Loop tester

Picked up an old loop tester with 25A L-E test current. Obviously this is not compatible with RCBOs. What exactly can one do with it & how?
NT
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On 09/09/2019 00:07, snipped-for-privacy@gmail.com wrote:

Test loop impedance, having bridged out the RCD first :-)
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Cheers,

John.
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On Monday, 9 September 2019 03:50:13 UTC+1, John Rumm wrote:

Just bridging it would be dangerous surely. Bridge N and fusewire or MCB the L. But Fs have R, changing the result. What's the way forward?
Could it test earth electrodes too?
NT
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On 09/09/2019 09:49, snipped-for-privacy@gmail.com wrote:

Well this is just for testing, not normal operation. If you wanted the ELI at multiple socket positions, then swapping it for a MCB for the duration of the test would be the simplest.
If you are seeking to measure the installation loop impedance and hence prospective fault current, then you could add a temporary "circuit" for the purpose.
The hardest situation to deal with is where there is no normal main switch, and only RCDs. If you need to do that with any regularity, getting a "non tripping" tester would be the way forward.

Yup, the old high current testers like the Megger LT5/6 are quite good for that, since they also put the electrode under some stress for testing. The figure you get will not be the true Ze, in that it will also include the supply impedance as well, however for most TT installs that will be negligible compared to the earth impedance. (e.g. typically less than 0.5 ohms for the supply, and 10 or more ohms for the earth)
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John.
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On Monday, 9 September 2019 13:12:43 UTC+1, John Rumm wrote:

shorting all protection has been deemed unacceptable. Fuse or mcb would work, mcb matching the RCD resistance better.

not a bad idea

Yeah. This one will do.

Thanks
NT
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