Insulation resistance problem

[Octopus]

Had a busy day today but managed to do a test on the circuit.
r1= 0.60ohms
rn= 0.61ohms
r2= 1.04ohms

Calculated R1+Rn= 0.3025ohms
Actual R1+Rn= 0.34ohms

Calculated R1+R2=0.41ohms
Actual R1+R2=0.45ohms

Insulation resistance test
Single circuit @ 250v
L-N = 0.01Mohms
L-E = >200Mohms
N-E = >200Mohms

Split the circuit and did as you said and found that it's the last run of cable between the last socket and CU but looking up the side of the boiler there is a single run of T&E leading to another fused spur but not had time to investigate it yet. At least I know where it is now.
Thanks will post what I find.

Good man - great feedback - is it the boiler supply?

 

[sparky1508]

Good man - great feedback - is it the boiler supply?

Not boiler supply, that on its own circuit but I think there's a spur in the loft as it's only single storey on that end of house. Need to do a bit more investigation and I'll nail it.

Cheers

 

[Midwest]

When you've sorted that one, can you have a bash at telling me why all my odd socks go

 

[sparky1508]

When you've sorted that one, can you have a bash at telling me why all my odd socks go

The washing machine eats them or they get binned once they get crusty. Just wear odd socks all the time and then you wouldn't have to worry about it.

 

[davesparks]

In Andover, Hampshire.

Ok, not too far away then, I'm based in Woking and do a bit of work in central London.

 

[westward10]

Are you doing a Periodic (I know, old phrasing) or fault finding. Try not to pull this circuit apart until you are absolutely sure a fault exists. Forget about trying to get a good reading across L/N initially and concentrate on the L/E and N/E readings. As already suggested try and identify if any appliances or spurred items are still in circuit, is it domestic and does it enter the garden and never assume a power circuit will only supply power points. Check for rcd sockets, these can often be present even if the DB already has rcd protection, these can give false readings. Any suppression filters in appliances or extension leads can also throw readings, try the insulation test at 250V, if you get a good reading this is an indication of their presence. As I said aim for getting good L/E and N/E readings. Good luck.

 

[sparky1508]

Are you doing a Periodic (I know, old phrasing) or fault finding. Try not to pull this circuit apart until you are absolutely sure a fault exists. Forget about trying to get a good reading across L/N initially and concentrate on the L/E and N/E readings. As already suggested try and identify if any appliances or spurred items are still in circuit, is it domestic and does it enter the garden and never assume a power circuit will only supply power points. Check for rcd sockets, these can often be present even if the DB already has rcd protection, these can give false readings. Any suppression filters in appliances or extension leads can also throw readings, try the insulation test at 250V, if you get a good reading this is an indication of their presence. As I said aim for getting good L/E and N/E readings. Good luck.

As in my previous post I have >200 Mohm on L-E and N-E all the way around the circuit. It's on L-N on the last length of cable before going back to CU. It's my own property I'm doing this on just for experience and practice. I still have one more thing to check but a bit busy at the moment.

 

[westward10]

Yeah sorry didn't read all posts, well done finding it.

 

[Simonslimline]

I think most time served electricians have low opinions on these so called fast track routes, there is no short cut to becoming a competent electrician. It takes years, simple as that.

Sent from my SGPT12 using Tapatalk

 

[David M]

To the OP - Welcome to the forum

Well its all good experience and you have had some sound advice given by experienced and knowledgeable folks here on this forum. So hopefully you have not taken things too personally.

Going back to your testing, hopefully you have now found the problem. Fingers crossed you have not inadvertently fried some sensitive equipment. Its easy done if you have missed isolating it from the circuit you are IR testing between L - N @ 500v.
But taking a positive from it, at least it may help you to understand exactly why and what you looking for.

No offence but a lot of inexperienced sparks tend not to understand exactly why they do the tests and what they reveal. The test result guides are there for you to compare against what is expected from a satisfactory installation. Interpreting the results if they are out of range is where experience and a sound understanding of the testing procedures is a must.

 

[sparky1508]

To the OP - Welcome to the forum

Well its all good experience and you have had some sound advice given by experienced and knowledgeable folks here on this forum. So hopefully you have not taken things too personally.

Going back to your testing, hopefully you have now found the problem. Fingers crossed you have not inadvertently fried some sensitive equipment. Its easy done if you have missed isolating it from the circuit you are IR testing between L - N @ 500v.
But taking a positive from it, at least it may help you to understand exactly why and what you looking for.

No offence but a lot of inexperienced sparks tend not to understand exactly why they do the tests and what they reveal. The test result guides are there for you to compare against what is expected from a satisfactory installation. Interpreting the results if they are out of range is where experience and a sound understanding of the testing procedures is a must.

Thank you and no offence taken. It is a good learning experience has helped me understand more. All the advice from the guys on here also very helpful. Just need to keep learning as I know it takes time.
Thanks again☺

 

[Octopus]

and just to add, unless you are very lucky, fault finding (properly) takes time. You need to be able to confidently set a customer's expectation that it could take hours and therefore cost a lot.

Just last week I was fault finding a socket (ring) circuit in a rambling, extended house. After 4 hours I found the fault and couldn't fix it! The section of damaged cable was under a recently made solid floor!

The MCB was downgraded and the "damaged" section was isolated, so they now have 1 radial with 2 cables at the OCPD!

 

[davesparks]

and just to add, unless you are very lucky, fault finding (properly) takes time. You need to be able to confidently set a customer's expectation that it could take hours and therefore cost a lot.

Just last week I was fault finding a socket (ring) circuit in a rambling, extended house. After 4 hours I found the fault and couldn't fix it! The section of damaged cable was under a recently made solid floor!

The MCB was downgraded and the "damaged" section was isolated, so they now have 1 radial with 2 cables at the OCPD!

Or it turns out like my one yesterday, I did the full explanation of how it could take any length of time, why I don't provide a quote, only an estimate etc etc. We arranged a day when there was no matinee show and got someone to open up the building early for me.

Then I had the fault found, fixed and everything back on and working within 1/2 and hour!

But on the up side they asked me to quite for a lot more work there and then

 

[richy3333]

and just to add, unless you are very lucky, fault finding (properly) takes time. You need to be able to confidently set a customer's expectation that it could take hours and therefore cost a lot.

Just last week I was fault finding a socket (ring) circuit in a rambling, extended house. After 4 hours I found the fault and couldn't fix it! The section of damaged cable was under a recently made solid floor!

The MCB was downgraded and the "damaged" section was isolated, so they now have 1 radial with 2 cables at the OCPD!

Nooooooooo! That will fry the brains of certain forum members!

 

[westward10]

Mmm, let's discuss it.