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Low Loop Impedance Reading.

Zoomup
I have been working at a property that is TT earthed. Normally around here the loop impedance readings are between 100 to 200 Ohms for TT systems.


Today I had a reading of just 8.5 Ohms at a distant socket in the property's garage about 30 metres from the main fuse and first earth rod. There is a second earth rod nearby as well.


The reason for the low reading is that the property is next to a staithe with a canal nearby. The water table is only about half a meter under the garden soil. I saw this as ground work is being undertaken. Amazing. The lowest rod resistance I have ever seen.


Z.


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  • 0
    Sparkingchip:
    Kelly Marie Angel:

    Zoomup I think you should just be releived you gota nice low earth loop enjoy not having to worry about will the fault current be enough cos clearly it will and then some. 



    It not unusual to get readings of less than one ohm in a TT earthed installation, which to me is an issue because the gas and/or water pipe is serving as the main earth conductor.


    I actually feel more comfortable with readings around 35 ohms than 0.35 ohms in a TT installation when I know the rod is more than 100 ohms.


    That worries me as well Andy, if large fault currents or diverted neural currents are flowing through your house installation heating up cables. The water here at this property is plastic supplied. An oil tank is above ground as is its short insulated oil pipe.


    Perhaps the rod at the road edge is close to a P.M.E. electrode. The supply is overheads.


    I put the low reading down to having two rods, each just reaching the water table which is only about half a metre below the surface of the ground. The house location has the word "marsh" in its title.


    Z.


     


Reply
  • 0
    Sparkingchip:
    Kelly Marie Angel:

    Zoomup I think you should just be releived you gota nice low earth loop enjoy not having to worry about will the fault current be enough cos clearly it will and then some. 



    It not unusual to get readings of less than one ohm in a TT earthed installation, which to me is an issue because the gas and/or water pipe is serving as the main earth conductor.


    I actually feel more comfortable with readings around 35 ohms than 0.35 ohms in a TT installation when I know the rod is more than 100 ohms.


    That worries me as well Andy, if large fault currents or diverted neural currents are flowing through your house installation heating up cables. The water here at this property is plastic supplied. An oil tank is above ground as is its short insulated oil pipe.


    Perhaps the rod at the road edge is close to a P.M.E. electrode. The supply is overheads.


    I put the low reading down to having two rods, each just reaching the water table which is only about half a metre below the surface of the ground. The house location has the word "marsh" in its title.


    Z.


     


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