Re: Soon to arrive my HDTV

Cinder Lane wrote:
> W_tom, you have stated many times in this thread that wall receptacles
> do not have earth grounds.  What about wall receptacles in concrete and
> steel buildings?  Aren't they in direct contact with earth ground?
> 
> Also, for the sake of arguement, let's assume that you are correct --
> that because of high inductance, wall outlets do not have a "true" earth
> ground according to the IEEE definition.  Are you saying that ALL
> plug-in surge suppressors offer NO protection whatsoever?
> 
Suppose you have a fairly strong surge that comes in on the power 
service that causes a current to earth of 1,000A. And further say the 
impedance to earth is a very good 10 ohms. The ‘ground’ at the power 
service will rise to 10,000V above ‘absolute earth potential’. If the 
power wires are all at 10,000V, equipment that only connects to power 
won’t know, like a bird siting on a high voltage wire.

A common problem is when equipment also connects to phone or cable. The 
phone and cable wires may not be at 10,000V. If they were, the equipment 
again wouldn’t know there was a surge. The way you keep signal and power 
wires at the same potential is to connect the phone and cable entry 
protectors with *short* ‘ground’ wires to the 'ground' at the power 
service. The author of the NIST guide has written  "the impedance of the 
grounding system to `true earth' is far less im****tant than the 
integrity of the bonding of the various parts of the grounding system."

According to NIST guide, US insurance information indicates equipment 
most frequently damaged by lightning is
     computers with a modem connection
     TVs, VCRs and similar equipment  (presumably with cable TV 
connections).
  All can be damaged by high voltages between power and signal wires.

The IEEE guide has an example of a surge coming in on a cable wire 
(starting pdf page 40). The 'ground' wire from the cable entry protector 
to the power service 'ground' is too long, so the cable wiring winds up 
at 10,000V with respect to the power wiring. TVs connected to both power 
and cable do not appreciate being treated this way. In many houses the 
phone and cable entry points are to far from the power service to permit 
a short interconnect.

Protection has more to do with keeping the voltages at the same 
potential than earthing, as in the quote above. A direct strike by 
lightning requires lightning rods, but direct strikes are unusual for 
houses.  The reason you are safe in the Empire State Building is that 
you are surrounded by steel and everything is at the same potential 
(suppressors also have to clamp the voltage on all wires to the building 
steel to protect equipment). It is the same reason equipment is safe in 
an airplane, as few airplanes have a connection to earth, let alone a 
connection 10 ft long.

Plug-in suppressors work the same way. If a computer has connections to 
phone and power, both phone and power wires must go through the 
suppressor. The suppressor has protection elements that clamp (limit) 
the voltage on all wires (power and signal) to the common ground at the 
suppressor. The wires going to the computer do not have damaging voltage 
between them. Because, as the IEEE guide explains, earthing is elsewhere 
in the system (not primarily through the plug-in suppressor) poor  w_ 
can’t figure how plug-in suppressors work. But it is explained in the 
IEEE guide starting pdf page 40 for anyone who can read and think. In 
the case above, where phone or cable entry points are too far from the 
power service, the guide says "the only effective way of protecting the 
equipment is to use a multi****t protector."

Power service suppressors are also a good idea, and covered in both 
guides. Because of possible problems of high voltage between power and 
signal wires the NIST guide says:
"Q - Will a surge protector installed at the service entrance be 
sufficient for the whole house?
A - There are two answers to than question: Yes for one-link appliances 
[electronic equipment], No for two-link appliances [equipment connected 
to power and signal]. Since most homes today have some kind of two-link 
appliances, the prudent answer to the question would be NO - but that 
does not mean that a surge protector installed at the service entrance 
is useless."
	

w_ has still never furnished a link to a source that agrees with him 
that plug-in suppressors are NOT effective.

And  w_ has still never explained why the IEEE guide has only 2 examples 
of protection, both of which use a plug-in suppressor.

-- 
bud--