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. A technician is working on a capacitor installed on a circuit operating at more than 600 volts. Which of the following is NOT a required capability for the group-operated switch used to switch this capacitor?
Answer: Automatically draining the stored charge after disconnection. While capacitors generally require an automatic means of draining stored charge, the specific list of capabilities for the group-operated switch itself does not include the draining function; that is a separate requirement for the capacitor.
29 CFR § 1910.305(j): “Group-operated switches shall be used for capacitor switching and shall be capable of the following: (1) Carrying continuously not less than 135 percent of the rated current of the capacitor installation; (2) Interrupting the maximum continuous load current of each capacitor, capacitor bank, or capacitor installation that will be switched as a unit; (3) Withstanding the maximum inrush current, including contributions from adjacent capacitor installations; and (4) Carrying currents due to faults on the capacitor side of the switch;”
2. A qualified electrician needs to temporarily defeat an electrical safety interlock to work on equipment. What is the mandatory requirement for the interlock system once the work is completed?
Answer: It must be returned to its operable condition. The rule requires that the safety interlock be restored to its normal, operable state immediately after the qualified person finishes working on the equipment.
29 CFR § 1910.333(c): “The interlock system shall be returned to its operable condition when this work is completed.”
3. A construction crew is setting up temporary electrical installations for power and light on a new jobsite. According to the scope of installation safety requirements, which of the following installations is covered by these rules?
Answer: Portable and vehicle-mounted generators used to provide power for equipment used at the jobsite. While general generation and transmission installations are excluded, the rule specifically notes that portable and vehicle-mounted generators used for jobsite equipment are covered.
29 CFR § 1926.402(b): “However, these regulations do cover portable and vehicle-mounted generators used to provide power for equipment used at the jobsite.”
4. A worker needs to inspect a circuit breaker panel. The definition of 'Readily accessible' implies that the worker should be able to reach the panel quickly for operation or inspection without which of the following?
Answer: Climbing over or removing obstacles or resorting to portable ladders or chairs. The definition excludes the need to climb over obstacles or use portable ladders/chairs to achieve ready access.
29 CFR § 1910.399: “Readily accessible. Capable of being reached quickly for operation, renewal, or inspections, so that those needing ready access do not have to climb over or remove obstacles or to resort to portable ladders, chairs, etc.”
5. An electrician is installing temporary wiring for a construction site. According to the definition of 'Premises wiring system,' which of the following components is EXCLUDED from this system?
Answer: Wiring internal to a motor control center. The rule states that premises wiring excludes wiring internal to equipment like motor control centers, while including the other listed wiring types.
29 CFR § 1926.449: “Such wiring does not include wiring internal to appliances, fixtures, motors, controllers, motor control centers, and similar equipment.”
6. Which of the following metal enclosures is exempted from the requirement to be grounded?
Answer: Metal sleeves used to protect cable assemblies from physical damage. The regulation specifically lists metal sleeves used for physical protection of cable assemblies as an exception to the general grounding requirement for metal enclosures.
29 CFR § 1910.304(g): “Metal enclosures such as sleeves that are used to protect cable assemblies from physical damage need not be grounded”
7. A worker is installing auxiliary nonelectrical connections, such as water hoses, to an electrolytic cell. To comply with safety standards, what material requirement must the hoses meet?
Answer: They must be made of nonconductive material. The regulation states that auxiliary nonelectrical connections like hoses must be made of nonconductive material to prevent hazardous conditions.
8. An industrial worker is inspecting a wiring system where single insulated conductors are supported by cleats and knobs on a wall surface, not concealed by the building structure. According to the definitions in 29 CFR § 1910.399, how is this specific wiring method classified?
Answer: Open wiring on insulators. The rule defines this exposed method using cleats and knobs as 'Open wiring on insulators,' distinguishing it from concealed premises wiring or cable types.
29 CFR § 1910.399: “Open wiring on insulators is an exposed wiring method using cleats, knobs, tubes, and flexible tubing for the protection and support of single insulated conductors run in or on buildings, and not concealed by the building structure.”
9. An electrician is installing a service disconnecting means for a building. Which of the following is a mandatory requirement for this device?
Answer: It must plainly indicate whether it is in the open or closed position. The rule states the device must plainly indicate its open/closed status; it must be near the entrance (not 10 feet away), accessible to employees (not just qualified persons), and disconnects ungrounded conductors (grounded conductor continuity is generally maintained unless specific exceptions apply).
29 CFR § 1910.304(e): “The service disconnecting means shall plainly indicate whether it is in the open or closed position and shall be installed at a readily accessible location nearest the point of entrance of the service-entrance conductors.”
10. A worker is connecting a flexible cord to a device and fitting. What feature must the connection provide to ensure safety?
Answer: Strain relief which will prevent pull from being directly transmitted to joints or terminal screws. The rule specifically requires strain relief at connections to devices and fittings to protect joints and terminal screws from pull.
29 CFR § 1926.405(g): “Flexible cords shall be connected to devices and fittings so that strain relief is provided which will prevent pull from being directly transmitted to joints or terminal screws.”
11. If an electrician determines that a lock cannot be applied to a disconnecting means, what is required to use a tag alone?
Answer: The tag must be supplemented by at least one additional safety measure equivalent to the safety provided by a lock. When a tag is used without a lock, the regulation mandates an additional safety measure that provides a level of safety equivalent to using a lock.
29 CFR § 1910.333(b): “A tag used without a lock, as permitted by paragraph (b)(2)(iii)(C) of this section, shall be supplemented by at least one additional safety measure that provides a level of safety equivalent to that obtained by the use of a lock.”
12. An electrician is installing a flexible cord with an attachment plug to connect a portable tool to a permanent receptacle. According to the definition provided, what is the primary function of this device?
Answer: To establish a connection between the conductors of the attached flexible cord and the conductors connected permanently to the receptacle. The rule defines an attachment plug specifically as the device that connects the flexible cord's conductors to the permanent receptacle's conductors.
29 CFR § 1926.449: “A device which, by insertion in a receptacle, establishes connection between the conductors of the attached flexible cord and the conductors connected permanently to the receptacle.”
13. When installing conduits in a hazardous (classified) location, what is the required method for ensuring the joint is secure if making a threaded joint tight is impractical?
Answer: Utilize a bonding jumper. The rule specifies that a bonding jumper is the required solution when a threaded joint cannot be made tight.
29 CFR § 1926.407(c): “Where it is impractical to make a threaded joint tight, a bonding jumper shall be utilized.”
14. An electrician is installing portable electric lighting inside a metal tank where the environment is wet and conductive. To comply with OSHA construction standards, what is the maximum operating voltage allowed for the lights if a ground-fault circuit interrupter (GFCI) is NOT used?
Answer: 12 volts or less. The regulation limits portable lighting in wet or conductive locations like tanks to 12 volts or less unless a GFCI is used.
29 CFR § 1926.405(a): “Portable electric lighting used in wet and/or other conductive locations, as for example, drums, tanks, and vessels, shall be operated at 12 volts or less.”
15. An electrician is installing a disconnecting means for a motor and its controller. To ensure the motor is safely isolated from the power source, what design feature must the disconnecting means have regarding its poles?
Answer: It must disconnect the motor from all ungrounded supply conductors and prevent any pole from being operated independently. The regulation requires that all ungrounded conductors be disconnected and that the poles operate together to prevent partial energization.
29 CFR § 1910.305(j): “The disconnecting means shall disconnect the motor and the controller from all ungrounded supply conductors and shall be so designed that no pole can be operated independently.”
16. When installing equipment with metric threaded entries in a hazardous location, what must the electrician ensure is provided to allow connection to standard NPT-threaded conduit?
Answer: Listed adaptors to permit connection to conduit of NPT-threaded fittings. The rule requires that metric entries either be identified as metric or that listed adaptors be provided to connect to NPT-threaded conduit or fittings.
29 CFR § 1910.307(g): “For equipment with metric threaded entries, such entries shall be identified as being metric, or listed adaptors to permit connection to conduit of NPT-threaded fittings shall be provided with the equipment.”
17. An electrician is installing equipment in a Class I, Zone 2 hazardous location. Which of the following protection techniques is permitted for this specific zone?
Answer: Type of protection “n”. Among the listed options, only Type of protection 'n' is permitted for Zone 2 locations; the others are restricted to Zone 0 or Zone 1.
29 CFR § 1910.307(g): “Type of protection “n”—This protection technique is permitted for equipment in the Class I, Zone 2 locations for which it is approved.”
18. An electrician is installing premises wiring for an AC system. Which conductor is required to be grounded for this system?
Answer: The identified conductor. The regulation mandates that the identified conductor is the one that must be grounded in AC premises wiring systems.
29 CFR § 1926.404(f): “For AC premises wiring systems the identified conductor shall be grounded.”
19. An electrician is using test instruments to check an energized circuit. What is the required procedure regarding the visual condition of the test leads and probes before use?
Answer: Visually inspect for external defects and damage, removing any defective item from service. The rule mandates a visual inspection for defects and damage before use, with defective items removed from service.
29 CFR § 1910.334(c): “Test instruments and equipment and all associated test leads, cables, power cords, probes, and connectors shall be visually inspected for external defects and damage before the equipment is used.”
20. An electrician is installing a receptacle outdoors in a location protected from the weather. To comply with OSHA standards for this specific installation, what condition must the receptacle's enclosure meet?
Answer: It must be weatherproof when the receptacle is covered (attachment plug cap not inserted and receptacle covers closed). For outdoor receptacles in protected locations, the enclosure is required to be weatherproof specifically when the receptacle is covered (no plug inserted and covers closed).
29 CFR § 1910.305(j): “A receptacle installed outdoors in a location protected from the weather or in other damp locations shall have an enclosure for the receptacle that is weatherproof when the receptacle is covered (attachment plug cap not inserted and receptacle covers closed).”
21. An electrician is installing a new electrical system and needs to ensure metallic parts are permanently joined to form a conductive path that ensures electrical continuity. According to the definition of 'Bonding', what is the primary capacity this path must have regarding current?
Answer: It must be able to conduct safely any current likely to be imposed. The definition states the path must have the capacity to conduct safely any current likely to be imposed, not just normal or fault currents.
29 CFR § 1910.399: “The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed.”
22. An electrician is installing fused cutouts in a building. Which type of cutout is prohibited from being used indoors, underground, or in metal enclosures?
Answer: Distribution cutouts. The regulation prohibits the use of distribution cutouts in indoor, underground, or metal enclosure locations.
29 CFR § 1910.308(a): “Distribution cutouts may not be used indoors, underground, or in metal enclosures.”
23. A worker is grounding a monorail hoist. Under which specific condition must a separate bonding conductor be provided to ensure the trolley and bridge frames are electrically grounded?
Answer: When paint or other insulating materials prevent reliable metal-to-metal contact. A separate bonding conductor is required only when insulating materials like paint interfere with the natural metal-to-metal grounding path through the wheels and tracks.
29 CFR § 1926.406(a): “The trolley frame and bridge frame shall be considered as electrically grounded through the bridge and trolley wheels and its respective tracks unless conditions such as paint or other insulating materials prevent reliable metal-to-metal contact. In this case a separate bonding conductor shall be provided.”
24. An electrician is installing a portable generator on a construction site. The generator is not part of a separately derived system and supplies only equipment mounted on the generator and cord-and-plug-connected equipment via receptacles on the generator. Under which condition may the electrician rely on the generator frame as the grounding electrode instead of driving a separate ground rod?
Answer: The noncurrent-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame. For a portable generator to use its frame as the grounding electrode, the equipment and receptacle grounding terminals must be bonded to that frame.
29 CFR § 1926.404(f): “The noncurrent-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.”
25. An electrician is servicing a panelboard in a passageway where normally enclosed live parts are exposed for inspection. What is the required condition for the working space in this location?
Answer: The working space shall be suitably guarded. If live parts are exposed in a general open area like a passageway, the regulation requires the working space to be guarded to protect personnel.
29 CFR § 1910.303(g): “When normally enclosed live parts are exposed for inspection or servicing, the working space, if in a passageway or general open space, shall be suitably guarded.”