Hi all,

We finally moved into our doer-upper house last Monday and, working my
way down a very long list of jobs, I've come fit a new CU in order to
get RCDs and a cooker circuit. The job is getting pretty urgent because
we're all getting cheesed off with takeaway food. It's only a temporary
fix I'm after - all of the final circuits are going to go when I do a
complete re-wire some way further down the job list.

The original plan was to site the new CU where the old fusebox was in
the bottom of a cupboard in the kitchen. In-case some of the wiring
needed extending inside the new CU, I bought some butt crimps and one of
these:-

http://www.tlc-direct.co.uk/Products/DVDHCR15.html

Of course, now I've got into the house, I've decided not to put the new
CU where the old one was, but to move it to the opposite side of the
wall, and at the top instead of the bottom. The new tails are going to
end-up 2.5M long. I've stuck with the previous 16mm^2 for the tails and
upgraded the CU earth to 16mm^2. It's a TN-C-S system.

The new CU is now in and I'm currently wiring up the extension wires to
it. Back at the meter, I'm left with this :-

http://www.stamp.plus.com/Photos/FuseBox.jpg

Tomorrow, I'll take the plunge, rip out the fusebox and connect the
extensions to the old soon-to-be-disused final circuits. My question is
how to make the connections. The easiest way would seem to be to use the
crimps I've already got, gut the old fusebox and put it back to enclose
the mess. Any ideas on a better way to do it?

Cheers,

Colin.

"Colin Stamp" wrote in message
o.uk...
Hi all,

We finally moved into our doer-upper house last Monday and, working my way
down a very long list of jobs, I've come fit a new CU in order to get RCDs
and a cooker circuit. The job is getting pretty urgent because we're all
getting cheesed off with takeaway food. It's only a temporary fix I'm
after - all of the final circuits are going to go when I do a complete
re-wire some way further down the job list.

The original plan was to site the new CU where the old fusebox was in the
bottom of a cupboard in the kitchen. In-case some of the wiring needed
extending inside the new CU, I bought some butt crimps and one of these:-

http://www.tlc-direct.co.uk/Products/DVDHCR15.html

Of course, now I've got into the house, I've decided not to put the new CU
where the old one was, but to move it to the opposite side of the wall,
and at the top instead of the bottom. The new tails are going to end-up
2.5M long. I've stuck with the previous 16mm^2 for the tails and upgraded
the CU earth to 16mm^2. It's a TN-C-S system.

The new CU is now in and I'm currently wiring up the extension wires to
it. Back at the meter, I'm left with this :-

http://www.stamp.plus.com/Photos/FuseBox.jpg

Tomorrow, I'll take the plunge, rip out the fusebox and connect the
extensions to the old soon-to-be-disused final circuits. My question is
how to make the connections. The easiest way would seem to be to use the
crimps I've already got, gut the old fusebox and put it back to enclose
the mess. Any ideas on a better way to do it?




I know that this doesn't answer your question in any way but I could not
resist asking
was there a specific reason why you clipped all of the cables individually
to the wall rather than using a length of trunking?

On 27/01/12 15:08, TMC wrote:

I know that this doesn't answer your question in any way but I could not
resist asking
was there a specific reason why you clipped all of the cables
individually to the wall rather than using a length of trunking?

I had clips but I didn't have any trunking. I actually prefer the look
of the cables too - it appeals to the engineer in me. Also, I don't need
to worry about de-rating the cables.

It's a temporary job, by the way. After the re-wire, only the tails and
earth will remain.

Cheers,

Colin.

In article ,
Colin Stamp writes:
Hi all,

We finally moved into our doer-upper house last Monday and, working my
way down a very long list of jobs, I've come fit a new CU in order to
get RCDs and a cooker circuit. The job is getting pretty urgent because
we're all getting cheesed off with takeaway food. It's only a temporary
fix I'm after - all of the final circuits are going to go when I do a
complete re-wire some way further down the job list.

The original plan was to site the new CU where the old fusebox was in
the bottom of a cupboard in the kitchen. In-case some of the wiring
needed extending inside the new CU, I bought some butt crimps and one of
these:-

http://www.tlc-direct.co.uk/Products/DVDHCR15.html

Of course, now I've got into the house, I've decided not to put the new
CU where the old one was, but to move it to the opposite side of the
wall, and at the top instead of the bottom. The new tails are going to
end-up 2.5M long. I've stuck with the previous 16mm^2 for the tails and
upgraded the CU earth to 16mm^2. It's a TN-C-S system.

The new CU is now in and I'm currently wiring up the extension wires to
it. Back at the meter, I'm left with this :-

http://www.stamp.plus.com/Photos/FuseBox.jpg

Tomorrow, I'll take the plunge, rip out the fusebox and connect the
extensions to the old soon-to-be-disused final circuits. My question is
how to make the connections. The easiest way would seem to be to use the
crimps I've already got, gut the old fusebox and put it back to enclose
the mess. Any ideas on a better way to do it?

I would install the new CU and connect the tails to it.
I would fit a suitably high current spare MCB or MCBO in the new
CU, and use that to daisy-chain to the old CU with suitably thick
cable, until such time as the old CU and wiring it all ripped out.
Don't run any high current load such as a hob or shower via the
old CU though.

BTW, have you really left the installation with exposed live
conductors (which is not safe even temporarily), or is the main
fuse removed?

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 27/01/12 15:59, Andrew Gabriel wrote:

I would install the new CU and connect the tails to it.
I would fit a suitably high current spare MCB or MCBO in the new
CU, and use that to daisy-chain to the old CU with suitably thick
cable, until such time as the old CU and wiring it all ripped out.

I must admit, I hadn't thought of that, but I'd rather continue with my
current scheme and get a proper two RCD setup until the big re-wire.

Don't run any high current load such as a hob or shower via the
old CU though.

I'm just putting in the temporary cooker circuit now, direct from the
new CU and all surface wired across tiles. It's going to look really
pretty. ;o)


BTW, have you really left the installation with exposed live
conductors (which is not safe even temporarily), or is the main
fuse removed?

When I took the photo, The lid was off so I could count how many cables
I'd need to extend. It's back on now until I work out how to make the
connections.

Cheers,

Colin.

On 27/01/2012 13:58, Colin Stamp wrote:

The new CU is now in and I'm currently wiring up the extension wires to
it. Back at the meter, I'm left with this :-

http://www.stamp.plus.com/Photos/FuseBox.jpg

Tomorrow, I'll take the plunge, rip out the fusebox and connect the
extensions to the old soon-to-be-disused final circuits. My question is
how to make the connections. The easiest way would seem to be to use the
crimps I've already got, gut the old fusebox and put it back to enclose
the mess. Any ideas on a better way to do it?

The short answer is yes, if you really want the circuits fed via
dedicated MCBs on the new CU, then you could make crimped connections
and use the old CU just as a "box" to enclose them.

However personally, I would not bother linking all the existing circuits
through to the new CU, I would either:

1) Install a henley block near the old CU. Take the existing tails into
the Henley, and then new short tails from there to the old CU, and also
connect your long new tails to the new CU. So you have both CUs
connected and working. Then as you migrate circuits, connect them to the
new CU. When all complete, simply remove the old CU and its connection
to the Henley.

or

2) As above with henley, but only connect the existing tails to the new
long ones. Then run a single high power submain from the new CU (say a
45A circuit (RCBO if you want)), to the incomer of the old one).


(it depends a bit on how long this temporary arrangement is going to last)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 27/01/12 17:31, John Rumm wrote:

The short answer is yes, if you really want the circuits fed via
dedicated MCBs on the new CU, then you could make crimped connections
and use the old CU just as a "box" to enclose them.

However personally, I would not bother linking all the existing circuits
through to the new CU, I would either:

1) Install a henley block near the old CU. Take the existing tails into
the Henley, and then new short tails from there to the old CU, and also
connect your long new tails to the new CU. So you have both CUs
connected and working. Then as you migrate circuits, connect them to the
new CU. When all complete, simply remove the old CU and its connection
to the Henley.

or

2) As above with henley, but only connect the existing tails to the new
long ones. Then run a single high power submain from the new CU (say a
45A circuit (RCBO if you want)), to the incomer of the old one).


(it depends a bit on how long this temporary arrangement is going to last)

The original plan was to get to the re-wire quite early since the whole
house currently needs heavily re-decorating but, knowing how these
things go, it could take a while before I get round to it. Loads of
"urgent" jobs have materialised that I wasn't expecting...

The submain option is tempting, making one of the RCDs in the new CU a
whole house one for a while, but I would like to give it some more
17th-ish leanings until the re-wire. The clincher is that the extension
wiring is all done now. Perhaps I should have asked the question before
starting the job ;o)

Anyway, it's good to hear that crimps in the shell of the old fusebox is
a reasonable way to go. Hopefully, a morning of crimpage tomorrow will
see us all up and running on the new CU. It'll have to - the in-laws are
coming in the afternoon. We've dug out the camping stove just in case...

Cheers,

Colin.

On 27/01/2012 21:35, Colin Stamp wrote:
On 27/01/12 17:31, John Rumm wrote:

The short answer is yes, if you really want the circuits fed via
dedicated MCBs on the new CU, then you could make crimped connections
and use the old CU just as a "box" to enclose them.

However personally, I would not bother linking all the existing circuits
through to the new CU, I would either:

1) Install a henley block near the old CU. Take the existing tails into
the Henley, and then new short tails from there to the old CU, and also
connect your long new tails to the new CU. So you have both CUs
connected and working. Then as you migrate circuits, connect them to the
new CU. When all complete, simply remove the old CU and its connection
to the Henley.

or

2) As above with henley, but only connect the existing tails to the new
long ones. Then run a single high power submain from the new CU (say a
45A circuit (RCBO if you want)), to the incomer of the old one).


(it depends a bit on how long this temporary arrangement is going to
last)

The original plan was to get to the re-wire quite early since the whole
house currently needs heavily re-decorating but, knowing how these
things go, it could take a while before I get round to it. Loads of
"urgent" jobs have materialised that I wasn't expecting...

Often the way ;-)

The submain option is tempting, making one of the RCDs in the new CU a
whole house one for a while, but I would like to give it some more
17th-ish leanings until the re-wire. The clincher is that the extension
wiring is all done now. Perhaps I should have asked the question before
starting the job ;o)

Well possibly. What you propose is ok, but perhaps more work than was
required...


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 27/01/2012 15:08, TMC wrote:

I know that this doesn't answer your question in any way but I could
not resist asking was there a specific reason why you clipped all of
the cables individually to the wall rather than using a length of
trunking?

Grouping factors. The rating factor for nine cables, bunched and
enclosed is 0.5 [Table 4C1]. Given that the rating for 2.5 mm^2
enclosed in conduit or trunking is 23 A [Table 4D2A], this gives an
as-installed rating of only 11.5 A - quite some way short of the 20 A
required for a ring circuit.

Bundling all the cables leaving a CU into a piece of 2x2 trunking is
commonly seen, but isn't necessarily compliant.

--
Andy

Colin Stamp wrote:
Of course, now I've got into the house, I've decided not to put the new
CU where the old one was, but to move it to the opposite side of the
wall, and at the top instead of the bottom.

Can I ask why you don't want the CU next to the meter?

JGH

On 28/01/12 04:44, jgharston wrote:
Colin Stamp wrote:
Of course, now I've got into the house, I've decided not to put the new
CU where the old one was, but to move it to the opposite side of the
wall, and at the top instead of the bottom.

Can I ask why you don't want the CU next to the meter?

It's not that I don't want it near the meter. If it had stayed where it
was, it would have ended up really inaccessible when we re-do the
kitchen. Ideally, the meter would move too but I bet that costs...

Cheers,

Colin.

On 27/01/12 23:15, John Rumm wrote:

Well possibly. What you propose is ok, but perhaps more work than was
required...


Yep. I sort-of led myself into the current scheme, since I was initially
going to put the new CU where the old one was, so the old one had to go.
More haste, less speed...

I do still like the idea of having the new CU fully up and running from
the outset though.

Right then. Let the crimping begin.

Cheers,

Colin.

Colin Stamp wrote:
It's not that I don't want it near the meter. If it had stayed where it
was, it would have ended up really inaccessible when we re-do the
kitchen. Ideally, the meter would move too but I bet that costs...

Looking at the photo, you've got one of those dinky modern ones and
the supply is PVC sheathed, not brittle lead'n'paper, so it should
be easily movable at some future point, especially as the backboard
is screwed to the wall with accessible screws. Try to arrange
whatever encloses it in such as way that somebody can moderatly
easily get the backboard off the wall and shift the lot en mass to
a new position.

JGH

Andy Wade wrote:

On 27/01/2012 15:08, TMC wrote:

I know that this doesn't answer your question in any way but I could
not resist asking was there a specific reason why you clipped all of
the cables individually to the wall rather than using a length of
trunking?

Grouping factors. The rating factor for nine cables, bunched and
enclosed is 0.5 [Table 4C1]. Given that the rating for 2.5 mm^2
enclosed in conduit or trunking is 23 A [Table 4D2A], this gives an
as-installed rating of only 11.5 A - quite some way short of the 20 A
required for a ring circuit.

Bundling all the cables leaving a CU into a piece of 2x2 trunking is
commonly seen, but isn't necessarily compliant.


But those derating factors assume all the cables are simulatenously fully
loaded IIRC, which is unlikely in a domestic setting - given that the sum of
the beaker capacities could easily exceed the main fuse capacity.

I must admit, I am unsure how to formally allow for diversity WRT grouping
factors - other than if the sum of the circuits is say 150A and the supply
is 100A then in the case above, factor for a grouping of 6 cables.

Is there a formal approach?


--
Tim Watts

On 28/01/12 09:47, Colin Stamp wrote:

Right then. Let the crimping begin.

All done, Just before the in-laws arrived )

Here it is, in all it's glory:-

http://www.stamp.plus.com/Photos/Crimps.jpg

And the new CU:-

http://www.stamp.plus.com/Photos/NewCU.jpg

We're all up and running again and we have a cooker now )

Right then, a couple of dozen little jobs and then TRVs next, I think...

Cheers,

Colin.

On 28/01/12 12:18, jgharston wrote:

Looking at the photo, you've got one of those dinky modern ones and
the supply is PVC sheathed, not brittle lead'n'paper, so it should
be easily movable at some future point, especially as the backboard
is screwed to the wall with accessible screws. Try to arrange
whatever encloses it in such as way that somebody can moderatly
easily get the backboard off the wall and shift the lot en mass to
a new position.

Yep. I'll try and keep it vaguely accessible. It'd be nice to get it
moved to the outside of the wall eventually. I'll have a think when I do
the kitchen...

Cheers,

Colin.

On 28/01/2012 18:20, Colin Stamp wrote:

On 28/01/12 09:47, Colin Stamp wrote:

Right then. Let the crimping begin.

All done, Just before the in-laws arrived )

Here it is, in all it's glory:-

http://www.stamp.plus.com/Photos/Crimps.jpg

Well done! (you can stick the old fuse carriers on ebay now ;-)

And the new CU:-

http://www.stamp.plus.com/Photos/NewCU.jpg

We're all up and running again and we have a cooker now )

Right then, a couple of dozen little jobs and then TRVs next, I think...

;-)



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 28/01/2012 15:19, Tim Watts wrote:

But those derating factors assume all the cables are simulatenously fully
loaded IIRC, which is unlikely in a domestic setting - given that the sum of
the beaker capacities could easily exceed the main fuse capacity.

I certainly agree with your drift. Domestic load factors are generally
low and the probability of having several circuits simultaneously
heavily loaded is low - unless there is an extensive space heating
installation. Even so, I don't think that it's a good idea to throw
all the outgoing cables in to one piece of trunking, without further
thought.

I must admit, I am unsure how to formally allow for diversity WRT grouping
factors - other than if the sum of the circuits is say 150A and the supply
is 100A then in the case above, factor for a grouping of 6 cables.

Is there a formal approach?

Not that I'm aware of, other than the full sizing procedure in Appendix
4 (of BS 7671). Section 7.2.1. in the OSG sets out some rules which, if
followed, mean that "derating for grouping is not necessary." Heating
and water heating circuits are excluded and the cable installation
conditions are constrained to avoid any bundling.

By the way the assessed FLC for an installation is the diversified sum
of the individual design currents (Ib), rather than of the OPD ratings
(In). There's no difference for the standard socket circuits, but for
most others there is.

--
Andy

On 28/01/2012 22:48, Andy Wade wrote:
On 28/01/2012 15:19, Tim Watts wrote:

But those derating factors assume all the cables are simulatenously fully
loaded IIRC, which is unlikely in a domestic setting - given that the
sum of
the beaker capacities could easily exceed the main fuse capacity.

I certainly agree with your drift. Domestic load factors are generally
low and the probability of having several circuits simultaneously
heavily loaded is low - unless there is an extensive space heating
installation. Even so, I don't think that it's a good idea to throw all
the outgoing cables in to one piece of trunking, without further thought.

I must admit, I am unsure how to formally allow for diversity WRT
grouping
factors - other than if the sum of the circuits is say 150A and the
supply
is 100A then in the case above, factor for a grouping of 6 cables.

Is there a formal approach?

Not that I'm aware of, other than the full sizing procedure in Appendix
4 (of BS 7671). Section 7.2.1. in the OSG sets out some rules which, if
followed, mean that "derating for grouping is not necessary." Heating
and water heating circuits are excluded and the cable installation
conditions are constrained to avoid any bundling.

Our summary of those references he

http://wiki.diyfaq.org.uk/index.php?..._for_Diversity

By the way the assessed FLC for an installation is the diversified sum
of the individual design currents (Ib), rather than of the OPD ratings
(In). There's no difference for the standard socket circuits, but for
most others there is.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/