Re: rf earthing and pme supplies
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Hi Ian, ? Also, if your shack is in your house it¡¯s also safest to make the house TT and not to use the PME terminal¡this prevents the nasty voltages appearing outside in the garden when UKPN have an issue or a tree takes out the neutral between you and the nearest NE point. ? It is surprising how many people (including electricians) are under the misapprehension that fitting a 30mA RCD makes it safe, rather than safer and don¡¯t pay much attention to providing a dedicated earth with a reasonable CSA also connected to the PME terminal to help carry neutral current when it all goes wrong. ? Rgds ? Dave ? ? ?
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From: g3trf@... [mailto:g3trf@...] On Behalf Of ian hope
Sent: 31 July 2012 19:39
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
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