John says:
>In modern installations the incorporation of an ELCB (earth leakage circuit
>breaker) is fitted which, as Ian points out, measures the imbalance between
>the live and neutral currents. Connecting either the live or neutral to
>the earth connection causes the main 2 pole ELCB to trip out and disconnect
>the utility supply from the entire installation. In this country the level
>is set to 20mA, earlier installations used 30mA settings.
An ELCB is NOT the same as an RCD. An ELCB looks for current in the ground
lead (actually it's often called a 'voltage trip'), so having a station RF
ground can bypass the ELCB coil. RCDs in the UK are only available in up to
30mA trip current in domestic installations: the 100mA variety are only
available for industrial use. (Found this out because I need the 100mA
variety for the lathe - it uses DC injection for braking which puts a
momentary unbalance on the supply).
Ian, G3SEK is right about the advice about grounding. Where Protective
Multiple Earthing is used ( i.e. where the neutral and ground are bonded at
the service entry and no local ground rod is provided) there's a potential
(no pun intended) problem when an external RF ground is provided. Supply
systems vary from country to country, so check on the local regs - or if in
doubt, consult a professional.
A description of the problems of PME in small radio installations was in the
1987 Conference on Land Mobile Radio at Warwick University (organised by the
IERE, Proceedings available from IEE, ISBN 0 903748 75 4) in a paper
entitled 'Killing the Customer, or PME Supplies in small base station
installations', by P. E. Chadwick, pp177 et seq.
73
Peter G3RZP
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