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## Re: what is the joule rating on surge protectors?

 Subject: Re: what is the joule rating on surge protectors? Sjouke Burry Sun, 13 Aug 2006 02:23:21 +0200 sci.electronics.basics
 ```John Popelish wrote: ``````John Larkin wrote: ``````On Sat, 12 Aug 2006 18:28:14 -0400, John Popelish wrote: ``````John Larkin wrote: ``````So any MOV can absorb a megajoule? `````` 100 of the largest of these in parallel might. http://www.littelfuse.com/data/en/Data_Sheets/CA.pdf (10 kj each) `````` Yeah, but the big one clamps at about 7 kilovolts! Some of the curves sort of imply a lifetime of 1 to 1e6 shots, depending on the energy per shot, with a fuzzy disclaimer. `````` Oh, you have a clamping voltage requirement, also? ;-) ```I would expect any MOV that absorbed its rated joules in a single pulse to have fulfilled its purpose and be ready for replacement. Derate that peak energy to half and it is an entirely different situation. Derate it to 1/10th, and it can be expected to last a long time, as long as it cools off between pulses. I don't think integrated energy is a very good way to calculate life. It wears out by hitting peak temperature. ```You want to replace the MOV anytime your air conditioner switches? Its no 1shot device, it acts like a zener diode, one voltage for any current you apply. It reduces any line transient to its rated voltage, whatever the current. Lightning by the way causes most damage by secondary induction, up to 1000+ volts/meter (or yard), and this happens much more than direct hits, those are almost always fatal. Those induction spikes can be found in a wide range of voltage and current, for which the MOV can be a nice protection, dont forget that a Megawatt pulse of one microsecond duration is only 1 joule, so that a 40 joule MOV can dissipate 40 MW for 1 usec, and thats much more than your electronics can stand. The rated joules is just the amount of energy/heat, that will cause a tolerable temperature jump,and some damage, because the MOV is overheated in some spots,with local failure. When to much local damage is done, the MOv voltage will go below the mains voltage,and it will burn out/blow the fuse. ```
 Current Thread Re: what is the joule rating on surge protectors?, (continued) Re: what is the joule rating on surge protectors?, John Larkin Re: what is the joule rating on surge protectors?, w_tom Re: what is the joule rating on surge protectors?, John Larkin Re: what is the joule rating on surge protectors?, John Fields Re: what is the joule rating on surge protectors?, John Larkin Re: what is the joule rating on surge protectors?, John Popelish Re: what is the joule rating on surge protectors?, John Larkin Re: what is the joule rating on surge protectors?, John Popelish Re: what is the joule rating on surge protectors?, John Larkin Re: what is the joule rating on surge protectors?, John Popelish Re: what is the joule rating on surge protectors?, Sjouke Burry <= Re: what is the joule rating on surge protectors?, John Popelish Re: what is the joule rating on surge protectors?, Rich Grise Message not available Message not available Re: what is the joule rating on surge protectors?, w_tom Re: what is the joule rating on surge protectors?, John Fields