All About Surge Protection Devices

At Global Power Products, we want to keep you protected from power surges. That's why we offer Surge Safe products and want to educate you about surge protection devices or SPDs. There are several different names for this type of equipment: surge protectors, surge suppressors, transient voltage surge suppressors (TVSS), or secondary surge arresters. But they all essentially have the same function of protecting against transient voltages or surges.

Higher Surge Current Ratings Don't Always Equal Better Protection

Using a higher-rated device, with its increased capacity and greater ability to withstand the large surges common to a service entrance environment, can provide better protection for the system. However, when you get above a certain surge current (kA) level, the higher kA does not provide better protection, only a longer life expectancy for the SPD itself. (Higher kA devices use more surge components; more components sharing the surge load means less stress on each component).

Failures of SPDs

Most SPDs fail because of MCOV (Maximum Continuous Operating Voltages). When the SPDs are installed incorrectly and are operating above the normal voltage, failure and explosion might occur. Other failures occur when the SPDs are made from inferior-quality components. Inferior components can easily overheat, setting the entire surge protector on fire. Additionally, the effectiveness of a surge protector can and will decrease over time. Therefore, the older a surge protector becomes, the more likely it will fail to protect against power surges.

Differences Between Large MOVs & Small MOVs

Large MOVs include the sizes of 32mm, 34mm, or 40mm, while small MOVs are sized 5mm, 14mm, or 20mm. the bigger the size, the more energy it can handle and the maximum surge current it can divert. A small MOV can be parallel to match a large MOV's rating. However, the pitfall is current sharing. If multiple small MOVs are used in parallel to increase its current rating, their voltage levels must be a perfect match. Otherwise, the weakest MOVs will be blown first, thus degrading the total system.

Comparing Our Surge Safe Products To Other Manufacturers

We use a single large-block TPMOV with thermal protection as a fail-safe device. In the event of an over-voltage breakdown, the metal oxide disk is securely disconnected from the system power by an arc shield. This means no additional fusing or over current protective device is required. With a short circuit current rating of 200kA, our surge provides L-N and L-L modes of protection. We use 10 or 12AWG wire gauge, since the bigger wire is always better. Our surge protectors also have visual and audio indicators for when the device fails.

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Terminology

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.

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