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 conductors that emerge from the ground in a high-voltage system. What is the required method for enclosing these conductors at the point of emergence?
Answer: Approved raceways. The rule specifically mandates that conductors emerging from the ground must be enclosed in approved raceways, not left open or in non-approved materials.
29 CFR § 1910.308(a): “Conductors emerging from the ground shall be enclosed in approved raceways.”
2. An industrial worker is replacing a snap switch in a location where no grounding means exists within the enclosure. Under what specific condition is a snap switch without a grounding connection permitted for replacement purposes?
Answer: If the switch is provided with a faceplate of nonconducting, noncombustible material and is located within reach of conducting floors or other conducting surfaces. The exception for ungrounded snap switches requires a nonconducting, noncombustible faceplate when the switch is within reach of conducting surfaces.
29 CFR § 1910.305(c): “Such snap switches shall be provided with a faceplate of nonconducting, noncombustible material if they are located within reach of conducting floors or other conducting surfaces.”
3. A worker is setting up temporary lighting in a warehouse and finds brass shell, paper-lined sockets. Under what condition are these sockets permitted for use?
Answer: If the shell is grounded. The rule states that metal-cased sockets like brass shell or paper-lined ones are only allowed if the shell itself is grounded.
29 CFR § 1910.305(a): “Brass shell, paper-lined sockets, or other metal-cased sockets may not be used unless the shell is grounded.”
4. An electrician is replacing a nongrounding-type receptacle in a location where no grounding means exists in the enclosure. Which replacement option is permitted under OSHA rules?
Answer: Replace it with a ground-fault circuit-interrupter-type receptacle marked “No Equipment Ground.”. When no ground is available, a GFCI receptacle marked 'No Equipment Ground' is a compliant replacement, provided no equipment ground is connected downstream.
29 CFR § 1910.304(b): “A nongrounding-type receptacle may be replaced with a ground-fault circuit-interrupter-type of receptacle that is marked “No Equipment Ground;” an equipment grounding conductor may not be connected from the ground-fault circuit-interrupter-type receptacle to any outlet supplied from the ground-fault circuit-interrupter receptacle;”
5. A worker needs to use a portable ladder in an area where the ladder or the worker could contact exposed energized parts. What is the required characteristic of the ladder's siderails?
Answer: They must be nonconductive. To prevent electrical shock through the ladder structure, the siderails must be nonconductive when there is a risk of contact with energized parts.
29 CFR § 1910.333(c): “Portable ladders shall have nonconductive siderails if they are used where the employee or the ladder could contact exposed energized parts.”
6. An electrician is installing a disconnecting means for a motor controller. The disconnecting means is located more than 50 feet from the controller. Under which specific condition is this out-of-sight installation permitted?
Answer: If the disconnecting means is for a motor branch circuit over 600 volts nominal and the controller is marked with a warning label giving the location and identification of the disconnecting means. The rule allows the disconnecting means to be out of sight only for circuits over 600 volts if the controller has a specific warning label identifying the disconnect location.
29 CFR § 1926.405(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 which is to be locked in the open position.”
7. A maintenance worker needs to service a monorail hoist. Under which specific condition is the worker permitted to omit the disconnecting means in the leads from the power supply?
Answer: The unit is controlled from the ground or floor level, is within view of the power supply disconnecting means, and has no fixed work platform for servicing. The exception to install a disconnecting means requires all three conditions to be met: ground-level control, visibility of the main disconnect, and no fixed service platform.
29 CFR § 1910.306(b): “The disconnecting means may be omitted where a monorail hoist or hand-propelled crane bridge installation meets all of the following conditions: (A) The unit is controlled from the ground or floor level; (B) The unit is within view of the power supply disconnecting means; and (C) No fixed work platform has been provided for servicing the unit.”
8. An electrician is installing power fuses indoors to protect conductors and equipment. Under which condition are vented-type power fuses permitted for this indoor installation?
Answer: If they are identified for the use. The regulation prohibits vented power fuses indoors unless they are specifically identified for that application.
29 CFR § 1910.308(a): “Power fuses of the vented type may not be used indoors, underground, or in metal enclosures unless identified for the use.”
9. An electrician is installing grounding for a portable high-voltage system on a construction site. To ensure safety, how must the grounding electrode for the system neutral impedance be positioned relative to other grounding electrodes?
Answer: It must be isolated and separated in the ground by at least 20 feet from any other system or equipment grounding electrode. OSHA requires physical isolation and a minimum 20-foot separation for portable high-voltage system grounds to prevent interference and ensure independent grounding.
29 CFR § 1926.404(f): “The grounding electrode to which the portable or mobile equipment system neutral impedance is connected shall be isolated from and separated in the ground by at least 20 feet (6.1 m) from any other system or equipment grounding electrode, and there shall be no direct connection between the grounding electrodes, such as buried pipe, fence or like objects.”
10. A technician is evaluating a device designed to open and close a circuit. According to the definition of a 'Circuit breaker', how does the device operate to open the circuit automatically?
Answer: On a predetermined overcurrent. The definition states the device opens automatically on a predetermined overcurrent.
29 CFR § 1910.399: “A device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating.”
11. When installing resistance welders, what is the minimum ampere rating requirement for the switch or circuit breaker used to isolate the welder and its control equipment from the supply circuit?
Answer: Not less than the supply conductor ampacity. The disconnecting means for resistance welders must be rated at least as high as the ampacity of the supply conductors feeding it.
29 CFR § 1926.406(c): “The ampere rating of this disconnecting means shall not be less than the supply conductor ampacity.”
12. When installing temporary wiring, what is the requirement for receptacles used for purposes other than temporary lighting?
Answer: They shall not be installed on branch circuits which supply temporary lighting. The regulation prohibits mixing receptacles for other uses with those supplying temporary lighting on the same branch circuit.
29 CFR § 1926.405(a): “Receptacles for uses other than temporary lighting shall not be installed on branch circuits which supply temporary lighting.”
13. An electrician is identifying the function of a specific component in a circuit. Which definition accurately describes a 'Disconnecting means'?
Answer: A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply. The rule defines a disconnecting means as the device or means used to disconnect circuit conductors from their source of supply.
29 CFR § 1910.399: “Disconnecting means. A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.”
14. A technician encounters a current flow that exceeds the rated ampacity of a conductor due to a short circuit. Based on the definitions provided, how should this condition be categorized to ensure proper safety protocol identification?
Answer: Overcurrent. The rule defines 'Overcurrent' as any excess current resulting from a short circuit, whereas 'Overload' is distinguished as operation in excess of normal rating that is not a fault like a short circuit.
29 CFR § 1910.399: “Overcurrent. Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.”
15. An electrician is installing a new switchboard in a facility built on September 1, 2007. What is the minimum required headroom for the working space about this equipment?
Answer: 1.98 m (6.5 ft). Since the installation date is after August 13, 2007, the minimum headroom requirement is 1.98 m (6.5 ft).
29 CFR § 1910.303(g): “For installations built on or after August 13, 2007, 1.98 m (6.5 ft), except that where the electrical equipment exceeds 1.98 m (6.5 ft) in height, the minimum headroom may not be less than the height of the equipment.”
16. An electrician is working on a circuit breaker panel where the handles are operated vertically. To ensure the breaker is in the 'on' position, how must the handle be oriented?
Answer: The handle must be in the up position. For vertical handles, up indicates closed (on) and down indicates open (off).
29 CFR § 1926.404(e): “Where circuit breaker handles on switchboards are operated vertically rather than horizontally or rotationally, the up position of the handle shall be the closed (on) position.”
17. An electrician is installing a limit switch on a new overhead hoisting mechanism. What is the primary safety function this device must perform?
Answer: Prevent the load block from passing the safe upper limit of travel. The regulation mandates a limit switch to stop the load block from exceeding the safe upper travel limit.
29 CFR § 1910.306(b): “A limit switch or other device shall be provided to prevent the load block from passing the safe upper limit of travel of any hoisting mechanism.”
18. A worker is extending an existing branch circuit that lacks an equipment grounding conductor. When is it permissible to ground a new receptacle to a grounded cold water pipe near the equipment?
Answer: If the extension was installed before August 13, 2007. This exception is strictly limited to extensions of existing branch circuits installed prior to the specific date of August 13, 2007.
29 CFR § 1910.304(g): “On extensions of existing branch circuits that do not have an equipment grounding conductor, grounding-type receptacles may be grounded to a grounded cold water pipe near the equipment if the extension was installed before August 13, 2007.”
19. An electrician is installing control systems for industrial radiographic equipment. To prevent ready access to live current-carrying parts, what two methods does the regulation allow for this type of equipment?
Answer: Effective enclosure or interlocks that deenergize the equipment automatically. For radiographic and fluoroscopic equipment, the regulation permits either effective enclosure or automatic deenergizing interlocks to ensure safety against live part access.
29 CFR § 1910.306(f): “Radiographic and fluoroscopic-type equipment shall be effectively enclosed or shall have interlocks that deenergize the equipment automatically to prevent ready access to live current-carrying parts.”
20. An electrician is installing extension cord sets for portable electric tools on a job site. What type of cord is required by OSHA construction standards?
Answer: Three-wire type designed for hard or extra-hard usage. The regulation mandates that extension cords for portable tools must be three-wire type and rated for hard or extra-hard usage.
29 CFR § 1926.405(a): “Extension cord sets used with portable electric tools and appliances shall be of three-wire type and shall be designed for hard or extra-hard usage.”
21. In a building with multiwire branch circuits containing more than one nominal voltage system, how must each ungrounded conductor be identified where accessible?
Answer: By phase and system. The rule specifically requires identification by phase and system for ungrounded conductors in multiwire branch circuits with multiple voltage systems.
29 CFR § 1910.304(b): “each ungrounded conductor of a multiwire branch circuit, where accessible, shall be identified by phase and system.”
22. A technician is working on a system that uses an isolating transformer and a line isolation monitor with ungrounded circuit conductors. What is the specific term for this type of system?
Answer: Isolated power system. The definition of 'Isolated power system' matches the components described: an isolating transformer, a line isolation monitor, and ungrounded circuit conductors.
29 CFR § 1926.449: “Isolated power system. A system comprising an isolating transformer or its equivalent, a line isolation monitor, and its ungrounded circuit conductors.”
23. When installing temporary wiring, which of the following practices is strictly prohibited for any type of temporary circuit?
Answer: Using bare conductors or earth returns. The rule bans the use of bare conductors and earth returns in temporary wiring, while the other options describe permitted or required practices.
29 CFR § 1910.305(a): “No bare conductors nor earth returns may be used for the wiring of any temporary circuit.”
24. An electrician is supporting flexible cords and cables in an industrial facility. Which of the following is an acceptable method of support that ensures protection from physical damage?
Answer: Staples, cable ties, straps, or similar type fittings installed so as not to cause damage. The regulation specifically lists staples, cable ties, and straps as acceptable supports provided they do not cause damage, whereas the other options risk physical damage or are not listed as approved support methods.
29 CFR § 1910.305(a): “Support shall be in the form of staples, cables ties, straps, or similar type fittings installed so as not to cause damage.”
25. An electrician is installing a controller for a group of coordinated motors on a multi-motor continuous process machine. Under what condition may a single disconnecting means be used instead of an individual disconnect for each controller?
Answer: If the controllers are mounted adjacent to each other and the disconnect is located adjacent to the group. The exception for a single disconnect applies specifically to coordinated controllers mounted adjacent to each other on a multi-motor continuous process machine.
29 CFR § 1910.305(j): “However, a single disconnecting means may be located adjacent to a group of coordinated controllers mounted adjacent to each other on a multi-motor continuous process machine.”