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 overcurrent devices in a location where they are readily accessible. To avoid creating an employee safety hazard, where must the electrician ensure the devices are NOT located?
Answer: In the vicinity of easily ignitible material. The rule prohibits locating overcurrent devices near easily ignitible material to prevent safety hazards.
29 CFR § 1926.404(e): “Overcurrent devices shall not be located where they could create an employee safety hazard by being exposed to physical damage or located in the vicinity of easily ignitible material.”
2. In a work area with uninsulated energized conductors, safety signs and barricades are in place, but they do not provide sufficient warning and protection from electrical hazards. What additional measure is required?
Answer: An attendant shall be stationed to warn and protect employees. When signs and barricades are insufficient, the regulation mandates the presence of an attendant to warn and protect employees.
29 CFR § 1910.335(b): “If signs and barricades do not provide sufficient warning and protection from electrical hazards, an attendant shall be stationed to warn and protect employees.”
3. A technician is working in an information technology equipment room and needs to disconnect power to the dedicated HVAC system serving the room. Where must the control for this disconnecting means be located?
Answer: At the principal exit doors. OSHA requires that the controls for disconnecting power to IT equipment and HVAC systems be readily accessible at the principal exit doors.
29 CFR § 1910.306(e): “The control for these disconnecting means shall be grouped and identified and shall be readily accessible at the principal exit doors.”
4. A crew is installing outdoor lighting. Where must the lamps be located relative to live conductors and transformers to ensure safe relamping operations?
Answer: Below all live conductors, transformers, or other electric equipment. The standard requires lamps to be located below live equipment to protect workers during relamping, unless specific lockout or clearance safeguards are in place.
29 CFR § 1926.404(c): “Lamps for outdoor lighting shall be located below all live conductors, transformers, or other electric equipment, unless such equipment is controlled by a disconnecting means that can be locked in the open position or unless adequate clearances or other safeguards are provided for relamping operations.”
5. When installing conductors in a tunnel, which of the following is a required method of installation?
Answer: Metal conduit or other metal raceway. The rule lists metal conduit or other metal raceway as an approved method for installing conductors in tunnels.
29 CFR § 1926.408(a): “Conductors in tunnels shall be installed in one or more of the following: (A) Metal conduit or other metal raceway, (C) Other suitable multiconductor cable.”
6. An electrician is about to deenergize a circuit for maintenance. When must the safe procedures for deenergizing that circuit be determined?
Answer: Before the circuits or equipment are deenergized. The regulation requires that the safe procedures be established prior to the actual deenergization of the equipment.
29 CFR § 1910.333(b): “Safe procedures for deenergizing circuits and equipment shall be determined before circuits or equipment are deenergized.”
7. For underwater lighting fixtures operating at more than 15 volts in a permanently installed pool, what safety device must be installed in the branch circuit?
Answer: A ground-fault circuit interrupter. GFCI protection is mandatory for underwater fixtures operating above 15 volts.
29 CFR § 1910.306(j): “A ground-fault circuit interrupter shall be installed in the branch circuit supplying underwater fixtures operating at more than 15 volts.”
8. Under the assured equipment grounding conductor program, who is responsible for implementing the program on a construction site?
Answer: One or more competent persons designated by the employer. The rule states that the employer must designate one or more competent persons to implement the program.
29 CFR § 1926.404(b): “The employer shall designate one or more competent persons (as defined in § 1926.32(f)) to implement the program.”
9. A worker needs to access a pull box for a system operating over 600 volts, nominal. What marking is required on the outside of the box cover to ensure it is readily visible and legible?
Answer: HIGH VOLTAGE. For pull and junction boxes in systems over 600 volts, the cover must be permanently marked with the specific phrase 'HIGH VOLTAGE' on the outside.
29 CFR § 1926.405(b): “Covers for boxes shall be permanently marked “HIGH VOLTAGE.” The marking shall be on the outside of the box cover and shall be readily visible and legible.”
10. A worker is accessing the working space about electric equipment. What is the minimum requirement for access to this working space?
Answer: At least one entrance shall be provided. The rule mandates that at least one entrance must be provided to allow access to the working space.
29 CFR § 1926.403(i): “At least one entrance shall be provided to give access to the working space about electric equipment.”
11. A worker is charging batteries on a construction site. What is the required status of the battery vent caps during the charging process?
Answer: They must be kept in place to avoid electrolyte spray. The standard requires vent caps to remain in place during charging to prevent electrolyte spray, rather than being removed or modified.
29 CFR § 1926.441(b): “When batteries are being charged, the vent caps shall be kept in place to avoid electrolyte spray.”
12. An electrician is installing a panelboard enclosure in a damp location and plans to mount it directly against a concrete wall. Under what condition is this installation permitted without the required airspace?
Answer: If the enclosure is nonmetallic. The regulation allows nonmetallic enclosures to be mounted directly against concrete or masonry surfaces, waiving the standard airspace requirement.
29 CFR § 1910.305(e): “However, nonmetallic enclosures may be installed without the airspace on a concrete, masonry, tile, or similar surface.”
13. A worker is servicing a separately derived AC system (50-1000 volts) supplied by a transformer with a primary voltage rating of 480 volts. The system is used exclusively for control circuits and continuity of control power is required. To legally leave this system ungrounded, what additional condition must be met?
Answer: Ground detectors are installed on the control system. One of the four mandatory conditions for exempting a separately derived control system from grounding requirements is the installation of ground detectors.
14. A worker is installing equipment with NPT threaded entries for field wiring connection in a hazardous location. What type of conduit or cable fittings must be used?
Answer: Listed conduit, conduit fittings, or cable fittings. The regulation mandates the use of listed components specifically for NPT threaded entries to ensure proper installation and safety.
29 CFR § 1910.307(g): “For equipment provided with threaded entries for NPT threaded conduit or fittings, listed conduit, conduit fittings, or cable fittings shall be used.”
15. During a tunnel installation, an electrician is wiring a motor. What is the specific requirement for the disconnecting means at the motor location?
Answer: It must simultaneously open all ungrounded conductors. OSHA requires that the disconnect at each motor or transformer location simultaneously opens all ungrounded conductors to ensure safe isolation.
29 CFR § 1910.308(a): “A disconnecting means that simultaneously opens all ungrounded conductors shall be installed at each transformer or motor location.”
16. An electrician is installing fixed lighting fixtures in a Class I, Division 2 hazardous location. According to marking requirements, which of the following is true regarding the marking of these fixtures?
Answer: They need not be marked to indicate the group. The regulation exempts fixed lighting fixtures in these specific Division 2 locations from requiring a group marking.
29 CFR § 1910.307(c): “Fixed lighting fixtures marked for use in Class I, Division 2 or Class II, Division 2 locations only need not be marked to indicate the group;”
17. A worker is running open conductors over an area subject to truck traffic, but it is not a public street, alley, road, or driveway. What is the minimum vertical clearance from the ground required?
Answer: 15 feet (4.57 m). Areas subject to truck traffic that are not public streets or driveways require a 15-foot clearance, distinguishing them from the 12-foot requirement for general vehicular traffic and the 18-foot requirement for public streets.
29 CFR § 1926.404(c): “15 feet (4.57 m)—over areas other than those specified in paragraph (c)(1)(ii)(D) of this section that are subject to truck traffic.”
18. A worker is maintaining a storage battery room. What provision must be in place to prevent the accumulation of explosive mixtures from the batteries?
Answer: Sufficient diffusion and ventilation of gases. The regulation specifically mandates sufficient diffusion and ventilation to prevent explosive gas accumulation in storage battery areas.
29 CFR § 1910.305(j): “Provisions shall be made for sufficient diffusion and ventilation of gases from storage batteries to prevent the accumulation of explosive mixtures.”
19. An electrician is connecting a single-throw knife switch to a circuit that is inherently capable of providing a backfeed source of power. If the blades and load terminals may remain energized when the switch is open, what must be installed?
Answer: A permanent sign on the switch enclosure or immediately adjacent to open switches that reads, “WARNING—LOAD SIDE TERMINALS MAY BE ENERGIZED BY BACKFEED.”. The regulation mandates a specific permanent warning sign for backfeed situations where load terminals may be energized while the switch is open.
29 CFR § 1910.305(c): “For such installations, a permanent sign shall be installed on the switch enclosure or immediately adjacent to open switches that read, “WARNING—LOAD SIDE TERMINALS MAY BE ENERGIZED BY BACKFEED.””
20. An electrician is installing control panels for an elevator that are located in a separate room from the drive machine. How must these panels be housed to comply with safety standards?
Answer: In cabinets with doors or panels capable of being locked closed. The rule requires control panels separated from the drive machine to be in lockable cabinets to secure them.
29 CFR § 1910.306(c): “Control panels not located in the same space as the drive machine shall be located in cabinets with doors or panels capable of being locked closed.”
21. An industrial worker is connecting a No. 12 copper conductor to a terminal using a pressure connector. To comply with the requirement for ensuring a good connection without damaging the conductor, which method is permitted for this size conductor?
Answer: Wire binding screws or studs and nuts having upturned lugs. The rule allows No. 10 or smaller conductors to use wire binding screws or studs with upturned lugs, whereas other methods listed are not permitted for this specific connection type in the rule.
29 CFR § 1910.303(c): “However, No. 10 or smaller conductors may be connected by means of wire binding screws or studs and nuts having upturned lugs or equivalent.”
22. An electrician is installing a service disconnecting means for a system rated over 600 volts, nominal. What additional safety measure is required for service-entrance conductors installed as open wires?
Answer: They must be guarded to make them accessible only to qualified persons. For services over 600 volts, open wire service-entrance conductors must be guarded to restrict access to qualified persons.
29 CFR § 1910.304(e): “Service-entrance conductors installed as open wires shall be guarded to make them accessible only to qualified persons.”
23. An electrician is working on the controls of a crane where the main disconnecting means is not readily accessible from the operating station. What safety provision must be in place at the operating station?
Answer: Means to open the power circuit to all motors of the crane. If the main disconnect is not accessible from the operator's station, a means to open the power circuit to all motors must be provided at that station.
29 CFR § 1910.306(b): “Means shall be provided at the operating station to open the power circuit to all motors of the crane or monorail hoist where the disconnecting means is not readily accessible from the crane or monorail hoist operating station.”
24. A qualified person is working on an aerial lift insulated for the voltage involved near energized overhead lines. Under which condition may the clearance between the uninsulated portion of the lift and the power line be reduced to the distance given in Table S-5?
Answer: If the work is performed by a qualified person. The regulation allows reduced clearance to Table S-5 distances only when using an insulated aerial lift and the worker is qualified.
29 CFR § 1910.333(c): “If the equipment is an aerial lift insulated for the voltage involved, and if the work is performed by a qualified person, the clearance (between the uninsulated portion of the aerial lift and the power line) may be reduced to the distance given in Table S-5.”
25. A worker is installing a new receptacle on a 15-ampere branch circuit. What type of receptacle is generally required?
Answer: A grounding-type receptacle. New installations on 15- and 20-amp circuits must use grounding-type receptacles, with specific exceptions only for replacements.
29 CFR § 1910.304(b): “Receptacles installed on 15- and 20-ampere branch circuits shall be of the grounding type except as permitted for replacement receptacles in paragraph (b)(2)(iv) of this section.”