UPS and Surge Protectors MOVs

Anonymous user · ‎2021-06-29

I've made that question before with no replies, but I tend to write too much stuff that people tend to overlook so I'm gonna try to write as little stuff as I can.

What I'd like to know is if the choice for 300V to 385V varistors (MOV) made by APC on some o their UPSses is the right thing? I mean, at least my UPSes come with these types of MOVs, are they enough for protecting any sensitive load against inside building generated surges and also natural surges like those from lightning strikes? I know that protection against lightning strikes is a very complex issue, but I just want to know if choosing varistors of such high voltage is the correct thing to do and why choosing them.

These MOVs tend to "clamp" the voltage at 750V for the 300VAC one and 1025V for the 385VAC one. Isn't it too high? APC Surge protectors tend to come with 130VAC MOVs that clamp at 330V...

Anonymous user · ‎2021-06-29

For the <330V UL rating, MOVs ara rated for working continuously at 130VAC and this is not the case of my UPSes, which are not american models I should say, but I don't understand why choosing varistors that are rated for working continuously at 300V (BE600-LM) and 385V (BE600-BR) Phase to Neutral. These MOVs are much thicker than the 130VAC ones, which indicates that they are rated for very high voltages and the data writen in its body confirms that they are 300VAC and 385VAC. This means that the let through voltage is about 750V for the 300V MOV and 1025V for the 385V MOV according to the GNR Varistors data sheet. I don't feel protected against all levels of surges by using such over rated MOVs and that's why I connect the UPSes to a surge protector. These MOVs will have a useful life much longer than the UPS itself since most of the small surges will not be shunt/ absorbed by the MOVs, only the biggest ones caused by lightning strikes will, which are relatively rare. I also have read here before that APC UPSes come with MOVs that are themal fused. Mine aren't thermal fused which kinda explain the over rated MOVs.

See Answer In Context

BillP · ‎2021-06-29

i dont know the details rau but i just know that all of the UPSs/surge protectors comply with UL1449 (in the USA at least) and have a let through voltage of < 330v which is the minimum rating that is accepted for surge protection as far as i know.

Anonymous user · ‎2021-06-29

For the <330V UL rating, MOVs ara rated for working continuously at 130VAC and this is not the case of my UPSes, which are not american models I should say, but I don't understand why choosing varistors that are rated for working continuously at 300V (BE600-LM) and 385V (BE600-BR) Phase to Neutral. These MOVs are much thicker than the 130VAC ones, which indicates that they are rated for very high voltages and the data writen in its body confirms that they are 300VAC and 385VAC. This means that the let through voltage is about 750V for the 300V MOV and 1025V for the 385V MOV according to the GNR Varistors data sheet. I don't feel protected against all levels of surges by using such over rated MOVs and that's why I connect the UPSes to a surge protector. These MOVs will have a useful life much longer than the UPS itself since most of the small surges will not be shunt/ absorbed by the MOVs, only the biggest ones caused by lightning strikes will, which are relatively rare. I also have read here before that APC UPSes come with MOVs that are themal fused. Mine aren't thermal fused which kinda explain the over rated MOVs.