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Hello

Over the last 2 weeks I have been doing some electrical work for the neighbour of my Daughter as they had been let down by 2 other Electricians. I normally do design work but am 18th Edition C&G 236 qualified, as I am waiting to start a new draughting contract I have been doing installation work mainly for family. My daughter told her neighbour that I was an Electrician and might be able to help them out! This neighbour told her that it was just a couple of extra sockets. Later I learned I was expected to create new 13A socket and FCU positions, move the cooker cct and add additional lighting points.
As we had the first meeting and discussed the job, the kitchen fitter/carpenter wanted a new ring main and a new cooker cct. The house owner however wanted the ring main and cooker ccts extended. I decided to go with the house owner and extend the ring main and cooker ccts. This I thought was better as I am not Part P registered and this work would not be notifiable
During the work I carried out insulation resistance tests on the original cooker cct and the new legs of the ring main. As I was told that new plasterboard was soon to be fixed to the walls.
These tests all returned values above 999M ohms. All good, I then decided to do an earth fault loop impedance test on 2 of the existing sockets, one read 1.7 ohms and the other 1.9 ohms. I believe the max value for a 32A EN60898 type B mcb cct is 1.1 ohms.
I know I will have to resolve this problem as when I have to connect the new cables into the existing ring main cables the new sockets will be over the 1.1 ohms also.
So I'm thinking I will need to check the terminal connections of all the existing socket outlets on this existing ring main and retest for Zs.
Yes I should have carried out an EICR but was told at the outset it was only a couple extra sockets needed!

Thanks in advance

Humdrum.
 

davesparks

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Mentor
Arms
Esteemed
You should resolve the Zs situation before any plastering happens, if that 1.9 ohms is genuinely the Zs of the circuit before you extend it you could be up a creek after everything is plastered and you have to start running a new circuit in!
It could cost you more in making good than you were going to make on the job, unless you can get your public liability insurance to pay for it.
 
What Ze have you got because those Zs readings are high for a dwelling. You often don't get that type of reading even for a lighting circuit.
 

Pete999

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Arms
Esteemed
Hello

Over the last 2 weeks I have been doing some electrical work for the neighbour of my Daughter as they had been let down by 2 other Electricians. I normally do design work but am 18th Edition C&G 236 qualified, as I am waiting to start a new draughting contract I have been doing installation work mainly for family. My daughter told her neighbour that I was an Electrician and might be able to help them out! This neighbour told her that it was just a couple of extra sockets. Later I learned I was expected to create new 13A socket and FCU positions, move the cooker cct and add additional lighting points.
As we had the first meeting and discussed the job, the kitchen fitter/carpenter wanted a new ring main and a new cooker cct. The house owner however wanted the ring main and cooker ccts extended. I decided to go with the house owner and extend the ring main and cooker ccts. This I thought was better as I am not Part P registered and this work would not be notifiable
During the work I carried out insulation resistance tests on the original cooker cct and the new legs of the ring main. As I was told that new plasterboard was soon to be fixed to the walls.
These tests all returned values above 999M ohms. All good, I then decided to do an earth fault loop impedance test on 2 of the existing sockets, one read 1.7 ohms and the other 1.9 ohms. I believe the max value for a 32A EN60898 type B mcb cct is 1.1 ohms.
I know I will have to resolve this problem as when I have to connect the new cables into the existing ring main cables the new sockets will be over the 1.1 ohms also.
So I'm thinking I will need to check the terminal connections of all the existing socket outlets on this existing ring main and retest for Zs.
Yes I should have carried out an EICR but was told at the outset it was only a couple extra sockets needed!

Thanks in advance

Humdrum.
Do you have a specific question. Humdrum
 

JBW175

Arms
I agree with Westy & Dave.

I’d be wanting to find the cause now, as You could have a right game on trying to resolve it afterwards.
 

SparkySy

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Arms
Esteemed
Doh should have taken some readings first! Too late now! I would be tempted to do some further testing first, what were your end to end ring values and R1+R2, has it RCD protection for the circuit? Could it be the RCD causing the high Zs readings? And what is the main Ze for the property?
Sy
 

ipf

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Mentor
Arms
Esteemed
Check the Ze before carrying out any works to see if it is high to begin with
Not always. Repairs due to a damaged radial circuit wall cable (picture fitting), not wired in correct zone. Dug out and repaired and then a terrible Zs reading.
I found it was a Ze problem but a previous check wouldn't have made any difference, whatsoever.
Any installation work, I agree.
 
Today new kids on the block would say Rcd it.
But we’re old school.
Its also the problem of the customer,your addition wI’ll be ok, it’s the connection to it the problem.
Re test the Zs,,check continuity etc.
 

radiohead

Arms
Esteemed
Today new kids on the block would say Rcd it.
But we’re old school.
Its also the problem of the customer,your addition wI’ll be ok, it’s the connection to it the problem.
Re test the Zs,,check continuity etc.
He's installing sockets, it will have to be RCD'd. Old school or not with 30ma RCD protection to the circuit then the maximum Zs permitted for the 60898 MCB need not apply and the maximum Zs for an RCD can be used. Nevertheless the reading is higher than expected and should be investigated...assuming of course it is a TN system which has not been stated by the OP.
 
First thing to do with a plug in tester lead is to plug it in press test then un plug it and try this several several times to see if the result changes...
Is it just high on just two of the sockets or all the socket...
 

Leesparkykent

Mod
Mentor
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Supporter
Esteemed
I would check the end to end readings on the RFC if r1 and rn are the same and r2 is proportional allowing for difference in CSA then its genuinely the length of the circuit.
 

pc1966

Arms
Esteemed
I'm with Leesparkykent here - a check on the ring ends to verify r1, rn & r2 are sane should be done in any case.

If they are OK then either Ze is high (which you could check at that time you are at the CU) or the sockets you tested have some abnormal resistance to them. I guess it would have to be CPC gone high (CPC to back box not to socket terminal?!), otherwise an odd ohm on L or N would cause quite a heat problem if you are loading them to several amps.
 

Bob Geldoff1234

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Arms
Esteemed
Test the main earth first(Ze) and get a reading.Then without removing the earth lead put the two test leads on the other side of the RCD.See if there a marked difference.Your high readings could be being caused by RCD uplift. Obviously if the readings are the same then your high Zs needs investigating.
 

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