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

On 09/09/2019 00:07, wrote:
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?

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


--
Cheers,

John.

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On Monday, 9 September 2019 03:50:13 UTC+1, John Rumm wrote:
On 09/09/2019 00:07, tabbypurr wrote:

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?

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

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

On 09/09/2019 09:49, wrote:
On Monday, 9 September 2019 03:50:13 UTC+1, John Rumm wrote:
On 09/09/2019 00:07, tabbypurr wrote:

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?

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

Just bridging it would be dangerous surely.

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.

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?

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)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Monday, 9 September 2019 13:12:43 UTC+1, John Rumm wrote:
On 09/09/2019 09:49, tabbypurr wrote:
On Monday, 9 September 2019 03:50:13 UTC+1, John Rumm wrote:
On 09/09/2019 00:07, tabbypurr wrote:

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?

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

Just bridging it would be dangerous surely.

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.

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

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.

not a bad idea

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.

Yeah. This one will do.

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?

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)

Thanks

NT