Like for like replacement and MWC

[Pete999]

Got a small job to do this week replacing an existing light fitting for a new customer. Im not familiar with the installation so dont know what sort of state it is going to be in. During my conversations with the customer they have asked for a certificate to be completed for the work. I told them that for such work i wouldnt normally issue a certificate as it falls under maintenance, but if that is what they're insisting on, and me
being keen to impress them, then i will go along with there wishes.

My question to you fellow sparks is how far you would go in regards to the testing and certification for such a small job. I have been told that i am unlikely to be able to gain access into the consumer unit other than to lock off the required circuit. With that in mind my plan was to take a Zs reading at fhe existing fitting prior to removal, so as to probe the means of an effective earth, and then once again when the new fitting is installed.

I was going to detail in the comments section my actions and results prior to removing the old fitting and then record my Zs value of the new fitting in the appropriate column. R1+R2 and IR readings i would detail as a limitation. Obviously i would record all other relevant info such as OCPD and type of earthing arrangement, but with regards to the testing have i done enough/not enough?

You need to ensure the circuit / system you are working on is safe don't you? tell them that you need access to the prperty to do some simple tests.

 

[Octopus]

1) R1+R2 or R2. 2) Insulation Resistance. 3) Polarity. 4) Zs. 5) RCD if applicable. I have an NICEIC 2392 learning guide, which suggests the essential tests are 3, 4 & 5 (5 if applicable) and if reasonably practicable 1 &2. BS7671 only refers to results of tests, as suggested in the model form App.6



From a thread a while back

I've given you a disagree because this is a commercial property - if the MCB is on a shared RCD then switching it off to test the RCD may simply be impractical.

Cert needs to read "like for like replacement of light fitting. Test for Zs only"

I normally note the Zs on my invoice - life is too short to do certificates for this sort of work.....

Obviously anything "unusual" should be commented on only ...........

 

[Deleted member 26818]

To be honest, I really don’t see the point of measuring either R1+R2 or R2 on it’s own in this scenario.
If this were a new circuit, then measuring R1+R2 would (with a known Ze) allow you to calculate whether the Zs would be acceptable once the circuit is energised.
Yes measuring R1+R2 or just R2 will confirm CPC continuity, but then, so would measuring the Zs.
Measuring the IR is another can of worms.