Electronic Products & Technology

A million and one uses for today’s voltage detectors

By Colin Plastow, industrial product manager, Fluke Electronics Canada   

Test & Measurement

The first electrical tester had a simple solenoid that pulled an indicator attached to a spring across a special voltage scale. The higher the voltage applied to the solenoid, the further the indicator would be pulled against the spring. High accuracy is not a big concern when installing lighting, switches, and other common electrical wiring and equipment. Often, you just need to differentiate common voltages from one another. However, the problem is that solenoid testers are no longer safe to use by some electrical measurement standards, and many companies are outright barring them from the field and floor.

Today’s electronic voltage testers are rugged and compact in design, relative to their old-technology counterparts. Thus, they are easier to carry around and less likely to break. But these advantages pale beside the significant safety advantages that come from the far higher input impedance. Some of these have an input impedance of one megohm—about 100 times that of the best solenoid-based testers. Even at the low end of 20kilohms, an electronic voltage tester is still twice as good as the best solenoid-based testers. Simply apply Ohm’s Law, and the advantages become clear. You’re going to be dealing with far less input current. That means more safety. It also means less time—if any—waiting for the instrument to cool between readings. They work at lower voltages, and typically carry an IEC Category rating. They allow you to troubleshoot a wider range of problems—safer and faster.

Non-contact voltage detectors are a quick, inexpensive way to check for the presence of live voltage on ac circuits, switches and outlets before working on them. Also known as voltage wands, sticks, “power sniffers” or pens, they clip into a shirt pocket and “chirp” or glow when they detect voltage on exposed conducting parts or through insulation.

These types of voltage detectors are designed for non-contact, live-not live voltage detection on electrical circuits found in residential, commercial and industrial buildings. Incidental contact with live electrical conductors is not an issue as long as the detector is rated appropriately for the voltage level and the electrical safety category in which it will be used. In addition, the user must exercise safe work practices and wear any appropriate PPE required.

Voltage detector safety

By telling you if a circuit is live before you work on it, voltage detectors provide a critical safety function. However, a circuit that shows as unpowered must be checked using a conventional contact measurement tool before assuming it’s safe to work on. Getting safe, reliable readings requires purchasing the right kind of voltage detector for your work environment and then following these 3 guidelines.

1. Always verify that the voltage detector is working properly before you rely on it. Use the detector to test a known live circuit both before and after you test an unknown circuit, and make sure it gives you the proper response. The same practice applies to multimeters. If there is any doubt in your mind about whether the circuit is truly live or dead, use an additional method to verify the test results. You only have to be right once to make it all worthwhile. Some voltage detectors, such as the updated Fluke 1AC II, have a self-test function built-in that will verify whether the detector is operational.

2. Ensure that the voltage detector you are using is appropriately rated for the measurement environment you’re working in and is within the voltage range you’re testing. Industrial environments are generally CAT III or CAT IV. Not all voltage detectors are safety rated, however, and they’re not equally sensitive. Some detectors will read small levels of voltage that others won’t detect at all. Don’t assume that the detector you’re using now will perform the same as others you’ve used in the past.

3. Capacitive voltage detectors have certain limitations. Correct operation depends upon the capacitance between the detector’s barrel and ground (normally through your hand and body). If this path is broken for any reason, the detector probably won’t work. For example, if you’re standing on a wooden ladder, the capacitance between your body and ground will be much less than if you were standing on a concrete floor. To help avoid incorrect detector readings, find an installation ground that you can touch when using the voltage detector. Remember, in a series circuit, the smaller the capacitance, the greater the voltage drop: there might be too much voltage drop from you to the floor and too little across the detector.

The detectors will also have a certain minimum voltage to turn on. In our wooden ladder scenario, the detector might not turn on despite the circuit being hot. By similar reasoning, the detector cannot detect live conductors inside a grounded metal conduit. For best results always hold the detector by the body and remember to keep your fingers away from the tip of the detector.


Five reasons to give up your old solenoid tester

1. A useful solenoid tester can measure up to 600 V or more. Having the ability to measure higher voltages limits the tool’s ability to detect voltages below 100 V, due to the poor dynamic range of its magnetics. Try using one on 24 V or 48 V control circuits, and you may as well be using a stick of wood.

2. Solenoid-based testers can appear on the circuit under test as a load and interfere with its operation. For example, the Fluke T+ and T+PRO testers have higher input impedance than traditional solenoid-type testers, but not so high that they have problems with ghost voltages.

3. The relatively high current draw of solenoid based testers means significantly more heat—enough that the testers can quickly overheat and even become damaged if you measure voltage too long. If you use a solenoid-based tester, allow for half-minute cool-downs.

4. Solenoid-based testers generally don’t comply with the CSA 61010 electrical safety standard due to excessive current draw, poor dielectric withstand performance, and impulse destruction from transients. When they fail, it can be catastrophic. Without CSA 61010 compliance, these testers also miss compliance with CSA Z462 or NFPA 70E and other standards that require appropriate safety ratings for the working environment.

5. Applying Ohm’s Law to the low-impedance solenoid-based tester shows that you can easily carry a lethal current through the tester. Wearing insulated gloves can reduce the shock hazard, but you’ll also be risking an arc hazard each time. Solid-state testers, on the other hand, provide additional protection against this type of occurrence.


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