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Discuss Testing after a consumer unit change in the Electrical Forum area at ElectriciansForums.net

TJC1

Regular EF Member
Had to change 40 consumer units the other day in a hostel/hotel/b&b and it come to the testing stage


I spoke to the NICEIC who said you need to test circuits for " safety only ". He said doing a global IR test (testing each individual circuit if less than 1M), and earth fault loop, RCD and end to end to any ring mains. He said not to bother with R1+R2 or R2 test as polarity would be verify due to the Zs test.

How much depth do you do?
 

telectrix

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if i could change 40 CU's in a day, I'd not be here. I'd be up there with Zeus, supping nectar ( Theakston's). otherwise, agree with niceic. by measuring Zs and getting acceptable readings, it's obvious thet the R1+R2 readings will be acceptable. however, nothing to stop you getting them prior to the CU change, just to satisfy your OCD.
 

Murdoch

Electrician's Arms
Had to change 40 consumer units the other day in a hostel/hotel/b&b and it come to the testing stage
This reads as if you didn't do any testing as you went along ...... please tell me I'm wrong!

And how many days did it take you?
 

TJC1

Regular EF Member
if i could change 40 CU's in a day, I'd not be here. I'd be up there with Zeus, supping nectar ( Theakston's). otherwise, agree with niceic. by measuring Zs and getting acceptable readings, it's obvious thet the R1+R2 readings will be acceptable. however, nothing to stop you getting them prior to the CU change, just to satisfy your OCD.
40 boards changes was a slow day for me!
 

telectrix

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i once did 20 CU changes in a night shift. then i woke up.
 

Dustydazzler

Regular EF Member
I wonder if the OP meant to ‘test’ 40 consumer units previously installed...?

This would make sense and you could probably rip through 40 boards if you are just doing a quick Zs and rcd test
 

Strima

Electrician's Arms
So you don't test before doing any changes to identify any safety issues?
 

happyhippydad

Member
Electrician's Arms
DIY
I'm guessing the 40 CU's were changed over a period of time. 40 in one day would even be a push for JRC holdings Limited or whatever his name was (rewire p/day).

Without highjacking the thread I think the question is a good one though.

How in depth do you go with the testing after a CU change?

A CU change generally takes (on average) 5 hours. This includes fitting the piece of wood behind (brought out from the wall) so you can bring cable in from behind. That leaves little time for testing if you want to get it done in a day.

1. Does everyone always do R1 +R2?
2. Does everyone do L-L IR testing (I often do just L/N-E IR testing on lights as to take all the downlights out would take too long). Also, 25% of the the time you can never remove all appliances from sockets so a L-L test on sockets is sometimes not viable, therefore a L/N-E test is done.

It would be interesting to get some honest answers on what testing is done after a CU change?
 

Dustydazzler

Regular EF Member
I think the answer regarding testing would be ask 10 different sparks and get 10 different answers

Imo the absolute bare minimum should be to confirm Ze , make sure rings are rings and then do Zs and rcd trip times
 

happyhippydad

Member
Electrician's Arms
DIY
Majority of tests I do are before the board change..
No point in changing the board if the installation is knackered or full of faults
I was about to say 'that's the boringly 'correct' answer but who actually does that'..... but it actually makes real sense! I guess you just want to get on with the job (i.e the CU change), but to do all the testing before is a really good idea. Apologies for even considering that you were giving a boring answer :)

But... would you still always do an R1+R2 and L-L IR testing on everything!
 

mhar

Electrician's Arms
Always do the tests before which are end to ends and Zs at every accessible point on rfc, lighting Zs but at switches if a ceiling full of downlights and dimmers involved, Zs on any radials. L&N - E ir for each circuit. Additionally when more than 1 lighting circuit I do a functional test (look) by disconnecting the neutral to make sure it is not affecting the other circuit (borrowed neutrals). After change Zs on a few random points and compare with original readings to confirm my earth terminations, Ze and rcd trips. Feels like an assessment answer!
 

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