ELECSA Certification Scheme Ring final continuity readings and Elecsa assessment looming...

[mpoy222]

One of the things you need to understand is that a Parallel earth path will bring the cpc reading (R2) down towards 0. Your cpc value is at 0.40 compared to 0.60 and 0.61 with line and neutral. This is why im leaning towards a parallel earth somewhere.

You got SWA on the ring at all anywhere?

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Yeah i will have to do that its odd that its not 0.40 all over it does vary from 0.28 at the C.U. to 0.40 on other sockets. Theres no SWA anywhere.

 

[onions1066]

You will never get the exact reading unless they are all brand new sockets, you have to work within the tolerances and use a bit of commen sense as well

 

[mpoy222]

It's late, and i'm not quite sure why i've just told you to energise the circuit. Have you had the power back on at all on the circuit since you've done the CU change...? If you have then crack on and do it again so you know whats what.

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Yeah power has been back on, i will have to go through it all again to find the fault. I need to know what im talking about when the Elecsa assessor comes so i dont look completely incompetent lol cheers for all your advice

 

[markc123]

It could just be loose connections, but to have lots is unlikley. First go round and make sure every earth connection on the ring is absolutley tight...and in the process check for other earths connected that shouldn't be. Onions has gone onto my next point though, heating systems.

 

[markc123]

You got any dual accessory boxes anywhere that could be linking two circuit cpcs together by mistake?

 

[mpoy222]

no dual accessory boxes BUT the boiler is in kitchen and the timer is on a FCU i did take it off but wasnt looking for any extra earths at the time so may have missed it. There aren't any earth clamps on the pipes that i can see though. The Immersion heater is on a seperate circuit upstairs though and all the heating controls are next to that. The only bonding clamps on pipes are on the gas and water as they enter the house.

 

[markc123]

All i can really say mate is have a proper thorough look tomorrow, and if it's still the same come back on here tomorrow night around tea-time and they'll be alot more members on to offer advice / pick more brains.

Im still convinced it'll be a parallel path somewhere though...obviouslly can't say for certain, but if i were you it would be what i was focusing my attention on.

 

[SYKRAPS]

Disconnect the earth in the supply flex to the boiler and I will hazard a guess that this will be the source of the parallel path mpoy

 

[DJ Ovengloves]

GN3 and GN8 are essential reading and reference materials IMHO mate...treat yourself!

There are a lot of FCU's in kitchen feeding everything from washing machine to under cupboard lights, fan, hob, cooker hood etc. No i dont have GN3 i thought i had spent enough on books and couldnt justify another £26 lol I havent carried out any other tests on the circuit as i run out of time. I havent tried the split ring method do you mean break the circuit down and test between sockets?

 

[mpoy222]

Thanks for all the advise, i haven't had a chance to investigate further but i will update as soon as i have, I like the boiler flex theory (fingers crossed!) That makes sense. It must be a parallel path somewhere as suggested. Thanks again
Michael

 

[markc123]

Aye fingers crossed. Let us know how it goes. It'll seem so obvious when you've solved it and you'll be wondering what the fuss was about lol.

 

[robsparky1975]

Dont stress yourself out too much as the elecsa blokes are mostly time served sparks and are not there to pick holes,just make sure that you meet the criteria,with the readings on the ring that you have at some sockets tolerances on mfts can jump around as mentioned,leads being the cause in a lot of instances,zero them before testing if you can,you will be fine just take a step back if needs be,GN3 is a good buy and at least if you cant answer a question on the spot you can pick it up for reference on your assessment.

 

[markc123]

Agreed with that...elesca guys are just there to make sure what you're doing is safe.

 

[mpoy222]

Just to update, I disconnected the earth to the boiler and the reading went straight up to 0.65 ohms! result, but still not the 1 ohm(ish) i was looking for so maybe another parallel path somewhere. I took off a few other earths but it stayed the same. I dont know if the Elecsa assessor is going to expect me to get a higher reading than that or maybe just explain why i think its that low? I dont want to get too side tracked by this one thing i know there is a lot of other things i need to worry about too!!!
Michael

 

[markc123]

Have you gone round and made sure all connections are tight?...could be a loose earth at a random socket on the circuit...

 

[partypest]

The assessor from Elecsa will be right behind you, in a positive way. They'll be very interested to hear how you searched for the cause of your unexpected readings. So long as you can demonstrate your safe isolation, testing technique and a bit of Part P knowledge, you'll be fine. The OSG is there for a reason, and they won't mind you looking at that for any answer you don't know off the top your head. I remember my assessment and I had complete panic blindness and they were asking me stuff that I would know at any other time but my head went blank. Other big things, make sure you've got all the other paperwork together and the right publications. It's stressful, but you'll get through it.

 

[Richard Burns]

Just to update, I disconnected the earth to the boiler and the reading went straight up to 0.65 ohms! result, but still not the 1 ohm(ish) i was looking for so maybe another parallel path somewhere. I took off a few other earths but it stayed the same. I dont know if the Elecsa assessor is going to expect me to get a higher reading than that or maybe just explain why i think its that low? I dont want to get too side tracked by this one thing i know there is a lot of other things i need to worry about too!!!
Michael

If you explain (if they should ask, unlikely) that you felt that the CPC resistance result was low due to parallel paths from the existing installation, you made investigations and found one partial resolution.
The calculations done indicate that the circuit would be complaint in either case (whether there was a parallel path or not) and so you believe that the addition you have made is safe for continued use and complaint with the regulations. The cost to the customer of further investigation was not justified since the addition is believed to be safe and compliant even if there are some unresolved earthing/bonding considerations in the existing circuit.

I think this will demonstrate that you are not blindly writing down figures with no understanding and that you have made your best efforts to ensure that there are no significant safety issues with your installation.

If your assessor has a problem with this then you can investigate further during the assessment and you can ask your assessor how this may be best resolved or if he can identify the cause himself, he may be able to help, that is potentially why they are there!

 

[Des 56]

i think I have lost the plot on this one

You have changed a consumer unit
You have verified a ring final has end to end continuity
You have established Zs on each outlet is within limits
You have spent days looking for and worrying about probable parallel earth paths that are making cpc readings better than expected

If this was a new installation and this were initial verification, then all well and good,but this is a consumer unit change,the circuit has been established as safe for reconnection,that is what you are expected to ascertain

You have the probable reasons why the readings vary and could answer the assessors questions if required
Why rip an "existing" installation to bits to find what can be explained by installation variations that are usual and often present

 

[Guitarist]

i think I have lost the plot on this one

You have changed a consumer unit
You have verified a ring final has end to end continuity
You have established Zs on each outlet is within limits
You have spent days looking for and worrying about probable parallel earth paths that are making cpc readings better than expected

If this was a new installation and this were initial verification, then all well and good,but this is a consumer unit change,the circuit has been established as safe for reconnection,that is what you are expected to ascertain

You have the probable reasons why the readings vary and could answer the assessors questions if required
Why rip an "existing" installation to bits to find what can be explained by installation variations that are usual and often present

I think it's more about understanding how it works for him. Better that he practices on his own installation than charge someone for the experience

 

[partypest]

Michael, how did it go?