On Fri, 10 Feb 2017 16:45:56 -0000, westom wrote:

On Thursday, February 9, 2017 at 9:36:52 PM UTC-5, Diesel wrote:
In part? Er, no. That's the primary reason the protector and
everything else wasn't damaged/destroyed. Your house protector does
the same thing the plugin surge protectors do on a larger level. It
tries to redirect excess current on either/both legs to ground, to
bleed it off as quickly as is possible.

You assumed resistance is relevant. It is not. Impedance is the relevant parameter. Plug-in protectors are all but completely disconnected from earth ground. Plug-in protectors must somehow 'block' or 'absorb' that energy. Plug-in protectors operate completely different from a properly earthed 'whole house' protector.

An answer without numbers is best ignored as speculation. That plug-in protector may connect to a breaker box by wire that is well less than 0.2 ohms resistance. That same wire may be 120 ohms impedance. If that plug-in protector tried to earth a tiny 100 amp surge, then 100 amps times 120 ohms impedance means protector and appliances approach 12,000 volts.

Plug-in protectors can make appliance damage easier if not part of a properly earthed 'whole house' solution.

Surge current finds earth destructively via attached or other nearby appliances. An example of why plug-in protectors can even make surge damage easier if a properly earthed 'whole house' solution does not exist.

We saw this even in studies that were even submitted for design review. In one case, a network of powered off computers were 'protected' by plug-in protectors. Those protectors earthed a surge destructively through the entire network. Best connection to earth was incoming via the network and outgoing destructively to earth via modems. Since both phone and TV cable already have effective protection for free as required by codes.

Solution was to replace every damaged semiconductor (which is why we knew every surge current path), remove those plug-in protectors (that have no earth ground), and implement properly earthed 'whole house' protection. Then no future damage occurred (in a location that suffered a high incident of lightning ground strikes).

'Whole house' and plug-in protectors are completely different. A most significant reason why: plug-in protectors have no low impedance (ie less than 3 meter) connection to earth. 'Whole house' protectors are only effective IF that low impedance (as short as possible with no sharp wire bends) connection to earth exists.

I have experience of a room full of computers and similarly fragile expensive equipment receiving 415V instead fo 230V (some building work was ongoing and the electricians ****ed up and confused the new and old wiring colours, resulting in two phases being given to a room instead of a phase and neutral). All the appliances with a surge protector plug survived. The plugs melted, literally, a mess of molten plastic all over the desk. The appliances without them lost at least a couple of bulk capacitors in their power supplies.

--
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