Overview of Voltage Electrical Troubleshooting
- MySafety LLC
- Apr 7
- 5 min read
Electrical Troubleshooting Tools can include an ammeter, ohmmeter, wattmeter, or multimeter to name a few. Voltage and amperage levels in industrial settings can be deadly if extreme caution is not used when working on or around electrical equipment. Regardless of the voltage level present, you must give low and high voltages the same amount of respect. Performing troubleshooting with the power removed is always the best way to troubleshoot an electrical circuit but the need to troubleshoot with the power energized is sometimes necessary. Refer to the tools specific manufacturer’s instructions for using, maintaining, and caring for the test instrument. A test instrument that is not working properly can put yourself and others lives at risk for injury or death.
Some basic test instrument inspections include:
· Damage or signs of wear to the probes/test leads
· Battery(s) condition
· Designed voltage or amperage rating of the test instrument
· Using and storing the test instrument in dry locations
Digital Multimeter (DMM) is one of the most used test instruments in industrial applications. This electronic device is used to measure various electrical properties like voltage, current, and resistance. This information is displayed on a digital screen for the user to analyze. Decades ago, it was common to need a separate tool for measuring voltage, current, and resistance. Some multimeters can even test diodes, transistors, frequencies, capacitors, and much more. But for this blog, we’re going to focus on a multimeter that is used for general purposes to measure voltage, current, and resistance.
Voltage Testing is the process of testing a circuit when the power is energized. Wearing the appropriate personal protective equipment (PPE) for the specific application must be followed when verifying equipment is de-energized and in a safe condition for maintenance or repairs. A common method to verify your test instrument is working properly is to perform a LIVE-DEAD-LIVE test. This means finding a known power source like a wall outlet that should have 110-120 volts present. Verify the test instrument selector is set to voltage (AC or DC) and is rated for the voltage to be tested.
To perform this test:
Live Test – touch the voltage test instrument red probe to the outlet hot slot (usually the short slot) and the other black probe to a grounded slot or grounded surface. If a voltage of 110-120 volts is displayed on the digital screen, this means the meter is functioning properly.
Dead Test – now verify the equipment to be worked on has zero voltage present after flipping the disconnect switch to the off position and applying appropriate lockout/tagout.
Live Test – the voltage test instrument needs to check the known power source again to verify it’s still working properly.
Note: If your test instrument has a “HOLD” button, make sure this button is not activated during your tests. If the button is activated, it will hold the voltage reading displayed (even if the voltage displayed is 0 volts). When you go to test for voltage, the display is going to read 0 volts if the hold button is activated, even though the circuit is energized. Usually, the meter will have a light that illuminates when power is present no matter if the hold button is activated or not, but just make sure this is verified, to prevent a false zero voltage reading.
The purpose of the LIVE-DEAD-LIVE test is to verify that the test instrument didn’t become damaged during the verification of a so called “de-energized” circuit. The extra live test is what verifies the meter didn’t blow the internal fuse or encounter some other issue that would display a false zero voltage state. In the world of electrical work, you always double or triple check your readings, your own or someone else’s life could depend on it.
How does the voltage tester know there is voltage present in an electrical circuit? Each probe/test lead is looking for a potential difference. If each test lead is put onto a 120 volts terminal, then the meter will read 0 volts!!!! Let that soak in. Understanding how your voltage tester works is so important for safety and efficient troubleshooting. The two test leads are looking for potential difference, if you place one lead on a 120 volts terminal and the other on a ground plug or grounded surface, it will now display 120 volts present. This potential difference concept can be applied to troubleshooting as well, when checking fuses with the power energized. If you take one test lead and place it on the top side of the fuse and the other test lead and place it on the bottom side of the same fuse – 0 volts displayed = good fuse, 120 volts displayed = bad fuse.
Voltage testing on 480 volts three-phase electrical circuits uses the same principles as single-phase circuits. You can check three-phase fuses the same way as previously stated, 0 volts displayed = good fuse, 277 volts displayed = bad fuse. Same with testing for voltage between each line (L1, L2, & L3), you place a test lead on L1 and L3 (should display 480 volts), L1 and L2 (should display 480 volts), and L2 and L3 (should display 480 volts). The key thing to remember with three phase voltage is that each phase is its own sine wave that is 120 electrical degrees out from each other and works independently from the other phases. Because if each phase is 277 volts and a test lead is placed on two phases, the voltage tester should in theory display 0 volts. The three phases are not perfectly in sync with each other. They are 120 electrical degrees out of phase. When one phase is at its peak voltage, the other two are at lower values, creating a measurable voltage difference between any two phases (google "3-phase sine wave" for a visual).
A 3-phase direct short occurrence is when any two phases have a path to each other. This can instantly cause an arc flash, make sure your test probes and/or tools don’t create a path for any two phases to come together. If your voltage tester is not properly maintained or used in moist environments, it can become this path and possibly explode in your hands.
Phantom Voltage is an anomaly that refers to a seemingly present voltage reading on a conductor that is not actually energized. This can happen frequently when testing electrical circuits inside control panels. Conductors that are installed near one another can become capacitively coupled to each other. Basically, the magnetic field from one wire is carried into the other wire and creates a small voltage reading (e.g. 2 or 3 volts). For example, a control wire that is powered by 120 volts is parallel to another wire that is powered by 480 volts. If the 120 volts wire has power removed and the 480 volts power remained on, then it’s likely for phantom voltage to be present. Phantom voltage is not harmful, but if you test a wire to ensure a de-energized state and 50 to 80 volts is still present. It's possible at some point along the wire that the insulation barrier is compromised and contacting some other hot wire or surface point. Making the wire partially energized (this is not in a safe de-energized state for maintenance or repairs).
Stay tuned to the MySafety blogs. Reach out to us if you have additional questions or concerns. Our team will be pleased to assist you.
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