Spending extra for surge protection

Wanting to buy a 'trailing-socket' I've just seen some in Tescos with inbuilt surge protectors, which they say is to protect computers and televisions.
Living in London is this a good idea or just another marketing ploy to get us to spend extra money unecessarily ?
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Could be the difference between losing your electronic goods if you have a surge. Are you liable to surges? Probably not, overhead supplies are the most likely to get surges, so should be protected, but if you have an underground supply, then it is very unlikely to need it, however, if you have expensive electronic goods, and dont have insurance to cover it, then a SPD may be worthwhile. The greatest threat of a surge is from pikeys stealing copper from your sub-station. Whole house surge protection can be bought for around £75, I've got it, just in case, and do recommend it when doing a rewire, but no-one wants to pay the extra for it to be fitted. I have seen £2000+ of household goods damaged through a surge, but it is not at all common. For a £20 extension lead, then get it, and your comp./tv would be better protected than without it. If you are worried, then whole house is better, for both quality of equipment, and protection, albeit at £100+ fitted.
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If you have examples of same I'd love to see them.
The only proper way I've seen to protect from surges is to disconnect the supply as supply impedance is far too low for any shunt only protector to provide worthwhile protection. You then have the issue of what to do when the surge is removed, re-connect and potentially leave a fault investigator at risk or leave off, leaving premises at risk from lack of heating and freezers at risk of food loss.

MOV based joke protection IME giving a false sense of security.

Examples please.
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fred
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Dehn: <http://www.dehn.co.uk/pdb2/p/DE_EN_Web/680/33274/Familie-html/33274/DEH Nguard%C2%AE%20modular.html>
Hager: <http://www.hager.co.uk/products/energy-distribution/protection-devices / surge-protection-devices/8028.htm>
Surge Devices <http://www.surgedevices.co.uk/
Google for Type 2 Surge protection, and you'll find some more.
According to the Dehn Rep.they automatically reset in milliseconds (apparently) after a surge, so the end user should not see any problems in their supply - he said most items cope with the very short break in the supply. They can cope with up to 20 surges, and are easily swapped over, if they do have that many surges, being fitted just like circuit breakers. Surge devices are a UK Co., and the cheapest, Hager most expensive.
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Thanks for the links, v useful.
I took a look at the Dehn data as it appears to be the most comprehensive.
MOV devices (which these all are) worry me as they are lifed items but I see they have that covered with failure indicators and at little extra cost you can add monitoring contacts that could feed an indicator or audible device in case of failure, nice features.
The biggest numbers they quote are for the absorption of short duration transients of the order of tens of microseconds. No problem with that as that is what the specs describe but I wonder how many domestic appliances would be damaged by these short transients on the power side? Heating loads, no sweat, small equipment with conventional transformers will probably absorb such transients in the secondary filter, switch mode supply powered equipment will likely lose these on the input filter.
The data also covers protection from what I would call proper surges, elevation of mains voltage for longer periods of up to 5 seconds (includes neutral bar theft risks). That protection is provided by shunting large currents to earth, and in the extreme, relying on the device to pass enough current to take out the supplier's main fuse. My concern there is the strain that puts on the integrity of the supply, its earthing arrangement and the protection device. In the case of the device I bet these are tested in explosion proof enclosures as that is the way that MOVs let go when they are overloaded. Mains fuses are ceramic cased and sand filled but these devices don't appear to be, so I'd worry about the safety of having them in a plastic CU when they are handling a big surge.
On cost, I see that RS (yes, I know, expensive) sell the a single pole device Dehn device for 70quid but I think it needs a 2 pole device to protect from neutral lift<?> in the case of neutral bar theft which bumps the price to £145.
In summary, I remain somewhat sceptical about the benefits of fitting these in underground fed locations not routinely affected by theft based surges. I would consider them for use in overhead fed at-risk locations but I would make sure the installation was up to the possible extra strain of circumventing a threat and would mount the device separately in a sturdy steel box in case of dramatic failure. In those cases I'd probably also add protection from brownout that could affect fridge and freezer compressors.
Thanks again for the data.
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fred
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Or even sacrificial items.
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Graham.
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On Saturday, December 29, 2012 8:04:13 PM UTC-5, Graham. wrote:

MOVs are sacrificial when grossly undersized. For example, one MOV manufacturer describes how to test MOVs. An MOV fails when its threshold voltage changes - and the MOV does not have any visual damage:

10,000 surges before the device only degrades? Yes, when a protector is properly sized. Grossly undersizing a protector (and the resulting catastrophic failure) gets the naive to recommend it. Promotes sales. And increases profits.
Effective protection means nobody knows a surge existed. A direct lightning strike causes no damage ... even to the protector.
Properly sized protectors connect low impedance (ie less than 3 meters) to single point earth ground. A minimally sized 'whole house' protector starts at 50,000 amps. Since a typical lightning strike is about 20,000 amps, then a protector does not fail; is not sacrificial.
Either hundreds of thousands of joules dissipate harmlessly in earth. Or the protector must somehow block or absorb that energy. So why does a protector (hundreds of joules) fail?
A surge, too tiny to overwhelm protection inside appliances can also destroy a grossly undersized protector. Grossly undersizing a protector, the resulting damage, and potential house fire increases sales. Only a fable would recommend a protector that fails catastrophically. Effective protectors even earth a direct lightning strike without damage.
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On Dec 30, 4:15 am, snipped-for-privacy@gmail.com wrote:

Nothing protects electronic/electrical equipment against a direct lightning strike. The energy amounts are colossal. Any stupid little box would be blown to bits should it happen.
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On Sat, 29 Dec 2012 20:15:13 -0800 (PST), snipped-for-privacy@gmail.com wrote:

Oh fuck; who left the door open?
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On Sun, 30 Dec 2012 23:00:01 +0000, Grimly Curmudgeon wrote:

Someone drops their guard for a moment and the idiot gets in...
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On Sun, 30 Dec 2012 23:00:01 +0000, Grimly Curmudgeon wrote:

OK, I've modified my sig again.
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On Sunday, December 30, 2012 4:15:13 AM UTC, snipped-for-privacy@gmail.com wrote:

hilarious
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Well, it depends on your experience. I had some issues some years ago, and probably against all health and safety, I merely wired a vdr in the plugs.
grin.
Brian
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"Dave West" < snipped-for-privacy@mail.invalid> wrote in message
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On Sat, 29 Dec 2012 12:39:36 -0000, "Dave West"

They work, once or twice, but never again, and don't let you know they've used themselves up. So next time, it doesn't work and the equipment might get damaged. It's mostly cock - buy a proper protector or run some essential stuff from a decent UPS if you're serious about it.
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Grimly Curmudgeon wrote:

I'd rather pay the money for a PDU with well made contacts - having seen a few cheap and nasty ones. In fact I have just bought 6 way metal 13A PDUs over regular trailing strips in order to bolt on the underside of my desks and round the back of the bookcase the TV sits on - because I have more confidence in their construction.
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On 29/12/2012 18:50, Tim Watts wrote:

What could the group build this R*** A****** product for? http://tinyurl.com/c3adxbz
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There is no such thing as a "surge". There are "transients", voltage spikes caused by lightning strikes (on o/head wires) and spikes caused by switching of large electric motors etc in factories. So if you think this is going on near to you then a "surge arrester" is a good idea. They won't protect against a close lightning strike.
Ligtning strikes to telephone wires are a greater danger to equipment connected to them.
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On Saturday, December 29, 2012 12:39:36 PM UTC, Dave West wrote:

When running electronics on a small portable generator they can be useful, for the other 99.99% of people they're a small risk, and of no significant genuine value.
NT
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On Sat, 29 Dec 2012 12:39:36 -0000, Dave West wrote:

Waste of money, assuming you have contents insurance which will cover you for damage caused by a nearby lighting strike. If the power as supplied goes seriously out of spec (neutral theft, connection across phases etc) then the claim off the power company.
Ones with "£50,000 conected equipment cover" read the small print *very* carefully.
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