Grounded Circuit

A single ground fault on an initiating circuit should not cause any malfunction, but a circuit trouble indication may be caused at the control unit or annunciator if ground-fault detection is a feature of the equipment. Even a single fault should be corrected so that a possible additional fault will not cause a serious deficiency in the alarm system. Two ground faults on opposite sides of the initiating circuit cause a short circuit between the two faults. Follow troubleshooting directions described earlier for a short-circuit fault.

Troubleshoot for a single ground fault using the following steps:

1. Tag and disconnect the initiating circuit at the control unit or annunciator terminals.

2. With an ohmmeter, check for continuity between each end of the circuit and an unpainted spot on the electrical conduit or another ground connection, such as a cold-water pipe.

3. Continuity confirms that at least one circuit ground fault exists. An infinite reading suggests looking in the control unit or annunciator for the ground fault.

4. At a point that is electrically about halfway between the source and the end-of-line resistor, break both sides of the circuit by disconnecting wires at a convenient initiating device or junction box. Check for continuity between each wire and ground separately.

5. Each time continuity to ground is found, move toward the ground fault at a new test point about halfway between the present test point and the last previous test point or the end of the circuit in that direction (source or end-of-line resistor). Look especially for wet, pinched, and damaged wire.

6. When the fault is located, repair it, reconnect wires at the control unit or annunciator, and restore alarm service.

INDICATING CIRCUIT FAULTS

An open- or short-circuit fault in an indicating circuit causes a trouble indication at the control unit. A ground fault may also cause a trouble indication if ground-fault detection is a feature of the control unit.

Short Circuit

A short-circuit fault in an indicating circuit is difficult to detect by the usual test methods because the normal circuit resistance is quite low. A short circuit is just a low resistance in parallel with the low-resistance indicating devices.

The symptoms would be a blown fuse at the control unit or power supply during a routine system test or fire drill and audible devices that do not operate as loudly as usual.

If you suspect a short-circuit fault, the following troubleshooting steps may help locate the fault:

1. There may be several indicating circuits powered from one power supply or fuse in the control unit. Separate the several circuits from each other by tagging the wires and disconnecting them from the control. unit terminals. It may be necessary to make continuity measurements to confirm that the wires from each circuit are tagged separately. Compare the resistance readings for the indicating circuits using the 1 resistance range of the ohmmeter. If there is a short-circuit fault, that circuit should have a lower resistance reading than the others. Insulate with tape the individual bare wires of the circuit being checked.

2. Determine how the circuit wires are routed, using the best available information you may have to trace the wire or conduit route. Move to a point electrically about halfway between the control unit and the most distant indicating device for the next check. At a convenient initiating device or junction box, separate the wires leading back to the control unit from those leading to the more distant indicating devices by disconnecting them at device terminals or at splices. Measure circuit resistance in both directions. The short-circuit fault should be in the direction of the lower resistance.

3. Move toward the fault to a new test point about halfway between the present test point and the last test point or the end of the circuit in that direction (power source or last indicating device). Separate the wires toward the control unit from those leading away from the control unit and again measure the circuit resistance on the 1 scale of the ohmmeter in both directions. The fault will be in the low-resistance direction.

4. Continue to move toward the fault, looking for pinched and damaged wires and for improper connections at indicating devices. Make careful measurements at each new test point since the difference between normal and abnormal resistance may be only slight.

5. When the fault is located, repair it, reconnect all wires, test the indicating devices, and restore the alarm system to service.

Open Circuit

In a two-wire parallel circuit, one open-circuit fault near the control unit would deactivate all the indicating devices. The only sign of an opencircuit fault is the failure of one or more indicating devices during an alarm system test or fire drill. The following troubleshooting steps will help locate the fault:

1. Operate the system test or drill switch at the control unit and check the operation of each indicating device on the suspected faulty circuit.

2. Check the circuit connections at any device with intermittent or weak signals. If a group does not work, check circuit connections at the working and nonworking devices at each end of the group. Make sure that terminal screws are clean and snug and that there are no broken wires at the devices checked.

3. If the fault was not located in Step 2, check the wiring between working and nonworking devices, looking especially for poor splice connections at junction boxes.

4. If all the indicating devices on a circuit fail to work, check for a blown fuse or poor connections at the control unit or at the first indicating device on the circuit.

5. When the open-circuit fault is found, repair the fault and retest the indicating circuit to confirm that all indicating devices work properly.

Grounded Circuit

A single ground fault in an indicating circuit may not cause any symptoms unless the indicating

circuit is ac-line powered. If the ground fault is on the "hot" side of the ac circuit and the indicating circuit is tested, a fuse or circuit breaker at the control unit or at the power panel supplying the alarm system will blow. A ground fault on the neutral side of the indicating circuit causes no symptoms. Two ground faults on opposite sides of the indicating circuit are also a short circuit. Troubleshooting for the short circuit may be accomplished as described earlier.

Troubleshoot for a ground fault using the following steps:

1. Tag and disconnect the indicating circuit wires at the control unit.

2. With an ohmmeter, check for continuity between each circuit wire and an unpainted spot on the electrical conduit or another ground connection, such as a cold-water pipe.

3. Continuity confirms that there is at least one circuit ground fault. An infinite reading suggests looking in the control unit for the ground fault.

4. If a ground fault in the indicating circuit is confirmed, insulate the bare ends of the circuit wires with tape. Move to a point electrically about halfway between the control unit and the most distant indicating device on the circuit. At a convenient indicating device or junction box, separate the wires leading back to the control unit from those leading to the more distance devices by disconnecting them at device terminals or at splices. Check again for continuity between each wire and ground separately.

5. Each time continuity to ground is found, move toward the ground fault at a new test point about halfway between the present test point and the last test point or end of the circuit in that direction. Look especially for wet, pinched, and damaged wires.

6. When the fault is located, repair it, reconnect all wires, and test the indicating circuit by operating the drill or test switch. If all devices operate properly, restore the alarm system to service.