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Single Phase Surge Suppressors Information

Single phase surge suppressors protect equipment from transient overvoltages present on AC single-phase power lines.

Understanding Single Phase AC Power

Single phase suppressors are designed to protect devices connected to single phase alternating current (AC) power. The term "single phase" simply refers to the fact that all the voltages in the AC system vary in unison. The graph below shows a typical single phase AC wavelength.

single phase surge suppressors selection guide

Image credit: Mike Gigi

This contrasts with three phase AC power, in which the conductors reach their peak voltages sequentially. While single phase AC is less powerful than three phase, it is considerably cheaper to install and operate.

Single phase AC power is widely used in residential applications. In the United States, commercial buildings will use single phase up to about 100kV A, or 417 amps at 240 V. Single phase power is not suitable for starting industrial motors or other heavy equipment.


When discussing single phase AC power and related devices, it is important to consider the number of conductors, or wires, the system uses. AC power is typically specified as 2-, 3-, or 4-wire. Because one wire is always neutral, the number of live or "hot" wires in the system can be determined by the formula

H = n-1

where H = number of hot wires and n = nominal number of wires. For example, a 3-wire system has two hot conductors and one neutral wire. The image below shows a typical 3-wire system. V1 and V2 represent the two hot wires, while N represents the neutral wire connected to ground.

single phase surge suppressors selection guide

Image credit: Charles Esson

When selecting a surge suppressor, it is very important to match the device's wire specifications to those of the power system it will be attached to.


For more information about a surge suppressor's technology, standards, and certification, please visit Engineering360's Surge Suppressors Selection Guide.

Form Factor

Surge suppressors may be manufactured as a number of different form factors or mounting types.

  • Wall / backboard devices feature mounting holes and are bolted to a wall.
  • Rack-mounted devices fit inside of a panel, which may be a standard 19" telecommunications rack.
  • DIN rail products mount on a rail standardized by the Deutsches Institut für Normung, a German national standards body. Common rail widths include 15 mm, 35 mm, and 75 mm.
  • Hard-wired suppressors mount directly on or within the device they protect.
  • Plugin products plug into an existing system or power module.
  • PCB surge suppressors are wired directly onto a printed circuit board (PCB).

Wires and Voltage

As discussed above, buyers need to match a surge suppressor's wire specifications with those of the system application. For example, a 3-wire surge suppressor is necessary for use with a 3-wire AC power system.

It is also important to match a surge suppressor's intended voltage with the voltage of the applicable system. Common residential voltages include 120 V, 240 V, or 120/240 V. Commercial or light industrial systems may use higher voltages, such as 380 V, 480 V, 600 V, or 347/600 V.


All About Circuits - Single Phase Power Systems


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