ADT490 TroubleShootingLocating Opens

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Power Supply Grounding

‣ Power Supply has circuit -> allows positive & negative outputs to float relative to ground

‣ Green AC input wire -> building Ground‣ Resistance to ground ≤ 10 kΩ

‣ results from abnormal operation‣ Originally, negative was ground

‣ System Fault -> Ground Fault‣ Non specific - one or many‣ Internal or External

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Bonding

‣ Exterior raceway components bonder to Ground conductor

‣ reduces interference -> EMI, RFI, & ESI

‣ Easirer to test ground during VI

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Bonding

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Ground-to-Ground Short

‣ False Alarm

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Positive Ground

‣ Higher end panels - may show as Positive on LCD

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Ground Fault Processing

‣ Often within 1 second to 90 seconds‣ Lower Priority than Alarms, & Supervisory conditions‣ Return to normals even lower Priority

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Finding Grounds in Small Panels‣ Remove field wiring & install EOLs

‣ Eliminates Panel itself‣ Field

‣ Remove EOL and install field wiring‣ Tag and remove

‣ Find All Circuits with Ground Faults

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Finding Grounds in Large Panels‣ Modules often have 8 circuits‣ CPU Communicates with modules through cables

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Finding Grounds in Large Panels‣ Boolean Search through cables

‣ De-energize panel remove cable

‣ Localize to one module‣ Do small panel search when localized

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Diagnosing Ground Correctly‣ Do not accept LCD info at face value‣ Ground can trigger at 50,000 Ω‣ On positive but can still be detected through

negative wire -> “pass through”

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Diagnosing Ground Correctly

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Measuring Grounds on Positive

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Measuring Grounds on Negative

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Measuring Grounds

‣ Most consistent method - A‣ Positive lead on panel chassis or ground lug‣ Negative Lead on system or circuit common‣ Always gives 0 to 30 V

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Measuring Grounds

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Causes of Grounds

‣ drilled through raceway‣ insulation stripped during insulation‣ wire loose to metal backbox or cover

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Locating Grounds on Class B Ccts

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‣ Boolean Search

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Locating Grounds on Class A Ccts‣ Boolean Search

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Boolean Searches for Grounds‣ Same approach as Opens and shorts‣ REMOVE BOTH WIRES

‣ Middle of circuit, remove both wires‣ If ground goes off -> toward EOL‣ f ground stays on -> toward Panel

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Internal Grounds on Small Panels‣ Remove field circuits with EOLs‣ Check Battery connectors‣ Foreign materials near chassis and mounting screws‣ Remove Circuit board -> closely inspect for foreign

materials ‣ If ground remains -> replace Circuit board

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Internal Grounds on Large Panels‣ Boolean search through Card Communication

Ribbons‣ Can sometimes remove card -> Ground clears‣ Replace cards or CPU as appropriate

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endofpresentation