![]() ![]() 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.
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