Clamping Voltage: Also known as Let-Through Voltage, this is the voltage at which a SPD start to clamp or shunt the surge from line to ground or absorbing the excessive energy.
Common Mode: When relating to SPDs, 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 being blown up or caught on fire.
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 (In): The peak value of an 8/20US 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 20kA and Type 2 devices can be tested using a 3, 5, 10, or 20kA.
Normal Mode: When relating to SPDs, 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, or N-G).
Per Phase: The maximum amount of surge current a SPD can shunt to ground during a surge event on one phase (such as L-N or L-G).
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.
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.
Surge Current Capacity: The maximum surge current the SPD device is capable of surviving on a single impulse basis without suffering degradation of performance of more than 10 percent. It is required to be listed by mode (in kA), since the number and type of components in any SPD may vary by mode. It can also be stated by phase.
Surge Current Per Phase: The per-phase rating is calculated from the total surge current capacity connected to a given phase conductor. For example in a WYE system, L1-N and L1-G modes are added together because surge current can flow on either parallel path. If the device has only one mode (e.g., L1-G), then the per-phase rating is equal to the per-mode rating because there is no protection on the L1-N mode. The industry standard is to publish surge current "per phase" by summing modes L-N + L-G in a WYE system and L-L + L-G in Delta systems.
Modes of Protection - Per Mode and Per Phase: A "mode" is a potential path for a surge to be diverted to (e.g. L-N, L-G, N-G). The number of modes depends on the configuration of the electrical system (single phase, 3-phase WYE, 3-phase Delta, etc.). The per-phase rating is the total surge current capacity connected to a given phase conductor.