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 new lighting fixture in an outdoor pool area. The fixture is positioned 1.2 m (4 ft) horizontally from the inside wall of the pool. To comply with safety standards, what is the minimum height requirement for any part of this fixture above the maximum water level?
Answer: 3.66 m (12 ft). Because the fixture is within the 5 ft horizontal exclusion zone, it must be mounted at least 12 ft above the water level to be permitted.
29 CFR § 1910.306(j): “In outdoor pool areas, lighting fixtures, lighting outlets, and ceiling-suspended (paddle) fans may not be installed over the pool or over the area extending 1.52 m (5 ft) horizontally from the inside walls of a pool unless no part of the lighting fixture of a ceiling-suspended (paddle) fan is less than 3.66 m (12 ft) above the maximum water level.”
2. An electrician is installing aboveground conductors for a system over 600 volts in an area accessible only to qualified persons. Which of the following conductor types is permitted for open runs in this specific location?
Answer: Bare conductors. The regulation permits bare conductors for open runs in areas accessible only to qualified persons, whereas braided coverings require specific support to prevent damage and are not the primary 'open run' exception for bare types.
29 CFR § 1910.308(a): “In locations accessible to qualified persons only, open runs of Type MV cables, bare conductors, and bare busbars are also permitted.”
3. An electrician is preparing to work in a manhole containing exposed energized parts. To prevent inadvertent contact, what must the employer provide and the employee use?
Answer: Protective shields, protective barriers, or insulating materials. The regulation mandates the use of shields, barriers, or insulating materials in confined spaces with exposed energized parts to prevent accidental contact.
29 CFR § 1910.333(c): “When an employee works in a confined or enclosed space (such as a manhole or vault) that contains exposed energized parts, the employer shall provide, and the employee shall use, protective shields, protective barriers, or insulating materials as necessary to avoid inadvertent contact with these parts.”
4. A worker needs to isolate equipment for inspection, but the isolating means is not designed to interrupt the load current. What must be provided to ensure safety?
Answer: A sign warning against opening them under load. If the isolator cannot interrupt load current, it must be interlocked or have a warning sign against opening it under load.
29 CFR § 1926.408(a): “Isolating means which are not designed to interrupt the load current of the circuit shall be either interlocked with a circuit interrupter or provided with a sign warning against opening them under load.”
5. A worker is running a flexible cord through a hole in a metal outlet box cover. What protection is required for the cord at this point?
Answer: Bushings or fittings. To prevent damage to the cord's insulation, bushings or fittings are required when passing through holes in enclosures like outlet box covers.
29 CFR § 1926.405(g): “Flexible cords and cables shall be protected by bushings or fittings where passing through holes in covers, outlet boxes, or similar enclosures.”
6. When an electrician installs an emergency power system for illumination, what is the required relationship between the emergency circuit wiring and other wiring?
Answer: It must be kept entirely independent of all other wiring and equipment. OSHA requires emergency circuit wiring to be independent from other wiring to ensure it remains operational during a failure of the normal supply.
29 CFR § 1910.308(b): “Emergency circuit wiring shall be kept entirely independent of all other wiring and equipment and may not enter the same raceway, cable, box, or cabinet or other wiring except either where common circuit elements suitable for the purpose are required, or for transferring power from the normal to the emergency source.”
7. A worker is entering a switchboard room where the control panels are 7 feet wide. What is the minimum width required for the entrance providing access to the working space?
Answer: 24 inches. The general requirement for an entrance to the working space is a minimum width of 24 inches.
29 CFR § 1910.303(h): “At least one entrance not less than 610 mm (24 in.) wide and 1.98 m (6.5 ft) high shall be provided to give access to the working space about electric equipment.”
8. Before reenergizing circuits or equipment, a qualified person must conduct tests and visual inspections to verify that which of the following have been removed so the circuits can be safely energized?
Answer: All tools, electrical jumpers, shorts, grounds, and other such devices. The regulation lists tools, jumpers, shorts, and grounds as the specific items that must be removed before reenergizing.
29 CFR § 1910.333(b): “A qualified person shall conduct tests and visual inspections, as necessary, to verify that all tools, electrical jumpers, shorts, grounds, and other such devices have been removed, so that the circuits and equipment can be safely energized.”
9. A worker is installing a cable rated at 2,500 volts with solid dielectric insulation. According to the definitions, what is the correct classification for this cable?
Answer: Medium voltage cable (Type MV). The rule defines Medium voltage cable (Type MV) as a solid dielectric insulated cable rated 2001 volts or higher, which includes the 2,500-volt cable.
29 CFR § 1910.399: “Medium voltage cable (Type MV). A single or multiconductor solid dielectric insulated cable rated 2001 volts or higher.”
10. An industrial worker is routing open power conductors on a pole where they are positioned below communication conductors. What is the minimum horizontal climbing space required for the power conductors?
Answer: 762 mm (30 in.). When power conductors are located below communication conductors on a pole, a specific horizontal climbing space of 30 inches is mandated.
29 CFR § 1910.304(c): “Power conductors below communication conductors—762 mm (30 in.);”
11. An industrial worker is inspecting the dedicated space above an indoor panelboard. The space extends from the top of the equipment to the structural ceiling. Under what condition are foreign systems (such as piping or ducts) permitted in this specific upper area?
Answer: If protection is provided to avoid damage from condensation, leaks, or breaks. Foreign systems are generally prohibited in the dedicated space above the equipment unless specific protection against leaks, breaks, or condensation is installed.
29 CFR § 1910.303(g): “The space equal to the width and depth of the equipment shall be kept clear of foreign systems unless protection is provided to avoid damage from condensation, leaks, or breaks in such foreign systems. This area shall extend from the top of the electric equipment to the structural ceiling;”
12. An industrial worker is marking the entrance to a room containing exposed live parts. What is the required marking for this entrance?
Answer: Conspicuous warning signs forbidding unqualified persons to enter. The regulation specifically requires conspicuous warning signs that forbid unqualified persons from entering these locations.
29 CFR § 1910.303(g): “Entrances to rooms and other guarded locations containing exposed live parts shall be marked with conspicuous warning signs forbidding unqualified persons to enter.”
13. An electrician is installing high-voltage equipment in a tunnel and needs to connect bare terminals of transformers and switches. What action must be taken to comply with OSHA requirements for preventing accidental contact?
Answer: Enclose the bare terminals to prevent accidental contact with energized parts. The regulation mandates that bare terminals be enclosed to protect workers from accidental contact with energized parts.
29 CFR § 1910.308(a): “Bare terminals of transformers, switches, motor controllers, and other equipment shall be enclosed to prevent accidental contact with energized parts.”
14. A worker is preparing to bond a metal raceway to an equipment enclosure to ensure electrical continuity. What must be done to the contact surfaces before making the connection?
Answer: Remove any nonconductive paint, enamel, or similar coating at threads, contact points, and contact surfaces. To ensure effective bonding and electrical continuity, nonconductive coatings like paint or enamel must be removed from contact points unless specific fittings are used.
29 CFR § 1910.305(a): “Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or be connected by means of fittings designed so as to make such removal unnecessary.”
15. When an electrician installs a new piece of equipment, they must ensure it is 'certified.' Which of the following criteria must the equipment meet to be considered certified under this subpart?
Answer: It must have been tested by a qualified testing laboratory to meet applicable standards and be subject to periodic production inspections by that laboratory. Certification requires both initial testing by a qualified laboratory to meet standards and periodic inspection of the production process by that same qualified laboratory.
29 CFR § 1926.449: “Equipment is “certified” if it: (a) Has been tested and found by a qualified testing laboratory to meet applicable test standards or to be safe for use in a specified manner, and (b) Is of a kind whose production is periodically inspected by a qualified testing laboratory.”
16. A worker is inspecting a wiring system and encounters an accessory, such as a locknut or bushing, that is intended primarily to perform a mechanical rather than an electrical function. How is this accessory classified under the definitions?
Answer: Fitting. The rule defines a 'Fitting' as an accessory like a locknut or bushing whose primary purpose is mechanical rather than electrical.
29 CFR § 1926.449: “Fitting. An accessory such as a locknut, bushing, or other part of a wiring system that is intended primarily to perform a mechanical rather than an electrical function.”
17. When grounding a vehicle-mounted generator system, which of the following is a required condition for the vehicle frame to serve as the grounding electrode?
Answer: The generator frame must be bonded to the vehicle frame. The regulation requires that the generator frame be bonded to the vehicle frame for the vehicle frame to serve as the grounding electrode.
29 CFR § 1910.304(g): “The frame of a vehicle need not be grounded and may serve as the grounding electrode for a system supplied by a generator located on the vehicle under the following conditions: (A) The frame of the generator is bonded to the vehicle frame;”
18. When providing work space about electric equipment where energized parts are exposed, what is the minimum clear work space height required, measured vertically from the floor or platform?
Answer: 1.98 m (6.5 ft). The regulation specifies that the minimum clear work space height for exposed energized parts is 6.5 feet.
29 CFR § 1910.303(h): “Where energized parts are exposed, the minimum clear work space may not be less than 1.98 m (6.5 ft) high (measured vertically from the floor or platform) or less than 914 mm (3.0 ft) wide (measured parallel to the equipment).”
19. An electrician is preparing to remove a capacitor bank from service on a circuit operating at more than 600 volts. According to OSHA requirements, what specific feature must the isolating means provide to ensure safe isolation from all sources of voltage?
Answer: A visible gap in the electric circuit adequate for the operating voltage. The regulation mandates that the isolating means must provide a visible gap in the circuit appropriate for the voltage level when removing capacitors from service.
29 CFR § 1910.305(j): “A means shall be installed to isolate from all sources of voltage each capacitor, capacitor bank, or capacitor installation that will be removed from service as a unit. The isolating means shall provide a visible gap in the electric circuit adequate for the operating voltage;”
20. An electrician is inspecting a facility to determine which electrical installations are subject to the design safety standards in §§ 1910.302 through 1910.308. Which of the following installations is excluded from these coverage provisions?
Answer: Installations in railway rolling stock used for transporting goods. The rule lists railway rolling stock as not covered, while mobile homes are specifically included as an exception to the automotive exclusion, and the other options are listed as covered items.
29 CFR § 1910.302(a): “The provisions of §§ 1910.302 through 1910.308 do not cover: (i) Installations in ships, watercraft, railway rolling stock, aircraft, or automotive vehicles other than mobile homes and recreational vehicles;”
21. An electrician is installing a Class 2 power supply unit for a remote control circuit in a construction site office. Before energizing the circuit, what specific marking requirement must the electrician verify on the power supply unit?
Answer: It must be durably marked where plainly visible to indicate the class of supply and its electrical rating. The regulation prohibits the use of Class 2 or Class 3 power supply units unless they are durably marked to show their class and electrical rating.
29 CFR § 1926.408(b): “A Class 2 or Class 3 power supply unit shall not be used unless it is durably marked where plainly visible to indicate the class of supply and its electrical rating.”
22. An electrician is installing a disconnecting means for an elevator driving machine located in a remote machinery space. What capability must this single disconnecting means possess to comply with safety standards?
Answer: It must be capable of being locked in the open position. For elevators with driving machines in remote spaces, the code mandates that the disconnecting means can be locked open to ensure safe isolation.
29 CFR § 1910.306(c): “Where the driving machine is located in a remote machinery space, a single disconnecting means for disconnecting all ungrounded main power supply conductors shall be provided and be capable of being locked in the open position.”
23. When a qualified person uses test equipment to verify that circuit elements are deenergized, what additional condition must the test determine exists, even if specific parts of the circuit have been deenergized and presumed safe?
Answer: If any energized condition exists as a result of inadvertently induced voltage or unrelated voltage backfeed. The test must specifically check for induced voltage or backfeed, not just the absence of the primary source.
29 CFR § 1910.333(b): “The test shall also determine if any energized condition exists as a result of inadvertently induced voltage or unrelated voltage backfeed even though specific parts of the circuit have been deenergized and presumed to be safe.”
24. An electrician is installing a metal raceway that supplies an equipment enclosure where reduction of electrical noise is necessary. How may the enclosure be isolated from the raceway while maintaining a proper ground path?
Answer: By using listed nonmetallic raceway fittings and supplementing with an internal insulated equipment grounding conductor. To reduce electrical noise, the enclosure can be isolated using nonmetallic fittings, provided an internal insulated equipment grounding conductor is added to ground the enclosure.
29 CFR § 1910.305(a): “an equipment enclosure supplied by a branch circuit may be isolated from a raceway containing circuits supplying only that equipment by one or more listed nonmetallic raceway fittings located at the point of attachment of the raceway to the equipment enclosure. The metal raceway shall be supplemented by an internal insulated equipment grounding conductor installed to ground the equipment enclosure.”
25. An electrician is inspecting the working space in front of a switchboard. Other associated equipment is mounted directly above the switchboard. What is the maximum distance this upper equipment may extend beyond the front of the switchboard?
Answer: 153 mm (6 in.). Associated equipment located above or below the main electrical equipment is allowed to protrude into the working space by no more than 6 inches.
29 CFR § 1910.303(g): “However, other equipment associated with the electrical installation and located above or below the electric equipment may extend not more than 153 mm (6 in.) beyond the front of the electric equipment.”