page_title: Varistor
section_title: Applications
hierarchical_section_title: Varistor / Applications
caption_attribution_description: English: The back &amp; front of the circuitry that's found in a special plug with built-in surge protection.
context_page_description: A varistor is an electronic component with an electrical resistance that varies with the applied voltage. Also known as a voltage-dependent resistor, it has a nonlinear, non-ohmic current–voltage characteristic that is similar to that of a diode. In contrast to a diode however, it has the same characteristic for both directions of traversing current. Traditionally, varistors were indeed constructed by connecting two rectifiers, such as the copper-oxide or germanium-oxide rectifier in antiparallel configuration. At low voltage the varistor has a high electrical resistance which decreases as the voltage is raised. Modern varistors are primarily based on sintered ceramic metal-oxide materials which exhibit directional behavior only on a microscopic scale. This type is commonly known as the metal-oxide varistor.
  Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages. When used as protection devices, they shunt the current created by the excessive voltage away from sensitive components when triggered.
  The name varistor is a portmanteau of varying resistor.
context_section_description: To protect telecommunication lines, transient suppression devices such as 3 mil carbon blocks (IEEE C62.32), ultra-low capacitance varistors, and avalanche diodes are used.  For higher frequencies, such as radio communication equipment, a gas discharge tube (GDT) may be utilized. A typical surge protector power strip is built using MOVs. Low-cost versions may use only one varistor, from the hot (live, active) to the neutral conductor. A better protector contains at least three varistors; one across each of the three pairs of conductors. In the United States, a power strip protector should have an Underwriters Laboratories (UL) 1449 3rd edition approval so that catastrophic MOV failure does not create a fire hazard.
caption: Plug assembly with surge protector circuitry
exif: {}