My electricity board recently fitted a double pole isolator after the
meter. The tails go to a Henley block and then to 2 CUs: one for the
house and one for the workshop and outbuildings. With the external
isolator, do the CUs still need their own isolators or can I save the
space and use it for a couple of MCBs?
On 03/01/18 03:19, firstname.lastname@example.org wrote:
Given you'll need terminals on teh busbar, you won't save any space as
terminals will probably take up a module each.
But in a more general sense, it would be good practise even if not
strictly required - people expect to find a main switch there and the
electricty co could remove theirs when they felt like it, leaving you
without a single point of isolation.
Fair point - though I wonder how they keep track of which company owns
what. Our DNO (UK Power Networks) say they don't own supply side
isolators unless they agree to do so and they are labelled as theirs.
We paid BG to fit it when they were both supplier and meter operator and
they're now neither. I suppose it could be the new meter operator.
Perhaps I ought to ask in case it get's stolen one day.
reply-to address is (intended to be) valid
They grumble a bit, but seeing as it's my board (as in I paid for it and
have to maintain it), they don't usually push that point. The main thing
is they might refuse to say upgrade your meter if it won't fit due to
your stuff being in the way.
But in reality, meter fitters are not unreasonable.
Silly question - or maybe not. When the electricity company needs to do work
on your wiring upstream of the consumer unit (and more specifically,
upstream of their company fuse) how do they isolate the power so they can
safely cut/join/move the wires - eg if the customer is moving their CU and
And similarly, when a new house is built and the builder has installed all
the wiring up to and including the CU, and the electricity board is ready to
connect it to the street wiring, how do they isolate their wiring to make
the final connection safely, especially if the feed comes as a tap from a
set of overhead wires? Is there a designated disconnection point between the
communal wiring and the company fuse? Obviously if the electricity company
disconnects your supply because you haven't paid the bill, they pull the
company fuse, but my question is about work on the wiring upstream of that.
Can they safely cut/join live wires provided they are suitably insulated? I
suppose if they make sure the CU is turned off, there will be no current
drawn so no spark.
When I first started work repairing radios and TVs, the shop
and workshops were in the process of being extended to the
rear. The incomer ran beind the original building line to/from
the shops on either side.
When the building work was finished there was a hole left in
the shop floor where the cable pased through and to which the
feed to our new consumer unit was.
A chap turned up from the electricity board with his tools and
little rubber mat which he placed over the edge of the hole.
He then sat down and merrily spliced our new feed into the
supply while we all looked on muttering things like: "Sod that
for a game of soldiers!"
When he left we went back to work on all those live chassis
TVs. As many of them had non-poarised two pin connectors on
the inputs, there was always a 50% chance that the entire
chassis was connected to the live side of the mains.
Did we ever check? Never!
After our recent move I got a panic phone call in the pub from
my wife because all the power had gone off! When I suggested
she look outyside the front door she found the entire street
in darkness, so not much I could do about it!
The pub was on the other side of the main road and not
affected so it was business as usual. When I left, there was a
lorry with a cherry picker beside a power pole on the other
side of the road which, I found, was blocking the footpath so
pedestrians were being shepherded along the edge of the road.
I enquired as to what was wrong and was told a transformer had
failed and all the power was being switched to another one.
Sure enough, half the street lights came back on as I was half
way down the road and, unbeknown to me, the power in our road
had already been restored but it didn't go off again so the
chap up the pole was obviously splicing all the feeds live.
Not silly and as my old man was an LEB engineer, I can answer that:
They don't for Low Voltage - it's all done live (LV = 230/400V 1-3 phase).
High Voltage (eg 11kV and up) is isolated at the switching equipment and
bonded to earth at both ends before anyone touches anything.
In my dad's time, they hot soldered the cables using two ladles and a
bucket of solder on a gas burner, whilst sitting on a rubber mat. The
joint was potted in hot bitumenous compound.
Think it's crimped or clamped now and the bitumen has been replaced by 2
Sure there are some YT vids: search for "street cable jointing" or
When they uprated the company fuse here, they also replaced the
cast-iron fusebox with a hard plastic one. They simply donned thick
rubber gloves, smashed the cast-iron box with a lumphammer, dropped the
new box on, made the connections and resin-filled the cable entries.
On Wednesday, 3 January 2018 03:19:42 UTC, email@example.com wrote:
I think consumer units contain main switches by definition and as part of their type approval, otherwise they'd be fuseboards or distribution boards, going back to olden days when fuseboards didn't have main switches.
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