ADT490 TroubleShootingLocating Opens A

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Introduction

• Breakdown in Circuit Integrity -> Trouble• Metallic continuity interrupted

• an “open” occurs

• System Trouble LED is lit.

• Open on a conventional Initiating circuit• Yellow Zone LED -> on

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Introduction

‣ Open on signal circuit indicate ‣ circuit is Open

‣ “Circuit” or “NAC” yellow LED

‣ System Trouble‣ LED

‣ Buzzer

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Introduction

‣ Class B Initiating circuit :

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Typical Input Circuit

‣ Continuous power 24 Vdc≅

‣ EOL Installed after last device‣ Regulates current 5 to 6 mA≅

‣ Current called -> supervisory current‣ Break -> current stops -> 0 mA‣ Sketch – why no supervisory current‣ Insert Multimeter (series) at FACP, set to mA -> 0.0 mA‣ Insert Multimeter (parallel) at FACP, set to V -> 25 Vdc

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Typical Input Circuit

‣ Break -> ome devices still operate‣ If 1st device is a Manual Station Operated

‣ Places short on circuit prior to break (still powered)‣ Causes Alarm Condition

‣ Remaining three devices electrically disconnected‣ Cannot cause Alarm

‣ Devices panel side of break – function‣ Device on EOL side of break - inoperable

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Simple Exercise - 1

‣ Example of using senses, logic and DMM to find an open circuit in a simple Class B circuit

‣ Imagine the circuit in Trouble is on Zone 2 on a 4 Zone FACP

‣ In this Apartment Building Zone 2 is the entire Second Floor

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Simple Exercise - 2

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Simple Exercise - 3

‣ Wire disconnected somewhere on this circuit.‣ “Disconnected” implies what type of a circuit fault?

____________________________

‣ What will FACP to tell us?

1) _____________________________

2) ____________________________

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Simple Exercise - 4

Visit 2nd floor. ‣ What will suggest where the open has

occurred?

1)_______________________________________

2)_______________________________________

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Simple Exercise - 5

The raceway layout might look like this:

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Simple Exercise - 6

After a visual inspection‣ open location not obvious (hanging device, damage

caused by renovation or repair, etc.), and‣ will probably require some meter work to locate it.‣ Visual inspection suggests problem -> middle to end

of circuit

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Simple Exercise - 7

What clue(s)?Remember:

“Any device on the panel side of a break in a Class B circuit will continue to work, while any device after the break is inoperable”.

1)____________________________________

2)____________________________________

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Simple Exercise - 8

Inspection -> both hallway smokes flashing LEDsFirst Manual Station workedLast one did not. Let’s look at the circuit again:

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Simple Exercise - 9

Open circuit has occurred between the last smoke detector and last Manual Station.

we haven’t to access into any suites.

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Simple Exercise - 10

‣ Convenient test point is second smoke because:

__________________________________and, because of the way the conduit is run,we can_______________________________

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Simple Exercise - 11

Remove the second smoke & Check with Meter

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Simple Exercise - 12

Meter to conductors into octagon-box from the FACP.

What should meter be set for?_______________________________

What reading is expected (app.)?______________________________

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Simple Exercise - 13

We got what we were looking forLook the other way down the circuit to the EOL.Locate other two wires removed from smoke detector.

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Simple Exercise - 14Do we leave the meter as previously set?

________________

What setting is going to be helpful?________________

If this part good (pretty sure it isn’t)What read should we expect? (app.)? _______

With circuit open between Test Point and the EOL What reading will you get? _____________________

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Simple Exercise - 15

Wiring looks like this:

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Simple Exercise - 16

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Simple Exercise - 17

Open is between octagon box and the EOL.

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Simple Exercise - 18

Resistance reading of 4.8 kΩ, seeing EOL.

Open is not between the octagon box and the EOL.

Open has seemingly between the heat detector in suite 203 or the heat detector in suite 204.

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Simple Exercise - 19Remove remaining Marrettes and short together RED and BLACK going to Suite 204.

Put your DMM (on resistance) across the returning blue and brown wires.

If shorted (0 Ω) -> the wires intact & connected to the detector -> wires to Suite 204 OK

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Simple Exercise - 20

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Simple Exercise - 21

Apply same routine and find there is an open-> DMM’s resistance is infinity.

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Simple Exercise - 22

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Simple Exercise - 23Access 203Dismount the detector &Blue wire broken off detector’s terminal screw,

-> causes open circuit.

Re-strip &re-connect blue wireRemake the connections in the octagon boxRe-mount the heat detector. Check to see that the FACP is clear.

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Discussion

How to troubleshoot an open on a Class A circuit?Typically a Class A looks like this:

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Discussion

1) There are 4 wires associated with the Class A “loop”, 2 leaving the panel and 2 returning.

2) The EOL function is inside the FACP.3) The circuit is actually working like a Class B loop, in

the normal mode.4) The arrows represent 2 “switches” that are “open

state”

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Discussion

When open occurs relay causes switches to close

Feeds the voltage to the other side of the open

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DiscussionAn open/break occurred. 1) FACP senses drop in current on loop and closes

the two “switches” (as indicated by the arrows).2) Now we have +24VDC being supplied to the 4th

terminal, and the 0VDC reference being supplied to the 3rd terminal.

3) The FACP is now back feeding the operating voltage and current to the devices beyond the break.

4) ALL DEVICES CONTINUE TO FUNCTION.

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Discussion

All devices work -> smoke detectors flash LED’s-> location of break more difficult to find

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endofpresentation