New consumer unit - testing existing circuits

[daza]

When changing a consumer unit is it required to test all existing circuits or is a visual inspection of the installation only ok?

I have been having this discussion with an electrician at work today. Please let me know your thoughts.

Many thanks

 

[NozSpark]

I asked my NIC assesor this on my annual inspection and was told that you need to carry out full testing as if you installed the circuits although your paperwork will only show that you've changed the CU

 

[Evans Electric]

The problem with replacing the C/U is that you become responsible for whatever you re-connect to it . Hence the usual one with the borrowed neutral .

There could be some dangerous wiring in the house somewhere, and you are the one who has now re- energised it .

 

[davetheglitz]

My understanding is as follows:-

As an electrician you undertake to leave the system in a safer condition than when you started work on it.

When replacing a CU you need to be sure:-

• All circuits are correctly fused for the wiring. If a ring circuit then is being supplied this means doing ring continuity.
  
• Earth continuity has not been compromised - hence R1 + R2
  
• RCD's trip within appropriate time at the required current. To this extent insulation measurements are well worthwhile.
  
• Earthing is to the latest standard (remember the Adiabatic equation - it's not always 16mm)
  
• Bonding is in place - ideally upgraded to the 17th edition - if not then justify why not - eg 10mm to gas, 6mm to water - however cross bonded at boiler via metal manifold. Continuity gas to water verified.
  

In effect this means doing the electrical testing associated with a PIR but not the inspection side. To hold you responsible for the whole installation is a bit ridiculous - even on a PIR it would be very easy to miss a borrowed neutral - in fact hard to pick one up - but you need to show that you haven't compromised what was already there.

If there are any faults on the existing system these should be highlighted.

If there are any aspects not to current regs - cover in your paperwork.

You are only certifying the work that you have done - which is changing the CU.

 

[batty]

Under British Standards we are told you have to ensure the changed protective device will disconnect under fault conditions so a loop test is required at each point. Now you have also got to ensure a ring is a ring and you have no earth to neutral faults as the RCD is going to trip or you are going to get nuisance tripping but you really cannot be responsible for whole installation that is just ridiculous you did not install wiring and do any dodgy part that has been done.