I-Gard MGFR Series, Instruction Manual

3. CURRENT SENSORS

It will be necessary to hold down the TRIP INHIBIT button until the SELF TEST is complete and the TRIP 
indicator has operated, and TRIP RESET is operated (if manual RESET has been selected).

2.8 POWER ON LED

A green LED on the faceplate of all the relays in the MGFR series indicates that the control power supply of the relay 
is ON.

2.9 PRE TRIP ALARM

Two terminals on the terminal block at the back of all the models in the MGFR series are provided for remote 
indication of ground fault current exceeding the pre-set FLASH setting of Section 2.6.1. This is a NORMALLY OPEN, 
DRY contact which CLOSES without delay, to annunciate an ALARM condition to a remote panel, PLC or monitor, 
whenever a fault condition greater than the FLASH setting occurs. The contacts automatically open when the fault is 
cleared without the need for a manual RESET.

2.10 ZSIP

The ZSIP system (Zone Selective Instantaneous Protection) is available on all types of MGFR with -ZB and -AB 
suffixes. The system allows the instantaneous operation of relays in different levels (zones) whenever a fault is 
detected which is within their zone only. Higher level relays will not trip because they will operate with user-set 
time delays, thus preserving coordination of the system. For this operation it is necessary to connect a restraint 
signal (ZSIP OUT) from each relay to the relay in the level above (ZSIP IN terminal). The scheme can be extended 
to any number of levels. Also a number of downstream relays can be connected to restrain a single main relay or 
more if necessary. Three terminals are provided on each relay ZSIP-IN, ZSIP-OUT and COMMON. The COMMON 
is connected to all other COMMON terminals in the system. The ZSIP-OUT of all downstream relays at a particular 
level is connected to the ZSIP-IN of the relay, at the next level up. All wiring is by No. 14 AWG wire. The one-line 
diagrams in Figure 4 illustrate examples of a 3 level TCP (Time Coordinated Protection) and ZSIP system.

To set the unit to the ZSIP mode it is necessary to remove the factory installed jumper between ZSIP-IN and ZSIP-
OUT of the relay involved. For TCP operation (Delayed Trip) the jumper between ZSIP-OUT and ZSIP-IN must be left 
in place. All units are supplied from the factory with the jumper connected. For proper coordination in the TCP mode 
the CURVE SELECT switch in upstream and downstream relays should be set to the same position (DMT or IDMT).

The sensors to be used with MGFR relays are I-Gard Zero Sequence sensors (ZSCT). These are listed below:

3.1 MGFR-1-ZB, MGFR-1-AB

Use with I-Gard Toroidal sensor type T2B, T3B and T5B ( 700 turns secondaries).

3.2 MGFR-2-ZB, MGFR-20-ZB, MGFR-200-ZB, MGFR-1200-ZB,
MGFR-2-AB, MGFR-20-AB, MGFR-200-AB, MGFR-1200-AB

These can be used with the following two different designs of current sensors depending on the application.

3.2.1 I-Gard toroidal zero sequence current sensors of type T2A, T3A, T6A or T9A. (1000 turns secondaries)

I-Gard rectangular zero sequence current sensors of type R4-17A, R7-13A or R8-26A for bus duct, switch board 
buses or for a large group of cables.