After taking a look at the best circuit breaker finders and trackers, we also want to cover how circuit breaker finders work. Some readers (maybe even some electricians) may not know what's going on behind the scenes of these tools. For most of us, the little plastic box works like magic. They can peer into walls and trace hot and open circuits. What's the difference between a circuit tracer and a circuit breaker finder? What makes these tools work, and why are some much more expensive and feature-rich than others? Hopefully we can answer at least some of these questions and give you a little more insight into these tools.
Circuit Tracer vs. Circuit Finder
"Tracer" isn't a good word for a simpler breaker-finding device. A tracer is generally a device used to trace the path of a circuit. Professionals use these more sophisticated devices to trace wires in order to remodel a home without losing sight of what's going on behind walls that you may or may not be removing. You can also use these tools to find short circuits or trace wires that are inside conduit. You can do this on an energized (live) or de-energized (open circuit) circuit.
Circuit breaker detectors are generally only suitable for energized circuits. The transmitter plugs into an outlet and draws a spike of current from the line – typically 6-10 amps. It does this for a very short amount of time, resulting in a very strong signal. Therefore, the transmitter portion of the system is fairly simple. Without a battery, it doesn't really have to do much other than extract the current pulses the receiver is designed to detect.
On the other side of the equation, receiver sensitivity doesn't have to be that high to determine a suitable circuit breaker. Don't need much gain. After all, it's only good for short distances between the current-carrying parts in the breaker and the tool — an inch or two at most, really.
How Circuit Breaker Finder & Tester Works
Advanced products like the Greenlee CS-8000 allow you to trace live circuits up to 3-5 feet overhead. This is possible because the circuit tracer is more sensitive, so it can adapt to both weak and strong signals. These different tools can achieve their goals in a variety of ways. One technique is to inject a signal burst at the transmit frequency and control the width of that frequency on the AC waveform. This is a live circuit. With a dead circuit, you have a burst of pulses at regular intervals – so a pulse followed by some quiet time alternates back and forth. The recipient then looks for these signatures.
Of course, choosing a frequency and modulation technique is a bit of voodoo. You're trying to define something without too much distraction. There are many more sources of noise than in the past (computer UPS systems, fluorescent lights, switching power supplies, etc.). What you're really targeting isn't something that happens naturally.
Another technique is to put your signal on the wire for a few full cycles, then take the signal away for a few cycles. Then you stack it again. This gives you some "label space" that the recipient can distinguish from anything found in the real world. Not everyone uses the same technique or the same frequency, but the principles are all very similar.
Why so sensitive?
Battery powered trackers don't draw that much current, so the receiver must be able to amplify the frequency of interest and differentiate that signal. Compare that to a very hot signal on a breaker probe that doesn't need to be close; y as much trick as possible. A circuit tracer can also detect open and powered circuits at the same time, so it needs to be able to look for two different signals.
When you have a complete circuit, you have current flowing, so you feel the magnetic field that the circuit creates on the wire. An open circuit will make you look for the static field more. So for circuit tracers, you actually need to have two types of pickups. For the magnetic field you use an inductor (100mH or similar). For static you may have a copper plate or an area on the circuit board to detect it.
at the core
There are microprocessors in both the transmitter and receiver. Simpler microprocessors exist in transmitters. This half of the system determines whether the line is energized or not. It also needs to detect the AC waveform (when it crosses the "neutral line") so it knows when and where to insert the burst. In the receiver, the microprocessor has a lot of work to do. A digital filtering algorithm is in progress. It also controls the programmable gain amplifier so it can correctly see the signal of interest.
When a circuit tracer traces an overhead live circuit, the range of signals you're looking at needs to be orders of magnitude more sensitive than when you're at a circuit breaker. But the tool can do both, so the processor has to be able to change the gain appropriately — and it has to be done quickly. On products such as the Greenlee CS-8000, the "waterfall bars" of the LCD screen are also controlled by this microprocessor. But regardless of the reading method, the microprocessor will handle it.
Who uses these tools?
Anyone who has done renovations is familiar with residential and commercial buildings where circuits are not properly identified. New buildings might mark circuits well, but older buildings aren't nearly as accurate or detailed. If you need to trace a short to ground or trace an overhead circuit, you need to understand how a circuit breaker detector works. These tools are great for tracing wires and save a lot of time and effort if you need to open up a space between two rooms.
Another use is working in more sensitive areas such as hospitals. With all the interference, you need a high quality circuit tracer. Plus, being able to identify the proper circuit breaker is even more important if it means you can avoid accidentally turning off grandma's respirator!
Pro Tool Reviews would like to thank Richard Duke, Greenlee's Electrical Test and Measurement Product Manager, for taking the time to answer our questions about circuit breaker probes and circuit tracers (and the technology behind these tools). If you're a product manager and have an interesting story to share about how a particular tool or technique works, feel free to drop us a line at editor-AT-protoolreviews.com so we can consider it for a future article or get in touch with you Get more information.