How to Protect your equipment from lightning |
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When an electrical storm is
imminent it is essential to disconnect all cables
from telephone sockets and TV aerial sockets. It's
also advisable to disconnect all plugs from mains
230v sockets and to disconnect satellite dish LNB
feeds. In addition, move leads away from the
sockets because lightning can jump huge
gaps! You can install some protective measures in case
you are not home when an electrical storm
arrives. Buy a phone line surge protector*, which
looks like a mains adapter. It must be plugged into
the nearest mains power socket (for earthing).
Connect a lead from the telephone socket to the
surge protector. Connect a lead from the surge
protector to your Wi-Fi router/modem. Connect your
phone to the router/modem. *Note: this type of surge protector, and also
the type which is integral with a mains power
socket strip, uses devices called "Voltage
Dependent Resistors" (VDRs). These are designed to
go short-circuit in the event of a surge. In the
event of a minor surge they might not go
short-circuit but they could be degraded, thus
offering little or no protection thereafter. For
this reason, if you know that there has been a
surge associated with a lightning storm, you should
replace the unit. (Alternatively, VDRs alone can be
replaced if you are handy with a soldering
iron.) (A well designed surge protector should not
affect your broadband speed, provided that it is no
more than 8 Mbps. If your speed is higher, then a
surge protector will probably have a
significant slowing effect.) Once a telephone line surge protector has
experienced a surge it should be replaced because
it will not be as effective the next time. You can also buy mains power strips which
include a telephone line surge protector and some
form of rudimentary mains surge protection. Electrical appliances should be connected to the
mains power socket via an Automatic Voltage
Regulator (AVR). The most common types are
rated at 500 Watts and 1000 Watts. Choose one that
is suitable for the appliance(s). You might be able
to connect more than one item to a single AVR
(check the power ratings). An AVR affords good protection against a
high-voltage surge and a momentary "brownout".
Connect anything that matters to an AVR. (It's a
good idea to include your electric blanket!) A fridge/freezer needs an (AVR) with a
timer function so that it doesn't switch
off/on repeatedly, since that can destroy a
motor. Do NOT connect a mains surge protector into an
AVR because it could short-circuit its output.
Check with your supplier if you aren't sure. Uninterruptible Power Supply To allow time to shut down your computer and/or
other equipment, you can install a UPS. This must
be plugged into the AVR output. (I had a UPS that was plugged directly into
the mains power socket and it was destroyed by a
mains surge, together with some of the equipment
connected to the UPS!) It's important to note that
a UPS will NOT afford
much (if any)
protection
against a mains voltage surge. Its
only purpose is to maintain power long enough for
safe disconnection of the equipment that it is
powering, in the event of power failure. Even if it
includes "surge protection", it will be no more
effective than a "surge protected socket strip".
And any such surge protection degrades with every
surge. If you want better protection, connect an
Automatic Voltage Regulator between the wall socket
and the UPS. Lightning struck the TV
aerial mast of a house not far from here (in a
valley!) It blew the aerial mast off
the wall, travelled down the coaxial cable into a
linen cupboard and arced across from the TV aerial
socket into the mains power socket ten centimetres
below. (In doing so, it set fire
to sheets in the cupboard - hence the smoke and
heat damage to the walls). It travelled down the mains
and aerial cables, blowing sockets off the walls
and dislodging several ceiling lights before
reaching the basement and damaging the electronic
circuitry of the boiler. It also killed the TV, DVD
player and audio Hi-Fi unit. (Curiously, the satellite
dish on the roof was undamaged and the satellite
receiver was also undamaged.) As you can see from the
photo, they were very lucky that the curtain didn't
go up in flames. Keep curtains and furnishings away
from sockets and wiring. When the TV aerial was
replaced, it was fitted to a long pole some
distance from the house. The cable was run
underground in suitable piping. You can
reduce the risk of damage by looping external
cables down to the ground, then up to enter the
house. Lightning goes for the
easiest path to ground, so some of the discharge
will go to earth at the loop, thus reducing the
power that enters the house. There will still be
damage but it will be less than would occur if the
full power of the strike entered the
house. You might further reduce the damage by
running your aerial or satellite cable
through an earthing bar at the bottom of
the loop (or before it enters the house if
you can't provide a loop at ground
level). A loop at ground level must be
protected against rodents. (Exposed cable
should also be painted to protect it
against sunlight.) To install the earthing rod, dig a hole
in the ground, place the rod into it, then
back fill with moist soil, tamping down
firmly as you fill. The earthing bar is connected by a
stout cable* to an earthing rod, which is
buried in the ground. This provides an
easier path to ground, making it less
likely that a large amount of energy will
enter the house. Whatever you use is likely
to vaporise very quickly in a strike! However, that
doesn't matter if the distance is short (and it
must be) because the ionised air will continue to
carry the current for the microseconds duration of
the lightning strike. Obviously, it doesn't have to
be insulated (but insulation will protect it from
the effects of bad weather). You could use multistrand
copper cable but anything thick enough will be very
expensive and available only in long lengths. Here
are some suggestions: Protect it from corrosion
by applying a thick coat or two of outdoor
paint.
I have a friend, a
geophysicist, who used to work in the oil industry
and carried out seismic measurements and test
drillings, mostly in remote desert regions of
America and New Zealand. Lightning strikes were
commonplace and the standard protection was to lay
a circle or oblong of metal grid ("plegma") around
the building, buried (horizontally) a few inches
beneath the sand. Then plant metal rods vertically
around the circle, connected together with stout
wire or more "plegma". Because the desert ground
was non-conductive, the metal grid was essential,
since it formed a large capacitance coupled to
ground over a wide area. The vertical rods -
effectively earthed - attracted lightning away from
the building and were easily replaced if they got
zapped. Now, I can only report this
as he told me. I can't guarantee success but it
might be worth a try. In some properties it might
be relatively cheap and easy to implement and
doesn't require the buildings to be touched at
all. ( Note: "Lightening" is
what baking powder does to cakes. Lightning
is the spelling you need. )
>During an electrical storm a
couple of weeks ago my son's satellite receiver 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-rise time 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 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 30 ma 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 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 flash over 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 adapters. 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 adapter 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!) |
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