Sky Digibox Sky Analogue Computer Car
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Protecting your equipment - Lightning Problems
>During an electrical storm a couple of weeks ago my son's satellite receiver
>(Pace MSS 300) was damaged by what we are fairly certain was a surge on the
>mains input. For reference, we also lost a cordless telephone base unit at
>exactly the same time. By the use of your excellent website information followed
>by purchase and fitting of one of your kits the receiver is now repaired -
>good as new. --- Many thanks. Sadly no such luck with the phone.
In the Master jack socket is a gas-filled surge arrestor which will protect the telephone from *some* surges but not, of course, a direct hit on the line. We used to put two avalanche diodes in back-to-back series across the line in addition to the surge arrestor. The avalanche diode can't absorb much power but it reacts much faster than the surge arrestor and "grabs" the initial fast-risetime pulse before the surge arrestor takes over. I think the diodes were 200 volt devices.
>I am now looking at ways of trying to ensure that we do not suffer this sort of
>problem in the future. I have located a number of devices that can be plugged
>into a mains socket which you then plug your equipment into. Hopefully these
>will protect against mains surges. These seem fairly expensive when you think of
>the number you might need. Can you supply anything cheaper ?
Yes. My mains surge arresting plug can be fitted to the end of the cord or into a (double) socket next to the plug of the unit(s) being protected. Bottom line is: you need ONE per *socket* not one per unit - so you can protect several pieces of equipment with just one surge arresting plug. This is not the same as a mains interference suppressor, BTW. It simply grabs momentary surges. Some give a visible or audible indication that they have been triggered and usually have to be replaced afterwards. Another good standby is a 30mA Residual Current Breaker. Most modern houses have these. They are slow to react but they can limit the damage.
>Although on this occasion we do not appear to have suffered any problems
>due to high voltages on the aerial downleads I am aware that this can be, and
>often is a problem. Do you know of any devices that can be used to overcome this
>Ideally I would like to locate units that would be suitable for the LNB, also
>UHF TV & FM Radio aerial downleads.
>I have had a look around on the Internet but so far without success.
Direct hits on aerials are (thankfully) rare because they usually destroy all electrical wiring in the house and set fire to it! The usual problem is static build-up on the aerial and dish, caused by charged dust particles blown by the wind. The voltage increases until it reaches flashover point and discharges through the weakest point - usually inside the first unit in line (the satellite receiver RF modulator).
The problem of static build-up on the dish can be eliminated completely by running a wire from all metal parts on the dish and connecting it to a grounding rod (typically a 3 foot copper rod or tube hammered into the earth).
The TV aerial mast can also be grounded in the same way. Naturally this involves some expense but so does replacing your equipment!
Additional protection can be provided by using a combined mains surge limiter and aerial surge limiter. In fact I can even supply one that protects the telephone as well!
As mentioned above, mains surges can be limited by fitting a surge protection plug to *one* equipment mains cord in each socket or by simply plugging it into an unused socket at the same outlet point. In other words, supposing you have a TV, VCR, Satellite Receiver and Computer all plugged into one double wall socket with adaptors. Simply fit a surge protection plug to *one* of these units (e.g. the TV) or just push it into a spare socket on the adaptor without wiring anything to it. The surge protector plug will grab any spike that arrives at that particular wall socket outlet. (It will NOT protect equipment in other sockets a few feet away).
Note that an "interference suppressor" is quite different from a surge protector but the two can be used together to increase the protection from surges and from interference. You can also buy combined units which suppress surges and interference spikes. Equipment such as electric lawn mowers, arc welders and even vacuum cleaners can cause both interference and voltage surges. It is a good idea to plug them into a surge suppressor and plug that into the most remote socket you have (and preferably not one that backs onto the living room socket!)
Martin T. Pickering B.Eng.
A SELECTION OF ANTI-SURGE DEVICES CAN BE SEEN IN THE ORDER FORM - SELECT "Anti-Surge" IN THE Order Form List.
If you have a large BUILDING that needs Lightning Protection, contact Sentinel Lightning at http://www.sentinel-lightning.co.uk
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Version 1.0 updated on October 8, 1999
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