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SILICON CHIP www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc. (Hons.) Technical Editor John Clarke, B.E.(Elec.) Technical Staff Ross Tester Jim Rowe, B.A., B.Sc Nicholas Vinen Photography Ross Tester Reader Services Ann Morris Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Brendan Akhurst Rodney Champness, VK3UG Kevin Poulter Stan Swan Dave Thompson SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Warwick Farm, NSW. Distribution: Network Distribution Company. Subscription rates: $105.00 per year in Australia. For overseas rates, see our website or the subscriptions page in this issue. Editorial office: Unit 1, 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. Fax (02) 9939 2648. E-mail: silicon<at>siliconchip.com.au ISSN 1030-2662 Recommended and maximum price only. 2  Silicon Chip Publisher’s Letter Debate on the MEN system Well, well, well. My Publisher’s Letter and article on the dangers of Australia’s Multiple Earth Neutral (MEN) system in the August issue has certainly triggered a lively discussion, as I thought it might. Some of the ensuing correspondence is featured in the Mailbag pages of this issue. No doubt we will have more next month. As you would expect, most of the correspondence has come from electricians who are very familiar with the MEN system and wiring practices as specified in the SAA wiring rules (AS/NZS3000:2007). Typically, these tradesmen are conscientious and concerned about any deviation from what they perceive as standard practice. As you will see, some readers were concerned about the standard of wiring shown in the photos of the meter box/switchboard in the article and claimed that it was not “up to scratch”. To be honest, the sight of the bundle of Earth wires behind the hinged-out panel on my switchboard was a surprise to me. If I had thought about it at all, I would have assumed there was an Earth link for all these connections. Prior to taking the photos in the article, I had never looked at it. But I am assured that it does meet the relevant clauses in the wiring rules. If you think about the number of connections necessary for an Earth link bar, it would be quite a long bar and a lot of screw connections, all of which can gradually come loose over time, due to the effects of creepage. So the soldered bundle is probably the better approach for long-term safety. Other readers were concerned with the fact that I found considerable current flowing in the Earth. Some were adamant that no current at all must flow in the Earth. If you think about it, there must always be some current flowing in the Earth. Consider an installation in which the Neutral circuit back to the power pole is 300 milliohms, a fairly typical value. Now the Earth circuit should also have a very low resistance and what if it, too, is 300 milliohms? This means that regardless of how much current flows in to the Active connection, half flows back to the distribution transformer (or sub-station) via the Neutral and the other half will flow via the Earth. Other readers maintained that the consumer’s Earth should only be a copperplated stake driven into the ground and no connection to the water pipes. Well good luck with that idea if you live in a hilly area where most of the houses are built on rock. That describes my house and while I do have an Earth stake, it was buried in concrete years ago and even then it must have been in a small pocket of shallow soil over solid sandstone. And good luck with the idea of keeping the area around the Earth stake wellwatered to keep soil conductivity high. How many people even know where their Earth stake is or what it is for, let alone the idea that it should be watered in periods of dry weather? This is why the water pipes become part of the consumer’s Earth – it is bound to be a better long-term connection. And that is the way it has been for a very long time. If not, why are plumbers generally aware of the hazards of removing a water meter? It must be bridged with a heavy jumper lead to provide an alternative path for the Earth currents while the water meter is removed. In that respect, plumbers seem to be more aware than electricians, even though they might not know the reasons why hazardous currents (or voltages) could be present. Finally, a couple of readers wanted to know if Energy Australia had subsequently made efforts to find out where the apparent Neutral fault in my immediate locality was. The answer to that is “no” and that was the subject of some discussion between the inspector who checked out my installation and his supervisor. The problem is that it could be anywhere or it might be the result of a number of less than optimum consumer Neutral connections, in their switchboard, at the pole or wherever. Overall, the reaction to the article has been very favourable and everyone agrees that if any person ever gets a tingle from water taps or pipes within their home, they should immediately contact their electricity supplier. Leo Simpson siliconchip.com.au