SPD Concerns: Surge protection for new and existing dwelling units

Shutterstock / Vizrad
Shutterstock / Vizrad
Published On
Mar 15, 2022

In “Ice, Washing Machines and a Phone” (ELECTRICAL CONTRACTOR, December 2019), I wrote about protecting electronic equipment in new and existing homes, and I mentioned surge-protective devices (SPDs) as a method of providing that protection. As we rely more on electronic devices in our homes, the 2020 National Electrical Code is keeping pace with the electrical industry.

The quantity and sophistication of electronic equipment in our homes is far outpacing what most of us projected even 5 years ago. The COVID-19 pandemic has many more of us working and studying at home than ever before. The electrical services at our homes must now supply large, sophisticated and expensive business-type electrical equipment, such as computers, high-resolution monitors and printers, rather than the small home-style machines we used to have. Now, more than ever, surge protection has become a necessity.

Section 230.67 has been added to the 2020 NEC to cover the SPD requirements for all electrical services supplying dwelling units. The SPD for dwelling unit services must be an integral part of the electrical service equipment or must be located immediately adjacent to the home’s electrical service.

An exception to this requirement (to be integral or immediately adjacent) states that it is not required that the SPD is located at the service if it is located at each next-level distribution equipment downstream toward the load. An example of that exception is where a panelboard or a number of panelboards are supplied downstream from the main service disconnect. The surge protective devices used for the dwelling unit services must be either Type 1 or Type 2 devices. If a service on an existing dwelling unit is replaced, the new service must comply with these new requirements in 230.67, and surge protective devices must be installed on the replaced service.

Further information on these surge protective devices can be found in new Article 242 in the 2020 NEC . Article 242 requirements were previously located in Article 285 in the 2017 NEC and previous editions. New Article 242 in the 2020 NEC is located closer to Article 240, which provides requirements for overcurrent protection for conductors, while Article 242 provides protection for overvoltage in systems.

New Article 242 is labeled as overvoltage protection, but does not contain the definition of these devices. SPDs are defined in Article 100 in the 2020 NEC . A surge-protective device is “a protective device for limiting transient voltages by diverting or limiting surge current. It also prevents continued flow of follow current while remaining capable of repeating these functions.”

Types of SPDs

Surge-protective devices are designated as Type 1, Type 2, Type 3 or Type 4 devices. A Type 1 is a permanently connected SPD intended for installation between the secondary of the service transformer and the line side of the service disconnect overcurrent device. A Type 2 is a permanently connected SPD intended for installation on the load side of the service disconnect overcurrent device, including SPDs located at the branch panel. The two key issues here are installing Type 1 on the line side of the service and locating Type 2 on the load side of the service. There are specific requirements in Article 242 addressing Type 1 and Type 2 devices that will be explained further.

A Type 3 device is called a “point of utilization SPD” since it is located at or close to the electrical loads further downstream from the service or panelboards. A Type 3 could be a surge-protective receptacle or a relocatable power tap with built-in surge protection.

A Type 4 is a “component SPD,” including discrete components and assemblies, and it is often built into the electrical equipment rather than being added into the equipment after installation. An informational note provides further information on SPD types 1, 2, 3 and 4 in UL 1449, Standard for Surge Protective Devices, the standard for testing and listing SPDs.

Based on 242.12, SPDs cannot be installed in circuits over 1,000V, so it is not a problem with dwelling units since the voltage cannot exceed 240V in most cases (or 600V for photovoltaic systems). SPDs cannot be installed on ungrounded systems, since connection to a grounding system is required as a method of shunting to ground any higher voltages that may occur on the system. The SPD must have a rating at least as large as the maximum continuous phase-to-ground voltage at the power frequency available at the point of connection to the application. SPDs are required to be listed.

When an electrical contractor installs surge protection, compliance with everything in parts I and II of Article 242 is required for an effective, Code -compliant system.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com.

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