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 a dry-type transformer indoors rated at 40kV. What is the required installation method?
Answer: It must be installed in a vault. Dry-type transformers installed indoors with a rating over 35kV are required to be in a vault.
29 CFR § 1910.305(j): “Dry-type, high fire point liquid-insulated, and askarel-insulated transformers installed indoors and rated over 35kV shall be in a vault.”
2. An electrician needs to install or remove a fuse in a circuit where one or both terminals are still energized. What tool requirement must be followed?
Answer: Special tools insulated for the voltage shall be used. The rule requires the use of special tools that are specifically insulated for the voltage of the energized terminals.
29 CFR § 1926.416(d): “When fuses are installed or removed with one or both terminals energized, special tools insulated for the voltage shall be used.”
3. An electrician is installing temporary lighting inside a concession tent. To comply with OSHA requirements for lamps used for general illumination, what specific protection must be provided?
Answer: A suitable fixture or lampholder with a guard to protect from accidental breakage. The regulation requires that temporary lamps for general illumination inside tents and concessions be protected from accidental breakage by a suitable fixture or lampholder with a guard.
29 CFR § 1910.306(k): “All temporary lamps for general illumination shall be protected from accidental breakage by a suitable fixture or lampholder with a guard.”
4. An electrician is maintaining an indoor sign exceeding 600 volts that is accessible to unqualified persons. To ensure safety, the doors or covers giving access to uninsulated parts must either have interlock switches or be fastened in what manner?
Answer: Such that the use of other than ordinary tools will be necessary to open them. The regulation allows for fastening doors or covers so that specialized tools are required to open them as an alternative to interlock switches for high-voltage indoor signs accessible to unqualified persons.
29 CFR § 1910.306(a): “Doors or covers giving access to uninsulated parts of indoor signs or outline lighting exceeding 600 volts and accessible to other than qualified persons shall either be provided with interlock switches to disconnect the primary circuit or shall be so fastened that the use of other than ordinary tools will be necessary to open them.”
5. An industrial worker is installing overhead open conductors rated at 480 volts across a flat roof. What is the minimum vertical clearance required above the roof surface?
Answer: 2.44 m (8.0 ft). The rule states that overhead spans must have a vertical clearance of at least 8.0 feet above the roof surface.
29 CFR § 1910.304(c): “Overhead spans of open conductors and open multiconductor cables shall have a vertical clearance of not less than 2.44 m (8.0 ft) above the roof surface.”
6. An electrician is working on a circuit over 600 volts where a permanent connection to earth is required to ensure that ground fault current cannot build up to dangerous voltages. What is the specific term for this type of connection?
Answer: Grounded, effectively. The definition for 'Grounded, effectively' specifies that for circuits over 600 volts, the connection must be permanent with low impedance and sufficient ampacity to prevent dangerous voltage buildup from ground faults.
29 CFR § 1926.449: “Grounded, effectively (Over 600 volts, nominal.) Permanently connected to earth through a ground connection of sufficiently low impedance and having sufficient ampacity that ground fault current which may occur cannot build up to voltages dangerous to personnel.”
7. What is the requirement for the test records of equipment grounding conductors under the assured equipment grounding conductor program?
Answer: They must identify each receptacle, cord set, and cord- and plug-connected equipment that passed the test and indicate the last date it was tested. The record must specifically identify the equipment that passed and the date of the test, and it must be available on the jobsite for inspection.
29 CFR § 1926.404(b): “This test record shall identify each receptacle, cord set, and cord- and plug-connected equipment that passed the test and shall indicate the last date it was tested or the interval for which it was tested.”
8. An electrician is selecting a device to protect personnel from shock in a wet environment. Which device functions to deenergize the circuit when a current to ground exceeds a predetermined value less than that required to operate the overcurrent protective device?
Answer: A ground-fault circuit interrupter. The GFCI is specifically defined as the device that deenergizes the circuit when ground current exceeds a set value lower than the overcurrent device's trip threshold.
29 CFR § 1926.449: “Ground-fault circuit interrupter. A device for the protection of personnel that functions to deenergize a circuit or portion thereof within an established period of time when a current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device of the supply circuit.”
9. An electrician is installing a new disconnecting means for a motor. What marking requirement must be met for this disconnecting means?
Answer: It must be legibly marked to indicate its purpose, unless located and arranged so the purpose is evident. The rule requires legible marking of the purpose for disconnecting means unless the purpose is already evident by location and arrangement.
29 CFR § 1926.403(h): “Each disconnecting means required by this subpart for motors and appliances shall be legibly marked to indicate its purpose, unless located and arranged so the purpose is evident.”
10. An electrician is wiring a resistance welder and its control equipment to the supply circuit. What type of device must be provided to allow the welder and its control equipment to be isolated from the supply circuit?
Answer: A switch or circuit breaker. The regulation specifies that a switch or circuit breaker is the required device for isolating resistance welders and their control equipment from the power supply.
29 CFR § 1926.406(c): “A switch or circuit breaker shall be provided by which each resistance welder and its control equipment can be isolated from the supply circuit.”
11. What is the requirement for test records under an assured equipment grounding conductor program for temporary wiring?
Answer: The record must identify each receptacle, cord set, and cord- and plug-connected equipment that passed the test and indicate the last date it was tested. Test records must specifically identify the equipment that passed and provide the date or interval of the last test.
29 CFR § 1910.304(b): “This test record shall identify each receptacle, cord set, and cord- and plug-connected equipment that passed the test and shall indicate the last date it was tested or the interval for which it was tested.”
12. An electrician is installing open runs of braid-covered insulated conductors in a high-voltage area. What requirement applies to the braid covering?
Answer: The braid shall be flame retardant or have a flame-retardant saturant applied after installation. To prevent fire hazards, the braid covering on open runs must be treated to be flame retardant either by material choice or post-installation saturation.
29 CFR § 1910.308(a): “The braid on open runs of braid-covered insulated conductors shall be flame retardant or shall have a flame-retardant saturant applied after installation.”
13. An electrician is selecting equipment for a hazardous location containing specific combustible dusts. Besides being approved for the class of location, what else must the equipment be approved for?
Answer: The ignitable or combustible properties of the specific dust present. Approval must cover both the general class of the location and the specific properties of the hazardous material (dust, in this case) present.
29 CFR § 1910.307(c): “Equipment shall be approved not only for the class of location, but also for the ignitable or combustible properties of the specific gas, vapor, dust, or fiber that will be present.”
14. A worker is installing aboveground conductors for a system over 600 volts in a general industrial area (not restricted to qualified persons). Which of the following is NOT a permitted method for installing these conductors?
Answer: Open runs of bare busbars. Open runs of bare busbars are only permitted in locations accessible to qualified persons only; in general areas, they must be in raceways, trays, or as metal-clad cable.
29 CFR § 1910.308(a): “Aboveground conductors shall be installed in rigid metal conduit, in intermediate metal conduit, in electrical metallic tubing, in rigid nonmetallic conduit, in cable trays, as busways, as cablebus, in other identified raceways, or as open runs of metal-clad cable suitable for the use and purpose.”
15. A worker needs to store spare conduit and tools temporarily. According to OSHA rules for transformer vaults, what is the correct action?
Answer: Do not store any materials in the transformer vault. The rule states a blanket prohibition on storing materials in transformer vaults, regardless of material type or safety equipment.
16. A worker approaches a room containing exposed live parts operating at over 600 volts. Under what condition is entry permitted if the door is not locked?
Answer: If the room is under the observation of a qualified person at all times. For circuits over 600 volts, the entrance must be either locked or continuously observed by a qualified person to restrict access.
29 CFR § 1926.403(j): “The entrances to all buildings, rooms or enclosures containing exposed live parts or exposed conductors operating at over 600 volts, nominal, shall be kept locked or shall be under the observation of a qualified person at all times.”
17. An electrician is installing general-purpose equipment in a Class I, Division 2 location. Under what condition is this installation permitted?
Answer: If the employer can demonstrate that the equipment does not constitute a source of ignition under normal operating conditions. General-purpose equipment is allowed in Division 2 locations only if the employer provides a demonstration that it won't ignite the atmosphere under normal use.
29 CFR § 1910.307(e): “General-purpose equipment or equipment in general-purpose enclosures may be installed in Division 2 locations if the employer can demonstrate that the equipment does not constitute a source of ignition under normal operating conditions.”
18. An electrician is installing a circuit breaker to serve as a switch for a 277-volt fluorescent lighting circuit. According to OSHA regulations, what specific marking must the circuit breaker have to be compliant?
Answer: It must be marked "SWD". The regulation requires circuit breakers used as switches in these specific lighting circuits to be listed and marked "SWD".
29 CFR § 1910.304(f): “Circuit breakers used as switches in 120-volt and 277-volt, fluorescent lighting circuits shall be listed and marked “SWD.””
19. A worker is preparing to service a capacitor rated over 600 volts using an isolating switch that has no interrupting rating. To prevent switching load current, what must the worker ensure is in place?
Answer: The switch is interlocked with the load interrupting device or has prominently displayed caution signs. For capacitors over 600 volts, isolating switches without interrupting ratings must be interlocked with the load interrupting device or have prominent caution signs to prevent switching load current.
29 CFR § 1926.405(j): “Isolating or disconnecting switches (with no interrupting rating) shall be interlocked with the load interrupting device or shall be provided with prominently displayed caution signs to prevent switching load current.”
20. A vehicle with its structure lowered is in transit near energized overhead lines with a voltage higher than 50kV. What is the minimum clearance requirement?
Answer: 4 ft. (122 cm) plus 4 in. (10 cm) for every 10kV over 50kV. For vehicles in transit with lowered structures, the base clearance is 4 ft, but it must be increased by 4 inches for every 10kV above 50kV.
29 CFR § 1910.333(c): “If the vehicle is in transit with its structure lowered, the clearance may be reduced to 4 ft. (122 cm). If the voltage is higher than 50kV, the clearance shall be increased 4 in. (10 cm) for every 10kV over that voltage.”
21. A qualified electrician is selecting a disconnecting means for a photovoltaic power source where the circuit grounding connection is NOT designed to be automatically interrupted by the ground-fault protection system. What configuration is prohibited for the switch or circuit breaker used as the disconnecting means?
Answer: It must have a pole in the grounded conductor. If the ground-fault protection does not automatically interrupt the grounding connection, the disconnecting device is forbidden from having a pole in the grounded conductor.
29 CFR § 1910.308(f): “Where a circuit grounding connection is not designed to be automatically interrupted as part of the ground-fault protection system, a switch or circuit breaker used as disconnecting means may not have a pole in the grounded conductor.”
22. An electrician is installing a disconnecting means for a monorail hoist. If this disconnect is not readily accessible from the operating station, what additional provision must be made?
Answer: Means shall be provided at the operating station to open the power circuit to all motors. When the main disconnect is not accessible from the operator's station, the regulation requires a means at the station to open the power circuit to all motors.
29 CFR § 1926.406(a): “If this additional disconnecting means is not readily accessible from the crane or monorail hoist operating station, means shall be provided at the operating station to open the power circuit to all motors of the crane or monorail hoist.”
23. A worker is using a temporary 125-volt, single-phase, 30-ampere receptacle outlet for a construction activity. The outlet is not part of the permanent wiring. What is required for this specific receptacle?
Answer: Ground-fault circuit-interrupter protection for personnel. Temporary 15-, 20-, and 30-ampere single-phase receptacles must have GFCI protection; the assured grounding program is only for receptacles outside this specific voltage/amperage range.
29 CFR § 1910.304(b): “All 125-volt, single-phase,15-, 20-, and 30-ampere receptacle outlets that are not part of the permanent wiring of the building or structure and that are in use by personnel shall have ground-fault circuit-interrupter protection for personnel.”
24. An industrial worker is about to perform housekeeping duties near live parts that present an electrical contact hazard. Under what condition is the worker permitted to perform these duties at a close distance?
Answer: Only if adequate safeguards, such as insulating equipment or barriers, are provided. The regulation permits close-range housekeeping only when specific safeguards like insulating equipment or barriers are in place to prevent contact.
29 CFR § 1910.333(c): “Where live parts present an electrical contact hazard, employees may not perform housekeeping duties at such close distances to the parts that there is a possibility of contact, unless adequate safeguards (such as insulating equipment or barriers) are provided.”
25. Before beginning work on a site, what must the employer do regarding energized electric power circuits that are exposed or concealed?
Answer: Ascertain by inquiry, observation, or instruments if contact is possible, and post warning signs. The employer is required to actively determine the presence of hazards using inquiry, observation, or instruments and then post warning signs.
29 CFR § 1926.416(a): “Before work is begun the employer shall ascertain by inquiry or direct observation, or by instruments, whether any part of an energized electric power circuit, exposed or concealed, is so located that the performance of the work may bring any person, tool, or machine into physical or electrical contact with the electric power circuit. The employer shall post and maintain proper warning signs where such a circuit exists.”