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Re: Down To Earth

CHRISTOPHER HALL #155 Hi I found this PPT demo on the web it might help if we are going to have an evening on power and earthing Chris Hall G6HTH toggle quoted message Show quoted text From: ian hope To: g3trf@... Sent: Wednesday, 1 August 2012, 10:12 Subject: Re: [g3trf] RE: Down To Earth ? Geoff , This Talk has come about because people keeping asking questions, the advice we will offer is based on guidance from the IET (IEE) Who i've had a long conversion with to get a deffinative answer, based on the rules and regulations and refferences to the the relevent sections of 17th edition. We also need to explain to people exactly what PME earthing is and how it works. I understand it, trev does and i would guess from yr background you should have a reasonable understanding, but most of the club will not. In a nut shell rf earthing on a pme supply should be of a size capable of carring the full fault current. the guidence is for a domestic supply is if the supply cables are less then 35mm then the bonding should be a minium of 10mm. the Rf earth should also be connected to the PME point at the supply. However if you want a much safer solution then should consider installing a TT system, As you are aware a TT system can be complex and is not a DIY issue. I feel we should explain how a TT system works and it's pro's and cons. we should also explain to the club exactly how RCD's work and explain why a earth fault on a pme system may not trip a RCD. Most new houses are PME, and if you your Cutout replaced 9 times out of 10 UKPN will change it to a PME version. We should explain TNS, PME and TT to the club. ian ? ----- Original Message ----- From: Geoff Harris Sent: 08/01/12 09:40 AM To: g3trf@... Subject: Re: [g3trf] RE: Down To Earth ? ? Trevor, ? I could not agree more. Modern earthing methods are at the very least complex even for the informed, and baffling to the uninformed; misunderstanding – even amongst those who purport to to be professionals – is quite common. ? I remember several years ago when I attended a week-long residential 15th edition regs course in Huddersfield Technical college, that the earthing module caused headaches to all of us: if we - as a club - are to put on a presentation about this, then we must be absolutely certain that what we say ds accurate; if it isn’t, we can inadvertantly cause more damage than we would ideally wish. We? should not present this until we have agreement that what we are saying is totally accurate. ? Geoff ? From: Trevor Collins Sent: Wednesday, August 01, 2012 8:23 AM To: g3trf@... Subject: [g3trf] RE: Down To Earth ? ? Hi All, ??????? This is a very important and very misunderstood subject which needs to be given very good coverage in great detail. Unfortunately it is also a subject that is hard for the un initiated to get to grips with.? It has become clear to me over the past years that as the editions of the regulations roll by and each one has a different story to tell, it becomes harder and harder to find anyone who really understands this subject. For Bruce:? I have somewhere a copy of CON SP1 which is the Basis of all of this work. I feel that we need to formulate a presentation that can be used as a basis for a Rad Comm Article and can be included in the RAE Syllabus as an essential part of the training. Trevor ? ----- Original Message ----- From: ian hope Sent: 07/31/12 07:38 PM To: g3trf@... Subject: RE: [g3trf] rf earthing and pme supplies ? hi dave, you've hit the nail on head it is about correctly sized cables etc and your right the ultimate would be a TT supply to your shack ? ? ----- Original Message ----- From: Dave Bruce Sent: 07/31/12 07:30 PM To: g3trf@... Subject: RE: [g3trf] rf earthing and pme supplies ? ? Ian, ? I will unlikely be able to make your talk ? But here’s my take on the subject ? The hazard? is not related to the RF earth but to exposed metal systems such as masts and towers that are connected to the mains earthing system via the screens of the coax cables. ? If the bonding is incorrect or inadequately sized and a supply network neutral fault occurs? the screens can end up carrying the neutral current of a number of network customers. ? ? The other issue is related to touch voltages that can exist external to the equipotential zone under fault conditions. ? An RCD offers no protection in the above scenarios….the answer is to ensure that bonding is correct and adequately sized. ? Or better still for ultimate safety don’t use the PME earth terminal and make your system in to a TT system with? a 30mA RCD with measures to reduce touch potentials outside to less than 25V. ? 73 Dave ? From: g3trf@... [mailto:g3trf@...] On Behalf Of ian hope Sent: 31 July 2012 18:39 To: g3trf@... Subject: [g3trf] rf earthing and pme supplies ? ? Hi all RF earthing with a pme supply. This has come up as a topic several times at the club, mainly due to it's inclusion in the exam syalbus. I have Today after speaking to the IET who write the 17th Edition wiring regulations got a definative answer to how a rf earth system should be installed if you have a pme supply to your house. With Trevors help I now propose one evening to do a short talk on this. Anyone suggest a evening Ian ? ? ? ? ? Reply to sender \| Reply to group \| \| (4) Recent Activity: Switch to: Text-Only, Daily Digest ? Unsubscribe ? ? . ? ? ?

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#155

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