[UK-CONTEST] shack design

[Paul Beecham]

Graham / callum, yes by doing this it would take the problem of  two earths 
off your radio but it would not satisfy the regs because  you would not have 
any automatic disconnection for protection against indirect contact, reg no 
413-02-09 expresses a preference to satisfy this by way of an rcd in a TT 
system.You must also assertain the Zs value (earth electrode resistance in 
this case ) is not exceeding (in many cases) not more than 100 ohms. This is 
important so as to satisfy disconnect times. Also if an earth electrode is 
used then due regard to mechanical damage to it and the protective conductor 
, cross sectional area and correct labelling be given, bear in mind that the 
resistance of an earth electrode depends on it's contact resistance, size 
and shape , buried depth and soil resistivity. Also if you take the earth 
out the plugtop even if suitably marked the danger exists of using it 
elsewhere and the appliance not being properly earthed. The whole subject 
can be a minefield  but what I DID to overcome  this problem was to run a 
seperate submain to the shack WITHOUT the supply authority earth  into a 
converted 3 phase board with 100ma slugged rcd for discrimination,  use a 
10ft gal scaf pole and 10x 3ft earth electrodes all bonded together for 
mains and rf purposes  suitably marked, run the main bonding conductor into 
the shack on 32mm copper tube to my main earth terminal (MET), cross bond 
and earth everything to this,  All shack power on main kill switch (not 
lights),  Also be mindful of computers as these are very leaky in terms of 
earth fault current so could trip rcds etc, use socket outlets that have 2x 
earthing terminals and connect circuit protective conductor (cpc)  of ring 
through them , 73 Paul  G6PZ  ----- Original Message ----- 
From: "Contesting" <contesting at m5aav.org.uk>
To: <uk-contest at contesting.com>
Sent: Tuesday, March 28, 2006 9:02 PM
Subject: Re: [UK-CONTEST] shack design


> Quoting from the message of Tue, 28 Mar 2006 20:52:38 +0100 from "Paul
> Beecham" <paul at prolectric.co.uk> :
>
>
>> On Earthing, the big mistake is when two or more earthing systems are 
>> used
>> in the same property and the risk that a lethal potential difference
>> between
>> these could occour. For example , you run power into a shed at the
>> bottom of
>> the garden, your main house earth is under the stairs via the supply
>> authortiy , ( there are different systems   tns, tncs etc all forms of
>> pme.)
>> You plug your rig into the 13A socket outlet, perhaps your aerial is an 
>> end
>> fed wire which is tuned against ground. You have an earth cable
>> connected to
>> the earth lug on the back of the rig  and connected to ground via an 
>> earth
>> spike just outside the shed. Here is where it all goes horribly wrong, 
>> that
>> earth spike could cause a lethal potential difference to occour, it could
>> effect dissconnect times of the supply voltage. The standard advice is to
>> have only one earthing system in your property and take only earth
>> connections from that point. ( This is often not achievable especially 
>> with
>> this shed model ) and probably useless anyway in terms of  RF because of
>> impedience issues. There are ways to achieve this with the use of a TT
>> system  rcd's and earth spikes TIED together but all works of this nature
>> will effect electrical safety and must be undertaken by properly 
>> qualified
>> people and tested to the current regs.with the appropriate test
>> certificate,
>> I hope this is of help. 73 Paul G6PZ
>>
>
> Is this not where it is acceptable to remove the Mains earth from any RF
> generating equipment [marking the plugtops accordingly] and then use an
> RF earth alone ?
>
> Graham
>
> -- 
>
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