do_not_spam_me RemoveThis @my-deja.com wrote:
> David Maynard wrote:
>
>>w_tom wrote:
>
>
>>>The only effective protector is one that makes a short (ie
>>>'less than 10 foot') connection to a single point earth
>>>ground. Ineffective protectors such as power strips avoid
>>>mentioning earthing to make excessively profitable sales.
>>
>>Nonsense.
>
>
> Even Consumer Reports' electrical electrical engineers thought plug-in
> protectors helped, and every bill for my home insurance includes a
> brochure advocating the use of plug-in and whole house surge protectors
> and arc fault detectors.
>
Of course they do. What w_tom does is takes snippets of electrical
principles and then misapply them.
Electronic devices won't be damaged if no damaging potential occurs across
them (the airplane example) so the task is to figure out how to prevent
that from occurring.
The whole house protector attempts it by shunting the potential to ground
but it's location presents some problems. For one, since it's at the entry
point it must deal with huge currents and that's the reason for his "10
foot" earth reference. But all wires have resistance, capacitance, and
inductance, even his '10 foot' earth ground, as do surge devices and
'earth' itself. The upshot of this is that transients, albeit greatly
reduced, can get past the whole house protector.
Whole house protectors also don't protect very well from transients
generated by devices *in* the home environment because, while his '10 foot
earth' at the entry point may have a relatively low
resistance/inductance/capacitance, the wires from, say, the backyard pool
pump motor all the way back to the entry point don't. So the potential at
the entry point may be wonderfully clamped to ground with high voltage
transients all over the interior.
A protector at the device itself can take care of those.
What if there isn't a whole house protector and only local protectors on
the device itself? They still work (if done properly).
w_tom is fixated on the length of the earth ground because he's fixated on
the whole house protector but, remember, it isn't being at 'earth
potential' that protects the device, it's if there is no damaging potential
*across* it and local protectors work by clamping the wires *at the device*
together. There's no potential difference.
The whole house protector *must* use 'ground' as the reference point
because it's trying to protect the 'whole house' but that's not the case
with the local protector. It makes no difference that the earth wire has
resistance because, from the perspective of protecting the device, it
doesn't care what potential is on it's 'earth terminal' as long as none of
the other wires are excessively different from it, and each other. And
since the local protector is clamping them together *at the device* there
isn't. The whole thing may 'jump' above earth ground, because of the earth
wire resistance, but they all 'jump' together, forced to by the protection
clamp, so there is no damaging potential across the device.
Btw, the whole house protector 'jumps' above ground too, as does the house,
it's just a matter of how far: the reason for the "10 foot" earth wire.
Ironically, the very thing w_tom claims is the major 'problem' with local
protectors is what makes them work. Specifically, wire resistance. As he
correctly notes, the amount of energy they can handle is a lot lower than a
whole house protector but the wire resistance from the entry point to the
interior limits the current into them. They simply do not have to deal with
the huge currents the whole house protector does so comparing them to one
is simply nonsense. Current limiting, btw, is not unique to the local
protectors. The whole house protector depends on the power company wiring
to limit the surge current into it as well.
Now, since the local protectors will work (assuming properly sized, wired,
and sufficient wiring resistance) why have a whole house protector? Well,
for one, you generally don't put local protectors on everything in the
house but I also said "from the perspective of protecting the device" and
there's another perspective: protecting the people. That 'jump' above earth
is irrelevant to the protected device but it isn't irrelevant to someone
who might be near, or touching, it. Hopefully, the whole house earth
protection shunts the huge currents and then the local protector shunts the
remaining so that things remain at a safe potential for the human inhabitants.
In practice, the power company is supposed to already provide a 'safety'
protector at their entry point, marginal at best, so the additional whole
house protector then further limits the surge so 'robust' devices will
likely survive, with that alone, and the interior protectors, on more
sensitive things, have less to deal with and so are more likely to survive.
So it's a protection *system*, not one device, with multiple methodologies,
considerations, and goals.
The biggest problem with local protection is that people don't connect them
correctly and, in particular, don't protect all the wires. E.g. a clamp on
the power might work fine but if you don't have the modem phone line
connection clamped to it as well then you haven't clamped all the wires
going in and out. And the same applies to the connected monitor, printer,
cable modem, etc. They should all be on the same local protector. Multiple
protectors, especially into different outlets, may not protect because of
the possibility they may each 'jump' differently during a surge.
Using local protection alone becomes progressively more difficult as the
system complexity increases because you can end up with connected devices
separated by significant distances, like with a local LAN, so that the
earth 'jump', that was irrelevant to the local device, becomes a problem
again. E.g. A computer on one end of the LAN 'jumps' relative to the other
end and now you have a potential difference. A whole house protector
reduces that problem because it reduces the magnitude of the surge
penetrating on into the interior and so reduces the 'jump' through the
local protector's earth ground.
As distances increase even more you can't depend on 'earth' being at the
same potential either but we have to stop somewhere
There's no 'magic' one thing and that's why responsible engineers will
recommend both whole house protection and local protectors on sensitive
equipment.
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