Wiki: Pattress

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember snipped-for-privacy@care2.com saying something like:

I see what you're getting at, but the pattress has always been just the wooden plate and the term 'pattress box' refers only to the surface box that would screw onto it. Lazy diction has led to a generation simply calling them patresses, missing the 'box' off - this may be worse in some parts of the country than others. Best to stick with the proper, traditional terms - damnit, we need standards these days.
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Dave
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Grimly Curmudgeon wrote:

There was an intermediate step between the wooden pattress and the modern surface mounting box.
Originally wiring accessories for surface mounting had terminals open at the back and were screwed to the wooden pattress. When the wiring regs introduced the requirement for all connections to be enclosed in fireproof material (12th or 13th edition?) many manufacturers introduced moulded mounting plates (aka back plates or pattresses) that could be used either on a wooden pattress or directly on a wall. Thus the wooden pattress started to disappear. The next step was the introduction of the surface mounting box as we now know it, enabling 'flush-mount' wiring accessories to be surface mounted.
I guess this is how common use of the term pattress passed from the wooden item to the surface mounting (pattress) box. There's no such continuity with flush mount wiring accessories and their metal back boxes, which were in use before the wooden pattress disappeared. That's why using pattress to refer to flush mounting boxes only confuses the issue and is quite wrong, IMHO.
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Andy

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Andy Wade wrote:

At one time, wooden boxes were used for flush mounting accessories, as well as for the construction of surface fuse boxes and the like.
Owain
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We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Andy Wade

Hah. I've come across some of those in in ancient installations. Another common one here are Bakelite cover / ceramic body incomer 2P switches on a distribution board. Still plenty of them in use here and were still being fitted in the late 60s - although I think in those cases it was the spark using new old stock to use it up.
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Dave
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On Sat, 23 Aug 2008 17:59:54 -0700, meow2222 wrote:

=================================http://www.redgwick.co.uk /
Cic.
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On Aug 24, 1:59am, snipped-for-privacy@care2.com wrote:

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
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wrote:

what are those white plastic spacers that can (Could) be bought to effectively increase the depth of a box by bringing the wiring accessory forward about 6mm?
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IIRC, called mounting frames.
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*Sometimes I wake up grumpy; Other times I let him sleep.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

Added, thanks. Just got the images to sort out now.
NT
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wrote:

Added, thanks. Just got the images to sort out now.
NT
Thanks - I was trying to refer to one recently but didn't know the name and couldn't find them.
http://www.tlc-direct.co.uk/Products/MKK2134.html
Would you say that using one as a spacer for (say) a deeper accessory is legitimate?
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I've never used them - didnt even know they existed. I expect someone else here has more experience of them
NT
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Yes - although you'll have to modify it somewhat. They have normal 2.5mm fixing threads - so if you wish to put it between accessory and backing box you'll need to drill them out. You may also need to remove the spare 'lugs' as these can interfere with some fittings.
It will look a bodge, though.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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For a start, the machine screws are M3.5 -- that is the normal variety for electrical boxes
You're not usually expected to drill them out but rather to use one set for mounting the spacer and the other set for mounting the accessory. Of course that sometimes causes problems of orentation and fitting of some accessories.
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Indeed.
Most will tend to get used with plaster depth boxes which have only two fixing lugs.
And you're not 'expected' to use them for this purpose - they're for mounting a standard accessory to trunking etc. Use as a spacing frame is a secondary one.

Some boxes also have only one adjustable lug - which most would fit so it can be used for horizontal fixing. See also my point about the large plastic lugs at the top fouling some dimmers, etc.
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*People want trepanners like they want a hole in the head*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

ah, well if you use the things designed for the purpose of extending a backbox rather than those designed for conduit, it all works much better - the same screws just fit through the unthreaded lugs on the extender and go into the original back box:
http://cpc.farnell.com/PL08925/electrical-lighting-security/product.us0?sku=bg-818
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Cheers,

John.

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http://cpc.farnell.com/PL08925/electrical-lighting-security/product.us0?sku=bg-818
Right - never seen those. Not that I'd be looking for them anyway. ;-)
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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And many boxes have -- or at least in the past had -- no adjustable lugs :-(

Been there, done that, got the t-shirt. Often :-(
Whilst they may still be current catalogue items, I think we're dealing with something which is largely a relic of the past. I dare say I could probably find one or two in a box of old bits somewhere around my storeroom, but then I could also find a few packets of mounting flanges. Remember them? Used to use them on 4 lug single-gang metal back boxes. Fix flange to box using two of the lugs, then fix box to skirting by woodscrews through the face of the flange. A whole lot simpler ( and easier to align) than screwing through the side of the box into the thickness of the skirting. But then flange boxes became readily available and the problem was solved in a different and simpler way.
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