June, 2018

Inspection News and Views from the American Society of Home Inspectors

Making the Case for Measuring Voltage


The ASHI Standard of Practice (SoP) requires inspectors to “describe” the “amperage rating” of the electrical service. In other words, we should state whether the electrical service is, for example, a 200-amp, 150-amp or 100-amp service. The SoP specifically states that we are not required to “measure amperage, voltage and impedance.”

I think there are issues with not doing some of these measurements, but my focus in this article is on the importance of measuring voltage. I also argue that it is not possible to describe the amperage of an electrical service without measuring and that inspectors should state this in their reports.

(Note: Checking for amperage on grounding electrode conductors or electric furnaces is a really good idea, but I will save that for another article.)

If we could assume that all the electrical services we check would be nominal 120/240 volts, we could probably get away without measuring voltage. However, there are lots of services in some areas of the country that are 120/208 volts (that is, two legs of a three-phase transformer), and there is a good chance that you will not be able to tell or confirm whether what you are seeing is a 208 service if you do not measure the voltage.

The 120-volt Side of the Equation
Why is it important to know the actual voltage? Let’s say that we measure the voltage line-to-neutral as 115 volts. This is a little bit on the low side by modern standards, but everything will still work—although the voltage drop over long runs may result in inefficiencies of appliances at the ends of those long runs. 

But let’s say the voltage measures 127 volts. This is on the high end and it could result in the shortened life of light bulbs that are rated for only 120 volts. In a situation where the voltage is high, the inspector could suggest that the client buy 130-volt rated bulbs so the bulbs will last longer.

208-volt Systems
Most inspectors probably have heard of 208-volt systems, but it’s likely that they think of them as being related only to commercial electrical installations. The inspectors I talk to are quite surprised to learn that it’s likely they’ve missed noticing 208 systems in the condos they’ve inspected. In addition, 208 systems sometimes can be found in developments that have power fed from underground transformers, so that whole neighborhoods may be 120/208 systems. There are different transformer configurations that can result in 208 volts, but the most common are what are called “wye” transformers. (If you’d like to do bit of homework, I suggest doing some research on high-leg delta transformers.)

The diagram shows a wye transformer. Between any two legs (that is, A and B, B and C or C and A), the voltage will be 208 volts. Between any single leg and neutral, the voltage will be 120 volts. In a condo building, this is done to balance the loads throughout the complex. For example, if there are 12 units, four units might be using legs A and B, another four units use B and C, and the remaining four units use C and A. 

When you remove the panel cover inside the condo unit, it’s likely that you will see nothing special about the panel to indicate that the voltage might vary from 240 volts unless you do some measurements. The panel might even be labeled “240 volts” or “208/240 volts.” This data plate, found in a Seattle condo, was labeled “120-240V.”

Three-Phase Systems
Three-phase systems can be very complicated, but home inspectors might want to have at least a rudimentary knowledge of these systems in some scenarios to provide the best information to their clients. Without getting overly technical, what a three-phase system means to the homeowner is that there could be 20% to 25% differences in performance, as in the following examples:

Besides the performance issues, a 208 system sometimes will end up with inappropriate circuit breakers for the given circuit. For example, instead of expecting to see a 30-amp breaker on a 208-volt electric water heater (as you would expect to see on a 240-volt appliance), the breaker might be limited to 25 amps.

Since most electric appliances are rated for either 208 volts or 240 volts, the choice of appliances is not generally an issue, but some are rated for only 240 volts (120/240). Some appliances are dual-rated, in which case, you might see numbers like 208/230 or 208/240. Typically, higher-voltage data plate ratings will be more about function than about safety. Technically, a “208-only” rated appliance on a 240-volt circuit would be wrong and the appliance could get damaged or worse—and the voltage rating certainly voids its UL listing. These concerns are problematic, especially for home inspectors who pay special attention to such things, as these systems might be difficult to determine without actually “measuring” the voltages being supplied.

We are not required to insert any probe into electrical panels and yet, some standards of practice (like those required in the state of Washington, for example) require inspectors to “describe the voltage and amperage” of the service. Although nominal amperages are straightforward, nominal voltages are not—without actually measuring.

If you have access to the meter room and condo unit disconnects, you could try to determine if a three-phase system is used in the building or you could make an educated guess. However, there are other types of three-phase systems besides wye-type transformers. So, the inspector is left with saying that he or she “could not determine voltage.”

Without inserting probes into the electrical panels, there are other locations at which voltage can be measured. But keep in mind that these voltages will be a bit lower than what would be expected right at the main lugs or other breakers in the panel itself. It also can be useful to take voltage readings to find imbalances between the hot conductors or the hot-to-neutral conductor.

If probing main lugs makes you uncomfortable, perhaps probing the lugs on any double-pole breaker in the panel might be less unnerving. For example, try this on a dryer receptacle, a window air conditioner receptacle, a dryer receptacle, at the AC/HP disconnect or an RV receptacle. These may be accessible locations at which voltage could be measured and there are other locations as well.

If you are not willing to actually measure the voltage, then my advice is to make it your practice to develop language for your reports that addresses this problem so that you keep your client informed. If you do think it is a good idea to measure voltage on your own, then my advice is to become trained on how to measure voltage safely.

A Case Study
A client called me to check out some work that had been done during a remodel. One reason the client wanted my consultation was because they were running out of hot water. They already knew that the electric on-demand heater, due to its size in relation to what was expected of it, was maxed out. They discussed this issue with the builder and decided that they could live with it instead of opting to change the whole electrical service to the unit, which would have made it necessary to install a unit with larger capacity. There simply was no space that my client was willing to sacrifice that could fit a full-size, tank-type heater. (Keep in mind, though, that even with a tank-type heater at 208 volts, it will take 25% longer to heat the water and that water heaters with electric tanks already have the slowest recovery rate.)

A backup plan, if the water heater proved to be insufficient, was to preheat the water going into the heater with a small tank-type electric heater to boost the effectiveness of the on-demand heater. What I found, and what the client was not aware of or prepared for, was that the condo unit’s electrical supply was 208 volts, not 240 volts. So, right from the get-go, the performance was 25% lower than the already anticipated marginal performance.

Even the on-demand heater installation instructions explained how the unit performance would have to be down-rated if the unit was installed on a 208 system. The instructions also stated that the temperature readout on the unit would be 25% inaccurate. This was borne out by the heater’s temperature display indicating 136 degrees F, while the water temp at the tap was 117 degrees F. 

There was ample culpability to go around in terms of this installation. For example, why did the electrician who installed the unit not say anything? In addition, the inspector listed the voltage as 120/240 in the original inspection report because home inspectors generally do not measure voltage.

I think it is a good idea for home inspectors either to measure the voltages or to use clear language as to what they are not reporting—especially as their report relates to condo units that are known to have 120/208 systems. It is common in some areas for housing developments with service laterals to be fed from three-phase transformers, which results in all the homes in the development having a 120/208 service. Ask the electricians in your area if 208 systems are common. Clients deserve to know about this issue.

Charles Buell, ACI, is a licensed home inspector in the state of Washington and he teaches residential home inspection courses at Bellingham Technical College. A long-time member of ASHI, Charlie presented a session at InspectionWorld® 2018 in Orlando and he serves on ASHI’s technical review committee.