Earth Fault

[yelloperil]

I have recently fitted some lights in an attic and when I came to testing found the cpc showing 60 volts. I switched each mcb off in turn and the fault dissapeared when I turned off the downstairs lighting mcb. I am going back this weekend to sort the problem out so will start with an IR test. the house is only 10 years old and the customer has changed all the downstairs lights and switches.Is it fair to say that the fault should be on the downstairs lighting circuit?

 

[pevvers]

Sounds to me like you have no earth continuity on the circuit you are working on. Have you carried out an R1+R2 test to check continuity? I've found lots of times you get crazy readings when the earth is floating, so this is where I'd start, and if there is no continuity, check at all lighting points on that circuit, as if there's been a DIY job, they may have disregarded the earth as not being important due to the fact "it's working fine isn't it?".

 

[Jason Smith]

Where is the earth getting its 60 Volts from?. Thats a major fault, and as the customer has changed a few lights, I would suggest a visual on their work, i.e. switch plates off, etc, lights off, and have a looksie.
Nothing obvious, then test.

 

[Bobby B]

Sounds like an earth has been left out somewhere, in the fittings most likely should be easy to sort out. an R1+R2 then I/R then Ze then Zs i reckon

 

[spadxiii1918]

Can I ask how the test was performed? was the 60V live to earth or Neutral to earth. (Live to earth should be 230V)any lower suggests (as said earlier) a loose connection on the earth or live.. like pevvers suggests

 

[alan.surry]

I've just discovered the same problem on the downstais lighting circuit in our house. I'm preparing for a new kitchen to be fitted in the next few days and on opening the consumer unit, discovered that the previous owners have deliberately disconnected the downstairs lighting CPC, presumably as a quick fix to "cure" a fault rather than finding & fixing it. At several switches, neutral to earth gives a reading of around 60v. I'm planning to test the whole lot over the weekend, but I don't understand how a loose live or earth would give a reading like this. Surely the likelyhood is that there is a partial break in the insulation somewhere, such as a nail or screw that has damaged a circuit?

I know this is an old thread, but any comments or suggestions would be appreciated. It's been a couple of years and very little practice since i passed G&G 2330 pt 3, so i should be OK testing & fault finding, though I could do without spending too much time as I need to get the kitchen done before my wife comes out of hospital next week (No stress there then!)

Regards, Alan.

 

[Deleted member 9648]

You need to carry out R1R2 tests at all points on the circuit initially and rectify any deficiencies there,(without cpc continuity an earth fault might not show up on an IR test).Once you have established that you have CPC continuity carry out full IR tests on the circuit and rectify if you get low readings....in thoery you should be looking for >2 megs...but in practice I wouldnt worry as long as it was >1meg. Once all that is satisfactory,check Zs readings.

 

[Deleted member 19807]

the 60v you are reading is an induced voltage, as said above a clear indication its not connected to an earth.

 

[alan.surry]

Thanks guys. I don't remember induced voltages being discussed in this context at college, but it's making a lot of sense now and the news that I may not need to pull plaster off of my walls is very good news indeed.

Best regards,

Alan

 

[jdtae]

Thanks for useful threads and it is very helpful and appreciate you all
Could anyone please help me to get my head round for the following questions?
1. If I extended a light from existing circuit I will need to carry out Zs test including other tests.
Which Zs value I need to put on the installation cert as I would not know if the measured value
is lower than other circuit?
Should I measure all other circuit to find out which point is highest value and record it then ignore
the value for the circuit that I have just installed?
Same question for a ring socket circuit
2. If I added a socket as a spur from existing circuit I will need to carry out Zs test including other tests.
Which Zs value I need to put on the installation cert as I would not know if the measured value
is lower than other circuit?
Should I measure all other socket point to find out which point is highest value and
record it and ignore the value for the spur socket that I have just installed?

JD

 

[malcolmsanford]

The Zs value would be the highest value after testing all points, as your extending the existing installation you would think logically that would now be the longest part of the circuit, but IMO I would still check other places.

If your extending a light circuit then all you need to do it the Zs for that light circuit on your MEIWC

You carry out the Zs test exactly the same way. Again logically you would think that your spur would be the highest value, but in our indsutry never take things for granted so test all.

You record the highest value no matter what.

 

[morph]

obviously you record the highest test , have you read the osg, gn3 etc ? this is what you need to be doing .

 

[jdtae]

The Zs value would be the highest value after testing all points, as your extending the existing installation you would think logically that would now be the longest part of the circuit, but IMO I would still check other places.

If your extending a light circuit then all you need to do it the Zs for that light circuit on your MEIWC

You carry out the Zs test exactly the same way. Again logically you would think that your spur would be the highest value, but in our indsutry never take things for granted so test all.

You record the highest value no matter what.

Thanks for your reply. I would like to ask one more thing.
Say for example.
If I added a spur socket to an existing ring final socket circuit with a short length of cable in a small commercial property but this ring final circuit leads of 30 sockets (example) and there are a couple of other ring final circuits. (For example Ring final circuit 1 : Office / Ring final circuit 2 : Meeting room / Ring final circuit 3 : Testing Lab )
In thoery, a spur circuit may be the highest value for the circuit where I added a spur socket as you say.
But it will be only against the circuit I have added to and there may be a more higher Zs value in the circuit 2 or 3.
Does this mean I still need to check all of them(Circuit 2&3) to find out the highest value which it would be more likley 60~70 sockets?

JD

 

[pushrod]

Thanks for your reply. I would like to ask one more thing.
Say for example.
If I added a spur socket to an existing ring final socket circuit with a short length of cable in a small commercial property but this ring final circuit leads of 30 sockets (example) and there are a couple of other ring final circuits. (For example Ring final circuit 1 : Office / Ring final circuit 2 : Meeting room / Ring final circuit 3 : Testing Lab )
In thoery, a spur circuit may be the highest value for the circuit where I added a spur socket as you say.
But it will be only against the circuit I have added to and there may be a more higher Zs value in the circuit 2 or 3.
Does this mean I still need to check all of them(Circuit 2&3) to find out the highest value which it would be more likley 60~70 sockets?

JD

On your minor works cert you only record the Zs value of the circuit that you have worked on.

 

[morph]

Thanks for your reply. I would like to ask one more thing.
Say for example.
If I added a spur socket to an existing ring final socket circuit with a short length of cable in a small commercial property but this ring final circuit leads of 30 sockets (example) and there are a couple of other ring final circuits. (For example Ring final circuit 1 : Office / Ring final circuit 2 : Meeting room / Ring final circuit 3 : Testing Lab )
In thoery, a spur circuit may be the highest value for the circuit where I added a spur socket as you say.
But it will be only against the circuit I have added to and there may be a more higher Zs value in the circuit 2 or 3.
Does this mean I still need to check all of them(Circuit 2&3) to find out the highest value which it would be more likley 60~70 sockets?

JD

should you be doing this work ! no wonder the industry is in a mess