I have a 30s house with some rubber-coated wiring.
Before replacing this, I'm going to put in a new consumer unit.
Before doing that, I'd like to ask a couple of questions.
There is no consumer fuse - tails go straight from the supply cable to
From the meter, the tails go to a small junction box (would this be a
Tails then go from the junction box to the consumer unit.
My plan is to carefully remove the old consumer unit tails from the
live terminals using an insulated screwdriver, then fit new consumer
unit and new tails.
My other problem:
The current wiring would not pass any sort of inspection, and I'm not
expecting to finish the rewiring very soon.
Q1: Who owns the junction box?
It is after the meter, but is sealed with wire and (old looking) lead
crimps. That might mean something official, or might be to discourage
me from the above dangerous manouver.
Q2: What exactly is inside the junction box?
Bakelite box, about 4" x 3". The meter tails enter on the bottom-right
one in front of the other (ie in a plane perpendicular to the wall)
and the consumer unit tails exit on the bottom-left, similarly one in
front of the other.
I'd doubt that it doesn't have a fuse, what's on the end of the incoming
cable? Our 1930s place had a metal "head" on the end of the cable, the
fuse was in there - although it didn't look like it...
LEB (as was) was quite happy to change it to a modern plastic
At least removing the tails from the junction box is considerably safer
than trying to do it with live tails from the meter ;)
Your procedure sounds high risk to me.
There should be a fuse on the incoming, maybe you haven't found it yet.
I'd ring your elec supply company and ask them to fit one pronto if there
The only downside of this is they may well condemn your wiring if they see
AFAIK the junc box after the meter is yours to do with what you like.
What the elec companys do care about is any tampering with the meter seals.
They don't seem to care if you remove those on the fuse before it.
Eeeeeeek! You (or I) *really* don't want to be doing that. "Live working"
is something to train for carefully, needing planning ("what if the wire
springs back, what will it touch") and well-tested tools and kit (VDE-rated
insulation, thick insulating mat). It's a *really**really* poor idea to
improvise. Even more so on an installation you're already saying is
(to use a technical term of art) crap.
Rather than a "big bang" changeover, many competent d-i-y'ers do the
"new CU" thing by running brand new wiring to a nice shiney new CU alongside
the old one, and feed the new CU's incomer from a suitable way in the old
one (30A or 40A rated) - diversity-for-real is your friend here - to allow
new and old circuits to both run during the week or five it takes to
do the job in evenings/weekends, while having power for joist-drilling
and the like!
But if you really have 60-yr-old rubber-covered cable, you're likely to
find it breaking off the cable as soon as you wiggle it even a bit. Are
you sure you can't scrape up the cash to do something safer - maybe
run new circuits for one or two "essential" power rings and lighting,
wired in to a lots-of-room-for-future-circuits new CU, then get a friendly
local electrician to connect it up (and cast an eye over your earthing
arrangements), leaving you to put in further circuits at your leisure?
I'd really not want to be living in, or responsible for, a house with
the wiring in the state you suggest...
It's really quite massively unlikely that you don't have a supply fuse
(conceivable, yes, but barely so); perhaps this Junction Box is indeed
a supply fuse and neutral link? How deep (front-to-back) is this
mysterious Box? Have you looked for a supply fuse further back from
the supply cable? (At this age I'd expect the supply cable to be a
tar-impregnated lead-sheathed thing: are you saying the inner conductors
emerge from that directly into the meter?) Maybe there's a supply fuse
further back, possibly at a previous meter location?
I've guessed at it being a supply fuse, incorrectly positioned beyond
the meter; but it sounds a bit small for that - and even in the 30s few
sparkies would muddle them up this way - so it could indeed be an
old Henley block (maybe put in when replacing a bunch of ancient-style
fuseswitches with whatever CU-substitute you now have... but haven't
had a chance to describe...)
Let me discourage you again from trying to keep this installation
struggling on: better to put up with a pain in the cash flow and
running with fewer, but safe, circuits for a while, than disturb the
old perished stuff which (from personal experience) starts to flake
off most worryingly when disturbed.
On 27 Oct 2003 14:33:51 GMT, firstname.lastname@example.org wrote:
I'd second everything that Stefek has said. *If* you have old PBJ (poly
butyl jute) Lead-Ins and no main fuse, contact your local distribution
company and tell them what you think the arrangement is. They are
required by statute to have a suitable means of fusing to protect your
property in the event of a fault in the meter or the tails to and from
the meter. Make sure you tell them that in your opinion you think their
installation is unsafe and needs inspecting as soon as possible. They
will also replace the lead in cables at their expense if they don't meet
modern safety requirements.
The only catch with this is that they also have a mandate not to
connect a supply to a system they consider unsafe, which yours
almost certainly is. One way of dealing with this is as follows:
(1) Install nice new consumer unit alongside.
(2) Install one 13A socket from the new consumer unit.
(3) Ask your supplier to come and make their supply safe,
connecting up to the new consumer unit.
They should now come and replace the dodgy setup, and
will probably upgrade the meter to a nice small one at the
same time. Depending on the electricity board they might
even fit a 100A isolator between the meter and the new
consumer unit. They will test your circuit to see if it is safe
(should be OK with only one 13A socket!), and off they go.
Now, you can run the old fusebox off a 40A circuit in the
new one (the other way round to what Stefek said). This
way all new circuits can come off the new CU as you fit
them, and eventually you just remove the old fuse box.
PS The 13A socket idea isn't mine - I read it on here a while ago.
On Mon, 27 Oct 2003 16:36:29 -0000, Al Reynolds wrote:
It may have changed, but the wording was something like 'where they are
prima facie satisfied that a danger to the public exists'. Unless things
have changed significantly in the last 7 or 8 years, no leccy company
will be too anxious to disconnect a supply unless it really is
dangerous, and not just old.
I thought the OP said he was going to remove the tails from the Henley
block, surely the tail won't actually be live once it's removed from the
block will it?
Or am I missing something obvious?
Agree with the point about the rest of the installation though, probably
best not to actually attempt to connect any of it back up... ;)
No, but... assuming it's a Henley block, he's still got to do
honest-to-goodness Live Working to get his tails *out* of the Henley
Block (or whatever it turns out to be), working with the thing open,
giving the securing screws *plenty* of heft (we hope they've been done
up tighter than the proverbial aqautic bird's back passage, right?), all
in an environment of known crapness and uncertain vintage. And then another
bout of Live Working when putting the new tails back into the aging
Henley-or-whatever. And there's allegedly no supplier fuse on this incoming
feed; so if there's a short on the new installation (we haven't heard the
poster make reassuring noises about taking a trusty low-ohms multimeter to
the new final circuits, have we?), the opportunity for flying shards of
damn hot copper and *severe* embarassment seems excessive.
Keen as I am on competent d-i-y'ing unencumbered by trade-body-monopoly
stuff, I do view Live Working as firmly on the *wrong* side of the
have-a-go line, and definitely in the category of "if you have to
ask, you don't have the knowledge to be safe". Asking is good, as it
helps to turn a vague "I wonder if I could get away with..." into a
firm and better-motivated "bloomineckerslike, off to Stores for another
of those Poles, Barge, Wooden, Full-length, Touching, For The Avoidance
DIY could turn into DOA if you've to make changes to a live mains supply. A
supply without a consumer fuse is a definite "get in touch with the
supplier" scenario to me. I too, like Stefek, would get a big long barge
Stefek Zaba wrote
| "bloomineckerslike, off to Stores for another of those
| Poles, Barge, Wooden, Full-length, Touching, For The
| Avoidance Of" implements.
Poles, Barge, Wooden, etc, no longer comply with the HSE requirements for
avoiding live working. They have to be Poles, Barge, Fibreglass, etc, now.
... is clearly a bog-standard 2-pole Henley block. In the past (pre the
coming of the consumer unit concept) they were often provided by the supply
co. in order to connect additional fuseboxes and were routinely sealed,
being part of the suppliers' works.
Just what I was thinking. The main fuse(s) must be there somewhere and my
guess is that it will turn out to be a pre-1937 cut-out with a fused
neutral. Sometimes these had really tiny fuses in - 15A or so!
If this is the case the cut-out, and just about everything else on the
supplier's side is likely to be seriously undersized - so any hope of just
connecting in to the block sounds a bit optimistic. The correct procedure
(AIUI & IME) is to consult with the supplier (the supply network operator)
regarding the need for upgrading of their side , then complete your new
installation - which must include inspection and testing and completion of
an electrical installation certificate to BS 7671. You can then call them
out to do their side and connect your new tails at the same time. Now that
the ESQC regulations are in force you won't get connected without the
certificate; the days when 'the board' would do the testing for you are long
since gone. But YMMV; it can depend on who you get.
 This is a good time to consider earthing arrangements, and check what
will be offered. If the service cable has to be replaced you'll almost
certainly be offered PME (TN-C-S) so you can base your new design on Ze 0.35 ohm. If an older cable is retained then TN-S conditions may obtain,
with Ze = 0.8 ohm.
Not necessarily - under the supply regs they`re not obliged to provide an
earth, and cutouts are usually replaced "like for like" without altering
existing earthing arrangements.
In our area, providing an earth is now a chargeable job.
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I think also you may be expecting a more 'sophisticated' situation
than there is in reality. When our supply was undergrounded a couple
of years ago the chap who actually made the connection said to me
'would you like an earth terminal?' to which I said yes without really
Since the existing installation was TT and, on inspection, the 'earth
terminal' was a TN-C-S (PME) one I have actually not used it as I know
that our earth bonding isn't up to the standards required by a PME
The undergrounding was done very well by the way and the installers
(24/7) were very helpful to me, they dug an extra trench to allow the
meter to be moved into the garage (from being a box on a pole outside)
and left me some bits and pieces to finish off my bit of underground
cable to the house.
What was missing was a proper interface to 'the electricity company'
which of course no longer really exists.
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