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■ HOW TO PROTECT YOUR ELECTRONIC EQUIPMENT Every year thousands of thunderstorms occur in Australia but most of them pass without note. But they can cause untold damage to electronic equipment - damage which runs into millions of dollars. Some of this damage is virtually unavoidable but you can avoid most of the risk to your own equipment. By LEO SIMPSON Virtually everyone acknowledges that lightning is spectacular and dangerous. It is especially dangerous to people who are exposed in open, flat areas. Every year several people are either killed or hospitalised by lightning strikes. And it does damage to large buildings and other man-made structures, not to mention the countless trees that are destroyed by direct strikes and the starting of lots of bush fires. These risks of thunderstorms arewell known and accepted by everyone. Not so well known are the risks of damage to electronic equipment. The fact is, after every large thunderstorm over a metropolitan area, lots of TVs, VCRs and many other appliances go in for service. The repairs are for damage which occurred during the thunderstorm even though the owners may not have realised it. For a TV set or VCR the risk of damage due to lightning comes from two sources. The most obvious one is via the antenna. Even though the antenna may not be directly hit [direct strikes on antennas are rare), the intense static discharge from a nearby strike can be enough to blow all the semiconductor components in the tuner. And while these components may only be worth a few dollars in themselves, the resulting repair bill can easily run to more than $100. A more common source of damage to VCRs and TVs is via the mains supply. Because the electrical supply grid is hit so often during thunderstorms, high surge voltages are unavoidable. It is these brief surges which do the damage. Often the damage is immediate and the TV or VCR stops working straight away. But in many cases the appliance keeps working and may not fail for a few hours, a few days or even weeks afterwards. The sort of faults which occur due to surge voltages on the mains supply are, naturally enough, usually in the power supply. They involve switchmode transistors, switching diodes and other associated components. The major power consuming component in a TV chassis, the horizontal output transistor, can also be damaged. How can components be damaged in lightning induced surges and not fail straight away? It is quite simple really. The very brief surge voltage over-stresses the component and thereafter its leakage current is higher than it should be even though it may keep working for the moment. Ultimately, the leakage current rises to the point where the component fails completely and a repair job is called for . It is unlikely that such repairs are thought of as being caused by thunderstorms but they are. Just how many repairs are caused by brief voltage surges on the mains supply is unknown but it is likely to be quite high. When you think about it, electronic equipment is very reliable once it has passed through its initial "burn-in" period. After that it tends to have very low failure rates so any major failures in semiconductors must be regarded as probably being due to an unusual surge voltage. In VCRs, power supply components are frequently damaged and ironically, those that are damaged are intended to protect the circuitry against high voltage surges. But the very fact that these components are sacrificed means that fuses are blown and a trip to the service centre is necessary. Again, the components involved may not be in themselves very expensive but the overall repair bill can amount to quite a lot by the time labour charges are figured in. And you have to add to that the inconvenience of not having the TV or VCR for a week or more. [Interestingly, the coming of summer always brings a rash of TV failures. Partly these are due to thunderstorms but high humidity also plays havoc with TV sets, particularly in the high voltage horizonFEBRUARY 1989 5 A graphic demonstration of the destructive power of lightning. On December 9, 1988, the transmitter building for Sydney radio station 2KY was struck by lightning and the subsequent fire destroyed the building. Photo by Bob Tregea. tal sweep circuitry and in the EHT (extra high tension) circuitry. Humidity causes current leakage and leakage leads to failures). Refrigerators and microwave ovens In the days before TVs and VCRs, the appliances most likely to be damaged by passing thunderstorms were refrigerators. Because they are always connected to the mains and always turned on, they were and are at high risk. These days, refrigerators are still commonly damaged by high voltage surges caused by lightning but they now tend to be over-shadowed by the newer and more fragile electronic appliances. Another expensive appliance which is at risk during thunderstorms is the microwave oven. As with refrigerators and VCRs, these are usually connected to the mains and switched on, 24 hours a day. They can't help but be damaged. Frequently the damage is to the power transformer and to the 6 SILICON CHIP microprocessor control circuitry. In many microwave ovens though, it is often the surge voltage protection components which go. These will be blackened or ruptured by the high voltage surge and fuses will be blown. The net result though is a trip to the service centre. You can easily pay $100 or more for routine repairs. Computers and modems While the domestic appliances listed above are the most common casualties of thunderstorms, the damage caused to computers and modems can be equally if not more expensive. Often the gear is out of service for longer too. Computers and modems can cop damage from two directions: from the power lines and from the phone lines. And when a modem is damaged from a high voltage surge via the phone lines or power lines, the computer is often a casualty too. Even if a computer is not damaged during a thunderstorm, peripheral components such as video monitors and printers can still expire, for the same reasons as set out previously. Filters and surge protection circuitry can be a help in this regard but with the double whammy of surges from mains and phone lines, computer systems are especially at risk. Facsimile machines If you have a facsimile machine in your home or business it is even more at risk than your computer, if only for the fact that it is usually left running 24 hours a day. Make no mistake, the biggest reason for service to fax machines is for damage due to voltage surges on the mains or via the phone lines. Fax machines are often regarded as temperamental machines. If they are it is partly because they are working in a tough environment. It goes without saying that they are not cheap to repair . Frequently, if a fax machine goes in for repair, the whole motherboard is replaced. Motherboards are usually not repaired because it is too time- consuming to do so - they are packed with surface mount components. Other equipment which is connected both to the mains and phone lines is also at risk. Under this heading come telephone answering machines and call diverters, mains powered wireless telephones and burglar alarms. Amateur and CB equipment Amateur radio operators have always recognised that their equipment is at risk during thunderstorms. This applies to installations which have large antenna arrays. Such arrays, if they have been installed properly, will be correctly earthed and will have lightning arrestors or spark gaps on the antenna lead-ins but even so they are still at risk. Citizens band radios are also at risk although their antennas are usually nowhere near as big as those used for amateur radio operation. What you can do to protect your equipment Let's not beat about the bush. There is only one foolproof way to protect your appliances during a thunderstorm and that is to disconnect them completely. Don't just switch them off you must physically disconnect them. Remember that most TVs and VCRs are still operating even when they are nominally switched off. And even if your TV is switched off and consuming no power, it is not disconnected as far as a high voltage surge is concerned. If lightning strikes a power line, substation or pole transformer, even quite some distance away, the resulting voltage surge on the mains supply can easily be several thousand volts or much more. Such a surge may only last a few microseconds but in that time it can cause a lot of damage. In the face of a surge of several thousand volts with a very fast risetime, the power switch in your TV is no barrier at all. The high voltage can easily jump across the switch, burn out tracks on the printed circuit board and do untold other damage whether the ap- Oddities of Lightning Damage There is no predicting the damage that lightning can do. The currents and magnetic fields generated by a major bolt of lightning can be extremely intense. Currents in a really big strike can exceed 50,000 amps and the strike can last for more than a second. Such extreme currents and the related high voltages can induce very high voltages in nearby metal structures even when they are some distance from the strike. It is quite common for electronic doorbells and burglar alarms to be triggered during thunderstorms - pliance is switched on or not. Having disconnected the appliance from the mains remember to disconnect the antenna lead too because it can damage the front ends of both the TV and the VCR. The same applies to your hifi equipment. Disconnect it from both the mains and antenna, if you have an FM antenna. Protective routine If you live in an area which experiences severe thunderstorms, or the thunderstorm you are experiencing is notably wild, you should go around your house, from room to room, disconnecting all the appliances. If you have a computer, modem, fax machine or phone answering machine, don't forget to disconnect the phone lines too. Pushbutton phones are liable to damage too and if you purchased them you are liable for any repairs, not Telecom. Disconnecting the phone during a thunderstorm has another advantage which may not be obvious. It stops anyone from ringing you. It is quite unnerving if you feel compelled to answer a ringing phone during a thundertstorm (and who doesn't). Telecom rightly warns against using the phone during a thunderstorm but the party at the other end may not know that there is a storm in your area. Disconnecting the phone stops that dillemma. the cause is high static voltages or induced voltages during a strike. And the high magnetic fields can cause damage to TVs even though they are completely disconnected from both the mains and antenna. We know of cases where the shadowmasks of colour TV receivers have been heavily magnetised and required subsequent external de-gaussing (demagnetising) before they could give a recognisable picture. Such cases must be regarded as extremely rare but they do show the extreme energy of lightning. Now we won't maJ<e any secret of the fact that having to disconnect everything during a storm is a pain. Switching on everything after the storm and resetting the clocks in your VCR, microwave oven, clock radios and so on is an even bigger pain. Is it really worth it? Without a doubt it is. It is a foolproof method of protection. Barring a direct strike on your home, it is highly unlikely that any damage can occur to an appliance which is completely disconnected (although we will give one instance which can occur). Cracking it hardy You may feel that the process of disconnecting every appliance in your home during a thunderstom and then powering everything up afterwards is just not worth the trouble. And you may be right. However, a number of · TV servicemen and service organisations we talked to in preparation for this article agreed that lightninginduced surges do undoubtedly result in a great many repairs to electronic equipment. If you feel that you can withstand the relatively low risk of damage to your appliances, then well and good. But remember that by using the "disconnect routine" during severe thunderstorms you will undoubtedly avoid the inconvenience of having equipment in for repair. Even if you don't do it for all apFEBRUARY 1989 7 Lightning: protecting your appliances And that brings us to lightning protection itself. We don't intend to go into the aspects of protecting buildings and structures from lightning. That is a complete subject in itself. Suffice to say that all large and exposed buildings and structures must have good lightning protection otherwise the risk of damage can be very high. In rural areas which have a high incidence of thunderstorms, individual homes should also have lightning protection. In metropolitan areas, there is no doubt that the electrical power grid itself gives quite considerable protection to smaller buildings and homes. And typically, it is struck hundreds or thousands of times every year in Australian cities. TV antennas This photo inside 2KY's transmitter building shows the aftermath of the fire started by lightning. The building also housed the transmitter for 2EA and this was destroyed too. Photo by Bob Tregea. pliances it is worth doing for major units such as computers, microwave ovens, TV and VCRs. Insurance claims There is a bright side to this subject too. If you are unlucky enough to have an appliance damaged during a thunderstorm, it may be possible to claim the repair cost on your home contents insurance policy. Many contents policies do have clauses involving lightning damage. To make a claim, the damage must clearly be identified as having been due to lightning. To give the claim some weight, the service organisation or repairman would have to make a statement to the effect that the repair was for lightning damage. If you want really strong evidence (some insurance companies are not the most willing payers) and the damage is graphic, take a Polaroid photo. Remember though that many lightning induced failures may not 8 SILICON CHIP be easily identified as being due to a thunderstorm. This is especially the case if the component fails days or weeks after the storm. Other means of protection Yes, you can use surge protected power outlets to protect your major appliances. These may contain metal oxide Varistors (MOVs) or gas filled spark arrestors and they can give a high level of protection. But they can only protect those appliances that are connected directly to them. They will not protect equipment against voltage surges or discharges on the phone lines or on TV antenna leads. So surge protectors are not foolproof. In the case of a severe voltage surge on the mains they themselves can be destroyed and the equipment they are connected too can still be damaged. At least one manufacturer, Click Industries Pty Ltd, recognises this fact , and includes $5000 free insurance with its Surgebuster protector. But while most Australian homes probably don't need a lightning protection installation, their external TV antennas are another matter, particularly if a high mast is involved. These should be earthed, if not as direct lightning protection then at least for static protection. The recommended method is outlined in the relevant Australian Standard, AS 1417.1 1987 [Receiving Antennas for Radio and Television in the Frequency Range 30MHz to 1GHz; Part 1- Construction and Installation). Briefly, the method involves earthing the antenna mast by a copper wire of 2.5 square mm cross-section. The wire should be connected to a copper clad steel earth stake via the most direct route. If wire other than copper is used, it should have equivalent current carrying capability. The reason for earthing the antenna is so that it does not present a hazard to the building it is mounted on or to its occupants. In our experience, very few antenna installations are earthed in this manner, even though most are professionally installed. These days, it is even more important for antennas to be earthed because there is no direct earth path via the antenna socket on VCRs or TVs. Nor are these appliances themselves earthed because they are mostly double insulated. ~