Cool Tools: Circuit Detectors

One of the most basic tools every electrician carries is the noncontact voltage tester. Essential complementary tools include circuit breaker finders and tone probes for tracing wires. Scanning devices are able to see through walls and floors to identify wires, conduits and other objects.

Voltage testers

Noncontact voltage testers are “simple, handheld, pen-shaped devices that detect the electric field generated by the presence of an AC [alternating current] potential,” said Sean O’Flaherty, director of product management, Klein Tools, Lincolnshire, Ill. “When such a detection is made, the tester typically delivers audible and visual warnings.” 

The latest generation has expanded the detection range.

“The ability to detect voltages as low as 12V [volts] AC up to voltages of 1,000V AC on the same handheld tester makes these products very useful for electricians who may encounter a variety of different wiring tasks in their daily work,” he said. “Whether the electrician is installing a doorbell or an industrial machine, the same noncontact tester can be used to check for the presence of voltage at the location where the device is being installed.

“Many manufacturers are engaged in new and innovative product development. Over the past few years, noncontact testers have been introduced with integrated flashlights for illuminating low-light workspaces and proximity sensors that indicate the strength and not just the presence of the potential being sensed,” he said.

Richard Wexler, director of instruments, Flir Systems, Wilsonville, Ore., said the noncontact voltage detector is a must-have tool for electricians.

“Simple voltage testers have evolved in two primary areas: increased versatility with added built-in functions and added flexibility in terms of adjustable accuracy,” he said. “These pen-sized devices often have a bright, built-in LED flashlight or infrared thermometer for added versatility. Voltage pens are handy for testing wiring or outlets. But when wiring is behind walls, shielding or conduit, they can miss live circuits, and a noncontact current detector is used.”

Keith Moffatt, senior product manager for test and measurement, Greenlee, Rockford, Ill., said a significant development for noncontact voltage detectors is the dual-blade tip, which works on tamper-resistant and conventional 110V outlets.

“The second blade opens the safety shutter on a tamper-resistant outlet, so the detector can be used very efficiently using only one hand,” he said. “Voltage testers have also evolved to include sound, sensitivity adjustment, the use of LEDs for increased brightness, improved grip surfaces and ergonomic cross sections.

“Another consideration is that the applications of noncontact voltage detectors are wide-ranging. Users want to detect weak signals, but, at the same time, they want to detect only the device or conductor they are specifically interested in. This is made more difficult by the fact that, often, devices of interest are very close to other voltage sources,” Moffatt said.

Christopher Forthaus, senior product manager, Ideal Industries, Sycamore, Ill., said most electricians carry noncontact voltage testers and a receptacle tester.

“In general, simple testers have become more ergonomic, smaller and lighter,” he said. “The superior testers have CAT III or IV ratings and UL listing, and some now include flashlights.”

Paige Bovard, group manager, Milwaukee Tool, Brookfield, Wis., said voltage detectors are the fastest, easiest way to detect voltage on a live circuit. 

“With the addition of many low-voltage systems, some voltage detectors now can automatically detect low voltage,” Bovard said. “Dual-range voltage detectors meet the demands of a growing building automation market, such as LED lighting, occupancy sensors, HVAC controls and security systems.

“By simply turning on the tool, the unit will light up the work area as well as detect and differentiate voltage systems under 50V that may have previously gone unnoticed. Once turned on, the product can be positioned near any wire carrying a current, and the user will be notified automatically if it delivers 10–49V or 50–1,000V by different colored LEDs and audible beeping,” she said.

Circuit breaker finders

“Unlike outlet-dependent circuit breaker finders, newer tools use wireless technology to identify light fixtures and even unlabeled wires mid-run,” Wexler said. “A compact transmitter notifies the electrician back at the breaker panel when the correct circuit is turned off or on. Outlet-based models are common, but circuit identifiers that clamp onto one of many wires mid-run are especially useful.”

There also have been developments in ergonomics.

“Today’s circuit breaker finders also are less fatiguing to use because of their ergonomic forms,” Moffatt said. “These devices once were much more rectangular and are now more sculptural. These more ergonomic forms also help to keep the signal antennae close to the item being scanned for better signal strength. Better signal processing improves the ability to discriminate interference from the signal of interest, producing a more reliable result in less time. The ­sensitivity-tuning process has become more automated, making circuit breaker finders faster to use.”

Alvin Lee, product manager, Southwire Tools, Carrollton, Ga., described advancements in circuit breaker finders.

“Years ago, the only way to identify a particular circuit breaker was to trip the breaker. Needless to say, this is very inconvenient. Today’s circuit breaker finders use a transmitter attached to an outlet of the circuit. The transmitter sends a locator signal through outlet wiring. The receiver is then used at the panel to identify the circuit breaker for that particular circuit. Advanced-design circuit-breaker finders with GFCI can pinpoint a single breaker to prevent service interruption. This transmitter can also test GFCI-protected outlets,” he said.

Meanwhile, Forthaus said the tools continue to evolve.

“Circuit-breaker finders [employ] digital signals and refined receiving antennae, resulting in more quickly identifying the breaker and reducing the misidentification of a breaker,” he said. “Some have been designed to be more ergonomic, making them easier to hold and use.”

Tone probes

“Tone probe kits consist of a tone generator and probe,” Klein Tools’ O’Flaherty said. “The tone generator modulates an electrical signal on the wire or wires to which it is connected, and a probe tuned to ‘listen’ to that signal can be traced along a bundle of mixed loose wires to find the wires that have been connected to the tone generator. This is commonly used to identify unlabeled wires by attaching the tone generator to the source of the wires and scanning for the correct connected wires at some destination. Standard tone-and-probe instruments commonly used in datacommunications cabling are not to be connected to circuits connected to the electrical mains supply.”

Harvey Trager, tools product manager, Fluke Networks, Everett, Wash., said tone-and-probe sets are important to a wide variety of workers.

“Tone-and-probe sets are considered an essential tool by many datacom techs, contractors, installers and on-premise techs, [who] normally have one in their personal tool kit or in the truck,” he said. “It also is common to see a tone probe hanging on a distribution panel in a wiring closet. Toners and probes are used to determine the routing of cabling and are used to verify that cables are connected properly, which is useful for installation and troubleshooting in new construction or for moves/adds/changes. More advanced models can be used to determine if the cable is wiremapped properly and even if the cable or part is connected to an ethernet switch.”

According to Wexler, these kits have many uses.

“Beyond their usefulness for telecom/data-wiring installation, tone-and-probe kits are useful for installation and identification of new electrical wiring or troubleshooting unenergized wiring,” he said. “Today’s more sophisticated cable identifier kits are equipped with a transmitter that can identify numerous wires, not just one set of wires at a time. One model can be used to identify as many as 16 wires at one time.”

Tone-and-probe kits are essential when tracing cables in bundles.

“They may also be used on electrical wire to trace behind drywall,” Lee said. “Powerful tone-and-probe kits can trace cables behind walls but are sensitive enough to identify individual connectors. Some also feature replaceable tips, an LED flashlight, LED signal strength indicator, rear-facing speaker and stereo headphone jacks.”

Wall and floor scanners

“Circuit tracers and wall scanners are the most commonly used tools for finding/tracing hidden conductors and other objects,” Ideal’s Forthaus said. “Circuit tracers are the most effective at finding de-energized/energized conductors and can be used to find many nonenergized but conductive materials as well as copper pipe and coaxial, doorbell, or alarm wire, to name a few. Our tracer can also be used to find common splice errors and dead shorts. Wall scanners can be used to locate conductive and nonconductive materials with extensive scanning activity.”

Steve Wilcox, product manager, Bosch Power Tools, Mount Prospect, Ill., said ultra-wide band radar technology offers detection performance of up to 6 inches.

“This technology often has as many as six detection modes, including concrete, wet concrete, deep concrete, in-floor heating, drywall and metal,” he said. “These scanners will detect live wiring, conduits and pipes, ferrous and non-ferrous metals, wood, and plastic pipes. The best models have a large illuminated display that shows object depth and location [center, relative width and edge].”

About the Author

Jeff Griffin

Freelance Writer

Jeff Griffin, a construction and tools writer from Oklahoma City, can be reached at

Stay Informed Join our Newsletter

Having trouble finding time to sit down with the latest issue of
ELECTRICAL CONTRACTOR? Don't worry, we'll come to you.