On Fri, 10 Feb 2017 08:45:56 -0800 (PST), 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.

That depends TOTALLY on what kind if plug-in protector you have. A 2
stage 3 mode protector protects against common mode AND differential
mode occurrences - usually employing 6 MOVs and 2 Gas Discharge tubes
along with 2 inductors. Each stage has an MOV across the line (phase
to neutral) as well as an MOV from both phase and neutral to theGas
Discharge device to Safety Ground. The two stages are coupled in
series through inductors on both Phase and Neutral.
A simplified (and slightly less effective) unit uses only a single
MOV in each stage for differential protection, (between Phase and
Neutral) and a gas discharge device between neutral and Safety
Ground, to handle common mode events. Again the 2 stahes are connected
through an inductor (which slows the rate if rise)

Better than MOVs, are silicon avalanche diodes, which being unipolar,
requires 2 back to back in place of each MOV. They are more expensive
and faster acting, - with much better clamping voltage
characteristics.

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.

The impedence of the wire will vary depending on the frequency and
DvDt of the surge.

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.

Is a Whole House protector a good idea? Most definitely - which is why
I installed on in my new panel. But saying plug in protection is
useless or worse, I say is a bit of Hyperbole.

Of course, a $5 "surge protected" power bar is not going to pritect as
well as one costing 30 or 40 dollars or more (unless you are just
buying a "name".)