Cable entry up thro C-shaped board into rear of MK CU IP2x

[Jason1961]

For domestic CU, cable entry must be performed with regard
to 412-03-02 for top most surface (IP4x, 1mm dia sphere) and
412-03-01 for sides/bottom surface (IP2x, 12.5mm dia sphere).

MK specified, but their CU is IP2x rated.
Only the MK 12-way fits the narrow alcove in dedicated cupboard.
DNO has advised they can not move SH/Meter more to the left.
Easement permits CU. I will not fit CU vertical (as previous).


I will not use top-entry with the MK CU.
Meter tails will enter LHS, the smaller cutout approximates
well to twin 25mm leaving partial voids well below 12.5mm.

All circuits will enter the REAR - which presents a problem.
The CU will be mounted to C-shaped varnished ply onto the existing
board. Open part of the C-shape faces the floor, permitting cables to
be pushed up & thro the large rear cutouts into the CU.

The C-shaped opening creates a void behind the CU >12.5mm, but it
is "not easily accessible" & could be closed with UL94V0 foam strip.

Anyone see anything wrong w/ proposed installation re 412-03-01?


Hager provide tacky bits of foam to contribute to IP4x.
Trunking is impractical, loose cables were a right mess in the
cupboard but once tidied have achieved an N=0 Cg separation.

 

[Jason1961]

Well MK say ok, no-one here nor they can suggest better.

It is now somewhat moot.
Sitting with the DNO in the alcove we both came to the
conclusion that whilst a horizontal CU is conventional &
does fit, the limited space suggests it is less acceptable
than vertical. All previous DB were installed vertically.

MK technical authorise vertical use where an installation
would be more acceptable through physical space restriction.
Additionally BS7671 does not prevent it. MG & Hager also
recommend it for similar situations, as 3-phase boards.

Brought to you by an architect making alcoves too narrow.
Solid floor, no way to move CU (bathroom/toilet/chimneys/gas).

So vertical it will be as previous.
I can improve on that by still using rear entry over a
C-shaped board with final circuit cables entering the side.
Removes existing mismash of cables & borderline IP2x K/O.

Off to see if there is a better vertical DB unit...

 

[Steve]

You swallowed a reg book?

Do you know what you're bleating on about? 'cos I haven't a clue!

Perhaps this is why nobody has replied.

By the way, you
dont have to keep
pressing enter to
start a new line
the forum software
wraps text for
you.

Reg
ards

S
te
ve

 

[Jason1961]

Heh - not all forums handle line wrapping correctly

My post was a little cryptic.


Regulations...
For a cable to enter any enclosure you must make a hole.
That hole must be sealed to one of two BS7671 standards.
412-03-02 requires holes in the top be protected to IP4x,
which means that a 1mm sphere can not pass through.
412-03-01 requires holes elsewere be protected to IP2x,
which means that a 12.5mm sphere can not pass through.

There is an exception based on "readily accessible".
For example you may need to meet IP4x on top entry holes if
you jam the CU 7ft up in the air 3mm off a ceiling surface.


MK Consumer units...
MK insulated CU use plastic cutouts in the top to IP2x rating.
From the above standards you can not pass a flat cable through a top
cutout and achieve the required IP4x rating. You have to use trunking
or create a ghastly mess with silicone or foam tape. It is probably
the most commonly broken regulation with MK CU.


Solutions...
1. Use a Hager CU which has IP4x on top by use of foam strips.
2. Fit MK CU to a thin board to block the open rear cutouts and then
mount CU/board to batons to space it 12mm off a wall. Feed cables
into the 12mm gap and into the lower rear cutouts. The 12mm space
ensures it passes the IP2x 12.5mm sphere test.

Some people do not bother with the board and just mount the CU
on 12mm batons. I do not like that re "fingers into the rear", hard
to describe but if you open an MK CU it will be obvious.

The 12mm space can be sealed with polyurethane foam strip to
fire retardancy DIN 4102 part 1, B1 (common intumescent std).



Earlier today I believed there was too little space to mount
the CU horizontally and leave an acceptable space around it.
Specifically space for 6491X cable bend radius into PME
service head Main Earthing Terminal (MET) access.

Wrong. Someone had stuck 12.5mm plasterboard on the wall to
hold up 23mm thickness totally blown plaster. I will not say
how this was found out, but we now have 23mm more space!


I said I was determined to get the CU mounted horizontally, despite
MK saying vertically is acceptable. Just need to refit two FTE 2.5mm
CSA cables, otherwise they turn 90-degrees out of brick within 24mm
against the CU side. Within Prysmian 4D min bend radius (minor axis)
but working to such tightness is not really acceptable.


The blown plaster was caused by someone fitting an SWA thro that
wall, with internal gland, inaccessible for inspection & testing, angled
DOWNWARDS from the outside, without a drip loop, and patched up
by adding plasterboard over the top. Why do people do it...