Schneider Electric 5.0A, 3.0A, 2.0A, and 6.0A manual Zone-Selective Interlocking

48049-136-05	Micrologic™ 2.0A, 3.0A, 5.0A, and 6.0A Electronic Trip Units
Rev. 01, 07/2012	Section 1—General Information

Zone-Selective Interlocking

Short-time and ground-fault protection can be interlocked to provide zone-selective interlocking.

Control wiring links several trip units in the distribution network and in the event of a fault, a trip unit will obey the set delay time only if receiving a signal from a downstream trip unit.

If the trip unit does not receive a signal, tripping will be instantaneous (with no intentional delay).

•The fault is cleared instantaneously by the nearest upstream circuit breaker.

•Thermal stresses (I2t) in the network are minimized without any effect on the correct time delay coordination of the installation.

Figure 6 shows circuit breakers 1 and 2 zone- selective interlocked.

•A fault at A is seen by circuit breakers 1 and

2.Circuit breaker 2 trips instantaneously and also informs circuit breaker 1 to obey set delay times. Thus, circuit breaker 2 trips and clears the fault. Circuit breaker 1 does not trip.

•A fault at B is seen by circuit breaker 1. Circuit breaker 1 trips instantaneously since it did not receive a signal from the downstream circuit breaker 2. Circuit breaker

1trips and clears the fault. Circuit breaker 2 does not trip.

NOTE: Use I2t off with ZSI for proper coordination. Using I2t on with ZSI is not recommended as the delay in the upstream device receiving a restraint signal could result in the trip unit tripping in a time shorter than the published trip curve.

NOTE: Setting short-time delay (tsd) or ground-fault delay (tg) to the 0 setting will eliminate selectivity for that circuit breaker.

Figure 6: Zone-Selective Interlocking

06133376

1 B

2 A

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