Ian coughed up some electrons that declared:


Watch who you get in as this type of work is often seen as an invitation
to do a full rewire, rip you off and cause a lot of mess which youdon't
need.
A consumer unit can start at £35 complete with 10 MCBs of values of
your choice. They can also go up to over £100 depending on the style
you want. I replaced mine for £35 and it took about 30mins as all the
cables were long enough.
People taking two or three hours, stringing the job out, then claiming not
to be able to connect anything up unless you agree to a rewire are
cowboys. What they should be doing before starting is giving you the
opportunity to pay for a full test if you want it...

Actually, if they are doing it correctly they *must* at least perform a
basic test of the final circuits. I know because I've just done the EAL
Level 2 Domestic Installer's course (and passed), which is the entry level
qualification to join a DI self certification scheme.

I'm also doing it for the purposes of DIY (to make the BCO feel warm and
fluffy about accepting my work and certification with no further checks) so
I don't have an axe to grind, but I think some understanding is needed, so
forgive me for speaking up :-)


The reason is, changing the circuit protection requires the circuit to be
checked to ensure the disconnection times are correct (0.4 seconds on a
final circuit upto 32A and 5 seconds on any other circuit).

You can only prove this by taking a Live-Earth loop resistance test (a
multimeter, unless *very* sensitive will not manage this reliably) and
combining with the supplier's Earth Loop Impedance value (which requires an
earth loop impedance meter to measure). Even assuming the worst case
supplier's Ze impedance of 0.8 ohm for TN-S and 0.35 ohm for TN-C-S, it
still needs to be checked.

A high resistance circuit may fail to trip the breaker quickly enough under
fault conditions and instead leave your cabling running hot (fire and cable
damage risk). I accept RCDs lessen this risk on L-E faults, but on L-N
faults the point stands.

You're also supposed to complete an EIC when changing circuit protection to
comply with the IEE Regs (changing the CU results in changing the
protection on many circuits) and apart from the above checks which are
recorded, you also need to check insulation resistance at 500V.

RCDs need to be checked for correct operation at specified levels even if
new (test button is one test but is not sufficient by itself).

You cannot really expect a professional who is subject to the standards of
his professional body (eg NICEIC, NAPIT etc) *and* his insurers *and* the
IEE/IET to not do the job correctly - eg if you didn't like something he
did, you could ask his body to inspect his work and any shortcuts will get
him/her into trouble.

But your point about needless rewires is quite valid - unless the circuit is
actually faulty, having RCDs on everything address most of the changes in
the 17th Edition affecting domestic work that are likely to be an issue.

The testing involved could take a few hours to conduct in a larger house and
a good hour or two on a small installation.

Of course, if you're doing yourself, without notifying and you feel
confident that all your wiring is good, then I agree that 30 mins is quite
possible. But the sparks you employ wouldn't be able to make those
assumptions. So it's not necessarily the case that they're ripping you off
if it takes 1/2 a day to a day depending on any faults that may be
discovered.

Cheers

Tim