Circuit analysis falls into three broad categories: commissioning, preventative maintenance and troubleshooting, said Greg McMurphy, assistant director for VEEP, LMS and rigging curriculum and training for the IBEW-NECA Electrical Training Alliance.
He summarized each category.
Commissioning is typically driven by contract requirements. It can offer a value-add benefit for a contractor’s customers that will—at the same time—provide documentation of the system performance at turnover. This data could prove very useful in the case of a warranty claim.
Preventative maintenance is a high-margin segment of the industry, but it is not necessarily easy to sell to customers. With customers who have regulatory drivers or are forward-thinking enough to put in place preventative maintenance programs, there are definite upsides for avoiding costs of downtime from unplanned outages, possible equipment damage or data loss. Primary points of failure are connection points and overcurrent protective devices (OCPD).
Ways to avoid downtime
There are many different methods of performing preventive maintenance to track parameters and possibly avoid downtime, ranging from simple tests that can be done with low-cost equipment to tests that are more time-intensive and use more elaborate equipment.
Measuring the full load voltage drop across an OCPD, for example, does not require expensive equipment, but does call for work on energized circuits, which will take time and thought to lay out and perform safely.
Another strategy would include measuring temperature with an infrared measuring device. These range from very simple spot measuring tools to infrared imaging cameras.
Flickering lights, equipment reboots of unknown origin, data loss and a ground fault circuit interrupter (GFCI) or arc fault circuit interrupter (AFCI) needing verification would all be troubleshooting calls requiring a circuit analyzer.
McMurphy said a circuit analyzer provides a flexible solution in one package that will put a load on the circuit and test for voltage drop and voltage from neutral to ground. In addition, it may be able to conduct multiple other tests.
“Digital multimeters can be used to check for low voltage and voltage drop. Using either a peak sensing meter or both, an RMS and average sensing digital multimeter can provide the data to find a flat-topped voltage wave shape indicative of high harmonics in the current,” he said. “However, the technician may have to provide a load and could actually overload the circuit and cause problems for the customer. Circuit analyzers use a short time load that is unlikely to trip an overcurrent protection device.”
Analyzing a circuit
According to McMurphy, these are the steps in analyzing a circuit.
First, gather information from the customer regarding symptoms to pinpoint the equipment experiencing problems and likely suspects for the cause.
As an example, laser printers have a preheat wire that draws a large current for a short amount of time every few seconds, and sometimes that dip in voltage can be enough to cause problems for other equipment on the same branch circuit. The problem may show up as a computer reboot. However, the problem isn’t with the computer, but rather the need to separate loads to different circuits that have bad interactions.
Start the investigation at the equipment being affected by the problem. Gather data on the voltages or other parameters of interest.
These are some findings that indicate call for action to prevent system malfunctions:
- A voltage lower or higher than the equipment’s tolerance
- High voltage drop
- A very low voltage drop, lower than reasonable given the circuit parameters
- Improper line frequency, which would be highly uncommon in main power in the United States, but it could be an issue in separately derived systems with sources such as generators.
- Indication of isolated grounding conductors that are not isolated
- GFCIs or AFCIs that do not trip at a low enough current, take too long to trip or trip at too low of a current
- Verify a source that may involve the time-tested split/half method. Record data and hypothesize about possible sources of the issues found.
- Analyze the cause of failure and repair, isolate, replace, filter or upsize conductors as necessary.
Training is essential
Technicians must be properly trained to analyze circuits.
“First and foremost, take the simple step of reading the instructions included with any test equipment prior to use. To understand the parameters being measured, the values of the measurements, the possible sources of problems, the susceptibility of various load equipment, and most importantly the safety considerations, a technician doing circuit analysis should be a well-rounded individual with training in DC and AC theory, test equipment use, electrical safety-related work practices and have experience in the field,” McMurphy said.
“Technicians should seek out training if they feel at all unfamiliar with safety analysis and mitigation, or the descriptions in the equipment manual of parameters being tested and results of test performed with a circuit analyzer. The Electrical Training Alliance provides training resources to NECA contractors and IBEW labor force, starting in apprenticeship with basic safety considerations continuing through DC theory, AC theory, test equipment usage, electrical safety-related work practices, power quality and VDV systems, as well as journeyman training on any of those subjects,” he said.
Testing circuits safely
McMurphy emphasized that technicians must follow NFPA 70E guidelines when performing work on energized electrical systems.
“Taking voltage and current measurements is of necessity justified energized work,” he said. “Technicians need to remember that justification for energized work does not eliminate the need to assess the hazards and apply appropriate controls.
“That may be as little as appropriate hand protection and eye protection given the low energies present at the end of a branch circuit. But it is easy to get complacent or hyperfocused, and as you move your way upstream to isolate or gather data, you could end up in a higher-energy situation very quickly and have inappropriate flash protection.
“Assess troubleshooting steps for all hazards present and take appropriate steps such as the choice of PPE for the technician and barriers to prevent unqualified people in the work zone if the work cannot be done in an electrically safe work condition,” McMurphy said.
Sean Silvey, product specialist at Fluke Corp., Everett, Wash., said typically, when analyzing a circuit, tests are made to determine if a failure would lead to a potential fault by checking for the correct line polarity, confirming the GFCI performs correctly, determining line voltage, grounding and insulation resistance values, and line and loop impedance.
“Testers needed could be as basic as a socket tester with polarity indication and a GFCI tester, to advanced testers like an installation tester,” he said. “In a simple circuit test, plug in a tester that would give a light indication that the polarity is correct. Incorrect wiring and grounding would be a first determination. Identify the correct voltage for the application and if the wiring is the correct size for the system.
“This type of tester has a button that, when depressed, will trip a GFCI outlet and confirm the circuit trips correctly. Another circuit tester would give a digital display of the voltage, frequency, determine polarity, AFCI and GFCI testing. With an installation tester, we can add additional testing such as an insulation test and a loop/line impedance test.”
“The GFCI test will measure the speed and the milliamperes it took to trip the GFCI. And safety always comes first—de-energize systems before working on them,” Silvey said.
Fluke offers a basic tester, the ST120+ GFCI socket tester with beeper, and the advanced installation tester, the 1664 FC multifunction tester with insulation test, GFCI test and loop and line impedance test.
Dave Kadonoff, technical sales specialist at Ideal Industries, Sycamore, Ill., said an understanding of basic electrical concepts and knowledge of what can increase or decrease resistance within a circuit are very helpful when testing circuits.
Testing devices can help a troubleshooter locate the problem location quickly without having to remove dozens of outlet covers looking for a bad connection.
“Testing to find poor circuit integrity caused by excessive resistance can allow a technician to identify issues and their location to correct poor connections, or possibly excessive cable runs with undersized conductors,” Kadonoff said. “Start at the furthest outlet from the panel, and if the voltage drop is less than 5%, the circuit integrity is likely good.
“If the percentage is higher, the technician should work outlet-by-outlet toward the panel and if a find a sudden change is found, that is the area of the branch circuit of concern.
“Sensitive loads require specific minimal amounts or levels of current and voltage to operate reliably and normally. Testing that the branch circuit can deliver and maintain those levels helps you to understand potential issues,” he said.
“Most often, testing is initiated after specific loads that are plugged into behave in an unreliable manner, such as shutting down, rebooting themselves, running hotter than expected or just not working properly. Examples could be laser printers, computers, home security systems or even UPS systems.”
Kadonoff said Ideal Industries’ 61-164 SureTest Circuit Analyzer measures voltage, applies a load and measures voltage in the loaded state to indicate voltage drop, which directly relates to the integrity of the branch circuit wiring from the outlet all the way back to the panel.
“Read and fully understand the instruction manual prior to using this product. Follow all safety procedures and wear proper PPE in accordance with NFPA 70E,” Kadonoff said.