For your perusal...


A '''pattress''' is the box that sits behind electrical sockets and
switches. Pattresses come in metal and plastic, and in surface mount
and flush versions.


==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 [[screw]]ed 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 2nd 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===
[[image: |thumb]]
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===
[[image: |thumb]]
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===
[[image:...]]
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
pattress. 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.


==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.


==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, and will look an eyesore if fitted to each 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).


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

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 usually have an earth terminal for connecting to the
circuit earth.


===2 core wiring===
A small minority of houses still have 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.

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.


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



[[Category:Electrical]]