Testing an earth. How?

[ericmark]

OK easy for me I have an earth loop impedance tester but what about the DIY guy? With a socket OK a plug in tester with a loop test may not be really good enough to ensure the loop impedance is low enough but it will show there is an earth connected.

But the main problem is pre-1966 lights and since unlike today in 1966 there was no internet so very likely houses up to 1970 still had no earth to the lights.

So how should a DIY guy be advised to test? I have considered a 13A socket with a tester plugged in with a set of leads. But would this be more dangerous than not testing. It needs three leads and we have two hands so at least one lead must be as a clip. The earth loop impedance tester has insulated clips but test leads able to take the plug in clips are expensive and also not sold in sheds.

So although I am happy telling a DIY he should test I am not happy saying how he should test. Thoughts please.

 

[PrenticeBoyofDerry]

If the DIYer intends or feels a need to test for earth continuity or loop impedance, the logical answer would be hire/borrow/purchase the correct equipment to perform these tasks.
Testing live should really not be a task taken lightly and should be something the DIYer takes a step back from and allows someone with the correct tools/equipment and knowledge to undertake.

 

[JohnW2]

... and since unlike today in 1966 there was no internet so very likely houses up to 1970 still had no earth to the lights.

I've been trying very hard to understand that statement, but have so far failed! Could you put me out of my misery?

So although I am happy telling a DIY he should test I am not happy saying how he should test. Thoughts please.

For reasons you give/imply, I would certainly not advise a DIYer to attempt to test a lighting circuit using 'improvised'methods. As you say, that could well be more dangerous than not testing. If the lighting circuit still has no earth, then it is presumably neither appropriate nor possible to test the EFLI of the circuit.

As we've discussed many times before, it's very difficult to know what to tell the 'occasional DIYer' what to do about testing. We all know that it should always be done. As you often say, a decent plug-in tester is a lot better than nothing for sockets circuits. However, how realistic it is to expect someone to acquire/hire proper testing kit, and learn how to use it (and interpret the results) when they, say, replace a light switch or rose, is perhaps a different matter.

Kind Regards, John

 

[EFLImpudence]

Is not continuity to the MET satisfactory for the task?

Should a DIYer want to confirm the supply earth then he will have to get the equipment or someone with it.

Not everything can be done by DIYers, in the accepted sense of the term.



I have said before, Eric, that you do seem to live in a very complicated world.

 

[ericmark]

... and since unlike today in 1966 there was no internet so very likely houses up to 1970 still had no earth to the lights.

I've been trying very hard to understand that statement, but have so far failed! Could you put me out of my misery?

When the Amendment 3 came out even people who did not buy a copy myself included knew from forums and the like what new things had been added.

Back in 1966 only if one had an apprentice at college would you likely know of any recommended changes.

It was a case "I've been doing it that way for the last 30 years why should I change?" and it took quite some time for new regulations to be adopted. Even working for a county council for me to read the regulations I would be quizzed as to why I wanted to read them and certainly did not have my own copy. So often ones knowledge of the regulations was by word of mouth not first hand reading.

When in 1991 the Sixteenth edition came out and in 1992 it became BS 7671:1992 there was for the first time that I remember an exam to show you could read the book. It was around the same time that the JIB got a foot hold rather than the Unions and electricians mates passing a 16th Edition exam we accepted as electricians some thing which after I am sure they regretted but once accepted it would seem no one was de-graded.

Although today getting a JIB card is not easy it was not always that way. I was under the NAECI agreement rather than JIB so no card was issued it was always a data base system "Advanced Electrician" was awarded after so many years in the trade no exam required.

But even in 2000 going to the office to view the regulations was met with why do you want to know. When I bought my own copy of the regulations in order to take the C&G 2381 as it was then I found there was a host of errors in my thoughts as to what was required.

In the main I thought there were regulations saying I needed to earth metal window frames and cooker isolators had to be within 3 meters of cooker and sockets needed to be at least one meter from sink non of which actually existed. But also there were regulations that I did not know about but as the internet arrived the dark ages vanished and over the years we tend to forget how slow changes took place.

I am sure today if I bought a new Book 3 there would be many changes. For one it would seem for rented accommodation it will now be 5 years not 10 years between inspections and it seems likely the insurance requirements will also slowly slide south of the boarder so we are all singing from the same sheet.

But back to the point of the thread. Some DIY guy wants to fit metal switches rather than the existing plastic. OK my house I have from time to time tested the earth and to date there has never been a problem built in 1979 to swap a plastic to metal is unlikely to cause a problem.

My mothers house 1954 however is very different and some switches have been moved so there may be PVC wiring to lights but there is no earth even if there is an earth wire. My son had an ex-council house wired with 16mm conduit which to be fair was originally earthed but alterations had removed some of the conduit and again PVC cables may have had earth wires but they were not connected to anything.

So unless like me you have lived in the house from new an earth wire in a switch box means nothing. Often ceiling roses are replaced with choc blocks and shoved up the hole with just line and neutral connected to the class II lamp and all too often the earth is lost.

So from answers it would seem one one likes the idea of a DIY guy using a make shift meter. So what other method? With the main isolator on and the MCB off then we should get continuity between neutral and earth with TN systems but often no neutral at a light switch.

So what? Be it a door bell (battery) and two leads or a multi-meter on ohm range and measuring to a know good earth would work even if the power was totally isolated. My house again all metal back boxes so simply measuring from 3.5mm fixing screw to another 3.5mm fixing screw one can show there is an earth. But plastic back box and that fails.

So ideas simple idea some one wants to fit metal switches how can they be instructed to do the tests to see if these can be fitted? I will set limit to £75 for test equipment total so come on how to test DIY style?

 

[JohnW2]

... and since unlike today in 1966 there was no internet so very likely houses up to 1970 still had no earth to the lights.

I've been trying very hard to understand that statement, but have so far failed! Could you put me out of my misery?

When the Amendment 3 came out even people who did not buy a copy myself included knew from forums and the like what new things had been added.

Ah, I see, thanks. In most walks of life, in pre-internet era, people tended to rely on things like trade journals to keep them informed of new developments, new regulations etc. - which seemed to be a fairly effective system.

So ideas simple idea some one wants to fit metal switches how can they be instructed to do the tests to see if these can be fitted? I will set limit to £75 for test equipment total so come on how to test DIY style?

AS EFLI said, a (dead) 'continuity' test back to the MET (or even to some other earthed item) would really be adequate - and that could be done for the cost of a cheapish multimeter and a sufficiently long lead.

Kind Regards, John

 

[bernardgreen]

AS EFLI said, a (dead) 'continuity' test back to the MET (or even to some other earthed item) would really be adequate

Would it ?

What if the CPC has continuity when tested with a few milli-amps of test current but melts at 5 amps.

Obviously a CPC that can carry 30 milli-amps without failing would be adequate for circuits protected by an RCD

 

[JohnW2]

AS EFLI said, a (dead) 'continuity' test back to the MET (or even to some other earthed item) would really be adequate

Would it ? What if the CPC has continuity when tested with a few milli-amps of test current but melts at 5 amps.

An interesting theoretical comment - but what test (what 'normally undertaken' test) would detect the fact that the CPC might melt at 5A?? A standard EFLI test certainly won't do it - my MFT uses 12A for 10 msec - which is not enough to melt 'anything'.

In passing, what test would you propose undertaking to demonstrate that (weaknesses in) L and N conductors would not 'melt' when they were fully loaded?

Kind Regards, John

 

[bernardgreen]

In passing, what test would you propose undertaking to demonstrate that (weaknesses in) L and N conductors would not 'melt' when they were fully loaded?

Testing on its own, ( other than loading with full load current for a significant period ) cannot prove a cable is OK. Testing and visual inspection have a better chance of accurate results.

That said an accurate measurement of the resistance compared to the calculated resistance of the cable would discover some defects in a cable route of known length and diameter(s).

 

[JohnW2]

In passing, what test would you propose undertaking to demonstrate that (weaknesses in) L and N conductors would not 'melt' when they were fully loaded?

Testing on its own, ( other than loading with full load current for a significant period ) cannot prove a cable is OK. Testing and visual inspection have a better chance of accurate results.

Quite so!

That said an accurate measurement of the resistance compared to the calculated resistance of the cable would discover some defects in a cable route of known length and diameter(s).

True, although probably of limited value in practice. Truly accurate measurements of low resistances are difficult (the connection between tester and conductors being the most problematic issue) and, in any event, a very localised problem (such as 'loose connection') might have a high enough resistance to produce local heating problems but might not have any great impact on the resistance of a long run of cable as a whole.

Whatever, I'm still not sure what you are proposing as a 'better' (than low-current continuity or EFLI measurement) method of testing which would detect a situation in which "a CPC might melt at 5A".

Kind Regards, John

 

[EFLImpudence]

Testing on its own, ( other than loading with full load current for a significant period ) cannot prove a cable is OK. Testing and visual inspection have a better chance of accurate results.

I feel that is different than the original question - testing for earth.

Testing the conductor would be the same as for the lives.

That said an accurate measurement of the resistance compared to the calculated resistance of the cable would discover some defects in a cable route of known length and diameter(s).

As would comparison with the other conductors of the circuit.

Is that not what we do for resistances?



Melting at 5A; what would that mean?

The conductor had become as thin as 2A or 3A fuse wire?

 

[Risteard]

Obviously a CPC that can carry 30 milli-amps without failing would be adequate for circuits protected by an RCD

How so? The RCD certainly won't and cannot limit the fault current to 30mA.

 

[bernardgreen]

How so? The RCD certainly won't and cannot limit the fault current to 30mA.

It will operate and turn off the supply if there is 30 milli-amp flowing in the earth conductor which has created a 30 milli-amp un-balance between Live and Neutral at the RCD sensor.

 

[bernardgreen]

I'm still not sure what you are proposing as a 'better' (than low-current continuity or EFLI measurement) method of testing which would detect a situation in which "a CPC might melt at 5A"

My point is that a simple continuity test on a CPC may not discover a fault that will render the CPC in effective when it is needed in a fault situation.

 

[JohnW2]

I'm still not sure what you are proposing as a 'better' (than low-current continuity or EFLI measurement) method of testing which would detect a situation in which "a CPC might melt at 5A"

My point is that a simple continuity test on a CPC may not discover a fault that will render the CPC in effective when it is needed in a fault situation.

I think we understood your point but, as I said, I still don't understand what test(s) you are proposing (over and above CPC 'continuity' {resistance}, or even EFLI) that would detect the (extremely unlikely) scenario you are postulating. Furthermore, you mentioned that the CPC might 'melt at 5A' but the reality is that, under L-E fault conditions, it would carry the full PEFC (probably hundreds of amps) for as long as protective devices allowed it to flow.

So I ask, again, what additional test(s) of a CPC are you suggesting should be undertaken (in the context of this thread, before a metal accessory is installed)?

Kind REgards, John