Transient Voltage Surge Suppressor

Transient Voltage Surge Suppressor

Created by: Glen Zhu | Updated Date: Mar 13, 2023

What is a Transient Voltage Surge Suppressor (TVSS)?

Surge & Transient Basics

Transients and surges are the same phenomena in the surge industry. These could be voltage, current, or both. They typically have a waveform with a very rapid ascent to the peak and a significantly slower falloff speed. See the spike shown in the below diagram:

It could be caused by external sources such as lightning or a short circuit, or from internal sources such as contactor switching, variable speed drives, capacitor switching, etc.

Transients are known to damage sensitive electronic equipment in homes, schools, commercial, industrial, and factories, etc. The damage caused to electronic loads costs billions of dollars a year.

A TVSS or Transient Voltage Surge Suppressor is designed to protect electrical and electronic equipment from transient over-voltages, spikes, or surges.

The key features of a surge protective device are its capacity to reduce voltage to the lowest possible level and to divert excessive current values to the ground.

Types of Transient Voltage Surge Suppressors

TVSS Types
  • Type I: Main AC power entrance protection, installed outside the building at the service entrance;
  • Type II: Distribution power – Panel protection, installed inside the building at branch panel;
  • Type III: Branch circuit and equipment protection, installed next to the protected equipment;

What’s the Difference Between a Transient Voltage Surge Suppressor and Surge Protective Device?


Both TVSS (Transient Voltage Surge Suppressor) and SPD (Surge Protective Device) refer to a device that can protect a low-voltage electrical system from transients, spikes, or surges (indirect lightning strikes induced by power lines).

How TVSS evolves into SPD?


Prior to the third edition of the ANSI/UL 1449 standard being introduced, there were various terms used when referencing devices intended to limit the effects of transient surge events like the terms Surge Arrester, and TVSS.

TVSS is the industry term for “Transient Voltage Surge Suppressor”.

With the adoption of ANSI/UL 1449 – Third Edition, the term “TVSS” has been officially replaced by Underwriter’s Laboratories with the term “Surge Protective Device (SPD)”.

Technical minor differences shouldn’t be ignored

At the technical level, TVSS and SPD are absolutely NOT interchangeable.

TVSS (Transient Voltage Surge Suppression) has always belonged to a larger family of surge protective devices (SPD).

SPDs are now classified as Type 1, Type 2, Type 3, or Type 4 and are selected based on application and the location where they are to be used.

For those applications similar to where a surge arrester would have been used on the line side of the system, it would now require a Type 1 SPD. In those applications where you once placed TVSS surge protectors on the load side of the system, these same installations require a minimum of a Type 2 SPD.

That’s to say, a formerly known TVSS surge suppressor is now a type 2 SPD as in the old version of the UL standard.

TVSS could be installed at the load side of the service entrance only. Yet SPD can be installed either at the load or line sides.

How Does TVSS work?

For protecting sensitive electronic equipment, the Transient Voltage Surge Suppressor (TVSS) is becoming more common in residential, commercial, and industrial facilities.

Since a TVSS is a voltage-sensitive switch, it constantly monitors the AC voltage input and output waveforms. Nothing happens under normal conditions.

When the voltage difference between the power source and the protected line gets high enough, the switch closes and diverts the transient away from the electronic equipment, ultimately protecting sensitive electronic equipment. A TVSS surge protector contains at least one nonlinear component.

Simply said, the purpose of SPDs is to minimize equipment damage and downtime by limiting transient over-voltages before they reach the devices they are designed to safeguard.

How to Select the Ideal Transient Voltage Surge Suppressor (TVSS)?

There are numerous factors that might lead to spikes and surges, and proper selection of TVSS can assist guard against equipment damage.

In UL 1449 standard, the type of a TVSS is mainly determined by its installation location.

  • Type I TVSS: Main AC power entrance protection

The type I TVSS is designed to protect commercial and industrial facilities from the damaging effects of lightning.

Power cables carry the damaging current into facilities. The device shunts these damaging currents safely to earth ground.

It is also applicable anywhere within the power distribution system.

  • Type II TVSS: Distribution power – Panel protection

The type II TVSS is designed to protect all standard power sub-distribution panel from damaging power line transients

  • Type III TVSS: Branch circuit and equipment protection

The type III TVSS is installed near the protected equipment connected to telephone lines, computers, communication, etc.

Transient Voltage Surge Suppressor Installation

TVSS wiring diagram


After many years of using the term “SPD (Surge Protective Device)” by UL, no standards group uses the term “TVSS” anymore. It is now more commonly used in UL-standard nations including the United States, Canada, and several nations in Central and South America.

LSP team offers a full range of TVSS Surge Suppressors designed to protect sensitive equipment, minimize preventative maintenance, and prevent unscheduled equipment downtime.

Reliability in surge protection!

LSP’s reliable surge protection devices (SPDs) are designed to meet the protection needs of installations against lightning and surges. Contact our Experts!

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