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Electrical Connections
==Screw connector blocks== Often called chocolate blocks, these are the most popular [[cable]] connector in fixed wiring.
The main weakness of these is that they can sometimes loosen in time, creating a [[fire]] risk. This makes them forbidden for inaccessible locations, such as under tiling etc.
There's a simple method to reduce this risk to some extent. This is to put both cables into the connector from the same side, with the stripped section of both extending to go under both screws. Now a bad connection only occurs if both screws loosen. The bare cable ends aren't bent over. Make sure the bare ends don't stick out on the far side. Its generally only possible to get 2 cables into a connector used this way.
A lot of screw connectors are found that haven't been tightened up enough. This creates reliability and fire risks.
Wrapping screw blocks with [[Tapes|insulting tape]] is not adequate. It provides no fire protection, and tends to fall off. The wiring regulations require a self extinguishing container for all fixed wiring junctions. Taped blocks are ok inside such containers, such as a junction box, [[pattress]] box or ceiling rose, but position them so they won't short to anything if the tape falls off.
Flex ends need twisting and folding over before use, and should not go in the same hole as cable, or the flex connection can be weak and electrically inadequate. Small cables going into a connector hole alone should be bent double to ensure proper grip.
==Junction box== Very popular in fixed wiring, these combine [[screw]] connections (usually) with a self extinguishing enclosure.
The connection screws often screw into a split hollow metal insert, which is in turn restrained by the plastic housing around it. If screwed too tight the hollow metal part can split apart, creating an unsafe connection. Some junction boxes use a better terminal design.
==Pattress box== A backbox and blanking plate plus a screw connector strip can be used like a junction box with lots of ways. Like junction boxes they normally lack a cord grip, though backboxes with cordgrips are available. Useful as a central heating wiring centre.
==FCU== An FCU (fused connection unit) does more than just connect wires together. They're used where a fuse and cordgrip are needed, ie when connecting an appliance flex to fixed wiring.
==Pushfit Connector== After a long history of use inside lighting fittings, these are becoming more popular for higher current cable junctions now. They're quicker to use than choc blocks, are permitted in inaccessible locations, and a tool is only needed when releasing the wires.
The bare cable end needs to be straight. Wago pushfit connectors are half the size of levers per way. Pushfit can't use stranded wire. Ashley make pushfit junction boxes with cordgrips.
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==Lever connectors== The cable clamp is clamped on these by moving a lever down. Levers are handy for temporary connections. [[Flex|Stranded wire]] works in lever connectors. If more than one wires is used in each entrance, they need to be identically sized.
==Crimps== [[Crimp]]ing makes a connection reliable enough to be permanently buried. A good crimping tool is needed. See [[crimp]].
==Soldering== Soldered joints are permitted in accessible and inaccessible locations. Practically you need to provide some sort of strain relief for the joint, as solder is very weak. The cable ends should always be twisted together before soldering, otherwise even very small movements during assembly can cause the bond to fracture. Twist at least a couple of full turns, otherwise some movement can still occur, and the joint break.
Soldering isn't a popular option for fixed wiring because of these issues, and because soldering takes a little equipment and skill. There's also no readily available junction box designed for soldering.
Wires need to be spotlessly clean to solder, making soldering old cable a slow process.
==Wirenuts== These are little ceramic hat-like items with a tapered coarse screw thread on the inside. The cables are pushed in and the wirenut rotated to screw it onto the cables. As it screws up, the [[cable]]s are pressed together.
These have been illegal to install on fixed mains wiring since the
1950s for reasons of reliability and safety. They're seldom seen now. A crimped version of these is used inside appliances, and is much safer than the original screw-on type.==Resin filled capsule== If a mains cable needs to be joined underground, the joint must be totally waterproof long term. The only realistic way to achieve this is to place the connection in a plastic housing, and fill it with resin. Suitable resin filled connector kits are available. Underground electricity distribution uses the same connectors, albeit in a larger size.
==Twist & tape== Much used in the past, [[Twisted Flex Joints|twisting wires together]] and [[Tapes|taping]] them is a recipe for [[fire]]. The UK has around
69,000 domestic fires a year, killing over 400 people. The main problem stems from the fact that such joints aren't gas tight, and the copper oxidises over time, creating resistance in the joint. This causes heating, causing more oxidation and resistance.==See also== [[Category:Electrical]]