Brochure

PowerPact H-, J-, and L-Frame Circuit Breakers

Glossary

271

02/2016

undervoltage trip (MN, UVR) = An accessory which trips the circuit breaker automatically when the

monitored circuit voltage falls below a predetermined percentage of its specified value.

Underwriters Laboratories Inc.

(UL

) = An independent, not-for-profit standards development,

product safety testing and certification organization.

unit-mount circuit breaker = A circuit breaker mounted such that it cannot be removed without

removing primary and sometimes secondary connections or mounting supports.

withstand rating = The level of RMS symmetrical current that a circuit breaker can carry with the

contacts in a closed position for a stated period of time–usually stated in cycles.

zero-blind time = Metering method used by the Micrologic H trip unit where a dedicated metering data

chain is separate from the protection data chain so that a greater number of data samples can be used

for metering. This increases the number of samples taken per time period, which in turn gives the H trip

unit a higher degree of metering accuracy.

zero-sequence ground-fault sensing = A means of providing equipment ground-fault protection

utilizing an external sensor (surrounding all phase and neutral conductors).

zone-selective interlocking (ZSI) = A communication capability between electronic trip systems and

ground-fault relays which permits a short circuit or ground fault to be isolated and cleared by the

nearest upstream device with no intentional time delay.

ZSI = Zone-selective interlocking.