We’ll look at how to trace a circuit in electronic devices and buildings using a multimeter and circuit tracer.
It might be easy to locate a circuit path using your eyes in simple electrical circuits.
But when dealing with complex circuits, such as in buildings or multilayer PCBs, you need a tool to track the wires/traces.
Circuit traces are equivalent to thin electrical wires. So tracing PCB circuits is similar to tracing larger circuits with circuit breakers in non-labeled electrical panels. Read on to learn more!
What Is Circuit Tracing?
Circuit tracing involves finding the location and direction of branch lines, control wiring, ground lines, neutral lines, feeders, and other circuit connections.
Types of Tracing
The types of wire tracers can either be active or passive.
With active tracing, the electrical wire tracer charges an electrical line using electricity, then detects the signal developed on the other end.
Some devices require direct branches to line, while others only need positioning on the ground above the line.
Instead of injecting electric signals into the circuit, passive tracing tests the electric flow or trace continuity without needing a receiver signal.
So the system must have power flowing through for the tracer to measure voltage or current (resistance or continuity).
Although effective, passive tracing cannot help you detect specific wires from a pair or bunch. Instead, it will point you to a distinct area.
Circuit Tracer Components
These active circuit tracing devices have these three components.
Transmitters are electronic devices that generate a modulated electric signal to propagate through the circuit.
This component sits on one end of the system, such as at the circuit breaker or outlet circuit wiring to inject the signal.
An electrical engineer using a multimeter in a circuit breaker panel
Receivers detect the electric signal injected by the transmitter. So the portable, handheld units connect to the other end of the circuit.
But receivers don’t connect to the wires directly. Instead, they sense the electrical signal when brought close to the conductor carrying this signal. So you’ll get an alert (buzzer or light) when close to the cable.
The receiver features a probe with three electricity detection sensors. These probes generate some electrical energy via switches, then determine the power generated by the signal in the circuit.
How To Trace a Circuit Using a Circuit Tracer
The most vital component in a circuit tracer setup is the receiver (with its probe). As stated earlier, probes contain three sensors.
- Electric Field Sensor: Locates the wire end in an open-ended conductor and differentiates a wire from a pair or bundle.
- Differential Electric Field Sensor: Determines the direction and location of open-ended conductors installed above ground.
- Inductive Sensor: Determines the direction and location of open-ended conductors installed below ground.
One of these sensors uses a switch to supply the output selectively. And this sensor can detect the signal’s magnitude based on the direction the probe points towards.
As the user, you can determine the direction and location of these conductors by swinging the probe end of the receiver back and forth while observing the readings.
So after injecting the modulated signal using the transmitter, the receiver will detect it if placed in the correct orientation to the breakers or wires you want to trace.
For instance, if the transmitter injects a fixed amplitude, 32KHz time-modulated signal, the voltage induces an electromagnetic field in the circuit.
And the strength of this field depends on several factors, but the most vital one is whether you have an open or closed circuit.
Overall, this active tracing system eliminates direct contact on the receiver end, making it safer to carry out repairs or maintenance.
How To Trace a Circuit Using a Multimeter
Although circuit tracers are effective for finding wires without physical contact, they are not ideal for tiny circuits, such as PCBs. So the only way to trace these thin wires is by using multimeters.
Multimeters are versatile tools that can test and measure different electrical properties. So you need to adjust to the correct test settings before use.
A multimeter with different settings labeled along the center dial
For instance, if testing AC voltage circuits, they usually have a high voltage range (110-240V). Most appliances and household devices connect to power outlets, which supply electricity in this voltage range.
So you need to set the multimeter to AC voltage when tracing circuit parts before the step-down transformer and rectifier.
On the other hand, DC voltages are lower because they max out at around 12V. So you need to set the correct voltage settings in your multimeter before testing other circuit components.
A technician holding multimeter probes when testing a PCB
But when testing the voltage, the PCB must have power flowing through. So in this scenario, the circuit tracer will be passive.
And we don’t recommend tracing energized circuits because you can short the system or damage some parts.
So consider tracing the circuit when off by setting the multimeter to resistance or continuity mode.
Circuit Tracing Using a Multimeter in Resistance Mode
Before grabbing the multimeter, check if you can trace the wires visually on the board to know the general directional area.
Once identified, set your multimeter to resistance mode. Unlike circuit tracers, multimeters don’t have separate transmitters and receivers or wireless sensing probes. So you’ll have to connect the red and black probes to the circuit ends.
In the multimeter, insert the red probe in the mAVΩ port and the black multimeter probe in the COM port.
A PCB testing lab with multiple multimeters on the bench
Use the red probe as the transmitter end and the black probe as the receiver end. So contact the red probe with any starting circuit point or component and hook the black probe along the conductive line or at the end.
In resistance mode, multimeters inject a tiny current into the circuit, then measure the voltage drop across the probes.
Multimeter Reading Analysis
If the multimeter gives you an OL or infinity reading, the wire end connected to the black probe has no connection to the one connected to the red multimeter probe. So there’s no continuity between the wires.
But if the multimeter reading is zero, the trace ending matches the source, and the path between them has zero (low) resistance.
A multimeter showing an OL reading
A resistance reading over 1 Ohm indicates continuity, but the circuit wiring has a problem. However, other components might be causing this resistance along the path.
So you should test across shorter trace lengths or remove these components to eliminate their impact.
Circuit Tracing Using a Multimeter in Continuity Mode
Set your digital multimeter to continuity mode, then use the red and black multimeter probes like in the resistance mode above.
The device will beep if there is continuity, which shows you the circuit path. But if there’s no continuity, the multimeter will not beep.
In most cases, the digital multimeter reading does not matter when doing continuity tests. Listen to the beeps. But if your device does not emit a beep, use its manual to determine what the continuity readings mean.
A multimeter in this mode operates like a signal tracer.
Circuit tracing might seem challenging to a novice technician, but it is easily doable when you get down to it. You only need to have the right tools for the job.
When dealing with PCBs, always have a multimeter in hand. But with electrical wiring in buildings, we recommend using a circuit tracer due to its wireless receiver.
That’s it for this article. Comment below to let us know if you have any questions.