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Clamping Voltage (Also known as Let-Through Voltage)
The voltage at which a surge suppressor performs its suppression tasks such as diverting (shunt) the surge from line to ground or
absorbing the excessive energy.
Common Mode
When relating to SPDs, common mode refers to surge protection components provided between L-G and N-G modes.
Maximum Continuous Operating Voltage (MCOV)
The maximum voltage that can be continuously applied to each mode of the SPD without degradation.
Maximum Surge Current Rating
The maximum 8x20us Surge Current Amps an SPD can withstand 1 time without performance degradation of more than 10%.
Nominal Discharge Current (I
N
)
The peak value of an 8/20 µs current waveform, selected by the manufacturer, for which an SPD (Type 1 or Type 2 only) remains
functional after 15 surges - Type 1 devices require testing at 10 or 20 kA and Type 2 devices can be tested using a 3, 5, 10 or 20 kA.
Normal Mode
When relating to SPDs, normal mode refers to surge protection components provided between L-L and L-N modes.
Per Mode
A “mode” is a potential path for a surge to be diverted to (such as L-N, L-G, N-G).
Per Phase
The maximum amount of surge current a SPD can shunt to ground during a surge event on one phase.
Short Circuit Current Rating (SCCR)
The suitability of an SPD for use on an AC power circuit that is capable of delivering not more than a declared current at a declared
voltage during a short circuit condition.
Surge
A short-duration overvoltage spike or disturbance on the ac power line, having duration of a few milliseconds or less.
Suppression Voltage Rating (SVR)
Term used to define the clamping voltage when subjected to the UL 1449 2nd Edition Measured Limited Voltage Test - this test has
proven insufficient to adequately evaluate SPD performance, and has been replaced by the Voltage Protection Rating (VPR).
Temporary Overvoltage (TOV)
An overvoltage on the AC power line that is at a given location of relatively long duration (seconds, even minutes) .
Type 1 Surge Protection Device
Permanently connected SPDs intended for installation between the secondary of the service transformer and the line side of the
service equipment overcurrent device, as well as the load side, including watt-hour meter socket enclosures and intended to be
installed without an external overcurrent protective device.
Type 2 Surge Protection Device
Permanently connected SPDs intended for installation on the load side of the service equipment over current device; including SPDs
located at the branch panel.
Type 3 Surge Protection Device
Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the electrical service panel to the point of
utilization, for example cord connected, direct plug-in, receptacle type and SPDs installed at the utilization equipment being protected.
Type 4 Surge Protection Device
Component assembly consisting of one or more Type 5 components together with a disconnect (integral or external) or a means of
complying with the limited current tests.
Type 5 Surge Protection Device
Discrete component surge suppressors, such as MOVs that may be mounted on a PWB, connected by its leads or provided within an
enclosure with mounting means and wiring terminations.
Voltage Protection Rating (VPR)
The new terminology for what was previously known as clamping voltage, suppression voltage rating (SVR), or let-through voltage. It
represents the clamping voltage when subjected to the UL 1449 3rd Edition Measured Limited Voltage Test. This newly modified test is
performed at significantly higher currents (6kV @ 3000A vs 6kV 500A) to more accurately reflect real world performance.
Glossary