November, 2018
Inspection News and Views from the American Society of Home Inspectors

TECHNICAL FOCUS Surge Protection for Smart Homes (and Smart Homeowners)


Along with the ever-growing development of new technology for electrical components, smart lighting and smart appliances comes advanced electronic-controlling systems. In simpler times, the use of relays, contactors, rheostats and hard-wired switches took care of most residential lighting- and appliance-controlling applications.

Practically all modern appliances are now controlled electronically, with the majority of the circuitry installed on printed circuit boards. This can account for more efficient and advanced operation options, all loaded into a compact space.

The benefits of advanced technology are many, but there is a potential downside. Electronic circuits and components are much more sensitive and easily damaged than older, hard-wired circuits. A printed circuit board can be destroyed by something as seemingly harmless as a static electrical charge. So, you can imagine the possible consequences that may occur in the event of a power surge.

Power surges and spikes can originate in many ways. Lightning strikes are one of the most common culprits. Power company switching, power restoration after blackouts, internal system surges, and automobile accidents involving power lines and transformers also are fairly common sources. A typical power surge lasts for a very short time, sometimes only milliseconds. But even though a surge passes quickly, the voltage and amperage can spike to high levels. 

Most homeowners are aware of and use surge protection devices (SPDs) to protect expensive electronics such as televisions, computers and stereo equipment. These devices are installed at the point of use and typically provide multiple receptacles. The surge protector is plugged into a wall receptacle and the individual components are plugged into the power strip.

Whole-house SPDs have been available for several years. Normally, SPDs are installed at the service entrance or service equipment location. They can be sacrificial from large surges, but also can take multiple hits from smaller surges and continue to protect. There are various types and designs of SPDs—each is rated for its particular use and designation.

Type 1 SPDs

Type 1 SPDs are permanently hard-wired, and normally are installed between the secondary part of the service transformer and the line side of the service equipment overcurrent protection device. They also can be installed on the load side of the main breaker or fuse or anywhere in the distribution system; however, they are normally placed on the line side of the service panel. These SPDs must be installed by a representative of the power utility company when the line side of the service is being set up.

Type 1 SPDs primarily protect against surges from lightning strikes and utility capacitor bank switching. One drawback to this type of SPD is that there is normally no way to know if they are still functional. Formally known as surge suppression arrestors (SSAs), all types of these SPDs are now listed as SPDs.

Type 2 SPDs

Type 2 devices normally are installed on the load side of the service overcurrent protection device. A provision in the National Electrical Code© (NEC) allows these SPDs to be installed on the line side of the service if they are installed as a part of listed equipment and if overcurrent protection and disconnecting means are provided. (Note: This type of installation is rare.) 

These devices are normally seen at the main service panel. They sometimes are installed in downstream remote panels for additional protection of equipment (for example, hot tubs, HVAC condensers, pool equipment). Type 2 devices also are known as transient voltage surge suppressors (TVSSs).

Most type 2 SPDs require a dedicated circuit breaker for overcurrent protection, although some have internal protection and do not require additional breakers or fuses. Some manufacturers offer SPDs that take the place of two single-pole circuit breakers. These are multipurpose in that they provide overcurrent protection for two branch circuits, and provide surge protection for the whole panel and downstream circuits. This type of SPD is usually available with either 20-amp or 15-amp breakers. Load centers also are available with the SPD already installed from some manufacturers. 

The installation procedure of SPDs often varies from one manufacturer to another. Some require that the device be installed at or connected to the breaker at the top of the bus bar in the first available space. The logic behind this requirement is that the closer the SPD is to the incoming power source, the less the let-through voltage will be affected. 

Other manufacturers do not specify a particular location in the panel for the breaker. Breaker-attachment type 2 devices come with four wires and a threaded nipple for panel attachment. The wire leads consist of two ungrounded (hot) wires, a neutral wire and an equipment grounding wire. The lead length should be kept to a minimum and should not be spliced to extend the length. This goes back to the same reasoning that longer wires will reduce the protection ability of the device. 

Another variable is the recommended overcurrent protection of the breaker. They usually are offered in 15-, 20- and 50-amp sizes. Some feel that a larger breaker size is better because the protective breaker for the SPD could actually trip from an overcurrent load and disconnect the power to the device before it can absorb the surge and protect downstream equipment. 

There is some controversy related to the 50-amp models because the wire leads are #12 gauge. Although the leads do not carry load current, some inspectors will report this installation as problematic, even though it technically meets manufacturers’ specifications. Type 2 devices typically have indicator LEDs to verify proper functioning. Many models offer connectors for low-voltage telephone and cable TV hookups. Spikes and surges can travel over these wires as well.

Type 3 Point-of-use SPDs

Typically, point-of-use surge protectors are either cord-connected, multi-receptacle power strips, direct plug-in SPDs or receptacle-type SPDs. These are located at the point of utilization of the connected equipment. These should still be used even if whole-house protective devices are installed.

Types 4 and 5 SPDs

It’s unlikely that inspectors will encounter Type 4 or Type 5 surge protection devices in residential services, so I will not cover the details about these devices.

Terminology, Ratings, Definitions and Information

  • Joule: This is the rating of the amount of energy the SPD can absorb before it fails. Marketing descriptions of many SPDs state the joule rating as “the higher the better.” Many engineers disagree with this assessment and promote the clamping voltage rating as being more important for protection.
  • Metal oxide varistor (MOV): An MOV is the primary electronic component used in SPDs to absorb the surge energy. Other protective components include transient-voltage-suppression (TVS) diodes, thyristor surge protective devices (TSPDs) and gas discharge tubes (GDTs).
  • Clamping voltage: Also called “let-through voltage,” this is the amount of voltage allowed to pass before the surge protector begins to absorb the energy from the surge or spike. Lower ratings provide better protection. 
  • Maximum surge current capacity: A rating of 40 kiloamperes to 120 kA is recommended.
  • Short circuit current rating (SCCR): This is the maximum current a surge protector can handle in the event of a short circuit in the home’s wiring.
  • Maximum continuous over-voltage (MCOV): This is how much voltage the device can handle in a continuous over-voltage condition, as opposed to a short duration spike or surge. In this case, a higher rating is better.
  • Modes of protection: The best SPDs have four modes of protection: line to line, line to neutral, neutral to ground and each line to ground.
  • Industry standards: SPDs are covered by article 285 in the NEC. Among other requirements, they “shall be listed” and “shall” be marked with a short circuit current rating. At present, there are no industry standards to determine an acceptable level of protective ratings of surge protectors.

Case Studies

One benefit of working as an electrician for several years is having opportunities to review many different electrical malfunctions and conditions firsthand. I would like to share some specific situations related to surges.

Case 1. I was called out to troubleshoot and make repairs related to several issues at an upscale home that had all the bells and whistles. The homeowners were out of town when a car crashed into a utility pole, causing the service transformer to short out. This caused a momentary surge on the electrical system of the home. When all was said and done, the homeowners lost the control boards on the hot tub, pool salt system, refrigerator, one condensing unit, control thermostat for a walk-in wine cellar and seven electronic dimmer switches. The televisions and computers were spared, but one of the point-of-use surge protectors was fried. The damage amounted to several thousand dollars. My repairs included installing two whole-house surge protectors (type 2) in the main panels.

Case 2. I was asked to check out some power loss to the receptacles in two bedrooms. It turned out that a surge had burned up the wiring on seven of the nine receptacles on the circuit. I’m still scratching my head trying to figure out this one because it only affected one circuit and the wire damage only extended a few inches from each receptacle. You can see the extent of the wire damage in the photo (below right). This was a line-to-neutral surge. The equipment grounding wires were totally unaffected. The branch circuit breaker never tripped. The owner was fortunate that there was not a fire.

Case 3. I also checked out a type 1 SPD that was installed on a control panel for a sewer pump lift station at a multifamily development. Although the device was sacrificed, there was no damage to the panel. The cost of replacing the surge protector was minimal compared with the possible consequences of losing a sewer system for a 40-unit development.

Tips for Home Inspectors

  • Look for improper installations and check the wiring as you would with other circuits.
  • The most common mistake made is double-tapping the SPD to an existing breaker or to the main lugs. This is usually done because there is no available space to install a dedicated breaker for the SPD.
  • If the device is not properly mounted, check to see if it is just lying in the panel unsecured. Not only is this sloppy work, but it also prevents easy visual access to the status LEDs to assure that the unit is functional. 
  • If the SPD is installed outdoors, check to see if the device is properly rated. Some are not rated for outdoor use. 
  • No splices should be made to the leads to extend the length. 

Other than these, there’s not much to it. 

We, as home inspectors, have a responsibility to not only report defects in the home, but also to make recommendations to improve the level of protection of the home’s primary systems. Adding whole-house surge protection is a valid improvement recommendation. 

I’m amazed by the number of high-end homes I inspect that do not have this protection. Why don’t owners of multimillion-dollar homes spend $300 to $400 to have this protection installed? Because they are unaware of the risk and nobody ever offered this information to them. Occasionally, an electrical contractor will offer this upgrade, but not often…at least where I live and work. In my opinion, home inspectors should include whole-house surge protection as a recommendation in their reports.

Several proposals were made for the 2011 NEC to require SPD installation in all dwellings. The proposals were rejected due to lack of “reliable support data.” I have no scientific data to support my beliefs on the value of surge protectors; however, I have installed 30 to 40 type 2 SPDs over the past 18 years. At first, I was unsure as to the effectiveness of their protection, so I asked all of my clients to contact me if they ever incur any damage or if the unit fails. I even offered free labor to replace the unit to encourage them to call me. I have yet to have a single call back. That’s not a scientific study, I know, but I’m convinced that SPDs do work and I recommend SPD installation in my home inspection reports. I encourage others to do so as well.
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.