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Earthing and the radio amateur

Stewart Mason
I've recently joined the IET forums. I replied to a  topic regarding amateur radio and PME on the old forum. Unfortunately I cant access the old forum anymore so I thought it would be best to start a new topic.


So. On the bench there is a transceiver with a metal case. Next to the transceiver there is a antenna tuning unit which is connected to a antenna system which is using an earth rod. Am I right in saying there is a chance of a potential difference between the two metal cases of the equipment regardless if it is a TT, TNS or TNCS?


What would be the ideal solution?  Put the shack on it's own TT supply and bond all the radio equipment back to the MET of the TT and if a earth rod is used for the antennas connect that back to the MET also?


If the TT system was not an option what would be best if the supply was a PME and you didn't want to use balanced antennas removing the use of an earth rod? 


To be honest I've never really given PME's and amateur radio much thought which in hindsight was probably a mistake. I do remember when I did my training an earth rod was recommended for the radios.


Apologies for being so random.


Stewart M0SDM
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    Purely from an electrician's point of view, a P.M.E. supply to a radio shack that has earthed equipment with conductive parts such as earthed cases that can be touched can present shock risks. The P.M.E. earth is connected directly to the neutral of the supply cable at the main intake meter position in the house. The neutral can attain a Voltage above true earth, as the neutral carries current and supply conductor cables' resistance cause a Voltage rise on the neutral. So, a P.M.E. earth terminal in the house can attain a Voltage above true earth, and this Voltage can appear on earthed equipment in the radio shack.


    If you have conductive parts in the shack that are earthed via an earth rod at the shack, there can be a Voltage appearing between TT earthed equipment and P.M.E. earthed equipment. This is undesirable, and could be dangerous.


    If the supply neutral was broken due to a fault before the house, the P.M.E. earthed equipment could reach a potential approaching full mains supply Voltage of 240 Volts in the shack. That coule be very dangerous.


    TT earthing  is the safest method for a radio shack using a suitable earth rod and R.C.D.s. Normally an earth rod (electrode) would be at least 4 feet long, or two may be joined together to extend the length. Alternatively two rods may be used spaced at least the length of a rod apart.


    It would be a good idea to get a qualified electrician to advise you and undertake the work.


    If we bond metalwork in an outbuilding, such as a metal radiator or metal water pipe which are extraneous-conductive-parts, to comply with B.S. 7671, we would run a 10.0mm2 green and yellow cable back to the main earthing terminal in the house.


    Generally it is best to keep TT earthed installations completely separate from P.M.E. earthed installations. So a fully TT earthed shack is ideal if it meets your radio requirements.


    Test any R.C.D.s regularly using the test button to confirm their operation.


    C.


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  • 0
    Purely from an electrician's point of view, a P.M.E. supply to a radio shack that has earthed equipment with conductive parts such as earthed cases that can be touched can present shock risks. The P.M.E. earth is connected directly to the neutral of the supply cable at the main intake meter position in the house. The neutral can attain a Voltage above true earth, as the neutral carries current and supply conductor cables' resistance cause a Voltage rise on the neutral. So, a P.M.E. earth terminal in the house can attain a Voltage above true earth, and this Voltage can appear on earthed equipment in the radio shack.


    If you have conductive parts in the shack that are earthed via an earth rod at the shack, there can be a Voltage appearing between TT earthed equipment and P.M.E. earthed equipment. This is undesirable, and could be dangerous.


    If the supply neutral was broken due to a fault before the house, the P.M.E. earthed equipment could reach a potential approaching full mains supply Voltage of 240 Volts in the shack. That coule be very dangerous.


    TT earthing  is the safest method for a radio shack using a suitable earth rod and R.C.D.s. Normally an earth rod (electrode) would be at least 4 feet long, or two may be joined together to extend the length. Alternatively two rods may be used spaced at least the length of a rod apart.


    It would be a good idea to get a qualified electrician to advise you and undertake the work.


    If we bond metalwork in an outbuilding, such as a metal radiator or metal water pipe which are extraneous-conductive-parts, to comply with B.S. 7671, we would run a 10.0mm2 green and yellow cable back to the main earthing terminal in the house.


    Generally it is best to keep TT earthed installations completely separate from P.M.E. earthed installations. So a fully TT earthed shack is ideal if it meets your radio requirements.


    Test any R.C.D.s regularly using the test button to confirm their operation.


    C.


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