Since it is impossible to prevent voltage surges from either entering a building or from occurring inside a building, surge protection was invented. The function of the surge protector is to stop or limit the effects of less-than-perfect power quality on solid-state electronic devices.

Surge protective devices (SPDs) reduce and divert transient voltage levels. Some SPDs may also be called Transient Voltage Surge Suppressors (TVSS). 

Surge protective devices are designed to reduce potentially damaging short-duration transients present on:

• data networks and computer servers

• telephone or facsimile lines

• HVAC equipment

• closed circuit and cable TV feeds

• any other power or control lines connected to electronic equipment, such as copy machines and computers. 

Surge protection is a cost-effective solution to prevent downtime and equipment damage. It is suitable for any facility or load 600 volts and below. 

Surge Arresters

Surge arresters are protective devices for limiting surge voltages by discharging or bypassing surge current.  They were developed for use in low, medium, and high voltage applications, primarily along transmission lines and upstream of a facility’s service entrance. However, they can be installed downstream of a facility’s service entrance. Their general requirements, installation, and connection are governed by Article 280 of the National Electrical Code^®. 

Surge Arresters are Listed as such by UL and other NRTLs using sections of ANSI/IEEE C62.11 "Standard for Metal-Oxide Surge Arresters for AC Power Circuits". They appear in the UL classification OWHX - Surge Arresters. Other terms often used include: surge arrester, secondary surge arrester, secondary MOV surge arrester, and secondary metal oxide surge arrester. Surge arresters less than 1000 volts are typically called secondary surge arresters.

Transient Voltage Surge Suppressors (TVSS)

A transient voltage surge suppressor (TVSS) is defined as a protective device for limiting transient voltages by diverting surge current in low voltage systems (600 volts and below). Their general requirements, installation, and connection are governed by Article 285 of the National Electrical Code^®.

TVSS devices are Listed as such under UL1449. TVSS appear in the UL classification XUHT - Transient Voltage Surge Suppressors. They are Listed for use on the load side of the main service disconnect, in circuits not exceeding 600V rms.

Surge Arresters vs. TVSS 

The main difference between a TVSS and an arrester is the location within the electrical distribution system which their respective Listing allow them to be installed. Surge arresters are generally on the line side of the main service disconnect overcurrent device and can be low, medium, or high voltage. Their main purpose is to protect insulation levels of the equipment.  

A TVSS, by code, must be installed on the load side of the main service disconnect overcurrent device and be 600 volts or less. Their main purpose is to protect the semiconductor junctions in microprocessor based loads by clamping the transient voltage to a safe level.

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