What is a Surge Protective Device (SPD)?

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 at least 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, or TVSS. 

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

• telephone or facsimile lines, 

• cable TV feeds, 

• security systems,

• entertainment center or stereo equipment, 

• kitchen or other household appliances, and 

• any other power or control lines connected to electronic equipment, such as 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 vs. Transient Voltage Surge Suppressors (TVSS)

Surge arresters are defined as 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^®. 

With the microprocessor revolution, clock speeds have become faster and faster.  A tradeoff has developed, between faster clock speeds and lower costs versus the loads becoming increasingly more susceptible to surges and transients.  

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^®.  

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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