Title: Electrical Safety and Protection
Course: 2016FA-MCO-110-401 > Section: Module 3: Power

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Electrical Safety/Protection

Many mission critical environments use DC power which is not always as familiar to electricians and other employees as AC. High voltages could be encountered when working with different systems in the environment. Capacitive voltages pose exposure risks on systems even after they are de-energized. Because of all these possible safety risks training, safety procedures, labels and warnings as well as strict adherence to standards require special attention in mission critical operations [26].

Grounding

A ground is a connection between something conducting electricity and the earth, or a set of shared points in an electrical circuit where the measured voltage is zero; it is usually connected to the power supply and acts as a sink for current that is flowing through the circuit [27]. Ground is sometimes interpreted to mean any type of current return path to an energy source. The terms ground and common are sometimes used interchangeably, however this is not always correct. All ground points (nodes) are “common” however not all common nodes are ground.

Grounding is something that is done for safety and can help prevent people from being shocked in cases where accidental contact is made. Having a path that connects to ground also helps to limit static buildup. Proper grounding also creates a constant and reliable reference point for communication and computational devices using voltage based signals [28].

An earth ground consists of a conductive rod or pipe that is driven into the earth until the earth ground resistance is below 25 ohms for power and 3 ohms for electronic equipment. It creates a path for current to flow through the earth.

Surge Protection

A spike in electrical voltage can be described as a surge. It is usually a fast transient (a quick burst of energy caused by a change in state) in voltage that does not last for a long period of time. To protect equipment and systems from extra voltage there are a number of lightning arresters and diverters are made to redirect high or extra voltages. Lightning rods and TVSSs are versions of surge diverters. An arrester can limit the amount of voltage that reaches systems while diverting excess to the ground; they only offer protection for equipment in parallel with them. Arresters work by utilizing materials that are non-conductive until they are exposed to higher voltages synonymous with lightning [29].

A TVSS (Transient Voltage Surge Suppressant) is a device that is designed to mitigate or avoid damage from voltage surges (or sub-cycle disturbances) to equipment and systems. It does this by limiting the transient or surge voltages and currents on electrical circuits. The discharge of stored energy from other equipment inside or outside of the facility can cause a transient surge. (Anything that can conduct an electrical current could also carry a transient voltage surge and it is possible that even telephone lines could be affected.) A transient surge can cause a lot of damage that could be very costly. In order to limit the transients, a TVSS absorbs or diverts the amount of voltage that is over and above the acceptable level. A TVSS is usually used at the service entrance[1] point, in distribution panels, in branch panels, and in individual circuits [30].

Cascaded surge protection devices like TVSSs are recommended in all Mission Critical facilities. This means that a TVSS should be placed both at the service entrance to the facility but also additional TVSSs should be placed in front of power panels and critical loads. The stages placed after the entrance should, in theory, be able to handle any residual voltage not absorbed or diverted [31].

Lightning Protection

Lightning strikes can cause multiple problems in the mission critical environment. Equipment and facilities can be damaged by the strikes or resulting fires. Lightning strikes can also cause voltage on systems to increase. Increased voltage can lead to power outages from overloaded circuit breakers,

Lightning rods are often part of the design of mission critical facilities. These rods attract and “catch” lightning and then direct it to the ground. Lightning rods are helpful in preventing fires and the physical damage that comes with a lightning strike [32]. Lightning rods are an example of a diverter. Diverters redirect or divert current flow.

Arc Flash Protection

Arc flash is a part of an arc fault, which is an electrical explosion, and is very dangerous. An arc flash can result in extremely serious injury or death. OSHA material explains that an arc blast (electrical explosion) could cause burns, fire, heat, a sound blast, projectiles, and fire that could potentially spread quickly through the entire facility.  Many protections exist and specialized training, an arc flash hazard analysis, and PPE (Personal Protective Equipment) must be carefully used together with safe work habits in order to prevent electric shock and other injuries.

“NFPA 70E, the Standard for Electrical Safety in the Workplace, was created to provide OSHA a standard for establishing safe work practices for electrical workers. Among other things, this document requires hazard analysis and aids in the selection of personal protective equipment (PPE). Minimum approach boundaries are also established” [33, p. 4].

[1] Service entrance – the place where an electrical supply line enters a facility [36].

Objectives met:
- C3
- 3.8