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leep82

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Hi all, yesterday i went to a property to do an EICR in preparation for a DB change next weekend. The existing DB has six circuits, cooker, 2 x rings and 3 x lighting circuits. Bonding to gas and water is in place and adequately sized so providing everything tested out ok a relatively straight forward job.

Other than a high resistance on one of the ring final circuits ( live-live) which was identified and put right i had no other problems with either ring or the cooker circuit. My first question is when i change the DB am i able to use these existing readings? Nothing is changing in regards to the wiring. I still need to perform an RCD tripping time test once the board is changed as there are currently no RCD's in place, but all my other test results for the 2 x rings and cooker circuit are fine.

And now for the 3 x lighting circuits! Had no problems with my r1 - r2 readings on any of the three circuits. However when it came to my IR test my readings were quite low although still greater than 2Meg. It wasnt practical to remove every lamp from circuit so my IR test was done between L-E and N-E, with the circuit completely removed from the DB. The lowest i got was greater than 10Megohms. I couldnt find anything on the circuit that might be bringing this reading down. Im happy enough to connect to the new DB without there being a problem with nuisance tripping but should i test these circuits again removing everything from circuit or simply record my low readings.
 
Well I would do a quick global IR test before you swap the CU over, you never know if someone has added/altered anything during the week since you last tested it, hardly likely but you never know.
 
Completing an EICR is far too much of a pre works visit if it is just for an CU change. Here are a couple of links showing a useful (at least I find It useful!) checklist to complete prior to a CU change, it will probably take about 45mins - 60 mins View attachment Cu checklist.pdf

Also, here is a link with some other useful info regarding CU changes http://www.electriciansforums.co.uk...ctrical-regulations/12971-cu-changes-you.html

If I got results of >2MΩ I would be completely happy and not feel the need to investigate further, after all this is 2,000,000Ωs we are talking about! It takes around 8000Ω to trip an RCD :smiley2:.
 
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You should re-test the circuits when you do the CU change, but have a copy of the EICR readings to hand to compare.

Remember any IR readings over 2 meg ohms is OK!

Just saying
 
I don't think I'd re-test if changing a CU within a month or thereabouts unless I thought there had been some change to the system. After all, you're probably going to recommend a re-test in 5 or 10 years, so a few days here or there makes no odds.
 
I would probably just do Ze Etc then IR the circuits as I connect them and then carry out Zs and RCD tests. The Zs and Ze will give you enough information to be able to indicate that no changes have occurred.

I'm not suggesting that any calculation of r1+r2 or anything like that is acceptable for obtaining test results, but just that it would be sufficient as a method of checking that no changes have occurred over a week.


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