On Thursday, September 6, 2012 8:36:49 AM UTC-4, The Natural Philosopher wrote:
And MOVS are not applied between phase and earth. That would result in instant RCD operation.
Discussion is confused by two completely different devices that, unfortunately, share a same name. An effective protector is from each phase to earth. It never tips an RCD (or GFCI) because the protector looks like an open circuit (disconnected) when a surge does not exist.
Effective protectors are for lightning strikes (and other lesser surges). Effective protectors even have numbers that say it is for protection from lightning - ie 50,000 amps.
Undersized 'profit center' protectors are for tiny surges that typically cause no appliance damage. As others have noted, protection already inside appliances makes that tiny surge (and that tiny protector) irrelevant. Those tiny protectors are rated maybe in hundreds of joules. The surge that can overwhelm protection already inside appliances is something like hundreds of thousands of joules.
A protector for appliance protection is for surges that are hundreds of thousands of joules. Is provided by other and more responsible companies including Keison, ABB, Siemens, General Electric and others. That undersized protector for tiny (irrelevant ) surges is often promoted with brand names such as Belkin and Tripplite.
An effective protector must remains functional even after direct lightning strikes. Protectors that are catastrophically destroyed (a potential house fire) or that degrade significantly are ineffective. Are profit centers sold because it happens to have a same name even though it is a completely different device.
An effective protector means surges, such as direct lightning strikes, do not overwhelm protection already inside appliances. Do not even harm the protector. These superior devices, that cost less money, make the 'always required' connection from phase to earth. Only when a surge exists. And too quickly to trip an RCD.