Electrical Safety
1. List at least 10 rules of electrical safety. Decide which two are the most important and why your think this is so. Make this list neat and clear since you and your instructor will be signing it.
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. How does low voltage kill?
3. What safety precautions will you take if you must work
on live electrical circuits?
4. Why work one-handed near panel boxes?
5. What happens when a person becomes grounded?
6. What is the function of a ground circuit?
7. What happens when you become grounded?
8. How does a ground fault interrupter work?
9. What is the purpose of a ground fault circuit
interrupter (CFCI)?
10. Why can extremely low amperage kill a person?
11. What national code regulates electrical safety?
12. What makes an electrical worker a qualified person according to the code?
13. What is an arc flash boundary and what is a general distance for an arc flash boundary at lower than 600 volts and a “low energy” circuit?
14. What is the definition of a prohibited boundary?
15. What is the definition of the restricted approach boundary?
16 What is the definition of the limited approach boundary?
17. In general, what electrical PPE will you expect to wear when doing routine troubleshooting and live readings on electrical circuits under 600 volts?
Learning Activities:
1. Study Industrial Maintenance (IM), ELECTRICAL SAFETY p. 31.
LOCKOUT/TAGOUT
1. What is the title and purpose of the law that governs lockout and tagout?
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. What must be posted near each complex machine?
3. List the steps for applying and removing a lockout.
4. What must happen at shift change?
5. How do lockout and tagout rules apply to outside workers coming into the facility?
6. State the rules regarding locks used for lockouts.
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. State the rules for tags used for tagouts.
8. List all the types of energy sources that must be locked out.
9. List the three groups of workers and describe their level of involvement with logout and tagout.
10. State the rules regarding inspections of lockout and tagout procedures.
11. How are group lockouts managed?
Learning Activities:
1. Industrial Maintenance (IM), LOCKOUTS AND TAGOUTS p. 32-33.
A useful supplement to the NFPA 70E is the NFPA 70 E Handbook for Electrical Safety in the Workplace. While the NFPA 70E code is written using legal and engineering terminology the Handbook expands upon each code section in an easier to understand wording.
Most electrical accidents requiring hospitalization are from arc-flash burns not electric shock. More than 2000 people each year suffer severe arc-flash burns. Arc-flashes can be fatal ten feet from the center of the flash.
Causes of Arc Blast: For example an arc blast can occur when connecting a DMM in the ammeter mode to an energized circuit using the in-line connection. The ammeter setting turns the DMM into a low resistance device since current will be flowing through the meter. Making this connection usually involves changing test probe locations and resetting the meter dial. If the troubleshooter goes from taking the in-line ammeter reading to taking a voltage reading without making these changes the effect is the same a placing a wire across two energized conductors. This results in a short circuit that can cause an arc blast. Since this is an easy to make mistake when concentrating on troubleshooting it is important to use a DMM that is fused in the in-line ammeter mode so that the fuse will blow rather than allow an arc blast. Only high quality meters are fused correctly to prevent this catastrophic accident. Never substitute off-brand fuses for the fuses specified in the meter. Ensure that the DMM in use has been tested by reputable testing agencies like Underwriter’s Laboratory (UL) so that arc blasts will not occur in this situation.
While it is safest to work on de energized electrical circuits this is not always possible, especially for maintenance troubleshooting and repair technicians. It is common for such technicians to take voltage and amperage readings on energized equipment when doing maintenance and troubleshooting tasks. In general the NFPA 70E requires that electrical work be do on de energized circuits, or if work must be done on energized circuits an Energized Electrical Work Permit is required. The purpose of the permit is to detail a plan for completing a specific task. The NFPA 70E Article 130 (B)3 Exemption to Work Permit allows qualified persons to test and troubleshoot energized circuits providing all safe work practices and approach boundaries are used. Qualified persons are those with skills and knowledge of electrical systems who are trained to recognize and avoid electrical hazards.
There are two approach boundaries around any electrical equipment, the Arc-flash Protection Boundary and the Shock Protection Boundary. The arc-blast boundary is to distance required to protect workers from second degree burns in the event of an arc-blast .Determining the arc-flash boundary can be complicated since it requires calculations involving the amount of current that could flow in a circuit and the rate of time, fractions of a section, that it will take for a fuse or circuit breaker to open. A general a four foot arc-flash boundary is established for circuits up to 600 volts so long as the potential fault current is less than 50 kA that clears in less than 2 cycles 2/60ths of a second on standard circuits. If the Release of energy and/or the time of release is grater than this level the boundary must be calculated by a person with specialized training in this field.
Shock Protection Boundaries are established to prevent electric shock and are separate from arc-blast boundaries. The Prohibited Approach Boundary must never be crossed because of the extreme danger of electrocution. When working close to this boundary every qualified worker must wear the correct PPE and follow all safety precautions. For example reaching into an electrical enclosure with the probes of a voltmeter will cause the fingers and hands of the work to become close to an energized conductor. for example, according to NEC 70E qualified workers testing a 480 volt circuit can come no closer than one inch to the energized conductors, so the technicians’ fingers on the test probes must be more than one inch from the conductor. Most high quality DMM test probes are designed to maintain this safe distance and to provide finger rests that prevent the fingers from sliding closer to the conductor. In addition, the meter being used must be safe for the level of voltage and current being encountered.
To reach into the enclosure to test the circuit qualified workers must enter the Restricted Approach Boundary which is the closest approach distance allowed for a qualified worker. To work in this zone, one foot from energized conductors for a 480 volt circuit, the worker must wear at least the following personal protective equipment: correctly rated leather gloves over insulated rubber gloves, properly rated flame resistant clothing, safety glasses and a face shield with a balaclava shock hood. This PPE is required to prevent the accidental touching of energized conductors while taking the voltage measurements and to protect against electrical arcing to the body. In some cases insulating pads can be placed over dangerous locations to further protect the worker who still must be wearing all required PPE.
An unqualified worker like a machine operator must get no closer than the Limited Approach Boundary, ten feet with a 480 volt potentially moving conductor like an overhead power line, or four feet from an exposed 480 volt fixed circuit like a wire connection point inside an enclosure. If unqualified persons have to work within the Limited Approach Boundary they must aware of all potential dangers, wear the appropriate PPE, and be constantly supervised by a qualified worker.
The reason for energized work permits and approach boundaries while working on energized circuits is to require technicians to carefully plan their movements and actions when working around electric circuits. For example qualified workers will inspect their PPE and test equipment, decide where to place their hands and arms so as to avoid accidently touching any energized parts of the circuit, and to ensure that there are no obstacles or hazards that could hinder their movements. Since the current in a 75 watt light bulb can be fatal it is important to remember that there are no safe electrical circuits and that all electrical work requires training and careful planning. All workers must conscientiously practice all electrical safety rules and practice careful planning before starting any electrical task.
When working on energized circuits the level of PPE is determined by the type of activity and the voltage level of the circuits involved. For example voltage testing on a circuit lower than 240 volts is a Hazard/risk Category 1 (HR CAT 1) requiring the use of rubber insulating gloves combined with leather over gloves and insulated and insulating tools. Fire resistant clothing and PPE for this level of work includes arc-rated long sleeved shirt and pants or coveralls, an arc-rated jacket or rainwear, an arc-rated face shield, hard hat, safety glasses, hearing protection, leather work gloves and leather work shoes. Working on circuits higher than 240 volts requires more PPE and higher rated clothing, perhaps including arc-flash suits. The requirements for boundaries and PPE can be confusing but all MTR technicians should carry and use at least the minimum required PPE and be vigilante regarding approach boundaries. When in doubt as to the level of hazard technicians should always opt for a higher level of PPE.
As the danger involved in the electrical task increases the need for more protection rises. The levels of danger are rated in the Hazard/Risks Category Classifications.
Additional material for Lockouts & Tagouts
While employers are responsible for supplying lockout locks and tags and creating lockout procedures MTR technicians must apply the principles of lockout tagout in situations that might not be covered by a written procedure. Before working on the equipment workers locate potential hazardous energy that could be released, they notify people working near the equipment that it is being shut down and then apply locks and tags to make the equipment safe before starting work. It is especially important to lockout equipment safely even if the work on the equipment will only take a short time. Of special concern is the automatic start up of equipment that is not completely energized, for example a pump that starts-up automatically because the water level in the tank reaches a certain level. Technicians working in such a tank might be in danger due to raise water levels.
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