Each item of equipment that operates at 50 volts or more and is not deenergized must be tested for arc flash and shock protection. This examination will define the true boundaries (i.e., forbidden, limited, restricted, and so on) and will tell the employee of what PPE is required. These examinations should be done before each employee begins work and whenever there is a significant change in duties or environment.
Arc flash protection is required for all exposed parts of the body that could be injured by an electrical discharge. This includes the hands, feet, face, and head. Protection for these areas is provided by wearing appropriate personal protective equipment (PPE).
There are three types of arc flashes: ground fault interrupting (GFI), line-to-line, and line-to-ground. GFI arcs prevent people from being electrocuted by their own power cords or appliances connected to the same circuit breaker as the source. This type of arc flash cannot be prevented by any single piece of equipment, but only by using good power distribution practices. Line-to-line arcing occurs between two conductors of a circuit when one conductor wears out or breaks. This type of arc can be prevented by changing out defective components or installing cable with separated metal shields. Line-to-ground arcing happens when current passes through a person to some other object with more resistance than another part of your body.
How to Avoid Arc Flash
The arc flash boundaries change depending on the danger level and the voltage of the device. A "limited" range, for example, is for reduced electrical overarc shock threats; a "restricted" range is for higher shock risks; and a "prohibited" range is for considerable risks of direct contact with electrified components. Limited-range circuits must be designed by following specific guidelines to prevent exposure to dangerous levels of electricity.
Arc flash is an intense form of lightning that occurs when an electric current passes through a gas or vapor instead of through air. It can also be called "sparkling water" because of its bright light appearance. The word "arc" comes from the Latin arcus, meaning "bow." This phenomenon was first observed by Aristotle and later described in detail by William Gilbert in his 1669 book De Magnete.
Electricity is the flow of electrons through a conductor such as a copper wire. Electric circuits contain these paths as well as other materials that conduct electricity but do not carry a current themselves, such as plastic or wood. Electricity travels along these connectors until it reaches one that will not conduct any further, at which point it is forced to find another path around the circuit breaker. These paths can be natural, like a tree's trunk, or man-made, such as a copper wire running inside a metal building. When enough electrons flow through a connection, it becomes charged with an electric potential.
The Arc Flash PPE Category system replaces the Hazard/Risk Category (HRC) category from the standard's 2012 version. Each category specifies the minimum Arc Rating (AR) value for the PPE required. The producer of the PPE determines this number, which shows the quantity of heat energy (in cal/cm2). Energy is released when circuits are complete with a good ground and no defects in equipment or wiring. An arc can result if there is an external fault on any conductor within the circuit. It can also be caused by internal faults due to material failure. These may occur during installation or maintenance work on the equipment.
Arc Flash protection devices must be selected to meet or exceed the requirements of the applicable category. For example, if the hazard is identified as "low" then only low voltage devices such as fuse blocks and circuit breakers need to be used. If the hazard is identified as "medium" then both medium voltage and low voltage devices should be used in parallel. A medium voltage device will take priority if they are used in series with a low voltage device - for example, a fuse box with fuses up to 20 kV and a breaker for circuits over 20 kV. If more than one type of device is available that meets all criteria, then select the device that provides the highest level of protection.
Arc Flash protection devices must be installed according to manufacturer's instructions. Failure to follow these instructions could result in inadequate or excessive protection.
OSHA and NFPA 70E both require Arc-Flash Hazard Assessments as part of an Electrical Hazard Assessment. Arc-Flash Assessments are a serious matter of life and death, and they are a vital component of a safe and thorough electrical safety program. Without an assessment, you cannot know if your facility is at risk from arc flashes.
An arc flash is a large amount of energy released in an instant when two objects with a voltage difference between them reach the point of breaking down conductive material inside them. This happens when the distance between the objects is very small (less than 10mm). The energy can burn through any material that will not conduct electricity. This includes rubber, plastic, wood, and paper. It can also start fires. People working around electric circuits should take special precautions to avoid being hit by flying debris or exposed to the elements during an arc flash.
Facilities need to perform regular arc flash hazard assessments to make sure they are complying with OSHA regulations. An assessment is simply a survey of all equipment on site to identify which items are electrified and where they are located. You then use this information to determine what steps must be taken to protect workers from arc flashes.
To estimate the degree of PC and PPE protection necessary, three procedures must be taken: