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Accurate earth loop impedance testers or MF tester recommendations for industrial type installations/supplies

CF52

Can anyone in the industrial world provide some recommendations for earth loop testers or multi function for accurately measuring very low impedances, close to transformer's or for utilising on circuits with MCCB's. I do not feel my older Megger 1741+ is particularly accurate. When I compare readings to a colleagues modern Metrel touch screen style multifunction tester the impedance readings he obtains are significantly lower. Thanks in advance Colin.

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    The answer is you cannot get accurate readings of loop impedance close to a transformer with an MFT. You can only get a" ball park" figure. Even EFLI instruments that have a resolution of 0.001 ohms the last digit is meaningless. Resolution is not an indication of accuracy.

    I have used a Megger MIM 1000A on a transformer at the request of a client and then I was not brave enough to use a higher test current than 500A dressed up in PPE. I would say why do this test anyway in the field? Is it a "so what figure" or a "thats nice" to write it down quickly on the form? Better to calculate the figure.

    If I could only take one MFT to my desert island it would be a Kewtech KT66DL. It will do a 25A EFLI test. Most single test and MFTs high current tests are 6A.The higher the test current the better.  

    Loop tester are good at measuring resistance but poor at reactance . The further you go from the source as the resistance of the cable is the larger part of the impedance so closer to the truth. One thing that you can be sure of is the figure you write down on the form is not the actual impedance. In most cases near enough is good enough provided the EFLI is well below the required figure to achieve ADS in the disconection time. 

    JP

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    The answer is you cannot get accurate readings of loop impedance close to a transformer with an MFT. You can only get a" ball park" figure. Even EFLI instruments that have a resolution of 0.001 ohms the last digit is meaningless. Resolution is not an indication of accuracy.

    I have used a Megger MIM 1000A on a transformer at the request of a client and then I was not brave enough to use a higher test current than 500A dressed up in PPE. I would say why do this test anyway in the field? Is it a "so what figure" or a "thats nice" to write it down quickly on the form? Better to calculate the figure.

    If I could only take one MFT to my desert island it would be a Kewtech KT66DL. It will do a 25A EFLI test. Most single test and MFTs high current tests are 6A.The higher the test current the better.  

    Loop tester are good at measuring resistance but poor at reactance . The further you go from the source as the resistance of the cable is the larger part of the impedance so closer to the truth. One thing that you can be sure of is the figure you write down on the form is not the actual impedance. In most cases near enough is good enough provided the EFLI is well below the required figure to achieve ADS in the disconection time. 

    JP

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