Lightning Surge Arrestors and Protectors Part #3
Lightning Surge Arrestors and Protectors Part #3
Joules rating: The term “joule” was originally named after physicist James Prescott Joule. There are several technical definitions and formulas associated with calculating joules, in terms of electricity it’s the amount of energy required to produce one watt for one second.
The joules number defines how much energy the surge protector can theoretically absorb in a single event, without failure. Counter-intuitively, a lower number may indicate longer life expectancy if the device can divert more energy elsewhere and thus will need to absorb less energy. In other words, a protective device offering a lower clamping voltage while diverting the same surge current will cause more of the surge energy to be dissipated elsewhere in the system. An excellent ground is required for this to work properly, have quality oriented master electrician check this out for you.
Better protectors exceed peak ratings of 1000 joules and 40,000 amperes. It is often claimed that a lower joule rating is undersized protection, since the total energy in harmful spikes can be significantly larger than this. However, if properly installed, for every joule absorbed by a protector, another 4 to 30 joules may be dissipated harmlessly into ground. A MOV (Metal Oxide Varistor) based protector with a higher let-through voltage can receive a higher joule rating, even though it lets more surge energy through to the device to be protected.
Joule ratings are commonly-quoted but are very misleading parameters for comparing surge protectors. The quality of a surge protector relies heavily upon both the clamping voltage and the joule rating. Any surge of any arbitrary ampere and voltage combination can occur, but surges commonly last only for microseconds to nanoseconds, and experimentally modeled surge energy has been far under 100 joules.[4] Expertly-designed surge protectors should not rely on MOVs to only absorb surge energy, but use them instead to survive the process of harmlessly redirecting the surges to ground. An overwhelmingly overloaded MOV should fail gracefully like a fuse, while diverting most of the surge energy to ground thus sacrificing itself, if needed, to protect equipment plugged into the surge protector. As an additional consideration, since energy in a MOV is stored as potential energy and is released as kinetic energy, a lower joule rating reduces fire and explosion hazards as long as a good to excellent ground exists.
Some manufacturers commonly design higher joule rated surge protectors by connecting multiple MOVs in parallel. Since individual MOVs have slightly different non-linear responses when exposed to the same overvoltage, any given MOV might be more sensitive than others. This can cause one MOV in a group to conduct more (a phenomenon called current-hogging), leading to overuse and eventually premature failure of that component. If a single inline fuse is placed in series with the MOVs as a power-off safety feature, it will open and fail the surge protector even if remaining MOVs are intact. Thus, the effective surge energy absorption capacity of the entire system is dependent on the MOV with the lowest clamping voltage, and the additional MOVs do not provide any further benefit. This limitation can be surmounted by using carefully engineered matched sets of MOVs, but this matching must be carefully coordinated with the original manufacturer of the MOV components.
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Lightning Surge Arrestors and Protectors Part #3
Lightning Surge Arrestors and Protectors Part #3
Joules rating: The term “joule” was originally named after physicist James Prescott Joule. There are several technical definitions and formulas associated with calculating joules, in terms of electricity it’s the amount of energy required to produce one watt for one second.
The joules number defines how much energy the surge protector can theoretically absorb in a single event, without failure. Counter-intuitively, a lower number may indicate longer life expectancy if the device can divert more energy elsewhere and thus will need to absorb less energy. In other words, a protective device offering a lower clamping voltage while diverting the same surge current will cause more of the surge energy to be dissipated elsewhere in the system. An excellent ground is required for this to work properly, have quality oriented master electrician check this out for you.
Better protectors exceed peak ratings of 1000 joules and 40,000 amperes. It is often claimed that a lower joule rating is undersized protection, since the total energy in harmful spikes can be significantly larger than this. However, if properly installed, for every joule absorbed by a protector, another 4 to 30 joules may be dissipated harmlessly into ground. A MOV (Metal Oxide Varistor) based protector with a higher let-through voltage can receive a higher joule rating, even though it lets more surge energy through to the device to be protected.
Joule ratings are commonly-quoted but are very misleading parameters for comparing surge protectors. The quality of a surge protector relies heavily upon both the clamping voltage and the joule rating. Any surge of any arbitrary ampere and voltage combination can occur, but surges commonly last only for microseconds to nanoseconds, and experimentally modeled surge energy has been far under 100 joules.[4] Expertly-designed surge protectors should not rely on MOVs to only absorb surge energy, but use them instead to survive the process of harmlessly redirecting the surges to ground. An overwhelmingly overloaded MOV should fail gracefully like a fuse, while diverting most of the surge energy to ground thus sacrificing itself, if needed, to protect equipment plugged into the surge protector. As an additional consideration, since energy in a MOV is stored as potential energy and is released as kinetic energy, a lower joule rating reduces fire and explosion hazards as long as a good to excellent ground exists.
Some manufacturers commonly design higher joule rated surge protectors by connecting multiple MOVs in parallel. Since individual MOVs have slightly different non-linear responses when exposed to the same overvoltage, any given MOV might be more sensitive than others. This can cause one MOV in a group to conduct more (a phenomenon called current-hogging), leading to overuse and eventually premature failure of that component. If a single inline fuse is placed in series with the MOVs as a power-off safety feature, it will open and fail the surge protector even if remaining MOVs are intact. Thus, the effective surge energy absorption capacity of the entire system is dependent on the MOV with the lowest clamping voltage, and the additional MOVs do not provide any further benefit. This limitation can be surmounted by using carefully engineered matched sets of MOVs, but this matching must be carefully coordinated with the original manufacturer of the MOV components.