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Discuss Live Earth loop testing on light circuits in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

EddieB

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Arms
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Help!! Every time I attempt a live loop test at the light the RCd trips, I have 2 loop testers and both are trip locked but the result is the same with both, so it must be something I'm doing wrong. I have a 3 lead set up which allows me to mate 2 of them together leaving a 2 probes to do the test with. Answers on a virtual postcard please.
 
D

DanBrown

I think you may be doing it wrong mate...
If you connect the 2 probes together to do a 2 lead test, this is a high current test method, and will trip RCD's regardless of trip lock etc..
Do the test using 3 lead method and see if that works. E.G. Live = Live, Neutral = Neutral and Earth = Earth.

What tester are you using??.

Let us know how you go...
 
T

Tiger

When you say trip locked, is this the same as a no trip loop tester.
have you performed this test before on a rcd with sucess.
I'am afraid i only have experiance with a megger and you can't really go wrong with that. Whats your tester
 
If you're sure you are doing the test correctly and the RCD is still tripping, try doing a ramp test on the RCD to see what current it is tripping at. It might be the RCD that is at fault!
 
Help!! Every time I attempt a live loop test at the light the RCd trips, I have 2 loop testers and both are trip locked but the result is the same with both, so it must be something I'm doing wrong. I have a 3 lead set up which allows me to mate 2 of them together leaving a 2 probes to do the test with. Answers on a virtual postcard please.
you need to grow another hand.
your live and neutral both go through the rcd,so you need to be useing your circuit neutral or else put a temporary bypass on your rcd.
 
S

Spudnik

I have had problems sometimes if the probes are not pushed in tight.

Although 2 wire high current loop testing will almost always trip the MCB/RCD.

Like others have said, bypass the RCD or maybe swap it out for a double pole main switch for the purpose of testing.
 
W

WarrenG

I think if you are mating 2 of the three leads together for the three lead test than that is where your problem is.

As Dan Brown has already said if you are using three leads, they all need to be connected to each terminal L. N. E. at the lighting point where you are taking your Zs reading.

If you tester has a low current test (no-trip @ 15ma) then it should not trip the RCD

Let us know how you got on?
 

slocm3105

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Arms
Without a doubt, use all 3 leads, I was working with a spark who was using two leads on his NEW meter and wondered why it tripped lol. If u got 3 leads, use 3 leads :).
 
S

super spark

Why bother with the Zs test? its unreliable and riddled with parallel paths!

I presume you have already taken your r1/r2 and Ze so just calculate it, its much more reliable and safe.

you wouldn't take a polarity test after continuity so why do people still take Zs ???????

Zs = Ze + (r1+r2) - job done

calculation = reliable, accurate result

meter = Parallel paths (lighting - chrome switches, back boxs, chrome fittings, cpc still connected in MET?)
 

EddieB

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Arms
  • Thread Starter Thread Starter
  • #12
I fully agree with you S/S, however there is a requirement on the test schedule for a measured Zs
 
G

Guest123

Why bother with the Zs test? its unreliable and riddled with parallel paths!

I presume you have already taken your r1/r2 and Ze so just calculate it, its much more reliable and safe.

you wouldn't take a polarity test after continuity so why do people still take Zs ???????

Zs = Ze + (r1+r2) - job done

calculation = reliable, accurate result

meter = Parallel paths (lighting - chrome switches, back boxs, chrome fittings, cpc still connected in MET?)
Would you not measure Zs after installing an additional light/socket onto an existing circuit at your new point?? By doing this you also confirm correct polarity as most meters will not perform the test otherwise.

You cant add that up.
 
Why bother with the Zs test? its unreliable and riddled with parallel paths!

I presume you have already taken your r1/r2 and Ze so just calculate it, its much more reliable and safe.

you wouldn't take a polarity test after continuity so why do people still take Zs ???????

Zs = Ze + (r1+r2) - job done

calculation = reliable, accurate result

meter = Parallel paths (lighting - chrome switches, back boxs, chrome fittings, cpc still connected in MET?)
What parallel paths??? You don't get them from a "chrome switch,back box or chrome fitting"(unless you are fixing to earthed metal)In a domestic situation the only parrallel path you are likely to encounter are thru the water/gas pipes.
 
S

super spark

Would you not measure Zs after installing an additional light/socket onto an existing circuit at your new point?? By doing this you also confirm correct polarity as most meters will not perform the test otherwise.

You cant add that up.
I would carry out a Ze & r1/r2 test prior to installation to ascertain whether the circuit was capable of carrying the additional load whilst still conforming with max Zs values, then on completion of the addition I would carry out an r1/r2 again.

Yes the NICEIC certificate asks for a (measured value), and as the r1/r2 & Ze values were measured, adding the r1/r2 value to the Ze is still measured.

If you used the designers method then it would be calculated and not appropriate.

What parallel paths??? You don't get them from a "chrome switch,back box or chrome fitting"(unless you are fixing to earthed metal)In a domestic situation the only parrallel path you are likely to encounter are thru the water/gas pipes.
You can encounter parallel paths from the MET, so unless you disconnect the MBC from the MET when carrying out the Zs test these paths will be present.

As a Zs test is live I would not recommend disconnecting the MBC, this could create a dangerous situation

(other poss parallel paths inc... supp bond conductors, steel conduit etc...)

I fully agree with you S/S, however there is a requirement on the test schedule for a measured Zs
As I stated this calculation is still derived from measured values thus it is a measured reading. Calculated Zs is a completely different calculation and much more in depth used by designers.
 
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G

Guest123

Well I for one will always carry out a Zs test.

Also everyone on this forum is equal and all we do share the knowledge and skills we have without an i'm superior attitude. I have all the qualies that you have listed and more but don't try and ram them down anyones throat.
 
S

super spark

Well I for one will always carry out a Zs test.

Also everyone on this forum is equal and all we do share the knowledge and skills we have without an i'm superior attitude. I have all the qualies that you have listed and more but don't try and ram them down anyones throat.
Im sorry if I came across rude or arrogant, I apologies as this was not my intention. I joined this forum to increase my knowledge and perhaps help others.

I used to always carry out Zs test until it was pointed out to me that the calculation in question is measured and more accurate, but each to there own and all circumstances and people are different. Circumstances may arise where a Zs test is justified and valid.

I hope you would accept my apology, forums work as the age old saying goes; 2 heads are better than 1.

This forum seems like a good one & I'd rather make friends than come across as a ****. sometimes just typing stuff I can get carried away and maybe come across that way.

Once again, My apologies if I offended anyone.
 
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EddieB

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Arms
  • Thread Starter Thread Starter
  • #18
S/S, you didn't offend me I think most of us are dyed in the wool contract sparks who take a bit of offending, thanks for replying to the original thread.
"its good to talk"
 
D

dynamite2000

hi pal can you tell me how to do a earth fault loop test on a ring circuit while it is still live please..?
 
M

m4tty

Use a kewtech plug adapter or the plug in lead which comes with the tester
 
Hi

How do you by-pass the RCD, surely if you have to go to the trouble of taking the RCD out, then it would be easyer to do Ze = R1+R2

Many Thanks
Steve
 
W

WayneL

Hi

How do you by-pass the RCD, surely if you have to go to the trouble of taking the RCD out, then it would be easyer to do Ze = R1+R2

Many Thanks
Steve
You could always link out at the light/rose and test Zs at the CU:)
 
W

WayneL

Hi Steve,

Safely isolate installation (obviously)

Ensure Main Switch, all MCBs and all RCDs are open (off)

Link out 'Line' and 'CPC' at furtherest point on circuit.

Using two lead 'Loop Tester', place one probe on the outgoing side of the MCB, for circuit you wish to test, and the other probe on the incomming 'Line' conductor at the 'Main Switch'.
Take Zs reading.:)

Alternatively, if you wish to test through the MCB, but skip the RCD, then close the MCB (of circuit under test), and place your probes on the outgoing 'Line' of the RCD and the incomming 'Line' of the 'Main Switch'
Take Zs reading.:)

Don't forget to remove the 'Link';)
 
W

WayneL

Hi Steve,

Some people cringe when this method is mentioned - and some just can't get their heads around it.

In my opinion, it could be a better option than standing on a set of 'steps' and trying to get your probes onto the terminals in a ceiling rose.
Also helpful if you haven't got a 'no-trip' tester as it won't trip the RCD.:)
 

Jimmy Boy

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Arms
I said this before on another thread I am not saying it's right or wrong just this is what the Nikky teach now.

As per Electricity at work regulations," No person shall be engaged in or or so near any Live conductor...." "Unless it is unreasonable in all circumstances for it to be dead".

taking of Zs using probes at non- socket points isn't necessary as it can be gained by calculation, therefore you don't have to test non-socket points with probes, you can use calcs, some may not agree but that is the NICEIC veiw or at least it was last time I was on a course at HQ Dunstable, whether thats an *** covering exercise is debatable but that's another discussion
 
W

WayneL

I said this before on another thread I am not saying it's right or wrong just this is what the Nikky teach now.

As per Electricity at work regulations," No person shall be engaged in or or so near any Live conductor...." "Unless it is unreasonable in all circumstances for it to be dead".

taking of Zs using probes at non- socket points isn't necessary as it can be gained by calculation, therefore you don't have to test non-socket points with probes, you can use calcs, some may not agree but that is the NICEIC veiw or at least it was last time I was on a course at HQ Dunstable, whether thats an a$$ covering exercise is debatable but that's another discussion
So what about testing Ze - done with probes at the CU (No different to the procedure I described above for Zs).:)

And before you say Ze can be obtained by enquiry - yes it can - they'll quote you the standard 0.35 or 0.8 - hardly an accurate Zs figure if you then add it to your R1 + R2.

AND....you won't have confirmed that you even have an earth path - everythings been calculated.

Remember, R1 + R2 tends to be tested before circuits are terminated into CU - so what happens if, on termination of the CPC, you accidently tighten down on the conductor insulation, giving a high resistance joint.
Your calculation isn't going to show that up.:)

I don't care what the NICEIC say - Zs measurement is an important test.:)

We are supposed to be competent to do this - and, in my opinion, 'live testing' doesn't constitute 'working' live - it is necessary.
 
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I'm with WayneL on this one, we all know that you CAN calculate Zs, you CAN get Ze by enquiry but what value do these figures really have compared to genuine, measured values?
 

Jimmy Boy

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Arms
I didn't say don't do it, neither did I mention either Ze or PFC in the post, I was merely reflecting current good practise as viewed by the NIC, at the end of the day it's your name on the cert, so the person in question is entitled to do it how he pleases, and BRB 612.9 says it can be determined by an alternative method that's not a matter of opinion that's a matter of fact, perhaps the IEE as well as the NIC are wrong 'eh ;)
 
N

nickblake

Well i see your point however i have come across this on several occasions do an R1 R2 test at a cooker switch / socket reading was 0.10 ,fine nice reading , then did the Zs and the reading was infinity , the fault was down to a faulty neutral within the cooker switch ,another one was an immersion heater High zs when continuitys were ok Zswas high and that was due agin to a neutral fault in the switch which do not show up when you do your R1 R2 tests or even IR which was detected by doing a live Zs test ,so thats part of the reason we do them , when i do a PIR i will test every socket in the installation with a Zs test it take ages but at least i know the sockets are ok . now these days there is an adaptor for almost (i said almost) every light fitting SES,GU10 Bayonet ES so you just plug yoiur testers into them and off you go still a few that need doing but
 
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Jimmy Boy

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Arms
Nick I still do live tests for Zs in fact I do them at the end of all non socket circuits, it's a good final reassuring test the point I was trying get across is that it isn't a 7671 regulation to meter it.

I was thinking about the adapters but wondered how you get the cpc connection on a class 2 ? I guess it has a flying neutral clip ?, and the other thing is on an ES the line will be centre N on side on BC the L/N could be on either terminal does that matter to the machine ?
 
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W

WayneL

I didn't say don't do it, neither did I mention either Ze or PFC in the post, I was merely reflecting current good practise as viewed by the NIC, at the end of the day it's your name on the cert, so the person in question is entitled to do it how he pleases, and BRB 612.9 says it can be determined by an alternative method that's not a matter of opinion that's a matter of fact, perhaps the IEE as well as the NIC are wrong 'eh ;)
Yes, it can be determined by an alternative method, but the regs are saying it for a different reason to the NIC.
The regs are giving you an alternative method of calculating it - doesn't mean you shouldn't still test it to see if that's the figure that you get.:)

Zs testing also confirms the earth path - and gives you your actual reading to compare to the BRB, the 'design spec' and the calculated figure.

Also, there is no requirement to measure R1 + R2 on a PIR - but there is a requirement to determine Zs - so how are you going to do that?

The NICEIC think they make the rules - they don't. They are pushing 'calculation' on safety grounds....they should put more effort into ensuring the competence of their members.:)

Ze + R1 + R2 does not confirm that you actually have an 'earth fault loop path' - only measurement can confirm this.

GN3 and the 2391 both have you testing ZS - 'live' testing is unavoidable and shouldn't be discouraged but safe ways of doing it should be encouraged.

My opinion:D
 
W

WayneL

Well i see your point however i have come across this on several occasions do an R1 R2 test at a cooker switch / socket reading was 0.10 ,fine nice reading , then did the Zs and the reading was infinity , the fault was down to a faulty neutral within the cooker switch ,another one was an immersion heater High zs when continuitys were ok Zswas high and that was due agin to a neutral fault in the switch which do not show up when you do your R1 R2 tests or even IR which was detected by doing a live Zs test ,so thats part of the reason we do them , when i do a PIR i will test every socket in the installation with a Zs test it take ages but at least i know the sockets are ok . now these days there is an adaptor for almost (i said almost) every light fitting SES,GU10 Bayonet ES so you just plug yoiur testers into them and off you go still a few that need doing but

Nick, you've lost me.

You're going to have to explain to me what the 'neutral' has to do with Zs.

And Steve, you've lost me with this:):...

I was thinking about the adapters but wondered how you get the cpc connection on a class 2 ? I guess it has a flying neutral clip ?, and the other thing is on an ES the line will be centre N on side on BC the L/N could be on either terminal does that matter to the machine ?
 

Jimmy Boy

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Arms
Wayne re adapters.

I assumed that Nick was referring to a plug in adaptor that replaces a light bulb to be able the measure Zs so we reduce the risk of touching live conductors with probes inside the rose.

To do this on a low loop test it requires a 3 wire set up, a high loop just L and E either way the flex on the light is going to only have L/N so we need to get an E ? on an ES L is always centre on BC you can put L/E on either terminal on holder ? so does the machine care if the L and N are reversed ?
Simples :)
 
S

Spudnik

Remember that you shouldnt be calculating anything on a new installation.

Plus, there is a debate as to whether actual R1 & R2 measuring is more reliable than actual live testing.

With a live test, you COULD have an earth path through main bonding and the like, rather than physically testing the CPC is intact throughout the circuit under test.
 

Jimmy Boy

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Arms
I agree BUT Zs is a Live test which in the sequence of testing is a long way down the list as regs state
612.2.1
612.2.2

Continuity must be proved inc the CPC so your earth path should be proved before doing a Live test
 
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P

paul1012

How do you put a temporary bypass on a Rcd main switch,to stop it tripping when you are testing with equipment that doesn't have the non trip function.
 

telectrix

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Mentor
Arms
Esteemed
????? it's not april 1st yet, is it? if there's no isolator before the CU, paul, don't even attempt it. graveyard's overcrowded as it is.

simple answer is to get a tester with no-trip or calculate the Zs from Ze+R1+R2.
 

Sintra

Admin
Supporter
How do you put a temporary bypass on a Rcd main switch,to stop it tripping when you are testing with equipment that doesn't have the non trip function.
There is a very simple way to do what you describe without by passing anything. The clue is in the word Loop and if you know your electrical theory then you should be able to work it out. As I don't know your level of competence I'm not going to explain any more.
 
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