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Circuit Tracing

Active Circuit Tracer / Wire Tracer


Circuit tracers consist of a transmitter and a receiver. The transmitter produces a unique signal onto the circuit to be traced. The receiver detects this unique signal when placed in the proper orientation to the wires being traced or breakers being identified. The receiver provides a numeric value and a variable pitch/tone that increase as the signal becomes stronger. The transmitter sends a 32 kilohertz, fixed-amplitude, time-modulated signal that injects a voltage onto the circuit to be traced which then induces an electromagnetic field onto the circuit.


Whether the circuit is open or closed greatly affects the strength of the electromagnetic field. In an open circuit, no current can flow, so the electromagnetic field produced is much weaker. However, in a closed circuit, the injected voltage also induces a current flow, which produces a much stronger electromagnetic field. This is the optimal method for tracing as this much stronger signal allows the receiver to detect it from a greater distance away from the circuit being traced. 

Electromagnetic fields radiate counter-clockwise in relation to the current flow. For example, current flows out on a hot conductor and returns on the neutral. This change in opposite current flow also creates opposing magnetic fields. So, when these two opposing conductors are close together, the two magnetic fields tend to cancel each other out. This canceling effect diminishes the circuit’s ability to radiate the transmitter’s strong signal making it more difficult for the receiver to detect the signal. To avoid the canceling effect of the opposing magnetic fields and optimize the transmitted signal, the conductor to be traced should be separated from the return conductor by utilizing a remote return path. The simplest method is to use the 25’ test lead to connect to a remote return path, such as a neutral or ground from another circuit or a water pipe. When identifying breakers, the hot and neutral are already separated at the electrical panel so the use of the AC outlet adapter is sufficient. If unsure that the remote return path chosen is a good one, use a multimeter to measure the resistance between the circuit neutral and the remote return path. If >100Ω, a different return path should be selected.

Finding Opens

‘Opens’ are dead-end conductors that are not connected to anything and therefore do not pass current. To find an Open, use a specialized transmitter and alligator clip set. The open will be at the point you begin to lose signal. At that point, select the ‘MID’ sensitivity mode (the LED must be ‘blinking’) in order to pinpoint the exact location of the Open. If you end up tracing the entire length of the wire without locating
the open, you may experiencing capacitive coupling, or ‘Signal bleedoff’ onto the adjacent conductors. This condition may be alleviated by: a) grounding all adjacent conductors; b) minimizing the distance between the point of connection and the open.

Tone and Probe Tracing

The basic idea is that at one end of the cable you place an electrical signal onto the cable with a tone generator and then follow that signal, using a tone tracer (or receiver) in order to follow or find where the cable is located. Although it is simple in theory, and usually in practice,  there are still some things in network cabling that manage to make things a little more complex. The design of Unshielded Twisted Pair (UTP) cabling is supposed to reduce the interference between the pairs of copper wire that make up the entire cable. All network cable types have four pairs of copper wire carefully twisted together to reduce interference. This creates a number of problems to anyone attempting to trace a CAT5 or CAT6 cable because it is imperative to maximize the signal on the cable in order to create the strength of the signal necessary to detect. The best way to minimize the damping effect of the cable twists is to place the signal on a single wire within the cable making sure other pair is grounded. If, on the other hand, a signal is placed onto both pairs in a cable the twists in the cable will work to dampen the signal, thus making difficult or impossible to isolate with the receiver. Tone tracing provides the only cable tracing technology that can be performed on a live cable. Contemporary tone tracers operate at frequencies well above the level that even very modern cable like CAT7 operate. Consequently, the tone signal does not interfere with the network signal.

 

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