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 important 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 multiport 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--
.

Relevant Pages

  • Re: Power supplies keep crapping out on me
    ... Few components in an Apple II power supply are custom.Inspection ... Damage from lightning is an electrical path from cloud to earth. ... electronics, through thermocouple, and to earth ground via fermenter. ... protection unless you have installed a 'whole house' protector AND have ...
    (comp.sys.apple2)
  • Re: Surge protectors to use with home electronics when grounding is not available?
    ... Most commonly damaged equipment has connections to both power and signal wires. ... A lot of surge protection is keeping the power/phone/cable wires at about the same voltage. ... Plug-in suppressors can provide protection but can shift the ground potential at the suppressor. ...
    (sci.electronics.basics)
  • Re: Are there likely to be severe power shortages
    ... uninterruptable power supply andsurgeprotection. ... Surge protection requires earthing. ... same plug-in suppressor, or interconnecting wires need to go through ...
    (uk.politics.misc)
  • Re: Lightning
    ... if a strike lifts a local earth potential, ... the buried 'phone line can do the damage. ... Protection of Buildings Against the Induced Effects of Lightning". ... Buried utility wires must connect to a building's sinlge point earth ...
    (comp.sys.acorn.misc)
  • Re: Lightning protection AND putting a receptacle on UPS
    ... Grounding for transient protection must ... Every incoming wire must connect to the same earth ground. ... wires are connected to earth by a dedicated wire. ... be better spent first on enhancing the earthing system. ...
    (alt.home.repair)