CHST - Construction Health and Safety Technician Electrical Safety and LOTO Questions and Answers 1 — Questions and Answers
Question 1: An electrician is preparing to work on a 480-volt motor control center. After shutting off the main breaker that supplies the MCC, what is the most critical next step they must perform before beginning work?
- Notify affected employees that work is beginning.
- Apply their personal lock and tag to the breaker.
- Verify the absence of voltage using a test instrument. (Correct answer)
- Complete the Energized Electrical Work Permit.
Correct answer: Verify the absence of voltage using a test instrument.
According to OSHA 1926.417 and NFPA 70E, after an energy isolating device is operated, the most critical step is to verify with a properly rated test instrument that the circuit and equipment parts are de-energized. This step ensures that the circuit is truly dead before any contact is made, protecting against mistakes in identifying the circuit, stored energy, or induced voltage.
Question 2: According to OSHA standards for construction (29 CFR 1926), what is the minimum clearance distance that must be maintained from overhead power lines rated 50kV or less for unqualified persons?
- 5 feet
- 10 feet (Correct answer)
- 15 feet
- 20 feet
Correct answer: 10 feet
OSHA standard 29 CFR 1926.1408, Table A, specifies that for voltages up to 50kV, the minimum clearance distance is 10 feet. This distance is crucial for preventing accidental contact by personnel or equipment like cranes and aerial lifts.
Question 3: Which of the following devices is considered an 'energy isolating device' as defined by OSHA's Lockout/Tagout standard?
- An emergency stop push button
- A manually operated circuit breaker (Correct answer)
- A control circuit selector switch
- An interlock on a machine guard
Correct answer: A manually operated circuit breaker
An energy isolating device is a mechanical device that physically prevents the transmission or release of energy. A manually operated circuit breaker meets this definition. Push buttons, selector switches, and interlocks are control circuit devices and are not considered energy isolating devices because they do not physically break the power connection.
Question 4: A construction crew is using a 120-volt portable generator to power cord-and-plug tools on a job site. To best protect workers from electric shock, the receptacles on the generator should be protected by a:
- Surge protector
- Fuse rated for the tool's amperage
- Ground-fault circuit-interrupter (GFCI) (Correct answer)
- Double-insulated housing
Correct answer: Ground-fault circuit-interrupter (GFCI)
OSHA 29 CFR 1926.404(b)(1) requires that all 120-volt, single-phase, 15- and 20-ampere receptacle outlets on construction sites, which are not part of the permanent wiring, be protected by ground-fault circuit-interrupters (GFCIs). GFCIs are essential for shock protection with portable equipment where grounding may be compromised.
Question 5: Under OSHA's Lockout/Tagout standard (29 CFR 1910.147), who is generally the only person authorized to remove a lock or tag from an energy isolating device?
- The site supervisor for the work crew.
- Any qualified electrician on site.
- The employee who initially applied the lock or tag. (Correct answer)
- The competent person for the jobsite.
Correct answer: The employee who initially applied the lock or tag.
OSHA standard 29 CFR 1910.147(e)(3) is very clear that the lock and tag must be removed by the employee who applied it. This ensures that the person who is in control of the hazardous energy is the one to re-energize the equipment. There are specific procedures for rare exceptions when the authorized employee is not available, but the primary rule is personal removal.
Question 6: Which of the following is a key requirement for an employee to be considered a 'qualified person' for performing electrical work, according to the OSHA 1926 construction standards?
- Holding a valid state electrician's license.
- Having successfully completed a four-year apprenticeship.
- Possessing a degree in electrical engineering.
- Having training and experience to recognize and avoid the specific electrical hazards involved. (Correct answer)
Correct answer: Having training and experience to recognize and avoid the specific electrical hazards involved.
OSHA's definition in 1926.32(m) defines a qualified person as one who, through recognized degree, certificate, or professional standing, or by extensive knowledge, training, and experience, has demonstrated the ability to solve problems relating to the work. The critical element is the demonstrated ability and specific training to identify and avoid the hazards associated with the task, not just a general credential.
CHST - Construction Health and Safety Technician Electrical Safety and LOTO Questions and Answers 1
An electrician is preparing to work on a 480-volt motor control center.
After shutting off the main breaker that supplies the MCC, what is the most critical next step they must perform before beginning work?