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Posted by Tom Horne, Electrician on June 12, 2006, 12:23 am
Pete C. wrote:
> w_tom wrote:
>> They are called shunt mode protectors. They work by earthing a
>> destructive transient such as a direct lighting strike and then remain
>> functional. If a 'whole house' protector could not earth that
>> transient, then what good willl a plug-in protector do trying to earth
>> to the same ground?
>
> The fact that they will operate in parallel. The transient will rise to
> the trigger point of all the suppresser devices and all will clamp the
> line. If there is sufficient clamping capacity the differential voltage
> will be substantially reduced.
>
>> So instead some assume plug-in protectors sit between the surge and
>> an appliance to block or stop surges. Bull. Will that silly little
>> less than one inch component stop what 3 miles of sky could not?
>> Effective protection was never about stopping or absorbing surges.
>> Effective protection is about diverting - shunting - a destructive
>> transient to earth. Divert - not stop or absorb.
>
> As I noted, nothing is going to stop a direct strike. Most strikes
> aren't direct however and are primarily inductive pickup from a nearby
> strike and therefore reduced to a much more manageable level.
>
>> Protector amperage is additive IF all protectors have a same 'low
>> impedance' connection. And that is the problem. Things such as sharp
>> wire bends, long distances, splices, etc all increase that wire
>> impedance. Now a plug-in protector has too much impedance. Instead of
>> seeking earth via safety ground wire, that transient may seek earth
>> through an adjacent appliance and phone line. This is how modems are
>> so easily damaged. Incoming on AC electric. Through an adjacent
>> protector. Into comptuer motherboard and modem. Out to earth ground
>> via phone line. Notice where most modem destructive transients come
>> from.
>
> Again for a direct hit. For a surge of the level of the much more common
> inductively coupled strike that does not apply.
>
>> Having learned this by tracing destructive surges, then what is a
>> most typically damaged component? The path through adjacent protector,
>> through modem (its DAA section), is often via a transistor that drives
>> an off-hook relay. The failure message is "No Dialtone Detected".
>> Incoming on AC. Through that transistor and off-hook relay. To earth,
>> destructively, via phone line and phone line surge protector.
>
> The MOVs that are located adjacent to the phone line connector on a
> quality modem should clamp the surge. The drive to the off hook relay is
> also not electrically connected to the line, nor is most of the rest of
> the modem. The DAA transformer, ring detect optoisolator and hook switch
> relay are about all that is connected to the line.
>
>> Why did damage result? A transient was not earthed BEFORE it could
>> enter the building.
>
> There is absolutely nothing magic about the building. The building wall
> is no different than the wall of an electrical panel, or the case of a
> computer.
>
> One thing you do buy by clamping the surge as far out as possible is to
> keep the current path of the clamped surge further away from other wires
> which helps limit further inductive coupling.
>
>> A surge protector basically shunts - connects all wires together
>> during a transient. If that wire makes a low impedance connection to
>> earth, then the transient is earthed. No damage. But plug-in
>> protectors don't have a good earthing connection. Above is one
>> example; demonstrated by tracing surges and replacing transistor. A
>> protector too close to transistors and too far from earth ground can
>> even contribute to damage of the adjacent (and powered off) appliance.
>> An effective protector makes a 'less than 10 foot' connection to the
>> building's earth ground.
>
> Again, reducing the current path and the potential for further inductive
> coupling.
>
>> Ineffective protectors (power strip and UPS) are easily identified.
>> 1) No dedicated earthing wire. 2) Manufacturer does not even discuss
>> earthing. Look at your protector. Does it meet these criteria for
>> ineffective protector?
>
> As I noted, every suppresser on the line adds some level of protection.
> Suppressers at the electric service entrance panel, the CATV and telco
> demarcs all with short connections to a proper grounding electrode are
> the first line of defense.
>
> Any suppressers downstream provide further protection against
> inductively coupled surges which don't have to come through the service
> entrance conductors and residual surges past what the primary
> suppressers were able to clamp. Also for #1, that third pin on the power
> plug *is* a dedicated earthing wire.
>
>> What does a telephone company do to protect their $multimillion
>> switching computer? Its computer connects to overhead wires everywhere
>> in town. Why do they not provide service for a whole week while
>> replacing that computer? Because the telco installs 'whole house' type
>> protectors on every single wire of every cable that enters the
>> building. Tehcnology even discussed in an Oct 1960 Bell System
>> Technical Journal article - because the technology is that old and that
>> well proven. An effective protector is ideally 50 meters from
>> transistors AND as close as possible to earth ground. That 50 meter
>> separation adds to protection. But most important is what makes that
>> 'whole house' type protectors effective. A low impedance - meaning
>> short - connection to a building's single point *earth ground*. Not
>> only is the connection short. Every protector is earthed to a same
>> ground - the single point earth ground.
>
> Yes, the closer you can locate the suppressers to the grounding
> electrode the more effective they can be. Those grounding electrodes are
> also rarely a single point ground particularly in a utility application.
> More commonly they will be a multipoint electrode array bonded together
> with quite heavy conductors, often with exothermic welded connections.
>
> The telco is also a good example since it employs multiple stages of
> protection from the primary suppressers at the drop entrance to the
> suppressers on the SLIC cards, the suppressers on the power system, etc.
> More is better for the most part.
>
>> For residential protection, manufacturers with responsible brand
>> names provide effective 'whole house' protectors. Siemens,
>> Cutler-Hammer, Square D, Leviton, Intermatic, and GE all sell 'whole
>> house' protectors that are available in Home Depot, Lowes, and
>> electrical supply houses. These protectors have a dedicated earthing
>> wire. These protectors costs tens of times less money per protected
>> appliance. And these protectors are properly sized.
>
> Again these should be the first line of defense along with quality
> suppressers at the telco and CATV demarcs. This does not mean that
> additional suppressers are of no value as lightning can induce surges in
> the building wiring inside the house just as easily as outside.
>
>> Why properly sized? Many plug-in protectors are so grossly
>> undersized (MOVs undersized; too few joules) as to vaporize during a
>> surge. Vaporized MOV provided ineffective protection. But its smoke
>> promotes more sales. Effective protectors, instead, earth direct
>> lightning strikes and remain functional. A human never knows that when
>> a properly sized protector is doing protection. Grossly undersized
>> plug-in protectors that vaporize and smoke will be recommended by the
>> naive. So many plug-in protectors are undersized - to promote sales
>> rather than provide effective protection.
>>
>
> I've never seen a vaporized MOV of any size. I have seen a few that have
> failed and cracked after being subjected to substantial surges. If you
> review the joule ratings of the various MOVs and gas discharge arrestors
> you find in typical small suppressers you'll see that their ratings are
> not at all far behind those of the common whole house suppressers. Some
> of the quite expensive service entrance suppressers intended for
> commercial services have higher ratings, but not the common ones.
>
>> Earthing - at minimum, the building must conform to post 1990
>> National Electrical Code earthing. Enhanced earthing means a protector
>> will be even more effective. And so we say, "a protector is only as
>> effective as its earth ground." What do those plug-in power strip and
>> UPS protectors manufacturers not even discuss? Earthing. Where is
>> that dedicated earthing wire? Did they just forget? Or do they hope
>> you never learn why earthing is so essential?
>
> Refer you to the dedicated grounding (earthing) conductor provided to
> every electrical device in a residence. The dedicated third pin on a
> NEMA 5-15 (or 5-20 or 5-xx, 6-xx, etc.) receptacle.
>
>> Some incoming wires are earthed using a protector. Telco provides a
>> 'whole house' protector where their wire enters your building. But
>> again, that protector will only be as effective as its earth ground.
>> Did you (or your builder) provide that essential earthing connection?
>> Cable needs no protector. Its ground block must connect directly to
>> the same earth ground - a 'less than 10 foot' connection. Every
>> incoming wire must be earthed directly or through a 'whole house'
>> protectors to the single point earth ground.
>
> Cable is not required by any code to have anything but the ground block
> at the demarc, however this only grounds (earths) the shield of the
> coax. The coax center conductor still can and often does convey
> significant surges into the premises. A quality coax surge suppresser
> will clamp surges on the center conductor to ground as well.
>
>> Ineffective protector manufactures and those who promote them hope
>> you never learn what a shunt mode protector does: makes a low impedance
>> connection to earth. No earth ground means no effective protection.
>
> Again, every single one of those suppressers has an earth ground
> connection. They wouldn't pass code and UL listing requirements if they
> didn't.
>
>> So where is that earthing connection in a plug-in UPS?
>
> The grounding pin of the NEMA 5-15 plug on the UPS.
>
>> Notice that
>> their own numerical specifications don't even define protection? How's
>> that for a damning overlooked fact.
>
> The specifications for my UPS indicate the clamping voltage and joule
> rating of the suppresser devices.
>
>> Appliances already contain internal protection.
>
> Some appliances do, many do not. Don't recall the last time I saw any
> suppression devices in a toaster or a blender.
>
>> Protection that can
>> be overwhelmed if destructive transients are not earthed where wires
>> enter the building. Earthing is why 'whole house' protectors are so
>> effective. No earth ground (such as with plug-in protectors) means no
>> effective protection.
>
> Again you are 100% incorrect, any plug in suppresser with a three prong
> plug *does* have an earth ground. What the heck do you think NEC article
> 250 is all about? NEC articles 280 and 285 relate to surge arrestors and
> transient voltage surge suppressers BTW.
>
>> If you don't earth incoming transients such as the direct lighting
>> strike, then protection inside that appliance can be overwhelmed;
>> appliance damaged. Plug-in protectors can even provide more
>> destructive paths through an adjacent appliance.
>
> If you have a direct lightning strike on your service entrance drop or
> service feeder on the poles, your glorious whole house suppresser will
> be in pieces along with your entire service panel.
>
> Pete C.
I work as a communications wireman whenever the electrical service
industry gets too slow. I have built alternative powered and utility
powered radio equipment shelters in remote places from Alaska to the
Argentine pampas. These room sized buildings are struck quite regularly
by lightning without loosing a single circuit. The inevitability of
damage secondary to a direct strike is a myth. If you are willing to
invest the necessary effort damage can be averted. Most home owners
will not find it cost effective to install fully effective lightning
protection.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
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