The article covers key aspects of electrical safety practices, including the importance of grounding, the dangers of electric shock, the role of ground-fault circuit interrupters (GFCI), lockout-tagout (LOTO) procedures, and electrostatic discharge (ESD) prevention. It emphasizes various safety measures to protect workers and equipment from electrical hazards in industrial and technical environments.
Abnormal surges in an electrical current, or an electrical fault, can cause great harm to appliances and people. Grounding an electrical system provides a safe path for fault current. The fault current is the amount of amperage flowing to earth from the electrical fault. The amount of fault current is limited by only the conductor resistance and the transformer impedance. A minimum ground fault current can be in excess of 10,000 amps.
Refer to Figure 1. A ground is established by driving a rod into the ground and connecting it to one of the conductors. Once this is accomplished, any conductor on the secondary side of the transformer is capable of completing a circuit through to the earth. In addition to driving a rod into the ground at the transformer, the electrical system is also grounded at the electrical meter or service panel. Residential and commercial electrical systems are grounded by a long rod driven into the earth and by a connection to a water pipe. This dual connection helps to ensure a solid grounding.
Figure 1. The ground for the electrical system is composed of two ground rods, one at the transformer pole and the other at the residence.
A grounded device provides a safe path for an electrical fault and has a 0-volt potential. This path is typically constructed by connecting a conductor between one of the electrical system conductors and the earth. Some electrical systems do not connect directly to the earth. Instead, the metal enclosures or metal conduits serve as a ground or a return path for current.
If a person contacts an energized system, that person can easily serve as a path to ground and experience electric shock. Also, if a system experiences an electrical fault, the metal enclosure or conduit may have a higher voltage potential than the earth ground. Thus, a person touching the enclosure or conductor can experience electric shock, as shown in Figure 2.
Figure 2. Ungrounded equipment presents a great safety hazard to workers. Just touching the outer enclosure can cause an electric shock.
Electric Shock
Electric shock is a discharge of electrical current passing through your body. This occurs when a person comes into contact with an electrical energy source. Direct physical contact is not required to receive a shock. High-voltage sources can pass electrical current through the air surrounding the source if you are too nearby.
A person can experience different levels of electric shock. These are rated by value of current flow and the effect that each current value has on the human body, Table 1.
The amount of resistance for the flow of electrons through a person’s body depends on many different factors. For example, a resistance path from hand to foot will be higher than from hand to hand, especially if the person is wearing dry shoes in good condition. Dry shoes in good condition increase resistance because they act as an insulator between our body and ground and do not let electricity transmit from body to ground.
We get electrical shock (electrocuted) only if the electricity passes from our body to ground. Another factor is the amount of skin surface area connected to the potential source. A person’s skin condition is the most influential resistance factor. A person with dry skin has a high resistance of about 100,000 ohms. When the surface of the skin is covered with sweat, the resistance can be 10,000 ohms or less.
The National Electrical Code (NEC) requires all electrical systems of 50 volts or higher to be grounded. This rule is to protect people from electric shock when they come into contact with components in an electrical system. A properly grounded device will produce a low-resistance path for current. When the properly grounded device comes into contact with an energized conductor, the fuse or circuit breaker will automatically trip or open the circuit.
Level of Current | Effects on Human Body |
1 mA | Threshold of feeling. Slight tingling. |
5 mA | Shock felt, but not painful yet. Involuntary muscle movements. |
10–20 mA | Painful shock. Sustained muscle contraction. Inability to release grip. |
100–300 mA | Paralysis of respiratory muscles. Can be fatal. Severe internal and external burns. |
2 A | Cardiac arrest (heart beat stops). Internal organ damage. Death is probable. |
Table 1. The effects of an electric shock can range from very slight tingling to death.
Safety
One of the best ways to avoid fatal electric shock is to keep one hand in your pocket while working with high voltage. This way, any current flowing through your body does not flow through one hand and out the other.
Ground-Fault Circuit Interrupter (GFCI)
A ground-fault circuit interrupter (GFCI) provides protection from excessive fault currents through the human body. The NEC requires ground-fault protection for specific locations where there is a high probability of electric shock, such as damp or wet locations.
A ground-fault circuit interrupter provides protection by monitoring and comparing the current through the hot and neutral conductors. A complete circuit has the same current in the hot and neutral conductors. If a ground fault occurs, part of the current will flow to ground. When part of the current flows to ground, the comparator circuit detects an unbalanced condition between the hot and neutral currents. If the difference between the hot and neutral conductor exceeds 5 mA, the comparator circuit will energize the trip coil and cause a contact to open in the hot conductor circuit. This stops the flow of current through both the outlet, and potentially a person holding a device plugged into the outlet. After the GFCI is tripped, the reset button needs to be pressed to reset the GFCI trip mechanism once more. See Figure 3.
Figure 3. The reset button of a GFCI receptacle is often red.
Ground-fault protection devices are not limited to power outlet designs. They are commonly incorporated in GFCI-style circuit breakers. Non-GFCI power outlets can be used with single GFCI-style circuit breaker. The non-GFCI power outlet will then provide the same protection that a GFCI outlet provides. This is a very cost-effective solution when several outlets are required to be GFCI type.
Lockout and Tagging
Lockout-tagout (LOTO) is a safety procedure used in various fields to isolate or shut off sources of energy. This prevents accidental startup of a machine or system while maintenance or repair work is being done. The energy source is deactivated and locked with a tag to alert others that the machine or system is being worked on, Figure 4. The key is kept by the person who installed the lock. They will remove the lock after their work is complete. Multiple locks can be installed when multiple personnel are working on the same system. This will ensure that all work is complete before the energy source can be turned back on, preventing potentially disastrous injuries to workers.
Figure 4. The LOTO devices on this system will prevent anyone from turning the power back on before both workers have removed their locks.
The six-step procedure for the lockout-tagout procedure is as follows:
- Plan and prepare to shut down. The first step in implementing LOTO is to identify all the power sources and plan to shut them down. To identify the sources and follow proper protocol for the shutdown process, we need to consult with the designated personnel at each source.
- Shut down. After consulting and planning for shut down, inform the employees working at each impacted location. Many machines have just one start and stop button, although some machines require following a sequence of steps to shut down. Complete the shutdown process at this stage.
- Isolate energy. After the machines are shut down, a proper method is followed to isolate each machine from energy sources such as pressure valves, hydraulics, and others. Disengage any lines that feed into each machine.
- Apply locks and tags. Once the machines are isolated from energy sources, lock the machine controls and valves with physical locks and place tags indicating who is working and other information. If multiple employees are working on the machine, all the personnel must place their individual locks and tags on it.
- Control stored energy. After applying locks and tags, ensure no energy is stored in the machine. This can be of many forms, including but not limited to compressed air, compressed springs, stored electrical energy, and others.
- Verify isolation. The final step of LOTO is to ensure all the previous steps are followed successfully. This gives us confidence that the machine is safe to work on.
Electrostatic Discharge (ESD)
Electrostatic discharge (ESD) is the transfer of static electrical energy from one charged object to another. ESD can destroy the miniature circuits inside an electronic chip and certain electronic components.
Static charges are usually created by friction, such as walking across a carpeted floor. When two dissimilar materials are rubbed together, an electric charge is produced. To prevent static discharge between two objects, you must create a condition where both objects are at the same static voltage level, or the same level of electric charge. When two objects have the same static voltage level, static discharge will not occur.
Technicians wear an antistatic wrist strap, also called a ground strap, when handling static-sensitive devices to avoid ESD, Figure 5. The antistatic wrist strap is designed to release any static buildup on a technician’s body, allowing for the safe handling of static sensitive devices. To prevent ESD damage to sensitive components, you should connect the alligator clip to the designated area identified by your supervisor.
Figure 5. An antistatic wrist strap is designed to help release any static buildup on a technician’s body, allowing for the safe handling of static-sensitive devices.
Figure 6 shows a mat that provides an antistatic surface for parts. Some workbenches used for electronics are designed with antistatic properties. The workbench is typically made of metal and then grounded to ensure no static charge can build up. When using an antistatic workbench, no antistatic mat is required.
Figure 6. An antistatic mat can provide a surface for resting static-sensitive components and devices.
Safety
Never wear an antistatic wrist strap while working on an energized circuit or project. The antistatic wrist strap connects directly to ground. Touching an energized circuit while wearing the antistatic wrist strap will result in electric shock.
Key Takeaways
Practicing proper electrical safety is critical in both residential and industrial environments to protect people, equipment, and systems from potentially fatal electrical hazards. Grounding, GFCIs, and LOTO procedures help prevent electric shocks and accidental energy discharge, while ESD prevention safeguards sensitive electronic components.
Practicing Electrical Safety Review Questions
- A(n) _____ device provides a safe path for an electrical fault and has a 0-volt potential.
- interrupted
- energized
- connected
- grounded
- _____ occurs when electrical current passes through your body.
- Arc flash
- Cardiopulmonary resuscitation
- Electric shock
- All of the above.
- True or False? Electric shock requires direct physical contact with an energy source.
- True or False? LOTO is a safety practice that ensures a system will not be powered up while work is being done.
- _____ can destroy the miniature circuits inside an electronic chip and certain electronic components.
- ESD
- EPS
- CPR
- PPE
Answers
- D
- C
- False
- True
- A