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PUBLISHER’S LETTER www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Peter Smith Ross Tester Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Rick Winkler Phone (02) 9979 5644 Fax (02) 9979 6503 Mobile: 0414 34 6669 Regular Contributors Brendan Akhurst Louis Challis Rodney Champness Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $69.50 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 8, 101 Darley St, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. E-mail: silchip<at>siliconchip.com.au ISSN 1030-2662 * Recommended and maximum price only. 2  Silicon Chip Use those Safety Switches for extra protection This month we feature an RCD Checker in our line-up of constructional projects. It is quite a simple unit and won’t take long to put together. It is the solution to a problem that we have been concerned about for some time – how do you do a proper test of an RCD or Safety Switch, as they are more commonly re­ferred to? Sure, you can press their self-test button but that does not simulate the normal fault condition whereby Active current gets shunted to the Earth wire. So the RCD Checker is our answer and we think it could even become the basis for a standard tester to be included in any electrician’s toolkit. That’s all well and good but we are also concerned that many people (our readers included) still do not use Safety Switches where they are in hazardous situations. Perhaps the most common situation is where people are using power tools outdoors and running them from long extension leads. On building sites it is mandatory to use safety switches but people working at home are often more at risk, using older and less well-maintained power tools and often with dodgy extension leads. That’s bad enough, but the situation with musicians and amateur theatre groups is often much worse. At least most power tools these days are double-insulated but the equipment used by many bands and musicians is often quite unsafe. In fact, it is not at all uncommon for musicians to disconnect the earth on amplifiers to eliminate hum loops. These situations are just accidents waiting to happen. Potentially even worse is the situation where people bring their compact music system out of the house and down by the pool so that they can have music while they frolic. But frolicking generally means splashing about, meaning that water can get splashed over the music system. If it does get splashed, nothing might happen but there is also the possibility that water finding its way into the equipment might create a leakage path between the 240VAC Active and the exposed metal parts of the case. If that happens, the appliance could be live and lethal. Paradoxi­cally, that is more likely if the equipment is “double insulated”, because there will not be an Earth connection to safely shunt leakage current away. The more you think about it, Safety Switches are a good idea. While they won’t necessarily protect people who are stupid, they are good insurance against unforeseen malfunctions in mains-powered equipment. If your home does not have a Safety Switch, now is the time to have one or two fitted. They are relatively inexpensive. Why have two? It is a good idea to have the power circuits split up with the kitchen and laundry protected by separate RCDs. That way, if a fault develops in the laundry and trips the RCD, it won’t kill the power to your fridge and freezer in the kitchen and possibly cause food spoilage. And if you often use power tools away from home, it is probably a good idea to buy a portable Safety Switch as well. What’s the point of being fully protected at home if you get fried elsewhere? Leo Simpson