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 arranging lighting outlets in a room containing live parts. What is the primary safety requirement for the placement of these outlets and their control points?
Answer: They must be placed so that persons changing lamps or turning on lights are not endangered by live parts or other equipment. The regulation specifically mandates that the arrangement of outlets and controls prevents personnel from contacting live or moving parts during maintenance or operation.
29 CFR § 1926.403(j): “The lighting outlets shall be so arranged that persons changing lamps or making repairs on the lighting system will not be endangered by live parts or other equipment. The points of control shall be so located that persons are not likely to come in contact with any live part or moving part of the equipment while turning on the lights.”
2. An electrician is reviewing the status of a conductor that has no covering or electrical insulation whatsoever. How is this conductor classified?
Answer: Bare. The rule defines a 'Bare' conductor as one having no covering or electrical insulation.
29 CFR § 1926.449: “A conductor having no covering or electrical insulation whatsoever.”
3. An electrician is installing a communication circuit in a tunnel that is exposed to accidental contact with light or power conductors operating at over 300 volts. What protective device must be provided for each circuit so exposed?
Answer: An approved protector. The rule specifically requires an approved protector for communication circuits exposed to accidental contact with conductors over 300 volts.
29 CFR § 1926.408(c): “Communication circuits so located as to be exposed to accidental contact with light or power conductors operating at over 300 volts shall have each circuit so exposed provided with an approved protector.”
4. An electrician is installing a multiwire branch circuit for temporary power in a construction site. At which location must the means to disconnect simultaneously all ungrounded conductors be provided?
Answer: At the power outlet or panelboard where the branch circuit originated. The regulation requires the simultaneous disconnecting means for multiwire branch circuits to be located at the origin point (outlet or panelboard), not at the load or other arbitrary points.
29 CFR § 1910.305(a): “Multiwire branch circuits shall be provided with a means to disconnect simultaneously all ungrounded conductors at the power outlet or panelboard where the branch circuit originated.”
5. A worker is installing a fixture canopy on a ceiling. If there is combustible wall or ceiling finish exposed between the edge of the canopy and the outlet box, what action is required?
Answer: Cover the exposed combustible finish with noncombustible material. The rule specifically requires covering exposed combustible finishes between the canopy edge and the outlet box with noncombustible material.
29 CFR § 1910.305(b): “Where a fixture canopy or pan is used, any combustible wall or ceiling finish exposed between the edge of the canopy or pan and the outlet box shall be covered with noncombustible material.”
6. An industrial worker is about to plug a flexible cord into a receptacle. What specific check must be performed first to ensure safety?
Answer: Check that the plug and receptacle contacts are of proper mating configurations. The regulation requires checking the mating configuration of the plug and receptacle contacts before connection.
29 CFR § 1910.334(a): “When an attachment plug is to be connected to a receptacle (including any on a cord set), the relationship of the plug and receptacle contacts shall first be checked to ensure that they are of proper mating configurations.”
7. A worker needs to operate a switch on a piece of electrical equipment. To comply with the definition of 'Externally operable', how must the operation be performed?
Answer: Without exposing the operator to contact with live parts. The key requirement for externally operable equipment is that the operator is not exposed to contact with live parts during operation.
29 CFR § 1926.449: “Externally operable. Capable of being operated without exposing the operator to contact with live parts.”
8. A worker is assessing whether a piece of apparatus qualifies as 'Explosion-proof' for use in a hazardous location. Which capability must the apparatus possess according to the definition?
Answer: It must be capable of withstanding an explosion of a specified gas or vapor within it and preventing ignition of the surrounding atmosphere. The definition requires the apparatus to withstand internal explosions and prevent ignition of the external atmosphere via sparks, flashes, or internal explosions.
29 CFR § 1910.399: “Explosion-proof apparatus. Apparatus enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and that operates at such an external temperature that it will not ignite a surrounding flammable atmosphere.”
9. An industrial worker is operating induction heating equipment with a hinged access door. Under which condition is an interlock switch NOT required on this access door?
Answer: When the applicator is an induction heating coil at dc ground potential. Interlocks are not required if the applicator is an induction heating coil at dc ground potential or operates at less than 150 volts ac; 200 volts ac exceeds the exemption threshold.
29 CFR § 1910.306(g): “Interlock switches shall be used on all hinged access doors, sliding panels, or other such means of access to the applicator, unless the applicator is an induction heating coil at dc ground potential or operating at less than 150 volts ac.”
10. An electrician is installing a controller for a motor branch circuit over 600 volts, nominal. Under what condition may the disconnecting means be located out of sight of the controller?
Answer: If the controller is marked with a warning label giving the location and identification of the disconnecting means that is to be locked in the open position. For high-voltage motor circuits, the disconnect can be out of sight only if the controller has a specific warning label identifying the disconnect location and its lock-out status.
29 CFR § 1910.305(j): “The controller disconnecting means for motor branch circuits over 600 volts, nominal, may be out of sight of the controller, if the controller is marked with a warning label giving the location and identification of the disconnecting means that is to be locked in the open position.”
11. Under an assured equipment grounding conductor program for temporary wiring, how often must cord sets and receptacles that are fixed and not exposed to damage be tested?
Answer: At intervals not exceeding 6 months. The regulation specifies a longer testing interval of 6 months for fixed cord sets and receptacles not exposed to damage, compared to the standard 3-month interval.
29 CFR § 1910.304(b): “All required tests shall be performed before first use; before equipment is returned to service following any repairs; before equipment is used after any incident which can be reasonably suspected to have caused damage (for example, when a cord set is run over); and at intervals not to exceed 3 months, except that cord sets and receptacles which are fixed and not exposed to damage shall be tested at intervals not exceeding 6 months;”
12. A worker uses a cord-and-plug-connected tool in a wet location. The tool is not double-insulated. Under what specific condition is the tool exempt from the requirement to have its exposed noncurrent-carrying metal parts grounded?
Answer: It is supplied through an isolating transformer with an ungrounded secondary of not over 50 volts. The rule specifies that the exemption requires an isolating transformer (not standard) with an ungrounded secondary (not grounded) limited to 50 volts (not 100 or 150).
29 CFR § 1926.404(f): “Tools likely to be used in wet and/or conductive locations need not be grounded if supplied through an isolating transformer with an ungrounded secondary of not over 50 volts.”
13. A worker is using a grounding-type device on a receptacle. For what purpose is this device allowed to be used?
Answer: For grounding only. The regulation restricts the use of grounding terminals to grounding purposes only, prohibiting other uses like neutral returns or mechanical support.
29 CFR § 1910.304(a): “A grounding terminal or grounding-type device on a receptacle, cord connector, or attachment plug may not be used for purposes other than grounding.”
14. An electrician is working near overhead electric light and power circuits of over 150 volts to ground. What is the primary requirement for the location of outdoor metal structures supporting antennas?
Answer: They shall be located as far away from the circuits as necessary to avoid the possibility of falling into or making accidental contact. The regulation requires sufficient distance to prevent accidental contact or falling into circuits over 150 volts to ground.
29 CFR § 1926.408(c): “Outdoor metal structures supporting antennas, as well as self-supporting antennas such as vertical rods or dipole structures, shall be located as far away from overhead conductors of electric light and power circuits of over 150 volts to ground as necessary to avoid the possibility of the antenna or structure falling into or making accidental contact with such circuits.”
15. In a tunnel installation, what is the requirement for the equipment grounding conductor when using a metal raceway or multiconductor cable?
Answer: It shall be run with circuit conductors inside the metal raceway or inside the multiconductor cable jacket. The rule mandates that the equipment grounding conductor be included within the same raceway or cable jacket as the circuit conductors.
29 CFR § 1910.308(a): “An equipment grounding conductor shall be run with circuit conductors inside the metal raceway or inside the multiconductor cable jacket. The equipment grounding conductor may be insulated or bare.”
16. A worker is evaluating a fence surrounding an electrical installation to determine if it qualifies as accessible to qualified persons only. If the fence is less than 8 feet high, what condition must be met for it to be considered adequate?
Answer: It must have other features that provide a degree of isolation equivalent to an 8-foot fence. The rule states that a fence under 8 feet is only adequate if it has other features providing equivalent isolation, not merely based on paint, material, or barbed wire.
29 CFR § 1926.403(j): “A wall, screen, or fence less than 8 feet (2.44 m) in height is not considered adequate to prevent access unless it has other features that provide a degree of isolation equivalent to an 8-foot (2.44-m) fence.”
17. An electrician is installing a disconnecting means for a resistance welder. The supply circuit supplies only this single welder. Under what condition may the electrician use the supply circuit switch as the welder disconnecting means?
Answer: Only if the circuit supplies only one welder. The regulation permits using the supply circuit switch as the disconnecting means specifically when the circuit serves only one welder.
29 CFR § 1910.306(d): “The supply circuit switch may be used as the welder disconnecting means where the circuit supplies only one welder.”
18. An electrician is installing a single-throw knife switch in a vertical position. To ensure safety, how must the switch be connected regarding the blades when the switch is open?
Answer: The blades must be dead when the switch is in the open position. The regulation requires that single-throw knife switches be wired so that the blades are not energized (dead) when the switch is open, preventing accidental shock during maintenance or inspection.
29 CFR § 1926.405(c): “Single-throw knife switches shall be so connected that the blades are dead when the switch is in the open position.”
19. An electrician is installing temporary wiring for experimental development work where the feeders are accessible only to qualified persons. Under which specific condition may these feeders be run as single insulated conductors rather than multiconductor assemblies?
Answer: When the installation is for experimental or development work and is accessible only to qualified persons. The rule allows single insulated conductors for feeders only if the installation is for experimental/development work (or emergencies) and is accessible only to qualified persons.
29 CFR § 1910.305(a): “However, if installed as permitted in paragraph (a)(2)(i)(C) of this section, and if accessible only to qualified persons, feeders may be run as single insulated conductors.”
20. When installing communications wires and cables on a pole shared with electric light or power conductors, which attachment method is prohibited by OSHA standards?
Answer: Attaching them to a crossarm that carries electric light or power conductors. The rule forbids attaching communications wires to the same crossarm that supports power conductors.
29 CFR § 1910.308(e): “Communications wires and cables may not be attached to a crossarm that carries electric light or power conductors.”
21. An electrician finds a damaged attachment plug that might expose an employee to injury. What is the required action?
Answer: Remove the item from service until repairs and tests render it safe. Damaged items posing an injury risk must be removed from service until repaired and tested.
29 CFR § 1910.334(a): “If there is a defect or evidence of damage that might expose an employee to injury, the defective or damaged item shall be removed from service, and no employee may use it until repairs and tests necessary to render the equipment safe have been made.”
22. An electrician is evaluating the dedicated space for an indoor motor control center. The space extends from the floor to a height of 1.83 m (6.0 ft) above the equipment. Which foreign items are permitted in this specific lower dedicated space if not isolated by height or physical enclosures?
Answer: None; piping, ducts, or equipment foreign to the electrical installation may not be located in this area. In the lower dedicated space (up to 1.83 m above equipment), foreign piping, ducts, or equipment are generally prohibited unless specific isolation measures are taken.
29 CFR § 1910.303(g): “Unless isolated from equipment by height or physical enclosures or covers that will afford adequate mechanical protection from vehicular traffic or accidental contact by unauthorized personnel or that complies with paragraph (g)(1)(vii)(A)(2) of this section, piping, ducts, or equipment foreign to the electrical installation may not be located in this area;”
23. A qualified electrician is preparing to work on a circuit that has been deenergized. Before considering the circuit safe to work on, what specific verification step must the qualified person perform regarding the equipment's ability to restart?
Answer: Operate the equipment operating controls or otherwise verify that the equipment cannot be restarted. The regulation requires the qualified person to operate controls or otherwise verify the equipment cannot restart before it is considered deenergized.
29 CFR § 1910.333(b): “A qualified person shall operate the equipment operating controls or otherwise verify that the equipment cannot be restarted.”
24. An industrial worker is performing a final check on an electrical cabinet before energizing it. Which condition regarding internal parts would violate the requirement for mechanical execution of work?
Answer: Internal parts are contaminated by paint or corrosive residues. The regulation prohibits contamination of internal parts by foreign materials like paint or corrosive residues, while the other options describe compliant conditions.
29 CFR § 1910.303(b): “Internal parts of electrical equipment, including busbars, wiring terminals, insulators, and other surfaces, may not be damaged or contaminated by foreign materials such as paint, plaster, cleaners, abrasives, or corrosive residues.”
25. A worker is setting up temporary lighting in a dry indoor area and needs to protect lamps from accidental contact or breakage. What is the required method for general illumination lamps?
Answer: Protected by a suitable fixture or lampholder with a guard. The rule mandates that all general illumination lamps be protected by a suitable fixture or lampholder with a guard, regardless of voltage or height, making the other options insufficient or non-compliant.
29 CFR § 1910.305(a): “All lamps for general illumination shall be protected from accidental contact or breakage by a suitable fixture or lampholder with a guard.”