How do I find a ground fault or missing SLC devices on a Silent Knight 6820 fire panel

Updated Source: LS10144-001SK-E Rev ESource: LS10144-001SK-E Rev E
Quick answer

A GROUND FAULT on the Silent Knight 6820 means the panel senses current flowing from one or more terminals to earth (Terminal 2). Find it by removing wiring connections one at a time, waiting at least five seconds after each, until the fault clears; the last wire you pulled is on the faulted circuit. If a computer is connected by serial or USB cable the panel also shows a ground fault, which clears when you unplug it.

Steps

From: 6820/6820EVS Addressable Fire Alarm Cont manual, pp. 149-150

  1. Confirm it is a real fault
    If a computer is connected to the 9-pin serial connector or USB, the panel goes into ground fault. Disconnect the computer; that trouble clears on its own.
  2. Remove one field wiring connection at a time
    Take off one circuit's wiring, then pause at least five seconds before removing the next one.
  3. Watch for the trouble to clear
    When the GROUND FAULT message goes away, the last circuit you removed is the one touching earth. Reconnect the others.
  4. Walk the faulted circuit
    And look for a conductor or shield touching a box, conduit or structure, then repair it and reconnect.
  5. For devices showing Missing, check addressing and polarity
    Make sure no address is used twice (that shows DBL ADDR), contact monitor DIP switches were set before power was applied, and SLC polarity is correct.
  6. Measure SLC loop impedance
    Disconnect both SLC wires at the panel and measure positive to negative and negative to positive: both must be greater than 500 k ohms. Then short positive to negative at the far end and measure again: both must be less than 50 ohms.
  7. Use the SLC device locater
    To find a device: Main Menu, 2 for Point Functions, 4 for SLC Single Device Locater, pick the loop and enter the address. The device LED flashes. The system shuts down while locating and resumes when you exit.

Specs & limits

From: 6820/6820EVS Addressable Fire Alarm Cont manual, pp. 139, 149

Earth terminalTerminal 2
Wait between wiresAt least five seconds
SLC open testGreater than 500 k ohms both ways
SLC loop testLess than 50 ohms both ways with the far end shorted
Contact ID codeGround fault trouble reports 310
Module supply27.2-27.4V at the 6815 or 5815XL terminals with AC present

Common mistakes

From: 6820/6820EVS Addressable Fire Alarm Cont manual, p. 149

  • Chasing a ground fault while a laptop is plugged in. The serial or USB connection itself causes the fault on this panel.
  • Connecting SLC devices to the SLC IN terminals of a 6815 or 5815XL. Devices go on the SLC OUT terminals.
  • Testing a T-tapped SLC as one loop. Test each T-tap individually.

Applies to

6820 · Manual LS10144-001SK-E6820EVS

Sources

  1. 6820/6820EVS Addressable Fire Alarm Control Panel Manual, p. 149 (LS10144-001SK-E Rev E)
  2. 6820/6820EVS Addressable Fire Alarm Control Panel Manual, p. 150 (LS10144-001SK-E Rev E)
  3. 6820/6820EVS Addressable Fire Alarm Control Panel Manual, p. 139 (LS10144-001SK-E Rev E)
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