met to allow these different systems to share the same enclosure?
Answer: The conductors must be separated by a partition or connected together. The regulation permits mixing PV source/output circuits with other system feeders/branch circuits only if they are separated by a partition or connected together.
29 CFR § 1910.308(f): “Photovoltaic source circuits and photovoltaic output circuits may not be contained in the same raceway, cable tray, cable, outlet box, junction box, or similar fitting as feeders or branch circuits of other systems, unless the conductors of the different systems are separated by a partition or are connected together.”
2. A circuit breaker has tripped, deenergizing a circuit. What must be determined before the circuit can be manually reenergized?
Answer: That the equipment and circuit can be safely energized. The rule prohibits manual reclosing until a determination is made that it is safe to energize the equipment and circuit.
29 CFR § 1910.334(b): “After a circuit is deenergized by a circuit protective device, the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized.”
3. An electrician is running open conductors across ceiling joints and wall studs where they are exposed to physical damage. At what height from the floor does the regulation consider this exposure significant enough to require protection?
Answer: Within 2.13 m (7.0 ft) of the floor. The rule specifies that conductors located within 7 feet of the floor are considered exposed to physical damage and must be protected.
29 CFR § 1910.305(a): “(v) Where open conductors cross ceiling joints and wall studs and are exposed to physical damage (for example, located within 2.13 m (7.0 ft) of the floor), they shall be protected.”
4. An electrician is replacing a nongrounding-type receptacle in an enclosure that lacks a grounding means. If the electrician chooses to install a grounding-type receptacle supplied through a ground-fault circuit-interrupter, what specific markings must the replacement receptacle bear?
Answer: It must be marked "GFCI Protected" and "No Equipment Ground.". The regulation requires these two specific markings when a grounding-type receptacle is used as a replacement in a non-grounded enclosure supplied by a GFCI.
29 CFR § 1910.304(b): “A nongrounding-type receptacle may be replaced with a grounding-type receptacle where supplied through a ground-fault circuit-interrupter; the replacement receptacle shall be marked “GFCI Protected” and “No Equipment Ground;””
5. An electrician is installing a new branch circuit in a commercial building and must select an enclosed channel to hold the wires. According to the definition of 'Raceway,' which of the following is included in this category?
Answer: Rigid metal conduit. The rule lists rigid metal conduit as an example of a raceway, while the other options are not listed as raceways in the rule.
29 CFR § 1910.399: “Raceways include, but are not limited to, rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, liquidtight flexible conduit, flexible metallic tubing, flexible metal conduit, electrical metallic tubing, electrical nonmetallic tubing, underfloor raceways, cellular concrete floor raceways, cellular metal floor raceways, surface raceways, wireways, and busways.”
6. An electrician is installing a device at an outlet to allow the connection of a single attachment plug. According to the definition of 'Receptacle,' what is this contact device called?
Answer: A receptacle. The rule defines a receptacle specifically as the contact device installed at the outlet for connecting a single attachment plug.
29 CFR § 1926.449: “Receptacle. A receptacle is a contact device installed at the outlet for the connection of a single attachment plug.”
7. An electrician is installing remote controls for applying power to heating equipment. How must the selector switch be interlocked?
Answer: To provide power from only one control point at a time. The regulation mandates that the selector switch prevents multiple control points from applying power simultaneously.
29 CFR § 1910.306(g): “If remote controls are used for applying power, a selector switch shall be provided and interlocked to provide power from only one control point at a time.”
8. If an electrician uses single-pole separable connectors where interlocking is not possible, what sequence must be followed for connecting and disconnecting the conductors to ensure safety?
Answer: Connect equipment grounding conductor, then grounded circuit conductor, then ungrounded conductor; disconnect in reverse order. To protect against shock, the ground must be connected first and disconnected last, ensuring the equipment is grounded before becoming energized.
29 CFR § 1910.306(k): “Line connectors are of the listed sequential-interlocking type so that load connectors are connected in the following sequence: (i) Equipment grounding conductor connection; (ii) Grounded circuit-conductor connection, if provided; and (iii) Ungrounded conductor connection; and so that disconnection is in the reverse order”
9. An electrician is installing open conductors rated 600 volts or less on a pole. The power conductors are located below communication conductors. What is the minimum horizontal climbing space required?
Answer: 30 inches (762 mm). The regulation mandates a 30-inch horizontal climbing space when power conductors are positioned below communication conductors.
10. An electrician is setting up a battery charging station on a construction site. What is the required distance for quick drenching facilities from the battery handling area?
Answer: Within 25 feet (7.62 m). The regulation specifies a maximum distance of 25 feet for quick drenching facilities near battery handling areas.
29 CFR § 1926.441(a): “Facilities for quick drenching of the eyes and body shall be provided within 25 feet (7.62 m) of battery handling areas.”
11. An electrician is routing conductors near a building's exterior. To comply with clearance rules from building openings, what is the minimum distance required from windows and doors?
Answer: 3 feet (914 mm). Open conductors must be kept at least 3 feet away from windows, doors, and fire escapes to ensure safety.
29 CFR § 1926.404(c): “Conductors shall have a clearance of at least 3 feet (914 mm) from windows, doors, fire escapes, or similar locations.”
12. A worker is installing receptacles on circuits with different voltages or types of current (AC vs DC) on the same premises. What design feature is required to prevent accidental misuse of attachment plugs?
Answer: The attachment plugs used on these circuits must not be interchangeable. OSHA mandates that the physical design of the receptacles and plugs prevents a plug from one circuit type from fitting into a receptacle of a different voltage or current type.
29 CFR § 1910.304(b): “Receptacles connected to circuits having different voltages, frequencies, or types of current (ac or dc) on the same premises shall be of such design that the attachment plugs used on these circuits are not interchangeable.”
13. In an industrial establishment where only qualified persons service the installed cable tray system, which single conductor cable type is permitted in a ladder cable tray?
Answer: No. 1/0 or larger single conductor cable listed and marked for use in cable trays. For industrial establishments with qualified supervision, single conductors in ladder trays must be No. 1/0 or larger and specifically listed/marked for cable tray use.
29 CFR § 1910.305(a): “Single conductor cable; the cable shall be No. 1/0 or larger and shall be of a type listed and marked on the surface for use in cable trays”
14. An electrician is installing a switch in a wet location on a construction site. According to OSHA standards, what is the required enclosure type for this switch?
Answer: A weatherproof enclosure. The regulation mandates that switches in wet locations must be enclosed in weatherproof enclosures to prevent moisture ingress.
29 CFR § 1926.405(e): “Switches, circuit breakers, and switchboards installed in wet locations shall be enclosed in weatherproof enclosures.”
15. An electrician is selecting a cable for a factory assembly consisting of one or more insulated circuit conductors enclosed in an armor of interlocking metal tape. Which cable type corresponds to this description?
Answer: Metal-clad cable (Type MC). The definition of Metal-clad cable (Type MC) specifically mentions conductors enclosed in an armor of interlocking metal tape.
29 CFR § 1910.399: “Metal-clad cable (Type MC). A factory assembly of one or more insulated circuit conductors with or without optical fiber members enclosed in an armor of interlocking metal tape, or a smooth or corrugated metallic sheath.”
16. An electrician is installing fixed dust-tight equipment (other than lighting fixtures) in a Class II, Division 2 hazardous location. According to the marking requirements, which of the following is true regarding the markings on this equipment?
Answer: It need not be marked with the class, group, division, or operating temperature. The regulation exempts fixed dust-tight equipment in these specific locations from requiring class, group, division, or temperature markings.
29 CFR § 1910.307(c): “Fixed dust-tight equipment, other than lighting fixtures, that is acceptable for use in Class II, Division 2 and Class III locations need not be marked with the class, group, division, or operating temperature;”
17. An electrician is installing metal raceways for conductors in a new construction project. Which of the following is the correct requirement for these metal raceways?
Answer: They must be grounded. The rule states that metal raceways shall be grounded, and the exceptions provided (such as the 25-foot rule) apply specifically to enclosures added to existing installations, not to new raceway installations.
29 CFR § 1926.404(f): “Metal cable trays, metal raceways, and metal enclosures for conductors shall be grounded, except that: (A) Metal enclosures such as sleeves that are used to protect cable assemblies from physical damage need not be grounded; and (B) Metal enclosures for conductors added to existing installations of open wire, knob-and-tube wiring, and nonmetallic-sheathed cable need not be grounded if all of the following conditions are met:”
18. An electrician is installing distribution apparatus, such as a transformer case, on a wooden pole. Under which specific condition is grounding of the exposed noncurrent-carrying metal parts NOT required?
Answer: If the apparatus is mounted at a height exceeding 2.44 m (8.0 ft) above ground or grade level. The rule lists distribution apparatus on wooden poles above 8 feet as an exception to the grounding requirement for fixed equipment.
29 CFR § 1910.304(g): “Distribution apparatus, such as transformer and capacitor cases, mounted on wooden poles, at a height exceeding 2.44 m (8.0 ft) above ground or grade level”
19. An electrician is connecting a grounded conductor to a terminal. What condition must be avoided to comply with polarity rules?
Answer: Attaching the conductor so as to reverse designated polarity. The rule strictly prohibits attaching a grounded conductor in a way that reverses the designated polarity of the connection.
29 CFR § 1910.304(a): “No grounded conductor may be attached to any terminal or lead so as to reverse designated polarity.”
20. A technician is working in an area where flammable gases may be present. To determine if the area is a 'Class I, Division 1' location, which condition must be true?
Answer: Ignitable concentrations of flammable gases or vapors may exist under normal operating conditions. The definition lists 'normal operating conditions' as a primary criterion for Class I, Division 1 locations, distinguishing it from less hazardous divisions.
29 CFR § 1910.399: “Class I, Division 1. A Class I, Division 1 location is a location: (i) In which ignitable concentrations of flammable gases or vapors may exist under normal operating conditions; or (ii) In which ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or (iii) In which breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment.”
21. An electrician is measuring the minimum clear working space in front of a switchboard where the live parts are enclosed within the cabinet. From which point must the distance be measured?
Answer: From the enclosure front or opening. For enclosed live parts, the regulation specifies that working space distances are measured from the enclosure front or opening, not the live parts themselves.
29 CFR § 1926.403(j): “Distances shall be measured from the live parts if they are exposed, or from the enclosure front or opening if the live parts are enclosed.”
22. An electrician is preparing to service a disconnecting means required by the subpart. What specific capability must this disconnecting means possess to ensure safe lockout procedures?
Answer: It must be capable of being locked in the open position. The regulation requires that disconnecting means be lockable in the open position to facilitate safe isolation of the circuit.
29 CFR § 1910.303(f): “Disconnecting means required by this subpart shall be capable of being locked in the open position.”
23. A safety officer is reviewing the definition of 'Ampacity' to ensure conductors are properly sized for a new industrial circuit. What does this term specifically define?
Answer: The current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Ampacity is defined strictly as the continuous current carrying capacity of a conductor limited by its temperature rating, not voltage limits or breaker trip settings.
29 CFR § 1910.399: “Ampacity. The current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.”
24. A crew is installing insulated conductors above a roof space that is accessible to employees on foot. What is the minimum vertical clearance required from the highest point of the roof surface?
Answer: 8 feet (2.44 m). For insulated conductors over roof spaces accessible to employees on foot, the minimum vertical clearance is 8 feet.
29 CFR § 1926.404(c): “Conductors above roof space accessible to employees on foot shall have a clearance from the highest point of the roof surface of not less than 8 feet (2.44 m) vertical clearance for insulated conductors”
25. When setting up wiring for an amusement ride at a fair, an electrician must ensure that flexible cords and cables used outdoors meet which specific listing requirements?
Answer: Listed for extra-hard usage, wet locations, and sunlight resistance. Outdoor flexible cords for carnivals must be listed for extra-hard usage, wet locations, and be sunlight resistant.
29 CFR § 1910.306(k): “Flexible cords and cables shall be listed for extra-hard usage. When used outdoors, flexible cords and cables shall also be listed for wet locations and shall be sunlight resistant.”