ADT490 TroubleShootingGrounds

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Prior to Troubleshooting

‣Before starting to work on the FACP, what do you do?

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How to Use Ground LED

‣ Can use LED as tool -> which circuit has a ground fault by systematically removing circuits until ground fault LED turns off.

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Finding Grounded Circuits

‣ Removing a circuit with a ground results in “ground fault” indicator LED turning off.

‣ CAUTION: There may be more than circuits with ground.

‣ For this reason, DO NOT replace circuit when removed -> may itself have a ground.

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8 Zone System‣ Remove & carefully tag and removing each circuit.

‣ When we disconnect Zone 7, we get this:

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Locating Actual Ground

‣ Check out the circuit arrangement on the floor

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Locating Actual Ground

‣ Zone 7 is laid out as below:

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Locating Actual Ground

‣ Straightened out it looks as below:

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Locating Actual Ground‣ Disconnect to Zone 7 EOL

‣ Now only one conductors has ground contact

‣ Go back to FACP and disconnect positive wire.‣ Does the “Ground” LED turn off?‣ If it does, then ground contact is on positive wire

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Locating Ground (Alternate Method)‣ Remove circuit from panel & measure positive conductor

‣ Resistance reading is value of conductor to ground + resistance value of raceway

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Locating Ground (Alternate Method)‣ Remove circuit from panel & measure negative conductor

‣ Resistance reading is read through EOL = value of conductor to EOL + value of conductor to Ground + resistance value through raceway

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Locating Actual Ground

‣ Note Zone 7 Trouble LED -> indicating an open circuit.

‣ It is open -> EOL is totally disconnected

‣ Positive wire at the FACP.

‣ Note that ground on the Zone 7 Initiating circuit did not cause the Zone 7 Trouble Led to turn on

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Locating Actual Ground

‣ Step 2 – Finding the Grounded point with Boolean Search.

‣ With 2 technicians (technician & helper)

‣ one person on to 7th floor and other at FACP.

‣ Re-connect positive wire to positive terminal of Zone 7.

‣ The Ground Fault indication returns.

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Locating Ground (2 Techs)

‣ The technician to the 7th floor, selects mid-point on circuit and opens circuit by removing a device ->

‣ Zone 7 Trouble is in Trouble(open) and Ground Fault are on with the System Trouble.

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Locating Ground (1 Tech)

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‣ Circuit disconnected from Panel

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Locating Ground (1 Tech)

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‣ Ground is between the TP and Panel

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Locating Ground (2 Techs)‣ Next device removed as a Test Point is Hallway

smoke detector ->

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Locating Ground‣ Next device removed is Hallway smoke detector ->

‣ According to panel technician, Ground Fault Led is off.

‣ Ground is between Hallway smoke detector and Fitness Room heat detector.

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Locating Ground (1 Tech)‣ Next device removed is Hallway smoke detector ->

‣ Ground between smoke detector & Fitness Room heat detector.

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Locating Ground (1 Tech)‣ Ground is toward the EOL

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Locating Actual Ground‣ Step 3 – Verifying contact to Ground

‣ Section of circuit looks like “straight line”.

‣ There is a ground contact somewhere along this section of circuit wiring.

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Locating Actual Ground

‣ Grounding point could be between Test Point and Party Room detector, or from Party Room detector onward.

‣ In Party Room, disconnect circuit leaving detector.

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Locating Actual Ground

‣ Now our DMM displays this:

‣ There is no longer a circuit between wire and pipe.

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Locating Actual Ground

‣ To confirm location of grounding point, connect DMM on wire in Party Room and take another reference with respect to ground.

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endofpresentation