Surge protection?

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The following is a quote from a Screwfix catalogue:
"6G 2m high spec surge protection lead, incorporates surge protection for BT / Modem supplied with 1 x BT Male to RJ11 connector and 1 x RJ11 to BT Female connector. LED confirms protection with audible alert warns when unit is not protected. Filters RFI which can interfere with TV / Audio Equipment."
What does it mean by alerting when it's not protected? Why would it not be protected?
a
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BT
unit
be
when it has exploded - which is what they do
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On Sun, 23 Nov 2003 19:59:51 -0000, al wrote:

When the "protection" isn't working it makes a noise to tell you.

Because a surge has destroyed the "protection" devices.
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So it's pretty much like a fuse - how does it not blow if there's a large load being driven by it (6 sockets could be powering quite a bit) if it's delicate enough to stop (and very quickly) a surge in power?
a
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Think of them as voltage, rather than current, sensitive fuses
Big ones would be mounted in an armoured case
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    "Chris Oates" <none> writes:

Yes - they short-circuit during spikes, absorbing some of the energy (rest lost in cable impedance). They have a fixed amount of energy they can absorb before they are destroyed, and each spike absorbed (except very small ones) uses up some of the device.

A large spike which would require more energy to be dissipated than the device is capable of can result in it exploding, and they can also fail to a permanent short circuit which might have the same effect. They can be destroyed by the back-emf from inductive loads too.
--
Andrew Gabriel

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Thanks all for the advice. It's only 11 from Screwfix, but I'm wondering if it's really worthwhile or not. Just about to get a new PC in a few months so the more protection the better. Ideally I'd like to have a UPS to condition the power and prevent loss from power cuts (battery life not really important), but I can't find anything that falls into the small, cheap and quiet category!! I'm used to dealing with 5U monsters in racks to power my servers - noisey and very expensive!
a
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to
to
small UPS at www.scan.co.uk
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"Chris Oates" <none> wrote in message

Interesting ... they got a 30 one there. I would still want to see it and hear it though. No way it's going to be allowed in the living room if it's anywhere near as loud as say a PC ...
a
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and
it's
we use them at work to avoid PC resets when the Starlings arrive at tea time to roost on the HV lines near us
Totally silent
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al wrote:

I bought a small Belkin UPS from PCWorld (of all places) partly to use as a power source when I'm away for a night in the van (powers the laptop and digicamera nicely) and also as a fallback supply at home. It earnt it's money in a couple of long weekends away last year and again last week when the leccy went off for nearly 2 hours. I bet I was the only one in the street with TV & Tivo & PC & lighting (aren't low wattage CFLs great) uninterrupted throughout :)
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a
How noisy is it when all your equipment (barring it) is off?
a
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al wrote:

No noise at all. There is a slight hissing type noise when it's under full load offline and it does beep at you when the power goes off but there's no fans to keep me awake.
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On Mon, 24 Nov 2003 20:41:42 -0000, al wrote:

I have an APC SmartUPS 700inet, 6" high 5" wide 18" deep, cheap well that depends on how you define "cheap" I paid about 200 inc about 3 years ago so I guess they'll be cheaper now and silent no fan at all, though when running off battery at 80% it does make a buzz.
You can get UPS's that'll give you the unclean shutdown protection for around the 70 mark but wether they do much in line conditioning or not I'm not so sure. My APC will boost low volts and trim high volts by adjusting "transformer" taps before deciding that the incoming supply is really crap and it's best to abandon it all together and make it's own.
--
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Surge protector that has failed catastrophically is indicated by the light. But a surge protector that fails catastrophically was grossly undersized - failure directly traceable to a human. Other modes of protector failure exist. For example, a properly sized protector will eventually degrade - the preferred mode of failure. Indicator light would never report this failure. No earth ground means no effective protection. That dedicated earthing wire to central earth ground must be less than 3 meters. These failure conditions also are not reported by that indicator lamp.
IOW it says that light reports failure. It forgets to mention which type of failure - or why. It forgets to mention that the light can not report a good protector. All an indicator can report is that the protector was grossly undersized for the task - a failure directly traceable to human installation failure.
Surge protectors do not operate like fuses. Fuses take so long to open that 300 consecutive transients could pass through a protector before that fuse even considered blowing. The fuse is only to protect humans because a surge protector was grossly undersized - too few joules.
The fuse keeps surge protector from burning down the house - which is why surge protectors under a pile of papers or behind a desk can add new dangers. Fuse would not disconnect appliances from AC power. Just another reason why effective protectors are located when utilities enter the building, at the service entrance, and less than 3 meters to central earth ground.
al wrote:

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On Sun, 23 Nov 2003 19:27:23 -0500, w_tom wrote:

Do I detect an American? Not quite UK terminology being used.

Fuses don't protect humans, they protect the wiring. RCDs protect humans.

Very few places in the UK have such protection installed there doesn't appear to be the need.
Another reason to suspect a US based poster (that and the Path:...). Our 230v mains doesn't suffer so badly from sags/spikes when heavy loads are switched on/off, apart from I^2R losses inductive effects are from the size of the current flowing not the voltage. Lower voltage = more current for same power, more current = bigger spikes/sags.
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Fuses protect humans. RCDs protect humans. Neither provides surge protection.
There is no need for plug-in surge protectors. Urban myth says that switching on and off an appliance creates a surge. If true, then we were replacing household appliances every day before computers existed. At most, switching creates a single digit voltage spike called 'noise'. Surge protectors remain inert until the transient exceeds hundreds of volts. Surge protector do nothing when appliances are powered on and off.
Surges are rare events that occur once every eight years - and even less so in the UK. But so destructive that surge protectors are installed. Surges cannot be stopped. Typically destructive surge must be earthed. Earthed by a protector that is up to the task (has sufficient joules), protects everything in the house at a cost that is typically tens of times less per protected appliance, and that has a less than 3 meter connection to earth to do as Andrew Gabriel has described: short circuit that transient to earth ground.
No reason for any building to suffer surge damage. Effective surge protectors are so cheap and so easily installed with the less than 3 meter connection to earth. Plug-in protector don't even claim to provide such necessary protection.
Dave Liquorice wrote:

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On Mon, 24 Nov 2003 11:26:57 -0500, w_tom wrote:

Only a very small fuse 100mA or less would protect a human. The bog standard 13A plug top fuse isn't going to bat an eyelid in the time it takes to toast you. Remember a 13A fuse will carry, indefinately, 3.25kW, at 6kW load it *might* blow in the next 30mins. It's not until you get up towards kA range that a 13A fuse is going to be anything like quick enough to save life.

Agreed.
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Dave Liquorice wrote:

<snip>
<snip> w_tom's lectures on the subject are a regular feature of the sci.electronics.* hierarchy. He does have a point (sometimes) but seems only interested in this 1 topic.
--
Chris
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Dave Liquorice wrote:

w_tom appears to be some kind of autoposter that springs up when someone mentions surge protection. It posts answers roughly related to the question. Most of what it posts makes sense, it just isn't presented very well.
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