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 Post subject: Kt63 MF tester question
PostPosted: Sat Jun 09, 2018 4:28 pm 
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Does anyone use a KT63 MF tester?
If so; in the manual for high current mode (Loop), states the following:
Use the 2-wire testing by one cable being brown, other cable blue with green prod or crocodile clip inter-connected.
My question is as follows:
Even though it highlights 2-wire testing, I now have 3 cables. Rather than me state the obvious, please can someone pass on the correct guidance as where these 3 cables are connected in the tester?
Once this confirmed, it would be great to pass on additional guidance to test my TT system. step by step

Hopefully clear, hopefully you can help, hopefully you have the time

A little new to this game!
Cheers


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PostPosted: Mon Jun 11, 2018 7:36 am 
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I do not have that tester, however I have used testers with three connections to a 13A plug for easy testing, with the higher quality testers loop is between line and earth, and PSCC between line and neutral, this can normally be confirmed by calculation, so 0.8 ohm ELI would be 230/0.8 = 287.7 amps, if using a cheap tester this is what you will get, switching from PSCC and ELI the meter simply does the calculation for you. However with the better quality it also auto switches between earth and neutral so you could read 40 ohm ELI and still show 287.7 amp at PSCC.

In theory we should test line - neutral and line - earth PSCC and enter the higher reading, however in practice unless getting some where near the limit, often 4.7kA we tend not to bother. In real terms I think only once have I measured the PSCC and found it over the limit. I read up what to do, and it talks about let through current of a fuse, so I fitted a 60A fuse, however a fuse has some resistance, so once fitted the PSCC was below the limit. This was on a tower crane for the banks man radio charger, so had a 600A supply. In real terms with a home the supply is normally through a 100A or less fuse, so it is highly unlikely a homes supply will ever show a PSCC over the limit for the MCB's.

So in real terms the PSCC is used to check volt drop. OK volt drop limited to 3% lighting and 5% power, but with electronic ballasts, and switch mode power supplies, even if over the limit it is unlikely to cause a problem.

I one point I worried about doing an EICR and missing excessive volt drop, then getting a claim because of it. So I made a java script program to work it out. However once I started to take readings I realised the error when using a loop impedance meter means it is near impossible unless well outside the limits to show anyone has been negligent, so I stopped worrying about that.

The other point is with a TT system the ELI is a combination of the DNO earth and your earth, I seem to remember the DNO is allowed 15 ohms, so you reading is up to 15 ohms higher than real reading. In general I look for around 60 ohms, above 200 ohms then it may not be stable, below 10 ohms likely there is some other item as well as the earth rod bonding the system to earth, often water pipe or gas pipe.

I find it is common for the ELI to be measured to whole system, we should in theory measure just the earth electrode, i.e. the bit we are sure no one else will remove, however if water, gas, rebar in concrete footing etc is measured as well, often we get readings as good as a TN system. As to if really necessary to measure just earth rod, well also seen where some one has forgot to re-connect, so not sure which is biggest risk?


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PostPosted: Mon Jun 11, 2018 5:34 pm 
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:welcomeuhm:

The cables are colour coordinated where they plug into the meter. Interconnect the blue and green cables as per the manual. Go to the high current test and put the brown lead to the live and the combined blue/green leads to neutral or earth depending on what you are wanting to test.

HTH. If not I am more than happy to try again.



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PostPosted: Mon Jun 11, 2018 5:36 pm 
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ericmark wrote:

The other point is with a TT system the ELI is a combination of the DNO earth and your earth, I seem to remember the DNO is allowed 15 ohms, so you reading is up to 15 ohms higher than real reading. In general I look for around 60 ohms, above 200 ohms then it may not be stable, below 10 ohms likely there is some other item as well as the earth rod bonding the system to earth, often water pipe or gas pipe.


There is no DNO earth on a TT supply.


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PostPosted: Tue Jun 12, 2018 7:22 am 
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OnlyMe wrote:
ericmark wrote:

The other point is with a TT system the ELI is a combination of the DNO earth and your earth, I seem to remember the DNO is allowed 15 ohms, so you reading is up to 15 ohms higher than real reading. In general I look for around 60 ohms, above 200 ohms then it may not be stable, below 10 ohms likely there is some other item as well as the earth rod bonding the system to earth, often water pipe or gas pipe.


There is no DNO earth on a TT supply.

Of course there is a DNO earth on a TT supply, the supply transformer is earthed, however there is no earth wire on a TT supply, it uses the ground, if you test the earth using the three spikes then you are actually testing the earth connection, but if you use a loop impedance meter, you are testing both your earth and the DNO earth. So you may have an earth pit with a reading of 4 ohms, but using a loop impedance meter it may well show 19 ohms as the DNO's earth is 15 ohms.

Much depends on how the DNO supply is brought to the house, a transformer on a pole is unlikely to have as good of a earth than a transformer in a building.

As to using test gear I will admit I got caught out, first test set I used was top of range Robin, it actually had the three leads to test earth spikes, and it auto swapped between neutral and earth when one turned from PSCC to ELI. I thought all test sets were the same, but I was wrong, the next one was a Siemens cheap and nasty, it came like the Robin with a 13A plug as well as leads, it was not until I tested a socket with no neutral connected that I realised it did not auto swap between earth and neutral. I walked away thinking it was a good socket, and in fact there was no neutral.

Not the only time I have made errors in testing, I had a phase rotation meter, which I thought was great, saved dragging equipment to sockets to check direction, until I went to a factory were are sockets were wired wrong way around.

There is a reason why so many people fail the C&G2391, testing and inspecting is not as simple as plug in the meter and press the button. OK today most meters do a self test and will not cause bonded items to become live during the test. However that does not mean we should stop doing the full test and rely on the meters safety features.

I was lucky, I have never killed anyone, but when I first started I made many mistakes which could have killed people, today I read reports and think there by grace of god go I, when I read about the foreman who sent an electricians mate to take reading with a loop impedance tester, I think I would have done the same, reading a loop impedance testers display and writing down the results is hardly rocket science. If it says OL then write down OL and I would then go and find out why, I would have never expected the guy to go to tea hut and ask advice on what to write down, or for him to fudge up any results. However that foreman got a prison sentence for trusting an electricians mate.



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PostPosted: Mon Jun 18, 2018 6:34 pm 
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ericmark wrote:
I do not have that tester, however I have used testers with three connections to a 13A plug for easy testing, with the higher quality testers loop is between line and earth, and PSCC between line and neutral, this can normally be confirmed by calculation, so 0.8 ohm ELI would be 230/0.8 = 287.7 amps, if using a cheap tester this is what you will get, switching from PSCC and ELI the meter simply does the calculation for you. However with the better quality it also auto switches between earth and neutral so you could read 40 ohm ELI and still show 287.7 amp at PSCC.

In theory we should test line - neutral and line - earth PSCC and enter the higher reading, however in practice unless getting some where near the limit, often 4.7kA we tend not to bother. In real terms I think only once have I measured the PSCC and found it over the limit. I read up what to do, and it talks about let through current of a fuse, so I fitted a 60A fuse, however a fuse has some resistance, so once fitted the PSCC was below the limit. This was on a tower crane for the banks man radio charger, so had a 600A supply. In real terms with a home the supply is normally through a 100A or less fuse, so it is highly unlikely a homes supply will ever show a PSCC over the limit for the MCB's.

So in real terms the PSCC is used to check volt drop. OK volt drop limited to 3% lighting and 5% power, but with electronic ballasts, and switch mode power supplies, even if over the limit it is unlikely to cause a problem.

I one point I worried about doing an EICR and missing excessive volt drop, then getting a claim because of it. So I made a java script program to work it out. However once I started to take readings I realised the error when using a loop impedance meter means it is near impossible unless well outside the limits to show anyone has been negligent, so I stopped worrying about that.

The other point is with a TT system the ELI is a combination of the DNO earth and your earth, I seem to remember the DNO is allowed 15 ohms, so you reading is up to 15 ohms higher than real reading. In general I look for around 60 ohms, above 200 ohms then it may not be stable, below 10 ohms likely there is some other item as well as the earth rod bonding the system to earth, often water pipe or gas pipe.

I find it is common for the ELI to be measured to whole system, we should in theory measure just the earth electrode, i.e. the bit we are sure no one else will remove, however if water, gas, rebar in concrete footing etc is measured as well, often we get readings as good as a TN system. As to if really necessary to measure just earth rod, well also seen where some one has forgot to re-connect, so not sure which is biggest risk?


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PostPosted: Mon Jun 18, 2018 6:35 pm 
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Great explanation
Thanks.


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