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4. TRIP RELAY AND AUXILIARY FAULT RELAYS
The Sigma 3 has four output relays:
- A TRIP relay
- An NGR FAULT auxiliary relay
- A GROUND FAULT auxiliary relay
- A WATCHDOG auxiliary relay
All relays are electrically held, i.e. when control power is off the relays are always in the de-energized state. The de-
energized states are shown on the front of the Sigma 3. Note that this is irrespective of the trip relay operating mode.
All relays can be in one of two states: idle or tripped. For the trip relay, its status (energized or de-energized) when in
each of these states depends on its operating mode, which is set by DIP switch 1.
4.1 Trip Relay (15-16, 17-18)
A trip relay consisting of an NO and NC pair is provided. Terminal 15-16 is normally closed and terminal 17-18 is nor-
mally open. This relay energizes on occurrence of a ground fault or NGR fault. The trip relay can be programmed for
shunt trip or failsafe operation.
When the Sigma 3 is operating in shunt trip mode, when there is no fault condition present the trip relay remains idle
(de-energized). If a fault condition is detected and qualied, the trip relays becomes tripped (energized).
When the Sigma 3 is operating in failsafe mode, when there is no fault condition present the trip relay is normally idle
or energized. The trip relay is tripped of de-energized if a fault condition is detected on the system. The trip relay is
also de-energized when control power is off.
4.2 NGR Fault (AUXILIARY RELAY)
A Form-C auxiliary contact for NGR faults is provided. This is located at terminals 39, 40, and 41. The NGR FAULT
auxiliary relay operates exclusively in shunt trip mode regardless of the setting of DIP switch.
4.3 Ground Fault (AUXILIARY RELAY)
A Form-C auxiliary contact for ground faults is provided. This is located at terminals 42, 43, and 44. The GROUND
FAULT auxiliary relay operates exclusively in shunt trip mode regardless of the setting of DIP switch.
4.4 Watchdog (51-52)
Terminals 51-52 is a system normal watchdog. When the Sigma 3 is de-energized it is open. When the Sigma 3 is
energized but not in alarm it is closed. If the Sigma 3 goes into alarm mode, the watchdog changes state and opens
back.
5. LED INDICATORS AND DIAGNOSTICS
The Sigma 3 has 4 indication LEDs located on its front panel: the Green PWR (Power) LED; the Red GND (Ground)
FAULT LED; the Red NGR FAULT LED; and the ZONE GR. (Zone Grading) LED.
5.1 Start-up and Reset Indications
The Sigma 3 has a start-up sequence where the Red GND FAULT, NGR FAULT and ZONE GR. LEDs ash twice
before being turned OFF. The Green PWR LED may also ash before it is turned ON.
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