which MCB rating to use for my computer

First we wish to create potential equalization. But try as we must - and that means all homes should be constructed with so inexpensive ufer
grounds - we still cannot obtain equipotential. So we attempt to make earthing as conductive as possible. But everything has impedance. We can never make earthing sufficiently conductive. So we also seek to make a building equipotential. Protection means we must do both which is why earthing is so critical to effective protection. Earthing in conjuction with 'whole house' protectors address both requirements for effective protection. Plug-in protectors do not.
If equipotential could be obtained, then a 'point of use' protector would be effective. But as demonstrated in a previous post, too many alternative paths exist. Equipotential at the appliance cannot be achieved. To have equipotential, the entire room must be constructed using techniques found in airplanes. So we address THE most critical component of a protection system to attempt equipotential. It is called a single point earth ground. As trivial as an earth ground rod or as superior as Ufer grounds when the building footings are poured. Either way, earthing is what defines electronic appliance protection.
Provided is a very long list of citations in which virtually everyone defines earthing as THE most essential component of a protection system. Citing airplanes, etc is not part of this topic. But airplanes accomplish the same thing in a more complex manner.
Even Martzloff has slowly conceded to earthing as being essential to protection which was not what his original work said. I had read much from Martzloff and NIST when I repeated what has so long been known by others - earthing as the most essential component for protection.
For example cited in you own URLs is this NIST publication: http://www.nist.gov/public_affairs/practiceguides/surgesfnl.pdf Page 8

Furthermore, this figure of fax machine protection is also from NIST. Notice again that earthing and how earthing is connected defines that fax machine protection: http://www.epri-peac.com/tutorials/sol01tut.html The figure demonstrates what could also be a deficiency in the protection. But we have too many other citations to discuss such details.
So yes even the NIST says earthing is necessary. Earthing is the purpose of protectors. More from Martzloff later. Just a warning - I know this stuff which is why this is a very abridged list of citations. I don't know how one can talk about effective protection and not discuss earthing. Earthing is literally exampled of every case study in a 4 Nov 1998 issue of IEEE Transactions on Electromagnetic Compatibility. For example a maritime communication facility was damaged by lightning. How did they fix it? Fix the earthing system and how protectors connected to that earthing system (van der Laan and Deursen). Or Montandon and Rubenstein's "Some Observations on the Protection of Buildings Against the Induced Effective of Lightning" demonstrate how to earth lightning through buildings without damage or data interruption. Their figure nine shows "Avoiding current through the building" with Bad and Good earthing techniques. But again protection from transients is about earthing.
Indeed the list of professionals that discuss earthing as essential to electronics protection is so long that another post is referenced with but a sampling - maybe one days worth of reading - in alt.comp.periphs.mainboard.asus on 30 Mar 2005 entitled "UPS unit needed for the P4C800E-Deluxe" http://makeashorterlink.com/?X61C23DCA
Even the British Standard BS6651 defines earthing as essential as discussed at: http://www.keison.co.uk/bowthorpe/docs/Application%20Guide.pdf

and
Figure on page 14 demonstrates what is meant by "equipotential earth bonding" and "Common earth bar connected to all electronic equipment and bonded to the earth ring". BS6651 demonstrates how earthing is essential to protection. Both for equipotential AND for conduction of the direct strike to earth.
Demonstrated by numbers (impedance) and other factors (including induced transients) in the previous post is why plug-in protectors are not effective. Wire impedance is why serious and more reputable protector manufacturers (and even all telcos) require short connections to a single point 'earth' ground.
Polyphaser - an industry benchmark - discusses earthing in every if not almost every post. http://www.polyphaser.com/ppc_ptd_home.aspx http://www.polyphaser.com/ppc_TD1023.aspx

I just do not see how anyone can claim earthing is not important since virtually every IEEE example of terrestrial protection includes and discusses earthing - the most essential component of a protection system.
Martzloff in his early days in NY for GE did much promotion of a GE product - Varistors - also called MOVs. In his original work, Martzloff made no serious mention of earthing that I ever saw. I assume he was an author of that famous GE application note on varistors that also did little to discuss earthing when promoting GE's MOVs. Even Martzloff has changed. Martzloff and Mansoor in 2002 wrote "The Role and Stress of Surge-Protective Devices in Sharing Lightning Current":

As the NIST noted, earthing is the purpose of a protector. Earthing is fundamental to what virtually every industry professionals requires. Service entrance is the single point earth ground - the most critical component in building protection. BTW, we are not discussing airplanes which must address 'shunting without damage' - a much more complex problem that involves same principles.
Martzloff still says that MOVs must 'cascade' protection. IOW he has slowly conceded to earthing as being essential which was not in his original work. His work now includes the all so important 'whole house' protector. In this paper, he notes how the 'point of use' protector is not sufficient without the 'cascade' - the earthed 'whole house' protector.
NIST says (quoted above) the purpose of a protector is

No earth ground means no effective protection. Some incoming utilities do not even need a protector. Cable, for example, has protection by direct connection to single point earthing. With a direct connection, cable needs no protectors to provide earthing.
Finally another professional defines earthing bluntly: http://www.harvardrepeater.org/news/lightning.html

I posted:

I stand by that statement citing many who would recommend plug-in protectors in direct violation of basic and so well proven electrical principles. Some such as Charles Perry do cite responsible publications. However it is embarrassing to be an engineer and see how Roy L Fuchs uses personal insults to defend his technically irresponsible recommendations of a "750 VA or more UPS". He is especially a reason why I used the word "Wow".
The original poster asked:

Any recommendation using a plug-in protector was wrong AND was not based in generations of proven science. No earth ground - which is plug-in protectors - means no effective protection. Those utility wires are similar to antenna connecting to radios - from lightning's perspective. Either lightning finds earth destructively via your appliances, OR a human earths before lightning can enter a building. The latter is called effective protection. Effective 'whole house' protectors are even sold in Home Depot and Lowes (however I believe the OP is in Britain). The most critical component in a protection system - the single point earth ground. Don't forget a days worth of reading from other industry scientists and people with real world experience. Earthing is so essential that it defines the quality of appliance protection. Plug-in protectors must ignore all references to earthing to promote their ineffective products.
Charles Perry wrote:

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If you have near perfect earthing (such as the 25 ohms called for in the NEC) and you have a multiport device, like a computer, and you have a whole house surge suppressor, you can still damage the computer. The phone line, for example, may be bonded to the electric service ground (often it is not, even though this is a code violation), but it will travel a different path, with different impedences, than the power system to the computer. When the transient occurs, there will be a potential difference between the telco ground and the power ground. This potential develops across your computers internal components. A plug in protector that protects both the phone line and the power line will PREVENT this.
Is earthing important? Yes. but earthing alone will NOT solve the problem. We performed many tests on this. We constructed a mocked up house with different circuit lengths and different communication runs. We could control the ground resistence from a few tenths of ohms to open. Without the multiport protector we could fail multi-port devices at will. We even use this as a demo when we perform lab tours. People love to see things blow up. With a multiport plug in protector, the devices survive. Simple as that.
Charles Perry P.E.
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As you have noted, phone service may not be bonded to same earth ground as AC electric, cable, or satellite dish. That failure is why damage occurs. The solution is not found in plug-in protectors. The solution is found in fixing the defect to even comply with NEC requirements. The code demands phone, cable, etc all connect to the same earthing. Cinergy even demonstrates how to fix bad earthing - a reason for surge damage: http://www.cinergy.com/surge/ttip08.htm
Polyphaser is an industry benchmark. Your plug-in protectors even violate Polyphaser's well proven and effective solutions. For that plug-in protector to work as described, then literally every conductive item in the room must connect to that protector's single point ground. The entire room must be part of the single point ground. As posted previously and as so many industry professionals demonstrate, that just is not going to happen in normal rooms. Remember items that are conductive and that must be part of this room's single point ground. Linoleum tile. Concrete. Wall paint. Baseboard heat. Air ducts. Every incoming AC wire to receptacles.
Meanwhile I keep citing a perfect example of why your adjacent plug-in protector is not effective. That telephone CO has better conductive materials all bonded. And still they want the protectors to be up to 50 meters from the switching computer AND - this is most important - connected short to earth ground. Earthing - not just a common ground - is essential.
So essential that plug-in protectors don't even try to make your claims about equipotential. Plug-in protector manufacturers hope no one learns well proven science about single point earth ground.
Effective protection means earthing at the service entrance - building wide protection that costs tens of times less money per protected appliance. It means all incoming utilities use the single point earth ground - a phrase that your last post implied you did not understand. Despite what was posted, experience demonstrates otherwise. Even Martzloff conceded to a need for earthing.
AND the other point - we still build new homes as if the transistor did not exist. Also cited were references to Ufer grounds. Important. Why? Again the bottom line point. A protector is only as effective as its earth ground. How to make the service entrance protection even better? It must be installed when footing are poured. Defined are two objectives that earth ground achieves - conductivity and equipotential. Plug-in protectors - as demonstrated repeatedly by numbers, examples, and professional citations - do not provide both nor do they provide either sufficiently.
Your reply was too quick. You did not read Polyphaser's app notes nor the discussion about BS6651, nor the many other industry professionals who demand earthing as the most critical component of protection. There can be no equipotential at the appliance for too many reasons. Effective protection is a building wide solution as demonstrated by so many IEEE papers and as well proven before WWII.
Just more examples of industry professionals demonstrating effective protection. In every case, it's about earthing effectively: http://www.arcelect.com/lightnin.htm

Orange County Emergency Response system upgraded by bonding to earth: http://www.psihq.com/AllCopper.htm
Protection for cell phone towers on page 14: http://www.leminstruments.com/pdf/LEGP.pdf
http://www.telebyteusa.com/primer/ch6.htm

US Army's earthing and bonding requirements defined in Training manual TM5-690
Need for Coordinated Protection http://www.erico.com/public/library/fep/technotes/tncr002.pdf
And finally, we have only been discussing secondary protection for a building. Each layer of protection is defined by each layer's earth ground. What to inspect for in the primary protection system: http://www.tvtower.com/fpl.html
Any protection that can be effective at the appliance is already inside that appliance. Effective protectors earth destructive transients before such transients get near to appliances - as has been standard installation in high reliability facilities where direct lightning strikes must never cause damage.
But again, if there is potential difference between telephone line and AC electric, well, you did not read those Polyphaser application notes. Reasons for that potential different must be eliminated at a building's service entrance - long before that voltage difference can get to electronics - as telephone switching stations have long demonstrated.
There is not effective plug-in protector - as made obvious by that protector having no dedicated earth ground, its manufacturer avoiding the entire topic of earthing, and technical specifications that don't even claim to provide such protection. Three damning reasons why plug-in protectors are not effective. A protector is only as effective as its earth ground. That's its purpose - to connect to earthing as even the NIST stated. Even your concept of equipotential adjacent to a computer is not possible without rebuilding the entire room. Exampled previously was how and why an adjacent protector not only damaged the powered off computer, but also passed through its network to damage other computers. But then that previous example I provided demonstrates how such equipotential protection at the computer not reasonable AND has caused computer damage.
There is no plug-in solution for a building wide single point earth ground. The 'whole house' solution also costs tens of times less money. The protector is only as effective as its earth ground.
Charles Perry wrote:

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I tend to agree. In my home for example, I have all phone, cable, and network wiring tied to the service ground. The service ground has two ground rods as well as a tie to cold water supply (all copper piping in this development, no plastic allowed, all the way to the mains).
When lightning struck a tree in the backyard, the large e-m pulse fried the computer network card and TV that were at the far end of the house from the service entrance.
My theory is that since TV cable and network wiring are routed different from the power wiring, there was a 'loop' exposed to the e-m pulse from the strike. While the 'loop' was closed and at equi-potential at the service panel area (same place as cable and network patch panel), the opposite end of the loops was 'closed' by my TV and computer. And these 'multi-port' devices couldn't withstand the energy induced in the loop.
If I had the type of plug-in protector you are talking about, I would probably not have had these failures.
FYI, other TVs and computers, located closer to the end of the house where the service panel is, survived.
daestrom
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Wow. You are a true dipshit.
Given the amount of fed back noise on the AC line in a typical 20 workstation business from the switchers in all the PCs being used, Those firms that put a UPS on their workstations have much less noise on their lines. This is easily verified with a scope and an open probe tip. I know as I have ran an R & D lab and we had problems with AC line noise affecting the readings on some of our developments. That baseline noise level was reduced to near nil after we placed OLD used UPSes on our workstations throughout the building. The only noise left were spikes from the nearby welding business. Ideally, we needed a shielded lab, but that was outside the budget at the time in question.
If it stops switcher noise from going OUT, it most certainly ALSO filters AC anomalies from going IN.
Get a clue, dipshit.
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So, you are saying that ALL of the makers of such devices are running a scam on the consumers of the world?
I think you have been standing under the HV towers for too long, boy.
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Funny. I have never seen one that was not a three pronged device with the fault return fed directly through.
In fact, I think it is a UL requirement, as well as NFPA.
Try again, boy.
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IMHO the most important way to protect equipment is to have a single common reference point and clamp voltages on power and signal wires to that point. 1 - One of these points is at the service entrance of these wires and since the neutral and ground/earth are connected at the electrical service entrance, the TELCO, and cable protectors must be connected to this point with low impedance, and to acomplish that they should be close. Preferrably the power wiring would have a TVSS. This is a single point ground. 2 - Another point can be at equipment, like a PC. The protection would be a good surge suppressor and needs protected wire-through ports for phone and other wiring to the computer. 3 - Common point clamping is more important than grounding, although grounding is also important.
Charles agrees with 2 and 3 and very probably 1 w_tom agrees with 1 but not 2 or 3
Also, with a very low ground impedance of 5 Ohms and a very reasonable surge/transient current of 1000 Amps there is a 5000 Volt difference with nearby earth. The protected building and some of it's landscape will be lifted off 'absolute' ground even with a good earth connection. If the ground is higher resistance the local island will float to a higher relative potential. Can you tell from inside the building? ----------------------
w_tom wrote:

Equipotential is important in computer rooms and similar facilities; would be nice but not likely in house. The equipotential importance is that the 'ground' is at an equal potential throughout, not so much what that potential is relative to 'absolute ground'.

I realy don't think a consumer oriented publication would discuss clamp vs earth. The publication does provide information on point of use surge suppressors (#3) which I agree with you aren't particularly useful to "divert it to ground" (must be they protect by clamping).

This shows a FAX machine with power service TVSS and TELCO NID with a very long connection between them. This violates #1 above. A multi-port surge protector as #3 above would protect the FAX machine.

The moral is the wires should be clamped to a single point ground.

This is one of your newsgroup threads. Sorry, I don't find them greatly enlightning. Although at least in this thread you don't say the "code says water pipe earthing ... is insufficient". Or recommend ground rods.

This document also advocates plug in surge suppressors (along with those at the service) which you say are useless. Their text does not describe or discuss the figure you are pointing out; single point is #1 above and equipotential is discussed above. I didn't see anything to suggest importance of earthing over clamping.

But your references advocate plug-in protectors. Please e-mail your sources with your findings.

This link just has links to about 30 papers. The problem with polyphaser is it is concerned with transmitters. Transmitters, even amateur, have antennas that stick up above everything else and make good lightning rods. This is a useful source for amateurs, but not in general for others. It does heavily stress single point service grounding (#1, which you and I and very likely Charles agree on). Kindly do not use this link; use links to specific papers that are relevant.

A lightning and transmitter paper. Your quote is a ringing endorsement of non-controversial single point grounding. Says nothing about earthing vs clamping.

> Martzloff in his early days in NY for GE did much promotion of a GE > product - Varistors - also called MOVs. In his original work, > Martzloff made no serious mention of earthing that I ever saw. I > assume he was an author of that famous GE application note on varistors > that also did little to discuss earthing when promoting GE's MOVs. > Even Martzloff has changed. Martzloff and Mansoor in 2002 wrote "The > Role and Stress of Surge-Protective Devices in Sharing Lightning > Current":

Not obvious how this is relevant ot earthing vs clamping or plug-in protectors.

Not demonstrated by your links.

Last I heard lightning arrestors were used with coax. Relevance?

Appears to be newsgroup-type conversations relating to transmitters and lightning.

Since your links advocate plug-in protectors does that mean you don't have basic electrical knowledge. (Roy is a part time troll and is best ignored when in that mode.)

Read YOUR sources.
bud--
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I definitely agree with all three points. I really don't understand his refusal to accept point 3, particularly when his own references support it.
I found it particularly funny that he mentioned a paper by Dr. Mansoor. I can assure you that he supports the use of suge equilization type plug-in protectors. Heck, he just sits down the hall from me. LOL.
Charles Perry P.E.
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Point three works for lower volttages and slower transients. But we must avoid damage from a transient that also found 3 miles of sky sufficiently conductive. If you only worry about a common point ground (equipotential) AND not provide a most conductive path to earth (conduction), then that transient will construct new conductive paths where none previously existed. For example, a destructive transient though a mouse cable or USB cable that was draped on a baseboard heat cover.
If point three - instead a need to make the path to earth so short as to be most conductive - was not important, then Polyphaser would not make protectors with no connection to earth ground. Polyphaser have products that mount directly on earth ground because that path to earth must be so conductive. Same applies to telephone switching stations. If equpotential was enough, then the East Orange facility was wasting so much money installing better earthing. Why after enhancing earthing did damage stop? That facility had sufficient common grounding - equpotential - and still suffered unacceptable damage. Same problems exist in homes where equipotential is even more difficult to achieve. And yet somehow a plug-in protectors will achieve this equipotential? How?
Homes are little different from radio stations when discussing transients. Those AC and telephone wires are no different than a radio station's antenna. To lightning, they are all electrically equivalent - potential paths to ground. What we once only did in commercial broadcasting, telephone switching centers, and emergency resonse centers is now required in homes. Not as extensive- but earthing is essential where transistors require protection. That even demonstrated in every cited IEEE paper about building protection.
Actually the argument that earthing is not important is rather silly. Earthing is so important that no professional citations even discuss single point grounds without earthing. Every picture shows earth ground because earthing is that essential - cannot be avoided - that standard - when installing ineffective protection. So routinely essential that every one shows earthing and none even bothers explaining why earthing must be provided.
Also noted was a long list of other citations. Bud assumed this was a newsgroup discussion. That newsgroup post - as was defined with the URL - constains about one days worth of more reading from industry professionals. alt.comp.periphs.mainboard.asus on 30 Mar 2005 entitled "UPS unit needed for the P4C800E-Deluxe" http://makeashorterlink.com/?X61C23DCA All and so many others define effective protection in terms of conduction and equipotential. No plug-in solution provides both essential requirements. As one industry professional says up front

Will you now say he is wrong? Is Dr Mansoor saying he is wrong? I doubt it.
Without that earthing - as is the problem with plug-in protectors - then what is a protector to do? As demonstrated by example, the plug-in protector without that all so essential earthing connection will even provide a transient with new and destructive paths through adjacent electronics. Demonstrated by example and explained by theory.
Meanwhile if equpotential and not earthing was so important, then clearly ESE lightning protection devices also are effective. They also create equipotential - not conduction - so that lightning does not strike. Effective lightning rods provide better earthing - conduction - for superior protection.
Yes Dr Mansoor does still recommend plug-in protectors. But he and Martzloff also define a most important part of a protector system - the properly earthed protector.
Does Dr Mansoor say that only plug-in protectors, no earth ground, and no service entrance protection is sufficient protection? This is what you are suggesting. His papers don't suggest that. Putting all equipment equipotential on a plug-in protector, then that equipement is fully protected? Not for one minute. That would completely violate everything I have seen and every citation I have provided. It would violate the example where a plug-in protector even contributed to damage of the adjacent computer AND other computers on that network.
The best you can claim is that plug-in protectors are supplementary protection. Supplementary protection made irrelevant by protection already inside appliances and by properly installed 'whole house' protectors. If 'point of use' protector were so effective, then those $0.10 parts would be inside appliances - not in power strips sell for an outrageous $25 or $100.
One can have effective protecton with only a 'whole house' protector that costs about $1 per protected appliance. Spending $25 only for a plug-in protector means the necessary :"equipotential and conduction" is not sufficient. Damage results if the protecton is only a plug-in protector. A protector will only be as effective as its earthing. Do you claim that Dr Mansoor says earthing is not important? His paper doesn't suggest that. And yet that is what you are claiming in direct oppostion to every figure cited previously.
Those who recommended only a plug-in protector soution did so without underlying knoweldge. Even Martzloff and Mansoor note earthing as necessary - as was well proven before WWII.
What do plug-in protectors not provide and therefore not even discuss? Earthing. It explains why those protector's technical specifications don't even claim the protection recommended by so many above misguided posters. No earth ground means no effective protection as demosntrated by every figure and citation provided. Plug-in protectors have all but no earthing. Somehow a plug-in protector alone only using equipotential will protect? Even my own experience tracing surge damage says otherwise.
Charles Perry wrote:

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On Mon, 06 Mar 2006 03:32:14 -0600, Bud-- wrote:

If I've read w_tom correctly over the years (this seems to be his hot button), he belives #1 is *most* important, with the others less important but still useful. IMO, a single point ground is the first issue. A lightning strike on one side of the house shouldn't be going through the house (and everything within). So, I'm on the #1 side of "most important".

Only if you have an anchor to another "ground". This IMO is the reason for the single point ground. Screw water pipes (though *THEY* should be connected *TO* the common ground).
<snip>
--
Keith

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Keith wrote:

In this thread (and in others I have seen) his main issue is earthing although he advocates #1 - common point. In this thread he has said that #2 - multi port plug-in surge supressors are not useful (and actually cause problems) because they do not have effective earthing (the impedance to earth is too high). I (and Charles) am saying that #3 - clamping all wiring to a single reference point is the important part - as is done in multi-port plug-in surge suppressors which work even though they are poorly earthed.

Not obvious what you are saying. Once you have a single point ground to which all wiring is referenced (which will be at the electric service because tht is where the neutral and ground are connected) that point can be connected to one or multiple grounding electrodes. Lower ground impedance is useful but not the critical issue. If you have an earth gradient between electrodes causing current flow through the electrde conductors it doesn't matter. The interior wiring is still referenced to a single point. A water service with a metal municipal water system is likely the lowest ground resistance in a house. Another of w-tom's themes, but not here, is that the water service is "insufficient" and a ground rod should be used. He may have moved on to a Ufer ground which is one of the good ones.
bud--
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