Recommended checks before CU change

I’ve made a decision to quote this job competitively to try and win it, as I need the experience, plus it’s for my reassessment.  I can use it as a learning experience too.  I’ll factor in a few extra hours for any remedial works in the quote and if they’re not need I won’t charge for them. 


A couple more questions though:


Both gas & water were bonded albeit in 4/6mm², gas is a pretty easy job to replace as I can run the cable externally to the gas cupboard in the utility room, kitchen stop c*** on the other hand is a bit more difficult as the stop c*** backs on to the conservatory, but in the garage is a water pipe coming up through the concrete garage floor at the back and this is where the water has been bonded.  Would this water bonding be suitable for the whole water installation?


Are Lewden RCBO boards ok?  Found out today that the plumbcentre are selling both lewden & bg populated rcbo boards at brilliant prices.  


Do you have to use C type rcbo’s if there are fluorescent lights in use, or should you always use C type rcbo/mcb on lighting circuits?

Is the incoming water pipe metal?


I have always found for domestic lights, even fluorescent types, a B6 M.C.B. is fine. I normally use B types of M.C.B.s for all circuits in a house, unless there is a big electric welder or similar load.


Z.

Fitzy71:

kitchen stop c*** on the other hand is a bit more difficult as the stop c*** backs on to the conservatory, but in the garage is a water pipe coming up through the concrete garage floor at the back and this is where the water has been bonded.  Would this water bonding be suitable for the whole water installation?

 

Stop cocks are irrelevant.


The water supply pipe - if an extraneous-conductive-part which it will be as it comes out of the ground - should be (main) bonded where it enters the premises where practicable.


If it is the same pipe as the one in an attached garage (not clear from the description), then that would suffice..

Sorry, only mentioned the stopcock (pipework above) as that’s were you bond the water 9 times out of 10.


i would assume the garage stand pipe is connected to the same house water supply, they said they do have a water meter, no idea were it is at the front of the property.

As the IR figures were really low (0.42mohms)

It's not that low - 20% higher and it would have actually have been acceptable under the 16th. That sort of value is quite normal where there's mineral insulation involved - e.g. traditional electric cooker heating elements or perhaps an immersion heater or two. Even if the elements aren't switched on at the time they'll still show on a N-PE test, and most likely on a L-PE test too if there's anything to bridge L to N - such as a timer or some other connected load.


The other common culprit for low IR is outside lighting or similar where water can get in.


The other gotcha for older installations is borrowed neutrals - especially on lighting. Lights were commonly wired in sheathed singles so N (and sometimes L) would be picked up from anywhere convenient rather than necessarily the correct circuit - landing light being fed from the downstairs lighting L (at the hall switch) but returning through the upstair's lighting's N was a common kludge - similarly wall lights (and occasionally outside lights) using a handy socket circuit for N.


  - Andy.