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
Living in London is this a good idea or just another marketing ploy to get
us to spend extra money unecessarily ?
Could be the difference between losing your electronic goods if you have
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
The greatest threat of a surge is from pikeys stealing copper from your
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.
To reply by e-mail, change the ' + ' to 'plus'.
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.
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
Surge devices are a UK Co., and the cheapest, Hager most expensive.
To reply by e-mail, change the ' + ' to 'plus'.
Thanks for the links, v useful.
I took a look at the Dehn data as it appears to be the most
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
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
Thanks again for the data.
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.
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.
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.
Tim Watts Personal Blog: http://www.dionic.net/tim /
"History will be kind to me for I intend to write it."
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.
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*
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.