Testing for Normally Open Circuits

Some circuits, in home security systems, are normally open. This means that switches are closed when a door or window opens or vibration (such as breaking glass) occurs. A typical circuit is shown in Figure 2-5. To test a circuit such as this, set the switches to NORMALLY OPEN and MOMENTARY and then turn POWER ON. Now connect one test lead to one end of a wire to be tested and the other test lead to the other end of the wire to be tested. The buzzer will not sound if the circuit is open. Closing any switch will cause the buzzer to sound.
Testing for Normally Closed Circuits
Also, some circuits, such as home security systems, are normally closed. This
means that switches are opened when a door or window opens or vibration.
occurs. A typical circuit is shown in Figure 2-6. Totesta circuit such as this, setthe switches to NORMALLY CLOSED and MOMENTARY and then turn POWER ON. Now connect one test lead to one end of a wire to be tested and the other test leaa to the other end of the wi re to be tested. The buzzer wi II not sound if the circuit is closed. Opening any switch will cause the buzzer to sound.

Testing for Intermittent Closures

Sometimes wires or circuits wi [I be intermittently open. For example, jiggling or bending a wire may cause the wire to break open for a short time and then close again. The same thing may happen in reverse. When two wires are close togethe: or switch contacts are very close, there may be no continuity until the wires are bent or stretched, at which time the wires or contacts may touch. There may ever be cases where wires have continuity (or no continuity) until the temperature rises.
_ :: :ce-:::.~ level, at which time the wire opens or two wires touch as the ~ :::_::~ or contracts. A typical case is illustrated in . _ :ce’, ittent openings or closings are hard to find. A latching continuity l8lle -::. -,0′ i-em easier to find by detecting very short openings or closings .
. ~ _ ~ _: :::e so short that you would not hear the buzzer - a hundredth of 1lE:J:iTC : - eo~. The latching continuity tester detects these small openings or
:: _::: :-en sounds the buzzer continuously until the tester is reset. You can ~ :_::: _ –e continuity tester to a circuit overnight. If you return in the morning _._~ : _::zer is on, an intermittent closing or opening occurred sometime
.~ ~-:
“: :::e:ect intermittent closings, set the switches to NORMALLY OPEN and
_’” _ = _ ::: :::,nnect the test leads to the circuit. Press the reset button if the buzzer is .,;;:”-,_’: _~. The buzzer should now be silent but will sound if the circuit is closed _ :::’ier period of time, or is permanently closed.
“: ::etect intermittent openings, set the switches to NORMALLY CLOSED “,e _:. -CH. Connect the test leads to the circuit.

Posted: July 18th, 2007 under Testing of Wires.
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Simple Continuity Tester
A simple $5 continuity tester is shown in Figure 2-3. It consists of a metal

probe and indicator light powered by two AAA batteries. The probe is one lead of the continuity tester and can be touched to the end of a wire or inserted into a connector hole. The second lead is a clip lead that comes out of the body of the
tester.
To use the continuity tester, insert the batteries and then touch the probe to the clip on the lead. The light should go on. (Always perform this preliminary step before using any continuity tester. It verifies that the continuity tester is working!) Now, connect the test lead to one end of the wire to be tested and the probe to the other end of the wire to be tested. If the wire is not broken, the light should come on.

Latching Continuity Tester

A latching continuity tester is shown in Figure . This tester is powered by a
9-volt battery inside the case and has an LED (light emitting diode) lightas well as a
buzzer. It has several different ways it operates.
Testing for ContinuityTo test for continuity, set the switches to NORMALLY OPEN and MOMEN-T ARY and then turn POWER ON. Now connect one test lead to one end of a wire to be tested and the other test lead to the other end of the wire to be tested. The buzzer will sound and the LED light will go on if the wire has continuity.

Testing for Normally Open Circuits
Some circuits, in home security systems, are normally open. This means that switches are closed when a door or window opens or vibration (such as breaking glass) occurs. A typical circuit is shown in Figure 2-5. To test a circuit such as this, set the switches to NORMALLY OPEN and MOMENTARY and then turn POWER ON. Now connect one test lead to one end of a wire to be tested and the other test lead to the other end of the wire to be tested. The buzzer will not sound if the circuit is open. Closing any switch will cause the buzzer to sound.

Posted: July 18th, 2007 under Testing of Wires.
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Solid and Stranded Wire

used for household wiring. Number 4 wire is often used for car battery “boosts cables. the AWe sizes for common types of wiring.

SAFETY WARNING

In the following testing procedures, we’re assuming that you will be tes: for continuity of wires used in telephone lines, speakers, audio cables, televis ” cables, outdoor low-voltage lighting, control wires for sprinkler valves, ~ security systems -low-voltage wiring. In this chapter we are not discussing tes: ” continuity for high-voltage household wiring.                Whenever testing any wires for continuity, make certain that the device -
with the wires is unplugged from household wiring so that no electrical vo ” exists on the wires. Also, be very carefu I in testing wires that are strung throug a house or outside of a house. The wires should not come in contact high-voltage household or exterior wiring. High-voltage electricity can KilL.

Continuity of Wires
Wires break when they are twisted around nails, subjected to cc bending, or just have normal use over a long period of time. Norrnal!x wire has a resistance of 1 to 100 ohms per 1000 feet, depending L = diameter and type of wire. This is virtually a “dead short”. When wire’ continuous, or “open”, their resistance is the resistance of air.

Posted: July 18th, 2007 under Testing of Wires.
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