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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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    Yes, you are correct that regardless of whether the installation earthing arrangements are TN or TT, the earthed side of the antenna connected to its own earth electrode is classed as an extraneous-conductive-part, and should be main bonded.


    If the shack is a separate outbuilding, and there are no simultaneously-accessible extraneous-conductive-parts or exposed-conductive-parts of both installations, you can provide a separate earth electrode for the mains and provide a separate TT system ... or use the antenna's earth electrode if it meets the requirements for protective earthing.


    If it's an attached building, then it may also be possible to provide a separate TT system provided again there are no simultaneously-accessible extraneous-conductive-parts or exposed-conductive-parts of the two installations, but depending on what materials are used for the construction and foundations, there could be undesirable effects in some cases, where the main installation is a TN system, under some circumstances of distribution network faults.


    It's recommended that the antenna electrode and the electrode of the TT system are kept at a suitable distance from buried metalwork connected to the MET or protective conductors of the main installation - the guidance comes from Figure 16 of BS 7430, and indicates a separation distance of between 3.5 and 8 m ... although at distances less than 8 m you may need to take into account ground potential rise and reintroducing touch voltages in some circumstances.
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    Yes, you are correct that regardless of whether the installation earthing arrangements are TN or TT, the earthed side of the antenna connected to its own earth electrode is classed as an extraneous-conductive-part, and should be main bonded.


    If the shack is a separate outbuilding, and there are no simultaneously-accessible extraneous-conductive-parts or exposed-conductive-parts of both installations, you can provide a separate earth electrode for the mains and provide a separate TT system ... or use the antenna's earth electrode if it meets the requirements for protective earthing.


    If it's an attached building, then it may also be possible to provide a separate TT system provided again there are no simultaneously-accessible extraneous-conductive-parts or exposed-conductive-parts of the two installations, but depending on what materials are used for the construction and foundations, there could be undesirable effects in some cases, where the main installation is a TN system, under some circumstances of distribution network faults.


    It's recommended that the antenna electrode and the electrode of the TT system are kept at a suitable distance from buried metalwork connected to the MET or protective conductors of the main installation - the guidance comes from Figure 16 of BS 7430, and indicates a separation distance of between 3.5 and 8 m ... although at distances less than 8 m you may need to take into account ground potential rise and reintroducing touch voltages in some circumstances.
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