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Author Topic: ADSL Surge Protector - a cautionary tale  (Read 36059 times)

roseway

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Re: ADSL Surge Protector - a cautionary tale
« Reply #15 on: May 15, 2009, 09:52:51 AM »

Actually it's not quite true to say that a surge protector without an earth does nothing. Some types of surge may exist between the two incoming wires, and an unearthed protector connected between the two wires can reduce the surge voltage. This is what the spark gap in the master socket does. But a comprehensive protector would indeed need a short, low-impedance connection to earth to be at its most effective.

But in truth, nothing will protect your equipment from a direct lightning strike to the wires nearby. This is true as much for the mains wires as for telephone wires. The amount of energy in a lightning strike is far too much for any practical domestic surge protector to be any use. The best you can hope for is to get some protection against lower level surges, such as distant lightning strikes. Whether it's worth bothering I have my doubts. I prefer to unplug everything when there's a thunderstorm nearby.
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westom

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Re: ADSL Surge Protector - a cautionary tale
« Reply #16 on: May 15, 2009, 06:46:55 PM »

But in truth, nothing will protect your equipment from a direct lightning strike to the wires nearby. This is true as much for the mains wires as for telephone wires. The amount of energy in a lightning strike is far too much for any practical domestic surge protector to be any use.

 Which is why no phone service for four days everywhere in town is normal?  A typical CO suffers 100 surges during every thunderstorm.  Phone service is lost everywhere for four days after every thunderstorm?

  Direct lightning strikes are routinely earthed without damage even to the protector.  If a protector works by stopping or absorbing surges, then no protector survives.  That popular myth (blocking surges) promoted in retail stores is not what a protector does.  Protector diverts (shunts, connects, bonds, conducts) energy harmlessly to earth. Massive energy must be absorbed somewhere - in earth.  Direct strikes that are properly earthed means a homeowner does not even know a surge existed.

  Proper earthing means a short connection - low impedance - ie 'less than 3 meters'.  That protector plugged into the wall is not earthed.  Low impedance means 'less than 3 meters', no sharp wire bends, no splices, wire not inside metallic conduit, wire separated from all other wires, etc.  Interior AC mains wire violates almost every 'low impedance' requirement.  AC receptacle neutral or ground wire cannot provide necessary earthing.

 An ethernet surge protector cannot dump surge energy to earth (when plugged in).  Worse, it may provide a surge with more paths, destructively, via nearby appliances.

  To have no surge damage, BT puts protectors as close to earth as possible AND up to 50 meters distant from electronics. 

  An ethernet protector (tens of volts) may interfere with or be destroyed by higher phone line voltages.  Obviously, an ethernet protector is unacceptable for phone lines.

 Protector for phone lines:
   http://www.keison.co.uk/furse/furse11.htm
also has the necessary stud to make that short connection (no sharp bends, no spliced, separated from other wires etc) to earth.

 And finally orainsear's question - is this the rare location where surges are more frequent?
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orainsear

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Re: ADSL Surge Protector - a cautionary tale
« Reply #17 on: May 15, 2009, 07:53:22 PM »

I prefer to unplug everything when there's a thunderstorm nearby.

Good advice and it's what I do myself.


If you did want to go down an earthing route I wouldn't use normal house earthing.  I'd install some gas discharge protection devices which were earthed with at least 8mm cable, larger diameter if the run was too long, connected to at least 1.5 metre copper earth rods driven into suitable ground.
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sevenlayermuddle

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Re: ADSL Surge Protector - a cautionary tale
« Reply #18 on: May 16, 2009, 12:05:54 AM »

The think is, lightning is close close to an an ideal current source.  It'll generate a voltage across any impedance according to ohm's law, based upon V = IR, where I is fairly constant.  So, if you leave you're TV connected to the aerial, but unplug it from the mains, the impedance from arial to earth will be many, many megohms.  So, the voltage of the spark that connects your TV to the wall socket will be many megavolts, and that's why your house may burn down, instead of just your TV being damaged. :)

But bear in mind also that most home insurance covers lightning damage, so I choose not to worry.  Especially in the UK where rain and wind are bigger problems than electrical storms.
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westom

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Re: ADSL Surge Protector - a cautionary tale
« Reply #19 on: May 16, 2009, 01:20:19 AM »

If you did want to go down an earthing route I wouldn't use normal house earthing.  I'd install some gas discharge protection devices which were earthed with at least 8mm cable, larger diameter if the run was too long, connected to at least 1.5 metre copper earth rods driven into suitable ground.
As noted, house grounding must be part of the earthing system.   Earthing that must be upgraded to also provide surge protection.  For example, that 8mm copper wire (for AC electric earthing) must be routed without sharp bends, not inside metallic conduit, as short as possible (ie 'less than 3 meters'), separated from non-grounding wires, etc.  All incoming utlities must connect to the same earthing electrode either via a 'whole house' protector (AC mains, telephone) or by wire (cable TV, satellite dish).

  Again, a protector is nothing more than a connecting device. A connection that meets many previous requirements to also provide low impedance (not just low resistance).  Cable TV and satellite dish make that 'less than 3 meter' connection using only wire; no protector required.

  GDTs (gas discharge) or semiconductor based protectors are for telephone service to provide that low capactiance requirement.  Semiconductors are preferred.  Telephone protectors are so inexpensive as to be installed on every subscriber interface in North America for free.  However, these protectors sell in the UK for surprisingly high prices.  Protectors are installed where phone cables enters a building.  Each wire in each cable is connected short to the nearby building ground via a protector.   Protection for all types of surges - longitudinal mode, normal mode.

  1.5 meter copper clad earthing electrode is too short.  Earth rod should be at least 2.5 meters.  Best earthing is provided by the bottom half of that rod.  Additional electrodes are installed if ground is a poor conductor (ie sand) or is often dry.  Examples of how a building's earth ground is upgraded to also provide surge protection.
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Ezzer

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Re: ADSL Surge Protector - a cautionary tale
« Reply #20 on: May 17, 2009, 09:07:43 AM »

One thing to consider with surges is the amount of energy recived from the surge. if its lightning causing the surge then this can be a real variable. If enough energy comes down the line then no protector is going to prevent damage; the only sure way to protect yourself is if there is a hint of a storm comming your way then physicaly unplug any sensitive equipment fron the mains, telephony and aerial. even though the house may not suffer a hit, the mains and telephony can act like a casting net bringing the energy of a strike home.

If you're in an urban enviroment then the tendency is the energy gets disipated amongst a number of properties so each recives less energy. in rural areas a property may take a larger proportion of the energy hence rural dwellings tend to have a greater history of lightning issues. bear in mind this is just a tendency not a sure thing.

Different parts of the country have differing rates of lightning damage dependant on weather patterns, conductivity of the soil. If the land is flat it dosn't mean (dispite popular belief) your less likely to suffer lightning damage.

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waltergmw

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Re: ADSL Surge Protector - a cautionary tale
« Reply #21 on: May 17, 2009, 09:28:38 AM »

Just to confirm Ezzer's data, I was once in a Herefordshire valley close to the Black Mountains. I was standing in a farmhouse doorway watching a storm when a lightening strike went some way up overhead, but not very near. I heard the new PVC guttering creak as it does in sunshine. I.e. even wet insulating material can absorb lightening energy from quite distant lightening.

Kind regards,
Walter
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westom

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Re: ADSL Surge Protector - a cautionary tale
« Reply #22 on: May 17, 2009, 05:19:40 PM »

One thing to consider with surges is the amount of energy recived from the surge. if its lightning causing the surge then this can be a real variable. If enough energy comes down the line then no protector is going to prevent damage; the only sure way to protect yourself is if there is a hint of a storm comming your way then physicaly unplug any sensitive equipment fron the mains, telephony and aerial.
  Which is why BT disconnects all phone service with every thunderstorm?  Because no protector can provide protection from those 100 surges?  BT's computers are connected to wires all over town - and BT never disconnects their computer.   Instead, BT uses protection that was that effective from direct lightning strikes even 100 years ago.

  Disconnecting for protection is very poor protection.  Humans are asleep or away over 16 out of every 24 hours.  A human can only protect electronics typically two out of 24 hours.  That is near zero protection.  And that assumes the human knows a surge is coming.  Most destructive surges are unknown until after damage happens.

  No protector is going to prevent damage if one believes a protector is protection.  When the protector is simply a connecting device to earth, then energy from direct lightning strikes are harmlessly dissipated in earth without damage.  100 surges to every BT switching center.  How many towns are without telephone service for four days while they replace that computer?  Ezzer must ignore 100 years of experience to post a popular urban myth.

Correctly noted: conductivity of earth is fundamental. Lightning more often strikes a mountain side rather than its highest top.  Geology is why lightning more often may strike the valley; ignore the mountain. Same is why a protector is only as effective as its earth ground.  Even with 40 direct strikes annually to electronics atop the World Trade Center, all those electronics work - no damage.  Routine is to have direct lightning strikes - and no damage - if earthing is properly installed.
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Ezzer

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Re: ADSL Surge Protector - a cautionary tale
« Reply #23 on: May 17, 2009, 05:29:24 PM »

I said "if there's a hint of a storm comming your way."

Otherwise as you say properly fitted lightning protection helps when your not there to take action your self. I'm not ignoring past experience, other wise I thought unplugging is a myth until I became a bt engineer. Unplugging means the equipment is isolated from the most likey path of energy 
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orainsear

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Re: ADSL Surge Protector - a cautionary tale
« Reply #24 on: May 17, 2009, 06:20:38 PM »

Of course BT will employ surge protection and correct and effective bonding arrangements to ground, as will many businesses and agencies who require that level of protection, however the costs to protect the equipment and maintain system integrity, particularly for critical systems, will be commensurate with the level of protection required.

Clearly a risk assessment would be needed to analyse the probability and severity of potential incidents, but for the average ADSL user I would speculate that the costs to implement such a system would not be worthwhile.  As has already been stated taking the precaution of simply isolating any sensitive equipment should be sufficient to mitigate any risk.

Also, while conductivity to earth can and is important, there are other scenarios and methods of protection, e.g. H.I.R.F. and lightening protection for aircraft, that can demonstrate other methods of suitable protection.
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Ezzer

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Re: ADSL Surge Protector - a cautionary tale
« Reply #25 on: May 17, 2009, 06:40:25 PM »

Incidentaly Kitz when you took the photos in the exchange of the mdf blocks did you get any which show the left side of the blocks with the colourful protection modules as they're part of the surge protection system
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westom

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Re: ADSL Surge Protector - a cautionary tale
« Reply #26 on: May 17, 2009, 07:46:49 PM »

I said "if there's a hint of a storm comming your way."
If a protection system is so inferior as to require unplugging, then why waste good money on that protection?  Why be dependent on a solution that has little knowledge of surges until after the event?

  We don't unplug and don't have appliance damage even when a 33Kv wire fell on local distribution.  Hundreds of meters even exploded from their pan.  How would unplugging protect from that unexpected event? Earth protection so that even that does not cause appliance damage.  So that unreliable unplugging is unnecessary.

  Should we disconnect smoke detectors, dishwasher, and furnace when a thunderstorm approaches?  Of course not.  Did telephone operators remove headsets and leave the room when thunderstorms approached?  No.  Solution was that well proven and that effective even that long ago.

  Early 20th Century ham radio operators would unplug their antenna and put the lead into a mason jar.  And still damage occurred.  Damage stopped when the antenna lead was earthed.  A solution that well proven even that long ago.

  Telco wire surge protection at each subscriber has been standard in North America for generations because it is so inexpensive, so easily implemented, and so effective.   Even protectors installed in the fifties are sufficient for DSL operation - if still properly earthed.
« Last Edit: May 17, 2009, 07:49:49 PM by westom »
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sevenlayermuddle

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Re: ADSL Surge Protector - a cautionary tale
« Reply #27 on: May 17, 2009, 08:09:42 PM »

Just because it's appropriate for big companies like BT to spend out on full lightning protection, it's no reason to assume it has any relevance to the home ADSL user.

One big reason for that is that the home insurance policy will already cover lightning damage.  That, with whatever small print there is, will generally replace any damaged equipment.   Such insurance would be much more complex for the likes of BT since the cost of lost equipment would be the least of their worries, compared to lost income from service provision while the equipment gets repaired.  So BT (or BT's Insurers) will probably mandate extra protection.

Anothert point that (I don't think) has been mentioned yet... last time I shopped for an extension socket I found the usual crop of 'surge protected' extensions at extra cost.  Reading the label, in the small print, many of them said 'does not protect against lightning strikes'.  I'm aware that there are other forms of surge apart from lightning, but I do suspect there's a whole 'surge protection' industry springing up that is simply cashing in on ill-founded fears of an event that, in any case (thanks to normal home) insurance, most folks really needn't worry about unduly.
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westom

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Re: ADSL Surge Protector - a cautionary tale
« Reply #28 on: May 18, 2009, 12:59:07 AM »

 Such insurance would be much more complex for the likes of BT since the cost of lost equipment would be the least of their worries, compared to lost income from service provision while the equipment gets repaired.  So BT (or BT's Insurers) will probably mandate extra protection.
  Insurance is irrelevant.  BT must work without failure - always.   How much will an insurance company pay for your lost time and lost data?  How much do you really get for a three year old computer?  Almost nothing.  How much money does it cost to file those claims?  Less expensive is to eliminate damage rather than accept failure as an option.  Insurance is irrelevant since damage is so easily aleviated.

 How much are protector components?  Pence.  A protector to effectively earth a subscriber’s ADSL line?  A quid - if that much – to actually protect from lightning.

  A protector that does not protect from lightning does what?  It protects from surges made irrelevant by existing protection.  So what are retail stores selling for how much?

  How much for protectors that *do* protect from destructive surges?  Compare that to an inflated price for protectors that do not.  Appreciate why BT probably wastes no money on insurance or plug-in protectors.  Appreciate why BT spends less money for the effective solution.  Same solution can be installed by a homeowner.

  Destructive surges are rare events especially in the UK.  A frugal and well protected homeowner spends nothing on plug-in protectors, and can earth one 'whole house' type protector.  For ADSL, that is a low capacitance protector for everything on phone lines, and one AC mains protector earthed short to the same electrode.  When damage must never occur, an earthed protector is the effective solution that also costs maybe tens or 100 times less money. Rather than accept failure, spend little to avoid damage.
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waltergmw

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Re: ADSL Surge Protector - a cautionary tale
« Reply #29 on: May 18, 2009, 07:12:11 AM »

Hi Westom,

It would perhaps be helpful if you could provide some links to protection equipment suppliers in the UK and detailed installation instructions if they are available on-line.

Kind regards,
Walter
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