Live Earth loop testing on light circuits

[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.

 

[IQ Electrical]

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]

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

 

[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

 

[Jimmy Boy]

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 ?

 

[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

 

[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]

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

 

[Jimmy Boy]

That was what I was looking for...

Lightmate Kit - Kewtech Lightmate Kit - Test Lights Faster with Light Mate Testing Adaptor - 17th Edition Test Equipment - 17th Edition Accessories - Kewtech Lightmate Kit - All 5 Lightmates

 

[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]

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

 

[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.

 

[shanky887614]

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.

Remove the flying lead from rcd should do it

 

[telectrix]

????? 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]

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.