On Aug 24, 1:59*am, wrote:
For your perusal...

Hopefully the final draft now, with lots of input added...


'''Pattress''' usually means the box that sits behind electrical
sockets and switches, though it has other meanings too. Modern
electrical pattress boxes come in metal and plastic, and in surface
mount and flush versions.


==Uses of the word 'pattress'==
'Pattress' has more than one meaning in DIY. Its also a word whose
meaning has changed relatively quickly over time, resulting in
significant disagreement over which meanings are correct.

===History===
[[image:Socket_(__)_785-4.jpg|thumb|old wood pattress plate]]

Pattress is derived from the latin 'pateras' meaning a shallow bowl or
plate.

In the 1800s 'pattress' was used to mean the flat wooden plates that
gas lighting equipment was mounted on.

In the 1930s electrical accessories were mounted on wooden plates, and
these were mainly referred to as 'pateras.' The anglicised version
'pattress' gradually took over from pateras.

When wiring regs required electrical accessories to be housed in
fireproof containers, a box was used between the wooden pateras and
socket, instead of mounting it directly to the pateras. This was known
as a pattress box. Over time this became known as a pattress.

Today many trade and DIY people refer to any electrical backbox as a
pattress. There are also many that consider only surface mount boxes
to be pattresses, and many that don't call any type of backbox a
pattress. Unfortunately this is equally true of the other names for
these things, so we just have to be aware of the differing usage of
the term.

The electrical boxes used behind sockets and switches are variously
known as pattresses, wiring accessory boxes, boxes, and backboxes,
with none of these terms being universal.


===Non-electrical pattresses===
The word 'pattress' also describes flattish iron plates used for load
spreading, as used to tie houses with structural defects together.



==Pattress types==

===Metal flush mount pattress===
[[image:Pattress metal 406-3|thumb]]
Metal recessed pattresses are used to mount sockets & switches flush
to a solid wall. A recess is chiselled out for the pattress to sit in.
Knockouts are provided for [[cables|cable]] entry. These are the most
common domestic pattresses.


===Plastic surface mount pattress===
[[image:Pattress dbl 759-4.jpg|thumb]]
Plastic surface mount pattresses are used for electrical accessories
that sit on the surface of walls. The pattress is [[screws|screwed]]
in place, and knockouts are provided for [[cables|cable]] entry,
either via the sides or the rear.

These are available in different depths. The shallowest ones are
suitable for light switches where no screw block connections need to
be made behind the switch. Deeper ones are usually used for sockets,
but fitting sockets into shallow patresses is often possible, if
tight, and light switches with a few screw block connections behind
them will need the deep ones too.

Plastic surface mounting patresses are the second most common domestic
type.


===Stud wall pattress===
[[image:Pattress PB 757-5.jpg|thumb]]
Plasterboard boxes are used to flush mount switches etc to [[Sheet
Materials|plasterboard]]. The picture shows the position of the grips
before and after fitting.


===Architrave pattress===
Architrave pattresses are used with little architrave switches.


===Metal surface pattress===
[[image:Metal skt & pattress 754-7.jpg|thumb]]
Metal surface pattresses aren't very common in homes. They are used
with metal accessories, and are ideal for workshops (and other
environments) requiring particularly tough accessories.


===Twin single pattress===
[[image:Twin pattress 849-4.jpg|thumb]]
Twin pattresses are designed to take two single accessories. These are
used when 2 different accessories in one position are wanted. These
are not the same size as a double pattress.


===Non-standard pattress===
[[image:Pattress ashley 758-5.jpg|thumb]]
Non standard pattresses are sometimes seen. These generally don't fit
standard sockets. They're designed to achieve some advantage, such as
styling or compact size.

===3 & 4 gang pattress===
3 way socket convertors use a pattress designed to [[screws|screw]]
onto the top of an existing single flush mount pattress. These turn a
1 way flush socket into a 3 way surface mount socket. Sometimes the
[[cables]] aren't long enough and need extending.

4 way socket convertors...


===Grid switches===
(pic wanted)
Grid switch pattresses are another type not often seen in homes. These
accept a number of accessories, which can be mixed at will in the one
box. Available accessories include various switches, dimmers, key
switches, indicators, etc. The accessories don't have any face plate,
a single full size faceplate is fitted last. MK is known for its grid
switch range.


===Round conduit boxes===
Round boxes forming part of a conduit system are sometimes seen in
houses, though not often.


==Junction boxes==
[[image: |thumb]]
[[Cables]] are often joined in pattresses, but their purpose is for
mounting switches and sockets. When a container is wanted only for
joining cables, a junction box is smaller & cheaper.

==Depth==
Plastic surface pattresses are widely available in different depths,
ranging from 16mm (mainly for switches) to 47mm (mainly for sockets).

Other types of pattress are also found in different depths, but less
often.


==Thermoplastic and Thermoset==
[[image: |thumb]]
Plastic pattresses intended for mains use are made from thermoset
plastics, mainly white bakelite. These don't soften when hot, and act
as a fire resistant container.

Similarly sized pattresses intended for phone networks are generally
made from thermoplastics. These come in more than one size, the larger
of which fits mains sockets. These can be bent slightly by hand, so
are easily recognised. They offer no heat or fire protection and don't
meet modern safety requirements for mains use.


==Style & fit==
[[image:Pattress corner detail Egatube & Tenby 850-4.jpg|thumb|Egatube
vs Tenby]]
Different brands of pattress have different corner detailing, intended
to match their own brand of accessories. Standard pattresses, switches
and sockets of different brands can be freely mixed, but the
difference in corner detailing can make a minority of combinations
look wrong. If mixing brands its best to check they look right
together before buying.

Non-standard pattresses can't be expected to fit standard sockets.

===Metal accessories===
[[image:Socket metal misfit 807-6.jpg|thumb|Oops!]]
Many metal accessories for surface mounting are a different size to
plastic pattresses. The screw spacing is the same, but the outer size
isn't. These are an eyesore if one type is fitted to the other.

This problem doesn't occur with the various retrofit metal accessories
on the market designed to fit standard plastic pattresses (and
recessed metal ones). It only applies to the traditional functional
metal sockets & backboxes.


==Breakage==
[[Screws]] holding plastic pattresses in place should be done up until
the screwhead touches the pattress surface, and no more. Any further
tightening is likely to break the brittle plastic.

Budget brand plastic pattresses can suffer a significant breakage rate
during installation, particularly if a fair amount of hole needs to be
made for [[cables|cable]] entry, or if the underlying wall is not
competely flat, or the installer doesn't appreciate their frailty.


==Earth connection==
Metal pattresses have an earth terminal for connecting to the circuit
earth. A sleeved wire should be run from the socket earth terminal to
the backbox.


===2 core wiring===
A small minority of houses still have old 2 core [[lighting]]
circuits. Metal pattresses or accessories should not be fitted to such
circuits due to the absence of anything more than functional
insulation as protection against shock.

Sometimes people fit them and borrow an earth from a nearby socket
circuit. This works but its not considered best practice, as there's
always the possibility of the socket circuit being decommissioned
later, leaving the [[lighting]] accessories unearthed. Hence its not
wiring regulations compliant.

Plastic pattresses and accessories are the only type recommended for
these circuits. However that doesn't imply that fitting them is always
safe; some [[Historic Mains Cables|historic rubber wiring]] is so
badly perished that moving the wires during fitting is sometimes a
sizeable risk. If perishing is limited to just the wire ends, sleeving
may be fitted to replace the function of the damaged insulation.


==Extension leads==
Surface pattress boxes are not designed for use on extension leads.
They have no cordgrip, and are brittle, which is not ideal for
portable use. Despite this they see fairly widespread use in extension
leads, so we will describe how to make these not-recommended leads as
safe as possible.

The main problem is the lack of cordgrip. There are 4 ways to
implement a cordgrip.
# Knockout 3 of the knockouts in a row on one side/top/bottom of the
pattress, and thread the lead through all 3 in a zigzag pattern. This
makes a fully effective cordgrip.
# The pattess box can be mounted on a piece of wood and a cordgrip
from a mains plug used to secure the lead inside the box. The 2 screws
go into the backing wood.
# Knotting the wire is sometimes used, but this is only partially
effective.
# A few surface pattress boxes do have cordgrips (eg Marbo).

Breakability can be reduced to some extent by mounting the pattress
box on a piece of chipboard that's larger all round than the box.
Chipboard and MDF are best as they're soft enough to reduce peak
impact forces.


==See Also==
* [[:Category:Electrical]]
* [[Special:Allpages|Wiki Contents]]
* [[Special:Categories|Wiki Subject Categories]]



[[Category:Electrical]]


NT