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 worker needs to access an outdoor electrical installation to deter access by persons who are not qualified. If the worker chooses to use a fence as the enclosure, what is the minimum height requirement for the fence itself?
Answer: 2.13 m (7.0 ft). The regulation states that a standalone fence must be at least 7.0 feet high; the 6.0-foot option is only valid if combined with a barbed wire extension.
29 CFR § 1910.303(h): “A fence may not be less than 2.13 m (7.0 ft) in height or a combination of 1.80 m (6.0 ft) or more of fence fabric and a 305-mm (1-ft) or more extension utilizing three or more strands of barbed wire or equivalent.”
2. An electrician is installing cartridge fuses in a circuit accessible to other than qualified persons. A disconnecting means is required on the supply side. Which exception permits a single disconnecting means for multiple sets of fuses?
Answer: Group operation of motors as permitted by the exception in § 1910.305(j)(4)(vi). A single disconnecting means is allowed for multiple sets of fuses if they are for group operation of motors.
29 CFR § 1910.304(f): “In addition, a single disconnecting means is permitted on the supply side of more than one set of fuses as permitted by the exception in § 1910.305(j)(4)(vi) for group operation of motors”
3. An electrician is installing a disconnecting means for X-ray equipment connected to a 120-volt branch circuit rated at 20 amperes. What component may serve as the disconnecting means?
Answer: A grounding-type attachment plug cap and receptacle of proper rating. For low-voltage (120V) and low-amperage (30A or less) X-ray circuits, a proper grounding plug and receptacle are permitted to act as the disconnect.
29 CFR § 1910.306(f): “For equipment connected to a 120-volt branch circuit of 30 amperes or less, a grounding-type attachment plug cap and receptacle of proper rating may serve as a disconnecting means.”
4. An electrician is evaluating a custom-made control panel designed specifically for a single customer's facility. To ensure the installation is considered 'accepted' and safe for use under OSHA standards, what condition must be met regarding the manufacturer's determination?
Answer: The manufacturer must determine it is safe for its intended use based on test data that the employer keeps and makes available for inspection. For custom-made equipment, acceptance relies on the manufacturer's determination of safety based on test data that the employer retains and makes available for inspection.
29 CFR § 1926.449: “With respect to custom-made equipment or related installations which are designed, fabricated for, and intended for use by a particular customer, if it is determined to be safe for its intended use by its manufacturer on the basis of test data which the employer keeps and makes available for inspection to the Assistant Secretary and his authorized representatives.”
5. An electrician is setting up temporary power on a construction site and needs to run an extension cord across a floor. According to OSHA construction electrical safety rules, how must the cord be secured?
Answer: None of the above; it must not be fastened with staples, hung from nails, or suspended by wire. The regulation prohibits using staples, nails, or wire to secure extension cords, making the negative option the only correct choice.
29 CFR § 1926.416(e): “Extension cords shall not be fastened with staples, hung from nails, or suspended by wire.”
6. When determining 'Voltage to ground' for an ungrounded circuit, what measurement must the electrician take?
Answer: The greatest voltage between the given conductor and any other conductor of the circuit. For ungrounded circuits, the definition specifies using the greatest voltage between the given conductor and any other conductor in the circuit.
29 CFR § 1926.449: “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.”
7. A foreman is reviewing a 'Separately derived system' for a temporary generator setup. What characteristic distinguishes this system from other premises wiring systems?
Answer: It has no direct electrical connection to supply conductors originating in another system. The definition specifies that a separately derived system lacks a direct electrical connection to other systems, whereas the other options contradict or are not part of the definition.
29 CFR § 1926.449: “A premises wiring system whose power is derived from generator, transformer, or converter windings and has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.”
8. An electrician is installing a circuit breaker with a straight voltage rating of 480 V. In which of the following scenarios is this installation permitted under OSHA rules?
Answer: In a circuit where the nominal voltage between any two conductors does not exceed 480 V. For straight-rated breakers, the phase-to-phase voltage must not exceed the breaker's rated voltage.
29 CFR § 1910.304(f): “A circuit breaker with a straight voltage rating, such as 240 V or 480 V, may only be installed in a circuit in which the nominal voltage between any two conductors does not exceed the circuit breaker's voltage rating.”
9. An electrician is applying a lock to a disconnecting means for a circuit that has been deenergized. How must the lock be attached to comply with the standard?
Answer: So that persons cannot operate the disconnecting means unless they resort to undue force or the use of tools. The lock must physically prevent operation of the disconnecting means unless significant force or tools are used to bypass it.
29 CFR § 1910.333(b): “The lock shall be attached so as to prevent persons from operating the disconnecting means unless they resort to undue force or the use of tools.”
10. An electrician is working in an electrical room where the illumination is controlled by a wall switch. To comply with OSHA requirements for working spaces about service equipment, how must the lighting control be configured?
Answer: The illumination may not be controlled by automatic means only. OSHA requires that lighting in electrical rooms cannot rely solely on automatic controls (like motion sensors or timers) to ensure workers can manually ensure adequate light.
29 CFR § 1910.303(g): “In electric equipment rooms, the illumination may not be controlled by automatic means only.”
11. An electrician is modifying an existing electrical installation. What restriction applies to changing the circuit protection?
Answer: No changes shall be made to increase the load in excess of the load rating of the circuit wiring. The rule prohibits increasing the load beyond the existing wiring's rating by changing the protection devices.
29 CFR § 1926.416(c): “In existing installations, no changes in circuit protection shall be made to increase the load in excess of the load rating of the circuit wiring.”
12. An electrician is working near exposed energized conductors using handling equipment that might make contact with those conductors. What is the mandatory requirement for this equipment?
Answer: The equipment must be insulated. The regulation mandates the use of insulated tools or handling equipment when there is a risk of contact with exposed energized parts.
29 CFR § 1910.335(a): “When working near exposed energized conductors or circuit parts, each employee shall use insulated tools or handling equipment if the tools or handling equipment might make contact with such conductors or parts.”
13. An industrial worker is connecting a remote pendant pushbutton control for a crane in a cell line working zone. To prevent hazardous electrical conditions, which characteristic must the supporting means and surfaces of the pendant have?
Answer: Nonconductive supporting means with nonconductive surfaces or ungrounded exposed conductive surfaces. The regulation requires the pendant to have nonconductive supports and either nonconductive surfaces or exposed conductive surfaces that are not grounded.
29 CFR § 1910.306(h): “Pendant pushbutton with nonconductive supporting means and with nonconductive surfaces or ungrounded exposed conductive surfaces; or”
14. When identifying conductors or terminals in a wiring system, what does the term 'Identified' specifically mean regarding the conductor's status?
Answer: It can be recognized as grounded. For conductors and terminals, 'identified' means they can be recognized as grounded, distinguishing them from ungrounded conductors.
29 CFR § 1926.449: “Identified (conductors or terminals). Identified, as used in reference to a conductor or its terminal, means that such conductor or terminal can be recognized as grounded.”
15. An industrial worker is operating equipment within the electrolytic cell line working zone. According to the definition of 'Cell line attachments and auxiliary equipment', which of the following is considered auxiliary equipment in this zone?
Answer: Exposed conductive surfaces of ungrounded cranes. The rule lists exposed conductive surfaces of ungrounded cranes as auxiliary equipment within the working zone.
29 CFR § 1910.399: “In the cell line working zone, auxiliary equipment includes the exposed conductive surfaces of ungrounded cranes and crane-mounted cell-servicing equipment.”
16. A technician is evaluating whether a metal rack supporting electric equipment is considered effectively grounded. What condition must be met for this status?
Answer: The equipment must be secured to and in electrical contact with the metal rack, which is itself grounded per fixed equipment rules. Effective grounding is achieved when the equipment is in electrical contact with a grounded metal rack or structure that supports it.
29 CFR § 1926.404(f): “Electric equipment is considered to be effectively grounded if it is secured to, and in electrical contact with, a metal rack or structure that is provided for its support and the metal rack or structure is grounded by the method specified for the noncurrent-carrying metal parts of fixed equipment in paragraph (f)(8)(i) of this section.”
17. An industrial worker is terminating a metal-sheathed cable where conductors emerge from the sheath and protection against moisture or physical damage is necessary. What device is required to protect the insulation of the conductors?
Answer: A cable sheath terminating device. The rule mandates the use of a specific cable sheath terminating device to protect conductor insulation in these conditions.
29 CFR § 1910.308(a): “Where cable conductors emerge from a metal sheath and where protection against moisture or physical damage is necessary, the insulation of the conductors shall be protected by a cable sheath terminating device.”
18. An industrial worker is installing electric equipment in a hazardous location where the ambient temperature exceeds 40 °C (104 °F). What marking requirement applies to this equipment?
Answer: It shall be marked with both the maximum ambient temperature and the operating temperature or temperature range at that ambient temperature. For equipment suitable for ambient temperatures above 40 °C, the rule mandates marking both the maximum ambient temperature and the operating temperature/range at that ambient.
29 CFR § 1910.307(c): “Electric equipment suitable for ambient temperatures exceeding 40 °C (104 °F) shall be marked with both the maximum ambient temperature and the operating temperature or temperature range at that ambient temperature;”
19. When inspecting knife switches mounted in a switchboard, what condition must the exposed blades meet when the switch is in the open position?
Answer: They shall be dead. The regulation requires that exposed blades of knife switches in switchboards or panelboards are de-energized (dead) when the switch is open.
29 CFR § 1910.305(d): “Exposed blades of knife switches mounted in switchboards or panelboards shall be dead when open.”
20. A maintenance worker needs to access a junction box located behind a locked electrical panel door to perform a repair. According to OSHA definitions, how is this equipment classified regarding accessibility?
Answer: Not accessible, because it is guarded by locked doors. Equipment guarded by locked doors is excluded from the definition of 'accessible' unless the lock is removed or bypassed by authorized means, but the definition itself states accessible equipment is 'not guarded by locked doors'.
29 CFR § 1910.399: “Accessible. (As applied to equipment.) Admitting close approach; not guarded by locked doors, elevation, or other effective means.”
21. A worker is installing metal raceways in an outdoor construction environment. What material requirement must the raceways meet?
Answer: They must be made of materials appropriate for the environment in which they are to be installed. The regulation requires that metal components be made of materials suitable for the specific environment to prevent corrosion and deterioration.
29 CFR § 1926.432(b): “Metal raceways, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, fittings, supports, and support hardware shall be of materials appropriate for the environment in which they are to be installed.”
22. An electrician is working on a transformer installation with exposed live parts. According to OSHA construction standards, how must the operating voltage of these exposed live parts be indicated?
Answer: By warning signs or visible markings on the equipment or structure. The regulation requires that the voltage of exposed live parts be indicated via warning signs or visible markings on the equipment or structure.
29 CFR § 1926.405(j): “The operating voltage of exposed live parts of transformer installations shall be indicated by warning signs or visible markings on the equipment or structure.”
23. A worker is turning on the lights in a room containing electric equipment. Where must the points of control for the lighting be located to ensure safety?
Answer: At the entrance, so persons are prevented from contacting any live part or moving part of the equipment while turning on the lights. The regulation specifically requires the location of light switches to prevent contact with live or moving parts during operation.
29 CFR § 1910.303(h): “The points of control shall be located so that persons are prevented from contacting any live part or moving part of the equipment while turning on the lights.”
24. An electrician is installing fixed equipment that requires grounding. Which method of grounding the noncurrent-carrying metal parts is compliant with OSHA standards for AC circuits?
Answer: Using an equipment grounding conductor contained within the same raceway, cable, or cord as the circuit conductors. For AC circuits, the grounding conductor must be contained within the same raceway, cable, or cord as the circuit conductors; running it separately is only permitted for DC circuits.
29 CFR § 1910.304(g): “Noncurrent-carrying metal parts of fixed equipment, if required to be grounded by this subpart, shall be grounded by an equipment grounding conductor that is contained within the same raceway, cable, or cord, or runs with or encloses the circuit conductors.”
25. An electrician is preparing to service a motor control center where live parts are normally exposed on the front. What is the minimum required working space in front of this equipment?
Answer: 3 feet (914 mm). The regulation sets the minimum front working space at 3 feet when live parts are exposed on the front of such equipment.
29 CFR § 1926.403(i): “Where there are live parts normally exposed on the front of switchboards or motor control centers, the working space in front of such equipment shall not be less than 3 feet (914 mm).”