On Sat, 23 Aug 2008 17:59:54 -0700, meow2222 wrote:

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]]

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