Loop test (kewtech) 'check'? Check my work?..

[Safety First]

We had a new consumer unit put in by electrician. <4 years ago.
Tested and certified as safe etc.

I just extended the ring upstairs.
Formerly a single socket in double bedroom. Now 3 double sockets.

Opened up single socket- found 3 wires. Ring and spur? Confirmed which was spur. Checked continuity on line, N and E, i.e. a ring.

As guide on this site, I took one of the cables (2.5mm T+E) out of socket- cutting into ring, and connected to 30 A box. Connected this off to series of two double sockets in same room, then back into original socket (though changed for a double socket.

Then I bought a Kewtech 107. All sockets in the house and those I installed were showing as wired correctly, though throughout the house shows loop test as 'Check' ; this is amber. It means that the impedance is higher than it should be.

Q. Could this be something as simple as my not *really* tightly screwing the earth cables in the back of the sockets?

Or could the Kewtech have a threshold that Electrician would have been accepting of, but that the Kewtech spec's are not happy with.

I used 2.5mm T+E so cannot work out how I have added poor connections or so much cable to have made impedance go up.

Any advice, gratefully received....

And if any of you own the KEwtech 107, I'd like to ask you a question about using it to test RCD too!

Edit- so basically, I cannot figure out whether my extra 12 or so metres of earth cable (within the T+E) could have raised the impedance so much. All I can think of is that I have not screwed the terminals tight enough??

 

[securespark]

Check end to end values at the board.

What EFLI reading do you have for the sockets and are they on a 32A 60898 device?

 

[Safety First]

Check end to end values at the board.

What EFLI reading do you have for the sockets and are they on a 32A 60898 device?

Thanks for your reply.

60898 device, is this the CU or the Mcb ?

I won't be going into the board-I read here that there's considerably greater risk for diyers there. Also I don't have a sensitive enough tester, just a £10 multimeter and my new k107 socket tester. It tells you (earth loop) below x threshold it will report safe-green etc, then amber, and red etc. Without going boldly into the CU, with a more sensitive meter, all I can do is check my screw connections? Right?

I get that these are not likely to be the issue but don't think there's anything else to do.

Then I will call electrician, needed anyway as are getting PME installed. In a way hoping that there is a problem and that he won't roll-eyes at my tale of socket tester amber lights and call it safe and sound! I did think that this was a good tester and there is a value in using one.

 

[deadshort]

I assume that the high ELI is the reason for the PME installation? If you already have a problem on existing sockets you have literally just added to it.

DS

 

[ericmark]

What earth system do you have? There are three basic systems.
TN-S = 0.8&#937; Max incoming
TN-C-S = 0.35&#937; Max incoming
TT = 200&#937; Max incoming
Clearly if you have a TT system then likely you will not light the instructions say 1.8&#937; and 93&#937; are the two limits with a 32A B type MCB the limit is 1.44&#937; with a RCD it is considered that 200&#937; is the safe limit as over that value it's likely to be unstable.

The 1.8&#937; value is the limit for a B25 MCB or C10 MCB or D6 MCB the reason for the value is a MCB is two devices in one. One is thermal and will trip if the current exceeds the rating for an extended time. This stops cable from melting the magnet part however is set to x5 (B) x10 (C) x20 (D) of the rated current and will disconnect in around 0.01 of a second if exceeded.

So with a B32 MCB = 160 amp to trip magnetic part = 1.4375&#937; we call it 1.44&#937; so that is the pass limit for short circuit protection and we would read both line - earth and line - neutral. However where RCD protected the line - earth reading can rise to 200&#937; although the line - neutral would remain the same. In fact the volt drop requirements will likely mean the Line - Neutral readings need to be lower. In the main volt drop is limiting factor.

Your device only measures line - earth and to ensure safety that is likely enough.

The Martindale does 0 - 1.7&#937;, 1.7 - 5&#937;, 5 to 10&#937;, 10 to 100&#937;, 100 to 200&#937;, 200 to 500&#937; so even that one does not show 1.44&#937; which is standard for a ring final.

 

[ericmark]

I looked at Socket&See and they don't give figures.
2008 was the date when we required RCD protection on all sockets so you should be OK if 4 years ago.

If I was extending a ring from a double socket I would replace it with a pair of grid sockets this gives you two sets of terminals to connect your four cables to so no need of a junction box.

Also could use a twin back box and two single sockets but the grid system means no need to change back box.

The RCD tester measures the time taken to trip the RCD as well as current and really if only testing it trips and not measuring time then the test button is likely good enough. I say likely as the test button on the RCD goes line - neutral not line - earth to test so will still work with no earth but your earth is being tested with loop test so you know there is an earth so no point in having RCD test on the plug in tester.

 

[JohnW2]

Then I will call electrician, needed anyway as are getting PME installed.

Do you know what earthing system you have at present (do you have an 'earth rod' outside your house, or does the earth come from the electricity supply), and why you are getting it changed to PME? As deadshort has said, it's possible that the reason is that the Earth Fault Impedance is known to be too high (in which case your findings would be 'as expected').

Kind Regards, John

 

[JohnW2]

... so even that one does not show 1.44&#937; which is standard for a ring final.

Until next year!

Kind Regards, John

 

[Safety First]

I assume that the high ELI is the reason for the PME installation? If you already have a problem on existing sockets you have literally just added to it.

DS

There were no problems with the ELI, we are having a new door fitted, the mains cable is to be moved from through-frame, to through-wall.
Western Power are booked to move this for us soon. Friend mentioned PME as being a tidier solution than routing earth cable.

We currently have a fugly cable down wall by front door and yes, an earth rod in the ground.

So it's not because of an earth issue that all this has started..

It might get sorted when WP fit their bit, and electrician does his part- which is when he will test EFLI all over again...

 

[Safety First]

What earth system do you have? There are three basic systems.....

.

Thanks for the very thorough reply. Confess i'll have to get my thinking cap on. Will dig out the similarly baffling reports that electrician gave me on commissioning our CU. Some of the questions/options you raise might be clear from reading that. Hopefully will allow me to answer your/my questions.

BTW the Kewtech 107 features a RCD testing button. It works; that is
it successfully trips at the CU from any sockets- my new ones or older ones.

This fact, and that all other K107 tests are good, makes me feel more confident in current setup.

What I have not gotten answer on- perhaps it's a very daft question- is whether ALL THIS could be due to not bending ends of wires into a u-shape, before inserting into terminals, or not screwing them up tightly enough? Anyone care to put this 'to bed'? TIA...



And another thing.... I took the KT107 to work today- 3 storey townhouse in commercial use, i.e. everything pat tested every 5 minutes. I got my (amber) ELI reading on sockets in one room, and green on those in another??

 

[JohnW2]

We currently have a fugly cable down wall by front door and yes, an earth rod in the ground.

In that case (a TT earth system), your Kewtech is giving you correct indications. As far as I can make out, the Kewtech 107 indicates 'Check' (Amber light) if EFLI is above 1.8&#937; but below 93&#937; (which is what one would normally expect of a TT system) and indicates 'Urgent Check' (Red light) if EFLI is 93&#937; or above (getting high even for TT) - so you ae getting the correct indications. Your Kewtech will hopefully become happy (with a nice green light, indicating <1.8&#937 as soon as you have a PME earth

Kind Regards, John

 

[Safety First]

....................................(with a nice green light, indicating <1.8&#937 as soon as you have a PME earth

Kind Regards, John

Thank you. I will think this....

 

[JohnW2]

What I have not gotten answer on- perhaps it's a very daft question- is whether ALL THIS could be due to not bending ends of wires into a u-shape, before inserting into terminals, or not screwing them up tightly enough? Anyone care to put this 'to bed'? TIA...

Yep, put that one to bed. There is no way that you will get a 'green' indication on your Kewtech with a TT earth, regardless of how you did your connections.

And another thing.... I took the KT107 to work today- 3 storey townhouse in commercial use, i.e. everything pat tested every 5 minutes. I got my (amber) ELI reading on sockets in one room, and green on those in another??

The green ones indicate that the building has a TN (quite possibly TN-C-S=PME) earth system, so the amber ones probably could do with having a proper EFLI measurement done - and may or may not be OK!

Kind Regards, John

 

[Safety First]

Your Kewtech will hopefully become happy (with a nice green light, indicating <1.8&#937 as soon as you have a PME earth

Kind Regards, John

You were quite right JohnW2; PME fitted today- they connected it to the CU also- for free.
And as you said, the Kewtech is now happy indicating <1.8ohms.

Very pleased with your info and today's result !

 

[JohnW2]

Your Kewtech will hopefully become happy (with a nice green light, indicating <1.8&#937 as soon as you have a PME earth

You were quite right JohnW2; PME fitted today- they connected it to the CU also- for free.
And as you said, the Kewtech is now happy indicating <1.8ohms. ... Very pleased with your info and today's result !

I'm pleased to hear that all is now well. Is this where I'm meant to say "I told you so"?

Kind Regards, John