On Sat, 29 Aug 2015 19:20:03 +0100, NY wrote:

"ARW" wrote in message
...
"Tough Guy no. 1265" wrote in message
news
On Sat, 29 Aug 2015 17:20:18 +0100, ARW
wrote:

I have no reason to believe a sparky went in there, all a sparky did
was
fit an electric shower, switching off the master switch on the fusebox
inside the house would have sufficed.

Well the sparks would need to see what sort of supply it was if he was
going
to fill in an electrical installation certificate for the shower.

What information could he possibly get from the meter box that would be
applicable to installing a shower? Everything he needs to connect to is
in the consumer unit, and labelled for him.

Let's see.

Type of supply (ie earthing arrangements), number and type of live
conductors, details of protective device.

More than you think.

All of that information may well be available at the "fuse box" (consumer
unit), without needing to visit the master fuse and meter. In my present
house it's difficult to distinguish because both are in the same place, but
in my last house which had separate meter and consumer unit locations, the
RCD (protective device) was part of the consumer unit - unless for all
electrical installation certificates the electrician also needs to inspect
the master fuse (a wire fuse rather than an MCB or RCD). Is house earthing
usually via the meter installation rather than via the consumer unit? I
*think* I remember a fat green-and-yellow wire coming from the CU and going
to the cold water rising main under the sink.

When we had a new electric shower fitted in our present house, I don't
remember the electrician going to the meter/CU area - rather trustingly he
relied on me saying "I've turned off the master switch" - and yet he gave us
a certificate of installation.

I hadn't realised that certificate of installing a device involved doing a
sanity check on the rest of the electrical installation in the house that is
not specific to the device being installed. It's good if this is the case.

Would the electrician actually need to know that there was a three-phase
cable of which one phase was connected to a meter and the other two were
"blind ends", and distinguish that from the more normal case of one phase
supply?

In the case of three-phase supply where the customer only now uses one, is
the disconnection only at the customer's end, or do they also disconnect at
the overhead pole in the street? Assuming overhead rather than underground.
And if the wire every needed replacing would it tend to be replaced with a
two-core rather than three-core pole-to-house cable?

Our house is a terrace of three with three cables from the pole to the end
of the terrace, but three cables are fastened to the house wall from our
neighbours to us (middle of three) and one goes into our house but two
continue to our neighbour on the other side, whereas I'd expect two cables
on the incoming side and one on the outgoing side.

What is the normal arrangement for the number of adjacent houses which are
fed from the same phase? Do they tend to alternate phases with every house
or do they tend to feed several (eg three) houses from one phase, then feed
the next three from the next phase, etc.

I remember at work when our lab was rewired, every bench was fed from a
different phase and there were warnings not to connect equipment on one
bench (eg by RS-232, Ethernet, USB or other low-voltage data cable) to
equipment on another bench, which caused us horrendous problems.

That's a weird idea, you'd think they'd at least have each room on its own phase.

Although I can't see the problem. USB for example would have its ground the same as the appliances earth, which remains constant for all the phases.

--
On the topic of mobile phones:
Anything bigger than 4 inches is getting into the region where most people would have difficulty holding and using the device comfortably -- Callum Kerr, 2013.