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. In an area where there is a danger of head injury from electric shock or burns due to contact with exposed energized parts, what protective equipment must employees wear?
Answer: Nonconductive head protection. The rule specifically mandates nonconductive head protection to prevent shock or burns from contact with energized parts.
29 CFR § 1910.335(a): “Employees shall wear nonconductive head protection wherever there is a danger of head injury from electric shock or burns due to contact with exposed energized parts.”
2. An industrial electrician is installing a new piece of utilization equipment in a factory. The equipment is not custom-made and is of a kind that a nationally recognized testing laboratory (NRTL) does not currently list or certify. To ensure the equipment is considered 'acceptable' under OSHA Subpart S, what alternative verification method is permitted?
Answer: The equipment must be inspected or tested by another Federal agency, or by a State, municipal, or other local authority responsible for enforcing occupational safety provisions of the National Electrical Code. For non-custom equipment not covered by an NRTL, OSHA allows acceptance if inspected or tested by a federal, state, or local authority enforcing NEC safety provisions.
29 CFR § 1910.399: “With respect to an installation or equipment of a kind that no nationally recognized testing laboratory accepts, certifies, lists, labels, or determines to be safe, if it is inspected or tested by another Federal agency, or by a State, municipal, or other local authority responsible for enforcing occupational safety provisions of the National Electrical Code, and found in compliance with the provisions of the National Electrical Code as applied in this subpart”
3. An industrial electrician is installing a Class 2 power source using a dry cell battery. Under what specific conditions is this battery considered an inherently limited Class 2 power source without requiring listing as such?
Answer: The voltage is 30 volts or less and the capacity is less than or equal to that available from series-connected No. 6 carbon zinc cells. The regulation limits the exemption for unlisted dry cell batteries to those with 30 volts or less and a capacity matching No. 6 carbon zinc cells.
29 CFR § 1910.308(c): “A dry cell battery is considered an inherently limited Class 2 power source, provided the voltage is 30 volts or less and the capacity is less than or equal to that available from series-connected No. 6 carbon zinc cells.”
4. An electrician is preparing to use a Type SJ flexible cord for general wiring. What marking requirement must be met before the cord can be used?
Answer: It must be durably marked on the surface with the type designation, size, and number of conductors. The rule lists the required markings (type, size, number of conductors) for these specific cord types.
29 CFR § 1926.405(g): “Type SJ, SJO, SJT, SJTO, S, SO, ST, and STO cords shall not be used unless durably marked on the surface with the type designation, size, and number of conductors.”
5. An electrician is determining the 'voltage to ground' for a specific conductor in an ungrounded circuit. How should this voltage be calculated according to OSHA definitions?
Answer: It is the greatest voltage between the given conductor and any other conductor of the circuit. For ungrounded circuits, the voltage to ground is defined as the greatest voltage between the conductor in question and any other conductor in the circuit.
29 CFR § 1910.399: “Voltage to ground. For grounded circuits, the voltage between the given conductor and that point or conductor of the circuit that is grounded; for ungrounded circuits, the greatest voltage between the given conductor and any other conductor of the circuit.”
6. An electrician is installing open conductors smaller than No. 8 in a dry location. To ensure rigid support, what is the maximum allowable interval between supports?
Answer: 1.37 m (4.5 ft). The regulation limits the interval between supports for these conductors to 1.37 meters (4.5 feet).
29 CFR § 1910.305(a): “At intervals not exceeding 1.37 m (4.5 ft), and at closer intervals sufficient to provide adequate support where likely to be disturbed.”
7. An electrician is installing high-voltage power distribution equipment in a tunnel. According to OSHA regulations, how must conductors be installed in this environment?
Answer: In metal conduit, other metal raceway, or other approved multiconductor cable. The regulation lists metal conduit, metal raceway, or approved multiconductor cable as the permitted installation methods for conductors in tunnels.
29 CFR § 1910.308(a): “Conductors in tunnels shall be installed in one or more of the following: (A) Metal conduit or other metal raceway; (C) Other approved multiconductor cable.”
8. A worker is preparing to open a compartment containing energized parts operating at 600 volts AC. What warning label must be plainly visible on the equipment before the worker opens the doors?
Answer: “DANGER—HIGH VOLTAGE—KEEP OUT”. The rule specifies the exact text required for warning labels on equipment with energized parts over 250 volts.
29 CFR § 1910.306(g): “Warning labels or signs that read “DANGER—HIGH VOLTAGE—KEEP OUT” shall be attached to the equipment and shall be plainly visible where persons might contact energized parts when doors are opened or closed or when panels are removed from compartments containing over 250 volts ac or dc.”
9. An electrician is installing a motor control center rated at 1,500 amperes and 8 feet wide in an indoor electrical room. What is the minimum required dimension for the entrance to the working space at each end?
Answer: 610 mm (24 in.) wide and 1.98 m (6.5 ft) high. For large equipment (≥1200A and >6ft wide), the entrance must be at least 24 inches wide and 6.5 feet high.
29 CFR § 1910.303(g): “For equipment rated 1200 amperes or more and over 1.83 m (6.0 ft) wide, containing overcurrent devices, switching devices, or control devices, there shall be one entrance not less than 610 mm (24 in.) wide and 1.98 m (6.5 ft) high at each end of the working space”
10. An industrial worker is routing communications wires and cables on a building near existing lightning conductors. What is the minimum separation distance required between these wires and the lightning conductors?
Answer: 1.83 m (6 ft). OSHA requires a specific 6-foot separation between building-mounted communications wires and lightning conductors.
29 CFR § 1910.308(e): “A separation of at least 1.83 m (6 ft) shall be maintained between communications wires and cables on buildings and lightning conductors.”
11. An electrician is labeling a circuit panel. The system operates at an actual voltage that varies slightly from the assigned value of 480Y/277. According to the definition of 'Voltage, nominal', what is the purpose of assigning this specific value?
Answer: To conveniently designate the voltage class of the circuit or system. The rule defines nominal voltage as a value assigned for the convenience of designating the voltage class, acknowledging that actual operating voltage can vary within a satisfactory range.
29 CFR § 1926.449: “A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (as 120/240, 480Y/277, 600, etc.).”
12. During a daily visual inspection of temporary cord sets under an assured equipment grounding conductor program, what specific condition requires that the equipment not be used until repaired?
Answer: External defects such as deformed or missing pins or insulation damage. Visual inspections must identify external defects like deformed pins or insulation damage, and such damaged equipment must be removed from service until repaired.
29 CFR § 1910.304(b): “Each cord set, attachment cap, plug, and receptacle of cord sets, and any equipment connected by cord and plug, except cord sets and receptacles which are fixed and not exposed to damage, shall be visually inspected before each day's use for external defects, such as deformed or missing pins or insulation damage, and for indications of possible internal damage. Equipment found damaged or defective shall not be used until repaired;”
13. An electrician is installing a new circuit and must select the correct conductor to connect the noncurrent-carrying metal parts of equipment, raceways, and enclosures to the system grounded conductor or grounding electrode conductor. Which specific conductor is required for this connection?
Answer: Equipment grounding conductor. The definition identifies the 'Grounding conductor, equipment' as the specific conductor used to connect noncurrent-carrying metal parts of equipment and enclosures to the grounding system.
29 CFR § 1926.449: “Grounding conductor, equipment. The conductor used to connect the noncurrent-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor and/or the grounding electrode conductor at the service equipment or at the source of a separately derived system.”
14. When installing power-limited fire alarm (PLFA) circuits, how must the power source be identified to ensure compliance?
Answer: It must be listed equipment marked as a PLFA power source. Unlike nonpower-limited circuits which have voltage limits, PLFA circuits specifically require the source to be listed equipment marked as a PLFA power source.
29 CFR § 1910.308(d): “The power source for a power-limited fire alarm (PLFA) circuit shall be listed equipment marked as a PLFA power source.”
15. An electrician is installing circuit breakers for overcurrent protection on a three-phase circuit operating at more than 600 volts. What is the minimum requirement for the relays and current transformers used in this application?
Answer: A minimum of three overcurrent relays operated from three current transformers. For three-phase circuits over 600 volts, the standard mandates a minimum of three overcurrent relays, each operated from its own current transformer.
29 CFR § 1910.304(f): “Circuit breakers used for overcurrent protection of three-phase circuits shall have a minimum of three overcurrent relays operated from three current transformers.”
16. An industrial worker is reviewing the documentation for a hazardous (classified) location established after August 13, 2007. Who must have access to this documentation?
Answer: Those authorized to design, install, inspect, maintain, or operate electric equipment at the location. The rule mandates that documentation be available specifically to authorized personnel involved in the lifecycle of the electrical equipment at that site.
29 CFR § 1910.307(b): “This documentation shall be available to those authorized to design, install, inspect, maintain, or operate electric equipment at the location.”
17. An electrician is installing a portable generator to power cord-and-plug-connected equipment. Under which condition is the generator frame permitted to serve as the grounding electrode without a separate ground rod?
Answer: The generator supplies only equipment mounted on the generator or cord- and plug-connected equipment through receptacles mounted on the generator, and noncurrent-carrying metal parts are bonded to the frame. The rule allows the generator frame to act as the grounding electrode only if it supplies specific equipment types and those equipment parts are bonded to the frame.
29 CFR § 1910.304(g): “The frame of a portable generator need not be grounded and may serve as the grounding electrode for a system supplied by the generator under the following conditions: (A) The generator supplies only equipment mounted on the generator or cord- and plug-connected equipment through receptacles mounted on the generator, or both; and (B) The noncurrent-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.”
18. An electrician is preparing to use a cord set on a construction site under an assured equipment grounding conductor program. Before using it for the day, what specific inspection must be performed?
Answer: A visual inspection for external defects such as deformed or missing pins or insulation damage. The regulation requires a visual inspection for external defects before each day's use, while continuity tests are performed at specific intervals or after repairs, not necessarily daily.
29 CFR § 1926.404(b): “Each cord set, attachment cap, plug and receptacle of cord sets, and any equipment connected by cord and plug, except cord sets and receptacles which are fixed and not exposed to damage, shall be visually inspected before each day's use for external defects, such as deformed or missing pins or insulation damage, and for indications of possible internal damage.”
19. When constructing a transformer vault to contain fire and combustible liquids, how must the vault door locks and latches be arranged?
Answer: They must be arranged so that the door can be readily opened from the inside. Safety regulations require that personnel inside the vault can easily exit, so locks must allow opening from the inside.
29 CFR § 1910.305(j): “Locks and latches shall be so arranged that a vault door can be readily opened from the inside.”
20. For a separately derived system, where must the equipment grounding conductor and the grounding electrode conductor be connected relative to the system disconnecting means?
Answer: On the supply side of the system disconnecting means or overcurrent devices. For separately derived systems, the bonding of the grounding conductors to the grounded circuit conductor must occur on the supply side of the disconnecting means or overcurrent devices.
29 CFR § 1910.304(g): “Both the equipment grounding conductor and the grounding electrode conductor shall be connected to the grounded circuit conductor on the supply side of the service disconnecting means or on the supply side of the system disconnecting means or overcurrent devices if the system is separately derived.”
21. An electrician is evaluating whether to ground the exposed noncurrent-carrying metal parts of fixed equipment operating at over 150 volts to ground. Which of the following items is exempt from this grounding requirement?
Answer: Metal frames of electrically heated appliances which are permanently and effectively insulated from ground. The regulation lists metal frames of electrically heated appliances as exempt only if they are permanently and effectively insulated from ground; the other options either change the condition (bonded vs insulated), the location (6 ft vs >8 ft), or the equipment type (service vs other than service).
29 CFR § 1926.404(f): “Metal frames of electrically heated appliances which are permanently and effectively insulated from ground”
22. An electrician is installing underwater lighting fixtures in a permanently installed pool. What is the maximum voltage allowed between conductors for these fixtures?
Answer: 150 volts. The regulation prohibits the installation of underwater lighting fixtures that operate at more than 150 volts between conductors.
29 CFR § 1910.306(j): “No underwater lighting fixtures may be installed for operation at over 150 volts between conductors.”
23. A worker is selecting a portable handlamp for use in a construction area. Which of the following features is required for the handlamp's guard if the guard is made of metal?
Answer: The metallic guard must be grounded by an equipment grounding conductor run within the power supply cord. OSHA specifically requires that if the handlamp guard is metallic, it must be grounded via a conductor inside the cord to ensure safety.
29 CFR § 1926.405(j): “Metallic guards shall be grounded by the means of an equipment grounding conductor run within the power supply cord.”
24. An electrician is installing equipment outdoors where it will be exposed to rain but not to snow, ice, dust, or extreme temperatures. Which construction characteristic is sufficient to meet the requirement for 'Weatherproof' equipment in this specific scenario?
Answer: Watertight. The rule states that watertight equipment can fulfill weatherproof requirements if factors other than wetness (like snow or dust) are not present.
29 CFR § 1926.449: “Rainproof, raintight, or watertight equipment can fulfill the requirements for weatherproof where varying weather conditions other than wetness, such as snow, ice, dust, or temperature extremes, are not a factor.”
25. An electrician is installing general illumination lamps for a temporary construction site setup. What protection is required for these lamps?
Answer: They must be protected from accidental contact or breakage. The rule mandates that all general illumination lamps be protected against accidental contact or breakage.
29 CFR § 1926.405(a): “All lamps for general illumination shall be protected from accidental contact or breakage.”