![]() It requires that an operating time be determined for both the expected arc current and the reduced arc current. This represents a more accurate arcing current variation based on the electrode configuration as well as other factors and applies for all voltages.ĪRCAD's arc flash assessment software makes possible both calculations for each case considered. Instead of a fixed 85% factor, the IEEE 1584-2018 2nd edition includes an Arcing Current Variation Correction Factor based on using a new equation. If the reduced arcing current resulted in a longer clearing time and larger incident energy, results based on the adjusted current would be used. The reduction was to account for variations that may occur in the actual arcing current which could affect how fast a protective device may operate. ![]() This addendum added an 85% factor for reducing the calculated arcing short circuit current for systems up to 1kV. The first addendum for the 2002 edition of IEEE 1584 was published in 2004. Incident energy is linear with time, so arc current variation may have a big effect on incident energy. Opening times for particular circuit breakers can be verifed by consulting the manufacturer's literature.įor protective devices operating in the steep portion of their time-current curves, a small change in current causes a big change in operating time. The circuit breaker opening time must be added. For relays operating in their instantaneous region, allow 16 milliseconds on 60 Hz systems for operation. If the curves show only the trip unit's operating time, a circuit breaker operating time (typically 0.05 s or three cycles) should be added.įor relay operated circuit breakers, the relay curves show only the relay operating time in the time-delay region. The time-current curves included with the replacement trip unit may, or may not, include the circuit breaker operating time. Note that some low-voltage power circuit breakers may be equipped with retrofit trip units. If the total clearing time at the arcing fault current is less than 0.01 s, then 0.01 s may be used for the time.įor low-voltage circuit breakers with integral trip units, the manufacturer's time-current curves include both the device tripping time and clearing time in most cases. If the curve only consists of the average melt time, ten percent of time plus an additional 0.004 s should be added, to determine the total clearing time. For fuses, the manufacturer's time-current curves may include both melting and clearing time. Use protective device characteristics, which can be found in manufacturer's data. HOA - Horizontal electrodes in open air.HCB - Horizontal electrodes in a metal box.VCCB - Vertical electrodes terminated in an insulating barrier in a metal box.VCB - Vertical electrodes in a metal box/enclosure.IEEE 1584 - 2018 model features five different electrode/bus configurations as illustrated below: Tests were also conducted in open air and included the original vertical configuration in open air and a new configuration with the electrodes oriented horizontally. Research has also indicated that if vertical electrodes are terminated into an insulating the arc hits the barrier and the plasma cloud is directed more towards the enclosure opening. When the electrodes are placed horizontally, the arc plasma is directed from the ends of the electrodes outward. As a result, the IEEE 1584 - 2018 project team conducted many tests using electrode orientations that include both a horizontal configuration and vertical electrodes that terminate into an insulating barrier. Relay actions include 49, 50, 51, 67, 79, 87.Research has shown that incident energy can be influenced by the electrode orientation. Automatic or user-defined source protective device search algorithm option to simulate worse arc flash hazard conditions. ![]()
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