August, 2017
Inspection News and Views from the American Society of Home Inspectors

Testing Electrical Systems


Home inspectors and electricians have many test devices available to them for evaluating electrical systems. Each has a specific purpose. Understanding the proper operation and application of these instruments is imperative to using them safely and accurately.

The methods used to test and evaluate electrical systems and components during a standard home inspection vary from one inspector to the next. The ASHI Standard of Practice and most (if not all) states’ standards of practice do not require measuring amperage or voltage. However, some licensed state standards include specific procedure requirements.

My home state of Tennessee’s standards state that the inspector “shall describe” the voltage and ampacity of the service, and “shall inspect” the proper polarity and grounding of all receptacles within 6 feet of interior plumbing fixtures and all exterior, garage and carport receptacles. To comply with these specific standards, some form of testing and measurement must be done.

I would assume that all home inspectors check receptacles with a tester that has the capablility to confirm polarity and grounding. But how would one accurately “describe” the incoming voltage without taking a measurement? One could use the rating on the panel label (if it is available) to give an estimated general description of the service voltage and, in most cases, that would be accurate. Some residential panelboard labels list ratings of both 240/120 volts and 208/120 volts, whereas others post a rating of 240/120 volts as maximum.

I recommend including a statement in the report about the method used to determine the voltage (whether referencing the label data or actually measuring the voltage) and here’s why: Most residential services in the United States are 240/120-volt systems. However, some services (particularly in urban areas and multifamily housing) could be 208/120 volts. The only way to know for sure is to measure the line voltage. Almost all appliances, HVAC units, water heaters, dryers, ovens and ranges are rated for both 240 volts and 208 volts so this is not really a big deal. It may take a little longer to dry a load of clothes or preheat the oven to bake a cake at 208 volts because the appliances will operate at a lower wattage, but the difference would be minimal.

How “in-depth” should the inspector choose to go in the electrical evaluation? This is a matter of personal preference. Inspectors should obtain proper training before using more advanced test equipment. Learning how to properly use these devices is not difficult, and having knowledge of them can reveal concerns and information that might otherwise go undetected. 

Always follow strict safety procedures and wear personal protective equipment when inspecting electrical systems. Common types of testing devices.

Common Types of Testing Devices

  • Digital multimeters and volt or ohm meters (VOM): These meters measure voltage (AC and DC), resistance and continuity. Higher-end models also can measure capacitance, frequency and amperage.

  • Analog volt or ohm meters: Basically, these have the same capability as the simpler digital meters.

  • Test coils: Test coils are used only to verify the presence of voltage. No batteries are needed. They operate as a solenoid that physically moves the indicator to an approximate voltage range. Normally, they are rated up to 600 volts and put a small load on the line, which eliminates “phantom” or “ghost” voltages that are common with digital meters. They also will accurately test the trip function of a GFCI device by reading across the hot and grounding contacts of a receptacle. A test coil is also known as a “Wiggy.”

  • Ammeters (clamp-on type): These come in both analog and digital models, and measure amperage by closing the clamp around a wire.

  • Non-contact voltage sensors or tracers: These can sense the presence of voltage through a cable, switch and even find energized wires concealed in walls. They also can give false positive or negative readings and should never be relied on for accuracy when there is a risk of electric shock.

  • Plug-in neon light testers: Most inspectors use these to test receptacles for proper wiring. They are handy, but can be inaccurate or inconclusive. Some have ground fault circuit interrupter (GCFI) test capability.

  • Circuit analyzers: These are advanced testers that can diagnose issues with loose wiring, improper wiring and voltage drop calculations. They also have the capability to test the trip function of GFCI and AFCI devices. Additional training and experience are necessary to properly interpret the information provided by a circuit analyzer.

  • Thermal imagers or cameras: These devices detect heat anomalies that will show up as “hot spots” at loose connections and overloaded circuits.

All test devices have specific use applications. The information they provide is only useful if properly interpreted and used in the correct situation.

Measuring Voltage
Measuring the incoming voltage available to a home or building is best done at the service equipment main panel, if possible. This measurement only adds a few seconds to the panel inspection process. A digital multimeter is best suited for this test. The meter should be set to AC volts on the selector and the test leads should be inserted in the proper connectors on the meter designated for voltage measurement.

A line-to-line reading will show the available voltage supply. The test leads are placed on the main “hot” lugs for this measurement. Typically, the voltage range will be approximately 230 to 250 volts for a 240-volt system, and 200 to 216 volts in a 208-volt system. Low or high readings outside of these ranges could indicate a problem with the utility supply and should be further evaluated. The next two readings would be from each hot lug to the neutral lug. This reading should be roughly 115 to 125 volts. The hot-to-neutral reading should be balanced from each line. An imbalance of three or more volts could indicate a possible concern. Large imbalanced readings could mean a problem with the supply neutral, which could become a serious concern if not corrected.

Measuring Amperage
Taking random amp readings is technically beyond the scope of a normal home inspection. Some inspectors will measure the amperage load on HVAC systems during operation to check for defective or failing compressors and motors. Unless one is completely familiar with this procedure, it is best left for qualified electricians and HVAC technicians.

A simple, informative test that home inspectors can do is to measure the grounding electrode conductor for current flow. This can be done with a clamp-on ammeter. There should be little or no measurable current on the GEC in a properly operating system. Small readings of 0.1 to 0.5 amps (100-500 milliamps) are common. Larger readings indicate a concern and should be checked out.

Measuring Voltage Drop
Voltage drop is the amount of energy that is lost between the supply voltage and the available voltage that is present at a particular point in a loaded circuit. High resistance in a circuit can be caused by long wire runs and loose connections. The combined losses (IR drops) along the circuit reduce the available voltage as the circuit continues. Circuit analyzers can calculate the voltage drop by testing at a receptacle. The tester can simulate a load of usually 10, 15 and 20 amps. The recommended maximum voltage drop by the NEC is 5% on feeders and 3% on branch circuits.

A circuit analyzer is very useful to troubleshoot and find specific problems for many applications including voltage-drop issues. However, if a home inspector decides to test for voltage drops and report on those that exceed the 3% in branch circuits, he or she is going to be doing a lot of writing! I personally have never inspected a home in which all circuits can comply within the recommended parameters. It’s just a fact of (electrical wiring) life. Keep in mind that the 5% and 3% thresholds are recommendations in fine print notes (FPN) in the NEC and are not enforceable requirements.

If one chooses to include this testing in their inspections, common sense should prevail. A 7% drop on a 125-volt supply would still leave over 116 volts available. That is sufficient to operate normal household appliances and devices. This would be a typical drop on a loaded receptacle that is on the opposite end of the home from the electrical panel. A large voltage drop to below 110 volts could very well be a concern and should be reported as such. 

Thermal IR Scanning
An infrared (IR) camera is another example of a useful device in the inspector’s “bag of tricks.” Thermal scans of electrical panels can reveal potential problems. It should be understood that these imagers are not magic. They, like all instruments, have proper operating procedures and applications. Proper training is imperative to be able to accurately interpret the information. 

Elevated temperatures of circuit breakers and wires do not necessarily mean that there is a problem. Arc-fault breakers and dimmer switches both operate at a temperature higher than standard switches and breakers and will stand out in a scan. A loaded circuit (photo) such as a running dishwasher will be evident compared with other non-loaded circuits. Uniformity of the wire temperature and terminal connection shows a normally loaded circuit. A large temperature difference (hot spot) between the wire and terminal would indicate a loose connection.

Loose connections, hot spots, overloaded circuits and other thermal anomalies will go undetected if there is no load on the circuit, at the time of the scan. A thermal camera can indicate a suspected overloaded circuit but only can be confirmed by following up with an amp reading on the loaded circuit. A loose connection can reach an extremely high temperature of up to several hundred degrees Fahrenheit. A visual inspection of the hot spot usually will have discolored conductors, lugs or terminals, and sometimes, melted wire insulation. Repair recommendations and corrections should be reported when these defects are found.

It should be noted that an in-depth comprehensive evaluation of an electrical system during a standard home inspection is not practical. Thermal scanning and other advanced testing can be offered as ancillary services for those who wish to add these services.

The electrical system is just one of the major sections that home inspectors encounter in their job. Failing to identify possible concerns could lead to injury of the occupants or could cause damage to the home. The ASHI Standard of Practice is designed to address these concerns as thoroughly as possible in a limited-time-scope inspection. These standards are the minimum requirements that an inspector should follow. Whether or not to go beyond the minimum standards is up to the individual.

Learning to take the inspection process a step further beyond the minimum standards can greatly upgrade the service that we provide to our clients.

Mike Twitty began his home inspection business after retiring from Ford Motor Company, where he worked as an industrial electrician.  Mike is a licensed electrician in Tennessee and holds certifications from the ICC as a residential building inspector and residential electrical inspector. Mike serves on the ASHI technical review committee and regularly teaches seminars for home inspectors.