QUOTE(paskal @ Sep 8 2017, 08:53 PM)
where does it differ than your concept of understanding westom?
Trends (concepts) are same. But details vary. Differences are found in perspective - numbers.
First, ohms are irrelevant. Impedance is relevant.
For example, an AC electric wire from main circuit breaker to a wall receptacle might be 15 meters. That means its ohms are probably less than 0.2. But impedance of that same wire might be 120 ohms. A trivial 100 amp surge down that wire would result in a voltage of less than (100 amps times 120 ohms) 12,000 volts. That is voltage on a class three protector and attached appliances at 12,000 volts.
An IEEE guide demonstrates this. A power strip protector in one room results in that surge being earthed 8000 volts destructively via a TV in an adjacent room. Protector was too far from earth ground. Impedance (not resistance) is the critical parameter. Any splices, sharp bends, metallic conduit, or wire that is too long compromises protection.
50 cm is better. How is each incoming AC electric wire (to the MCB) connected 50 cm to that earthing electrode? Connection from each incoming AC electric wire to an earthing electrode must be as short as practicable. 50 cm is better. But a connection from the MCB connected wire to the earth ground electrode through and including that SPD should be less than 3 meters, no sharp bends, etc. The entire distance is relevant; which includes distance through an SPD.
Second, plug-in (called class three) protectors are near zero protection. As demonstrated by numbers. As demonstrated by an above cited IEEE guide. As demonstrated by so many professional paper including one from the legendary Dr Martzloff.
Third, speed of a protector is also irrelevant. All are more than fast enough. For example, how fast is an MOV (varistor)? That speed varies significantly if measured at the body or measured 5 cm down its lead. Protector parts are so fast enough that even wire length significantly changes its reaction time.
Those are nanosecond numbers. Surges are microsecond events. Protector part are more than fast enough. How to make it faster? Lower impedance (not resistance).
Class 1 or class 2 protectors are more than sufficient by themselves. That class number says nothing about protection. That class number only defines how it must be installed to protect human life. What makes both effective for all types of surges? Again the relevant specification number. Effective protectors are rated to connect to earth at least 50,000 amps. A protector rated to earth direct lightning strikes and remain effective means protection from lesser surges is also superior - even better. Then best protection inside all appliances (that make irrelevant those class three protectors) is not overwhelmed.
No numbers are posted to justify a class 3 protector. Numbers are provided that explains why a class 3 protector can make damage easier. Numbers are also provided that explains why class 3 protectors must not be used if the class 1 or 2 (service entrance) protectors do not exist and are not properly earthed.
Numbers also explain how much protection an expensive class 3 protector provides. About 0.2% of the protection.
Again from that industry standard that defines 99.5% protection:
QUOTE
Still, a 99.5% protection level will reduce the incidence of direct strokes from one stroke per 30 years ... to one stroke per 6000 years ...  Protection at 99.5% is the practical choice.
Where must most all homeowner attention focus? On that low impedance (ie less than 3 meter) connection to and quality of earth ground electrodes.
This post has been edited by westom: Sep 9 2017, 03:37 AM