Electrical Safety Practice Test
Lockout and tagging in the order the regulation sets out, approach distances, working space and GFCI requirements — every question cited to the OSHA paragraph it comes from.
20 questions · free · no sign-up
- Instant feedback on every answer
- Worked solutions, not just a score
- Progress saved in your browser
What it is, and why electricians need it
The governing rule is short and absolute: live parts to which an employee may be exposed shall be deenergized before the employee works on or near them. Energized work is an exception that the employer must justify, and there are exactly two acceptable justifications — that deenergizing would introduce additional or increased hazards, or that it is infeasible due to equipment design or operational limitations.
The second principle is the one that most often goes wrong on real jobs: a circuit that has been deenergized but not locked out or tagged must be treated as energized. Opening a breaker and walking away is not isolation, because nothing stops someone closing it again. That is why the lockout and tagging procedure exists, and why OSHA states explicitly that its steps shall be followed in the order in which they are presented: determine the procedure, deenergize and release stored energy, apply locks and tags, then verify. Verifying before the locks go on proves nothing about the state of the circuit once work begins.
Verification itself has a detail worth knowing cold. A qualified person must test the parts employees will be exposed to, including checking for inadvertently induced voltage and unrelated voltage backfeed. And above 600 volts the test instrument must be proved good immediately before and immediately after the test, because a meter that has failed open reads zero on a live conductor.
The rest of the topic is dimensional: working space depth, width and height around equipment; the elevation and guarding requirements for live parts at 50 volts or more; and the approach distances, which differ sharply between qualified persons — who may work within a few feet under defined conditions — and unqualified persons, who must stay 10 feet from an overhead line at 50 kilovolts or below.
Formulas and principles
Deenergize first; two exceptions only
Increased or additional hazards, or infeasibility due to equipment design or operational limitations.
Parts under 50 volts to ground need not be deenergized where there is no increased exposure to burns or arc explosion.
Deenergized but not locked/tagged = energized
The full energized-work requirements apply.
Lockout order: procedure → deenergize and release stored energy → lock and tag → verify
The steps shall be followed in the order in which they are presented.
A tag without a lock needs at least one additional safety measure giving equivalent safety.
Over 600 V: test the tester immediately before and after
Verification of the deenergized condition, by a qualified person.
Unqualified: 10 ft to 50 kV, plus 4 in. per 10 kV above
Person or longest conductive object, elevated or on the ground.
Vehicles and mechanical equipment: same 10 ft, reducible to 4 ft in transit with the structure lowered.
Guarding threshold: 50 volts or more; elevation option 8 ft
Live parts must be guarded against accidental contact.
The two distance tables
These come up as straight recall questions, and the figures are specific enough that guessing does not work.
Qualified employee approach distances
| Voltage range, phase to phase | Minimum approach |
|---|---|
| 300 V and less | Avoid contact |
| Over 300 V, not over 750 V | 1 ft 0 in. (30.5 cm) |
| Over 750 V, not over 2 kV | 1 ft 6 in. (46 cm) |
| Over 2 kV, not over 15 kV | 2 ft 0 in. (61 cm) |
| Over 15 kV, not over 37 kV | 3 ft 0 in. (91 cm) |
| Over 37 kV, not over 87.5 kV | 3 ft 6 in. (107 cm) |
| Over 87.5 kV, not over 121 kV | 4 ft 0 in. (122 cm) |
| Over 121 kV, not over 140 kV | 4 ft 6 in. (137 cm) |
Working space depth, 600 volts or less
| Nominal voltage to ground | Condition A | Condition B | Condition C |
|---|---|---|---|
| 0–150 V | 3 ft | 3 ft | 3 ft |
| 151–600 V | 3 ft | 3 ft 6 in. | 4 ft |
Condition A: exposed live parts on one side, no live or grounded parts on the other, or live parts on both sides effectively guarded by insulating material. Condition B: exposed live parts on one side, grounded parts on the other — and concrete, brick and tile walls count as grounded. Condition C: exposed live parts on both sides with the worker between them. Width is the equipment width or 30 inches, whichever is greater, with at least a 90-degree door opening. The working space may not be used for storage.
Source: 29 CFR 1910.333 Table S-5 and 1910.303(g)(1) Table S-1, from OSHA 29 CFR 1910 Subpart S. These are public-domain federal regulations.
Now try it on 20 questions
One question at a time, marked the moment you answer, with the reasoning and the source behind it. Anything you miss is saved so you can come back to it.
Start the Safety drillWorked examples
Scenario: An unqualified worker will operate a boom near an overhead line whose voltage to ground is 90 kilovolts. What minimum clearance applies?
- The base clearance for 50 kV or below is 10 feet, which is 120 inches.
- The line is 90 kV, so it is 40 kV above the threshold.
- Increments of 10 kV: 40 ÷ 10 = 4.
- Add 4 inches per increment: 4 × 4 = 16 inches.
- Total: 120 + 16 = 136 inches, or 11 feet 4 inches.
Answer: 136 inches, or 11 feet 4 inches
Scenario: A 480-volt panelboard is to be installed with a concrete wall 3 feet 2 inches behind the working position. Is the working space adequate?
- 480 volts to ground falls in the 151–600 V band.
- A concrete wall counts as a grounded surface, so with exposed live parts on one side and grounded parts on the other, this is Condition B.
- Condition B at 151–600 V requires 3 feet 6 inches of depth.
- 3 feet 2 inches is less than 3 feet 6 inches, so the space is not adequate.
- Also check width — equipment width or 30 inches, whichever is greater — and height of 6.5 feet, and that the space is clear of storage.
Answer: No. Condition B requires 3 ft 6 in., and only 3 ft 2 in. is available
Common mistakes
- Believing a third exception exists for working energized. There are two: increased or additional hazards, and infeasibility due to equipment design or operational limitations. Schedule pressure, cost and the size of the job are not among them.
- Treating an open disconnect as a safe disconnect. Deenergized but not locked out or tagged must be treated as energized. The lock is what makes it safe, not the position of the handle.
- Performing the lockout steps out of order. OSHA requires them in the order presented. Most commonly people verify before the locks are applied, which proves nothing about the circuit once work starts.
- Using a tag without any supplementary measure. A tag is a warning and physically prevents nothing. Where a lock cannot be applied, the tag must be supplemented by at least one additional measure giving equivalent safety, such as removing an isolating circuit element or blocking a controlling switch.
- Removing someone else's lock. Each lock and tag is removed by the employee who applied it or under that employee's direct supervision. Where that employee is genuinely unavailable, a designated qualified person may remove it, but the employer must ensure the applying employee is made aware before work resumes.
- Assuming low voltage means safe. Parts under 50 volts to ground need not be deenergized only where there is no increased exposure to electrical burns or arc explosion. A 24-volt circuit fed from a high-current source can still produce a serious arc.
- Confusing OSHA's GFCI rule with the NEC's. OSHA's permanent-wiring rule names bathrooms and rooftops. The NEC dwelling list is far longer, extending to garages, outdoors, crawl spaces, unfinished basements, kitchen countertops, within 6 feet of sinks, boathouses, near tubs and showers, and laundry areas. Read which document the question is about.
Related practice topics
Topics that come up alongside this one on the exam.
Questions about this topic
What is the general rule about working on energized parts?
OSHA states that live parts to which an employee may be exposed shall be deenergized before the employee works on or near them. Energized work is the exception, not a matter of preference, and it is permitted only where the employer can demonstrate that deenergizing would introduce additional or increased hazards, or is infeasible due to equipment design or operational limitations.
What counts as an acceptable reason to work energized?
Only two. Increased or additional hazards — OSHA's examples include interrupting life support equipment, deactivating emergency alarm systems, shutting down hazardous-location ventilation, or removing illumination from an area. Or infeasibility due to equipment design or operational limitations — for instance testing that can only be done energized, or a circuit integral to a continuous industrial process. Convenience, schedule pressure and "it is only a small job" are not on the list.
Why must a deenergized circuit that is not locked out be treated as energized?
Because nothing prevents someone restoring it. An open breaker is not a secured breaker. OSHA requires conductors and parts that have been deenergized but not locked out or tagged to be treated as energized parts, with the full energized-work requirements applying.
Why test the meter before and after verifying a high-voltage circuit?
Because a meter that has failed open reads zero volts on a live conductor, and that false zero has killed people. For circuits over 600 volts nominal, OSHA requires the test equipment to be checked for proper operation immediately before and immediately after the verification. Checking it afterwards confirms the instrument did not fail during the test itself.
What makes someone a qualified person?
Training in three specific skills: distinguishing exposed live parts from other parts of electric equipment, determining the nominal voltage of exposed live parts, and knowing the clearance distances and the corresponding voltages they will be exposed to. OSHA notes that a person must have this training in order to be considered qualified — it is not a matter of experience or job title alone.
How far must an unqualified person stay from an overhead line?
Ten feet for voltages to ground of 50 kilovolts or below, increasing by 4 inches for every 10 kilovolts above 50. The same distance applies to the longest conductive object the person might contact, whether working from an elevated position or from the ground, and for most overhead-line voltages any object without an insulating rating counts as conductive.
Why do these questions cite OSHA rather than the NEC?
Because OSHA 29 CFR 1910 Subpart S is federal regulation in the public domain, so we can cite it by paragraph and link you straight to the governing text. It is also the standard that governs work practices rather than installation, which is what safety questions mostly test. Note that OSHA's installation requirements are narrower than the NEC in places — its permanent-wiring GFCI rule names only bathrooms and rooftops, where the NEC dwelling list is much longer.
Keep going
- Full electrician practice test — mixed questions from every topic
- Journeyman practice exam — timed, built to the published outline
- Browse all exam questions — search the bank by topic and difficulty
- Fault current calculator — check your working