ADT490 TroubleShooting Locating Opens

2 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

3 Bonding ‣ Exterior raceway components bonder to Ground conductor ‣ reduces interference -> EMI, RFI, & ESI ‣ Easirer to test ground during VI 3

4 Bonding 4

5 Ground-to-Ground Short ‣ False Alarm 5

6 Positive Ground ‣ Higher end panels - may show as Positive on LCD 6

7 Ground Fault Processing ‣ Often within 1 second to 90 seconds ‣ Lower Priority than Alarms, & Supervisory conditions ‣ Return to normals even lower Priority 7

8 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 8

9 Finding Grounds in Large Panels ‣ Modules often have 8 circuits ‣ CPU Communicates with modules through cables 9

10 Finding Grounds in Large Panels ‣ Boolean Search through cables ‣ De-energize panel remove cable ‣ Localize to one module ‣ Do small panel search when localized 10

11 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” 11

12 Diagnosing Ground Correctly 12

13 Measuring Grounds on Positive 13

14 Measuring Grounds on Negative 14

15 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 15

16 Measuring Grounds 16

17 Causes of Grounds ‣ drilled through raceway ‣ insulation stripped during insulation ‣ wire loose to metal backbox or cover 17

18 Locating Grounds on Class B Ccts 18 ‣ Boolean Search

19 Locating Grounds on Class A Ccts ‣ Boolean Search 19

20 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 20

21 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 21

22 Internal Grounds on Large Panels ‣ Boolean search through Card Communication Ribbons ‣ Can sometimes remove card -> Ground clears ‣ Replace cards or CPU as appropriate 22

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