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SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $70 12 issues (1 year): $127.50 24 issues (2 years): $240 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Editorial Viewpoint Avoid cheap extension cords! My wife decided to mow the lawn one day while I was at work, and when I got home, she complained that the plug-in electric mower was not working. She said it just stopped. I was worried that the motor had failed and dreaded having to buy a new one. I took it out, found an extension cord, plugged it in and did a little mowing. It seemed to be working fine (whew!). Imagine my shock when my wife called me at work the next day, panicked because the extension cord had caught fire! When I got home, I found the cord in the state you see in the photo here. I don’t think there was any external damage to the cord. Instead, flexing the cord repetitively caused the internal insulation to break, allowing Active and Neutral to come in contact with each other, causing enough arcing to burn through the outer insulation. This could easily have caused an electric shock had someone come in contact with it in this state. Yes, we have RCDs, and they likely would have prevented serious harm in this case. Still, you can’t rely on an RCD. After all, their typical trip current is 30mA, while the lowest current that has been determined to stop a heart beating is 7mA for three seconds, less than one-quarter of the trip current! We have been using this mower for several years without any other incidents, so I think the fault lies with the cord more than anything else. We also have some thicker, yellow extension cords that hold up to this sort of use case a lot better. They have much thicker and more flexible insulation and probably finer wire strands. We’re only going to use those for mowing from now on. Even if you use the cheaper cords in more static situations, it’s entirely possible that over their life, they will eventually fail from being moved, furled, unfurled etc. Funnily enough, we have some ancient grey extension cords at the Silicon Chip office that are probably more than 30 years old and, except for the brass being a little tarnished, they still seem in reasonable condition and work fine. We have also had reports of cheap power boards and double adaptors failing, so I guess you need to think hard when buying mains accessories to determine if it’s worth the risk of buying the cheapest one you can find. I’m not saying you need to spend heaps on a high-end brand, but perhaps spending another $5 or $10 on that extension cord or power board will get you something a bit safer! by Nicholas Vinen Cover image source: Dan Nelson https://unsplash.com/photos/black-iphone-5-beside-brown-framed-eyeglasses-and-black-iphone-5-c-ah-HeguOe9k Australia's electronics magazine siliconchip.com.au