Maximum Continuous Operating Voltage

[David]

The instruction manual lists the MCOV value at 470V for the 300V version.  What are the values in parentheses indicating?   (423-517)

[Westbranch]

Looks like a confidence limit, +- 47 v

[Robin]

The 300V SPD has a max AC operating voltage of 300 and a max DC operating voltage of 385. The higher voltages mentioned are where the SPD is supposed to start conducting 1 milliamp of current. You definitely do not want to operate there. Keep things at or below the max operating voltage. There are many different voltages, currents, timings, joules etc associated with MOV's it is really confusing. We get confused too because not all manufacturers use the same methods for their ratings. There are also voltage ratings that the mov's are suppose to clamp to with a certain number of amps of surge. Just keep in mind the max operating voltage and don't go above that or things may go wrong in a hurry. I have been responsible for blowing up a hundred or more inverters due to not understanding these ratings. Who would have thought that in the DR, they would ever have a line voltage of 145 VAC? I didn't think so, but they do and that mistake caused a hundred inverters to be destroyed. Years before I made a similar mistake on a generator MOV. The MOVs back then blew up and spewed molten metal across the circuit board. There was no fixing that mess. The solution was to just remove the mov in both cases. My other mistake was placing them where they could do damage when they blew up. The MOV's we use today have a fuse built in. They aren't supposed to blow up. They seem to work! 40,000 SPD's later we have had just two real issues. I am aware that at least one of the problem SPD's did protect the inverter before totally self destructing. It must have been a direct strike that greatly exceeded the 115 amp capacity of the SPD because there was nothing left of it. This happened one other time also, but I do not know if it was able to protect the loads before vaporizing. We have lots of e-mails explaining how the SPD's protected loads during lightning storms and still work just fine. That is how they are supposed to work.