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Old 15th Sep 2019, 8:55 pm   #85
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Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 8,643
Default Re: Antenna recommendation for 40 and 80M bands

Originally Posted by G8BBZ View Post
The current trend towards PME (TN-C-S) wiring systems has nothing to do with safety and everything to do with cost.
TT systems applied at household level require an isolation transformer rated to carry the maximum household load of 15kVA - an item which will cost several thousand pounds. TT systems also require that the householder install and maintain an "installation earth electrode" to which exposed conductive parts of the installation can be bonded. Electricity suppliers are , perhaps rightly, concerned that this requirement may not always be satisfied, leading to possibly hazardous situations.
Strangely, my DNO is happy to provide, at zero cost, such a transformer (it sits on a pole about 200 yards away from my house) along with the incoming overhead lines and TT ground-spike.

None of the locals or myself have ever been under any pressure to switch from this TT-grounded 3-phase setup. I'm happy with this.

The old "PME" approach [which required loads of earth-bonding between pipework/significant metal-lumps like cooking-ranges/wood-burning-stoves and the like] has always seemed a horribly overcomplex and expensive nuisance to me; I suspect it was the product of the same mindset that inflicted the 13A "ring-main" on us.

OK, if you've got an old-style PME system then you have the big issue that your local-earth arrangement [which includes your radio earth] may - under fault-conditions - end up carrying the entire 'neutral current' of your own installation and that of other customers on the same feed. Equally, it's not a good idea to 'export' the earth from a PME/TN-C-S system to a shed/shack or other remote location.

For me, this is a good-enough reason to do all you can to avoid such a system!

When I've been faced with remote sheds/shacks/garages I've never 'exported' the TN-C-S earth, and have essentially had it "TT"d at the remote location with an earth-spike and RCD. The armour of the SWA cable being grounded *ONLY* at the head-end and not connected to anything at the remote location.
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