| ??? 01/17/06 14:08 Modified: 01/17/06 14:09 Read: times |
#107593 - Of course!! Responding to: ???'s previous message |
John said:
I think you should also connect a fuse or a disconnect device, since the MOVs failure mode is a "short" most of the time. Of course, of course. Using fuses is so evident, that I didn't mention it! There must be a bank of fuses, where each switched mains line gets its own fuse. Best there, where the mains enters the circuit and becomes distributed to the individual relays. By the way, according to the CE standards and following the dimensioning example in this link http://www.epcos.de/web/gener...amples.pdf only suited varistors are allowed to be used at mains! So, the S20K275 is allowed, but the S14K275 is not. John said:
Another negative aspect of the MOVs are the wear out mechanism, they are supposed to wear out as they absorb each spike and then ultimately fail. That's why sufficiently strong varistors must be used at mains! John said:
Transzorbs do not have these properties. But the varistor can absorb more energy than the transzorb, and the transzorb is constructed to guaranteedly provide a short circuit when being overstressed! The best idea is to put a temperature fuse in close contact to the varistor. But this is bit overengineering for most cases and can seldom be seen. So far I have only seen this in lightning protection applications. The standard smelting fuse in front of it is enough protection for the very most applications, though. Kai |
| Topic | Author | Date |
| surge/spike suppression?? | 01/01/70 00:00 | |
| Depends on the circuit | 01/01/70 00:00 | |
| Varistor again | 01/01/70 00:00 | |
| where should i connect the varistor? | 01/01/70 00:00 | |
At input of transformer | 01/01/70 00:00 | |
| Varistor | 01/01/70 00:00 | |
| Connect a fuse.. | 01/01/70 00:00 | |
| Of course!! | 01/01/70 00:00 |