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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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    TT earthing for an outbuilding is quite easy. You just do NOT export the earthing system from the TN-C-S of the house supply. TT is good for outdoor supplies such as caravans or farms etc. The supply is just Line and Neutral to the outbuilding, with say an earthed armouring of a supply cable from the house. At the outbuilding the earth is insulated back and does NOT continue to exposed conductive parts or socket earth terminals. The outbuilding is then earthed via a local earth electrode (rod) A 30mA double pole R.C.D. is normally used to provide shock protection. The earth fault loop impedance Zs can be up to 1666 Ohms. (Table 41.5 B.S. 7671) But anywhere around a stable 200 Ohms is good.


    TT earthing of the outbuilding is good as no metalwork can be raised to a dangerous Voltage by an external fault on the supply cable to the house.


    Exporting a TN-C-S earth to an outbuilding can introduce potential shock risks and should be avoided if possible, especially if there is metalwork that is in contact with the ground, true earth.


    C.
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  • 0
    TT earthing for an outbuilding is quite easy. You just do NOT export the earthing system from the TN-C-S of the house supply. TT is good for outdoor supplies such as caravans or farms etc. The supply is just Line and Neutral to the outbuilding, with say an earthed armouring of a supply cable from the house. At the outbuilding the earth is insulated back and does NOT continue to exposed conductive parts or socket earth terminals. The outbuilding is then earthed via a local earth electrode (rod) A 30mA double pole R.C.D. is normally used to provide shock protection. The earth fault loop impedance Zs can be up to 1666 Ohms. (Table 41.5 B.S. 7671) But anywhere around a stable 200 Ohms is good.


    TT earthing of the outbuilding is good as no metalwork can be raised to a dangerous Voltage by an external fault on the supply cable to the house.


    Exporting a TN-C-S earth to an outbuilding can introduce potential shock risks and should be avoided if possible, especially if there is metalwork that is in contact with the ground, true earth.


    C.
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