Arc flash hazard is the energy released in an arc flash and is proportional to the duration of the arcing fault; hence arc flash hazard can be reduced by lowering time delay settings of the ground fault overcurrent protective devices.
Continuity of service is very important, and is maximized by time-current coordination of the ground fault devices. The drawback of time-current coordination is that an extra time delay is required on upstream protection devices.
Zone Selective Instantaneous Protection (ZSIP), improves arc flash safety upstream in the distribution system without affecting service continuity.
With ZSIP, the Sentri relay senses a fault and trips with no intentional delay unless it receives a restraint signal from the Sentri relay immediately downstream; if so restrained, the Sentri relay waits to time out before tripping allowing the downstream Sentri to clear the fault.