On Jul 28, 4:51*pm, "gb" wrote:
My old mother has just had a new consumer unit fitted
(old one was rewireable fuses).

What are her cables - Lead-sheathed, Rubber or PVC?

The old cables were not long enough, so some had to be lengthened via a block.

I know who wired the house - "cables as short n taut as the crow
flies" :-)


Does the sparky have to issue a full test cert for all circuits,
as the cables were lengthened.

Consumer unit change requires an EIC, typical info is...
a - IR test & continuity test of any rings
b - CPC present (Yes or No)
c - Ze measured or assumed from type of supply / DNO enquiry
d - Zs limit (80%) from tables for that circuit breaker type (B) &
rating (20A)
e - Zs measured / calculated for each circuit and within Zs limit (d)
f - RCD actual measured trip times are absolutely vital

In replacing the CU, any spark should at least check...
a - There is no borrowed live/neutral condition (eg, on hall 2-way
lights). A giveaway that there is would be both Lights-UP & Lights-
DOWN on the same RCD rather than split between 2 RCD as 17th reg 314.1
would require.

This check takes 5 min.

b - That Light-UP & Light-DOWN have CPC (earth) present in the cable.
If not she should have at least been advised plus a quick check that
all lights are Class-II, backboxes are plaster or earthed-metal
(separate 4mm 6491X earth) or plastic (Class-II), wiring accessories
are plastic or M3.5 plastic screws used (not easy to find).

This check takes 5 min.

c - That MEB (Main Equipotential Bonding) is in place to Gas & Water
if necessary, plus 17th bathroom requirements met
- Verification that no class-1 lights are in use without a CPC on the
lighting circuit. The Green/Yellow 6491X bonding cable. Addtional work
is required if the supply is TT (ie, she has her own earth rod).

This check takes 15 min. Earth rod tests & validation can take about
2hrs.

d - There are no obviously unsafe circuits, ie, insulation falling
off, blackened & broken kitchen socket, 2-pin cord plug into light
fitting (still have one of those myself, predates RCDs too :-)

There are a few more checks, but you get the idea.
Most electricians would check for a-b-c before changing the CU as part
of a "PIR" or Periodic Inspection Report, or check for them on their
own. It is pretty "no-brainer" stuff for any spark as they do it day-
in-day-out.

CU type.
a - All circuits require RCD protection unless cables are surface run,
50mm from the surface, in steel conduit or BS8436 cable. For your
mother everything would require RCD protection almost certainly.

b - CU should be a minimum of Split Load with at least 2x RCD. Lights
UP should be on RCD #1, Lights DOWN on RCD #2. That is to say not all
lights should be on one RCD - if they are I would suspect there is a
borrowed neutral/live which has not been corrected and really needs to
be re "all lights out and mother down the stairs".


Was he right originally in saying that he could not install
a new circuit, without a new consumer box being fitted.

Depends on what was there previously.

If your new circuit was a single socket (outdoor) or light (kitchen)
he could run that off an existing final circuit if that circuit would
then not be overloaded (by that I mean its functionality not reduced).
He would have to run surface wiring from that fuseholder to an
external RCD such as a 13A RCD protected fused spur or 20A RCD
protected enclosure etc.

If the new circuit was for something like a cooker, the meter tails
could have been Henley Block split to a new CU with 32A RCBO
protection, then check MEB is correct. There may not have been space
in the CU location for this.


CU Change is notifiable to Building Control under Part P.
- Some DIYers do ignore this part, preferring to fix something unsafe
and spend the £200 notification fee saved on RCBO or smoke alarm or
fixing an otherwise unsafe install - but if they break BS7671 or
equivalent named standard it is on their head re any faults introduced
or potentially not rectified.
- Electricians ignoring it are another matter, not so much re breaking
the law but the work *might* not be up to scratch. Realise an
industrial spark with C&G 2382 2392 can not legally do a CU change
unless he is a member of a competent body such as NICEIC ESC BSI
(Electra?) and so on, whereas a 5-day trained NICEIC Domestic
Installer can do it and need not actually comply with BS7671 or
equivalent named standard in doing so, just be "reasonably safe".

A CU change to 17th should be about £450-650 depending on the work
(and extending CU tails can be a fair bit of work and added cost re
enclosures, checking circuits and so on).

Bottom-line.
Do you have a piece of paper with the proper RCD test results on it?
Does the CU have at least 2x RCD? Is the persons name on the Part P
Competent Installer list? Are the lights on 1 RCD or split between 2
RCD? Is there a green/yellow wire running to the gas & cold water
pipes if they are copper (or lead) in the house?