Wiki: Electrical connectors

Feedback welcome...

NT

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.

  • formatting link
    Wage connectors]
  • formatting link
    Ashely pushfit JB with cord grip]
  • formatting link
    Ashely pushfit JB with cord grip]
  • formatting link
    TLC direct]

==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]]

Reply to
Tabby
Loading thread data ...

Often seen on US-sourced DIY TV programmes, to shouts of "argh!" from educated viewers.

JGH

Reply to
jgharston

And don't put solder on the flex end.

Reply to
Bob Eager

Yes, they're everywhere over here. I hate them. The only thing worse (other than 120V supply meaning it takes forever to make tea ;-) are plug sockets (outlets) where people have wired them with the push-fit connectors rather than the screw terminals; they have a nasty habit of working loose over time, resulting in all manner of electrical gremlins.

cheers

Jules

Reply to
Jules Richardson

Good feedback, thank you folks. Heres the latest version...

NT

Electrical Connections

'when cables connect'

=3D=3DScrew connector blocks=3D=3D 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.

=3D=3DJunction box=3D=3D 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.

=3D=3DPattress box=3D=3D 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.

=3D=3DFCU=3D=3D 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.

=3D=3DPushfit Connector=3D=3D After a long history of use inside lighting fittings, these are becoming more popular for higher current cable junctions now. These have been widely used for years in America, and don't have a great record for safety or reliability at the current levels used by sockets. 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.

  • formatting link
    Wage connectors]
  • formatting link
    Ashely pushfit JB with cord grip]
  • formatting link
    Ashely pushfit JB with cord grip]
  • formatting link
    TLC direct]

=3D=3DLever connectors=3D=3D 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.

=3D=3DCrimps=3D=3D [[Crimp]]ing makes a connection reliable enough to be permanently buried. A good crimping tool is needed. See [[crimp]].

=3D=3DSoldering=3D=3D 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.

Wire needs to be spotlessly clean to solder, making soldering old cable a slow process.

=3D=3DMains plugs=3D=3D Soldered wires should not be put into screw connections, the 2 aren't a safe combination. The first problem is that solder is soft and tends to creep under screw pressure, leaving a weakly clamped joint after a while. The other is that the soldering of stranded wire makes strands more likely to break. Soldering screwed wires increases the odds of fault & fire.

Crimped flex ends can be safely used in mains plugs and other screw connectors. Ideally the flex should be twisted before the bootlace ferrule is applied, to avoid concentrating stresses on a small number of strands.

A small number of old mains plugs use screw connections where the flex goes under the screw head and around the screw shank. There is a tendency for these screws to push strands out when tightened, and its easy for most of the strands end up not connecting. Make the stripped flex end long enough to go nearly all the way round the screw shank, and twist the strands fairly tightly to minimise strand pushout. A small washer under the screw head also minimises the problem.

Small diameter [[flexes]] and some cordgrip designs result in the plug cordgrip failing to grip the flex. This can be remedied by putting the flex 360 degrees round the cordgrip before tightening, like so:

__ wire follows a circular path /__\ wrapping round the cordgrip ______\__/_____ going under it twice

=3D=3DFlex extenders - name?=3D=3D These oval connectors are a good way to extend a flex. They incorporate screw connections, cordgrips and a robust insulating case.

=3D=3DIn-line connectors=3D=3D These low profile plugs & sockets come in pairs and are used to extend flexes and provide a local disconection point. Mostly used with outdoor power tools, but can be used elsewhere.

They come in 2 and 3 pin versions. 2 pin connectors must not be used on 3 core appliances, on 2 core supply leads, or with appliances that require a polarised supply. There are also different pin configurations that have seen popular use over the years, so not all connectors are compatible with others. Many such connectors are rated at less than 13A, and should not be overloaded. A 5A connector is good for a 1kW motor.

It shouldn't need saying, but what a world... ALWAYS connect the plug with sticking out pins to the appliance, and the socket to the flex with the mains plug.

A standard 13A plug and socket is more versatile, enabling a (3 core only) lead to be used on any appliance. But its bulkier. If using 13A sockets outdoors, its wise to use unbreakable ones, shatterable indoor sockets generally get broken.

=3D=3DResin filled capsule=3D=3D 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.

=3D=3DWirenuts=3D=3D 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 here now (but the US still uses them). A crimped version of these is used inside appliances, and is much safer than the original screw-on type.

=3D=3DTwist & tape=3D=3D 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.

=3D=3DSee also=3D=3D [[Category:Electrical]]

Reply to
Tabby

Is it worth stressing that pushfit and lever connectors need an enclosure? Eg

Wago need an enclosure which provides strain relief - eg a Wagobox

Again, these should be used in enclosure which provides strain relief.

>
Reply to
Robin

On 21/03/2011 22:58, Tabby wrote

Any special reason why both cables need to go in from the same side instead of one from each side but both long enough to go under both screws. I tend to prefer one each side because it's easier to be sure that the outer insulation is pushed fully home.

Reply to
Mike Clarke

Are thoses 69,000 domestic fires attributable to twist & tape connections? I'd be surprised if they were but as written that's certainly the implication.

Mathew

Reply to
Mathew Newton

^^^^ Wago I think.

Thanks for this.

Reply to
Martin Bonner

Pushin connectors: is strain relief required by 17th edn, or is it just sensible? Levers: I dont know why these should have strain relief, who exactly says they should?

cheers, NT

Reply to
Tabby

Like a flex outlet plate?

Reply to
ARWadsworth

I am sad and so RTFM before I first used Wago connectors recently.

Wago's guide for installers

formatting link
includes the following 3 Q&A:

Should WAGO connectors be used in an enclosure?

In order to comply with the requirements of the 17th Edition IEE Wiring Regulations/BS7671, all connectors should be used in a suitable enclosure of material complying with the relevant glow-wire test requirements of BS 458-2.1. (Fire hazard testing for electrotechnical products). This will provide mechanical protection for the connectors as well as protection against dust, damp and accidental damage. Although WAGO connectors are IP20 (finger touch) with Polyamide 6.6 housing for strength and durability.

Do they need to be fixed in an enclosure?

The junction box connectors do not have to be fixed down in the housing provided that the cables are secured on their way into the box. However, fixing provides a more secure and professional looking finish. (See figs

2 and 3, page 9)

Does there need to be strain relief on the cable?

Yes, there should be strain relief on the cable. This could be the cable clipped outside the enclosure or cable glands within the enclosure to prevent the cables being pulled out of the connectors. (See fig 6) "

I thought strain relief was all just part of the regs general requirement for no appreciable mechanical strain on connections. And also that the manufacturer's guidance must be followed in any event. Am I wrong pl?

Reply to
Robin

If that's true, there's a whole lot of noncompliant wiring about.

NT

Reply to
Tabby

Or overtightened either stripping the thread or the back of the holder.

You could mention crimped bootlace terminals in that bit.

Reply to
ARWadsworth

Would insulating tape be any better? :-)

John

Reply to
JohnW

Robin's right and, yes, there is. Traditional round junction boxes with no internal cable clamps should be fixed in place and the cables clipped near to the points of entry.

Reply to
Andy Wade

latest version.... I think its about there now. Thanks for lots of good feedback.

NT

=3D=3D=3DScrew connector blocks=3D=3D=3D [[image:Leuchterklemme_75dpi.jpg|185px|right]]

Often called chocolate blocks, (and seldom lustre conectors) these are the most popular [[cable]] connector in [[House Wiring for Beginners| fixed wiring]].

The main weakness of these is that they can sometimes loosen in time, creating a [[fire]] risk. This makes them [[Regulations|forbidden]] for inaccessible locations, such as under [[tiling]] etc. Also many screw connectors are found that haven't been tightened up enough, creating reliability and fire risks. (Connector failure due to overtightening are far less common.)

There's a simple method to reduce this risk to some extent. The stripped conductor of both [[cables]] extends under both screws, so both cables are screwed down at 2 points. This can be done with the cables entering at opposite sides or both on the same side. 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.

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. Lone cables going into a connector terminal are bent double to ensure good grip.

=3D=3D=3DJunction box=3D=3D=3D Very popular in fixed wiring, these are [[screw]] connections (usually) in a self extinguishing enclosure. Rotating the lid exposes a varying number of entry holes.

The connection [[screw]]s 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.

The wiring [[regulations]] require junction boxes to be fixed in place, and [[cable|wires]] entering them to either be clipped, or secured in the box with a cordgrip. The lack of cord grip on most junction boxes makes them unsuitable for wires that aren't clipped in place. Plenty of fixed wiring exists that fails to comply on this point.

=3D=3D=3DPattress box=3D=3D=3D [[Image:Pattress_double_with_cordgrip_1085-6.jpg|185px|right]]

A [[Pattress|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, and for complex flexible house wiring schemes.

=3D=3D=3DFCU=3D=3D=3D 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.

=3D=3D=3DPushfit Connector=3D=3D=3D After a long history of use inside [[lighting]] fittings, these are becoming more popular for higher current [[cable]] junctions now. These have been widely used for years in America, and don't have a great record for safety or reliability at the current levels used by sockets. 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 per way of lever connectors. Pushfit can't use [[Flex|stranded wire]]. Ashley make pushfit junction boxes with cordgrips.

  • formatting link
    Wago connectors]
  • formatting link
    Ashely pushfit JB with cord grip]
  • formatting link
    Ashely pushfit JB with cord grip]
  • formatting link
    TLC direct]

=3D=3D=3DLever connectors=3D=3D=3D The [[cable]] is [[clamp]]ed on these by pushing a lever down. Levers connectors are handy for temporary connections. [[Flex|Stranded wire]] works in lever connectors. If more than one wire is used in each entrance hole, they need to be identically sized, and check both are properly secured.

A variant on these just uses a pushbutton to release the clamping force on the cable. They're not often seen in [[House Wiring for Beginners|house wiring]].

=3D=3D=3DCrimps=3D=3D=3D [[image:RedCrimp.jpg|60px|right]]

[[Crimp]]ing makes a connection reliable enough to be permanently buried. A good crimping tool is needed. See [[crimp]].

=3D=3D=3DSoldering=3D=3D=3D 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. Its a good enough option if you've got the skill to do the job properly.

Wire needs to be spotlessly [[Cleaning|clean]] to solder, making soldering old [[cable]] a slow process.

=3D=3D=3DMains plugs=3D=3D=3D [[image:Moulded_and_rewireable_BS_1363_plugs.jpg|185px|right]]

Soldered wires should not be put into screw connections, the 2 aren't a safe combination. The first problem is that solder is soft and tends to creep under [[screw]] pressure, leaving a weakly [[clamp]]ed joint after a while. The other is that the soldering of stranded wire makes strands more likely to break. Soldering screwed wires increases the odds of [[Fault finding|fault]] & [[fire]].

[[Crimp]]ed flex ends can be safely used in mains plugs and other screw connectors. Ideally the [[flex]] should be twisted before the bootlace ferrule is applied, to avoid concentrating stresses on a small number of strands.

A small number of old mains plugs use screw connections where the [[flex]] goes under the [[screw]] head and around the screw shank. There is a tendency for these screws to push strands out when tightened, and too often most of the strands end up not connecting. Make the stripped flex end long enough to go nearly all the way round the screw shank, and twist the strands fairly tightly to minimise strand pushout. A small washer under the screw head also minimises the problem.

Small diameter [[flexes]] and some cordgrip designs result in the plug cordgrip failing to grip the flex. This can be remedied by putting the flex 360 degrees round the cordgrip before tightening, like so:

__ wire follows a circular path /__\ wrapping round the cordgrip ______\__/_____ going under it twice

If using 13A plugs & sockets outdoors, its wise to use unbreakable ones, shatterable indoor sockets are usually soon broken.

=3D=3D=3DRound pin plugs=3D=3D=3D [[image:BS-546-3-pin-plugs-4.jpg|100px|right]]

Available in 2A, 5A and 15A sizes, these historic plugs are still used on [[lighting]] circuits to enable a wallswitch to control plug-in lamps.

=3D=3D=3DFlex connector=3D=3D=3D These oval connectors are a good way to extend [[flex]]. They incorporate screw connections & cordgrips in a robust insulating case.

=3D=3D=3DIn-line plug & socket=3D=3D=3D These low profile plugs & sockets come in pairs and are used to extend [[flex]]es and provide a local disconnection point. Mostly used with outdoor [[power tool]]s, but can be used elsewhere.

They come in 2 and 3 pin versions. 2 pin connectors must not be used on 3 core appliances, on 2 core supply leads, or with [[appliance]]s that require a polarised supply. There are also different pin configurations that have seen popular use over the years, so not all connectors are compatible with others. Many such connectors are rated at less than 13A, and should not be overloaded. A 5A connector is good for a 1kW motor.

It shouldn't need saying, but what a world... ALWAYS connect the plug with sticking out pins to the [[appliance]], and the socket to the [[flex]] with the mains plug.

A standard 13A plug and socket is more versatile, enabling a (3 core only) lead to be used on any appliance. But its bulkier.

=3D=3D=3DResin filled capsule=3D=3D=3D If a mains [[cable]] needs to be [[Taking electricity outside|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 [[Adhesive|resin]]. Suitable resin filled connector kits are available. Underground electricity distribution uses the same connectors, albeit in a larger size.

=3D=3D=3DWirenuts=3D=3D=3D These are little plastic or ceramic hat-like items with a tapered hollow coarse screw thread on the inside. The [[cable]]s 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 here now (but the US still uses them). A crimped version of these is used inside some [[appliance]]s, and is much safer than the original screw- on type.

=3D=3D=3DTwist & tape=3D=3D=3D 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. One problem stems from the fact that such joints aren't gas tight, so the copper oxidises in time, creating resistance in the joint. This causes [[heating]], causing more oxidation and resistance, causing more heating and fire.

A variant on this used in the 1930s was the tobacco tin junction box. The wires inside were simply twisted together. Filling the tin with [[bitumen]] solved the wire oxidation issue and provided a cordgrip. However twisted connections have much higher resistance than the rest of the wire, so the junction boxes were prone to getting hot enough to melt the flammable bitumen and expose the joint to oxidation. These are rarely seen today, and if spotted indicate a seriously substandard installation.

=3D=3DSee also=3D=3D [[Crimp]] [[House Wiring for Beginners]] [[Fault Finding]]

[[Category:Basics]] [[Category:Electrical]]
Reply to
Tabby

Not sure if you missed or misunderstood my comment about soldering...

Might be worth warning about *not* using a coating of solder on twisted wires that are to go into a terminal.

Reply to
Bob Eager

Its already in there Bob, thanks for bringing it up before.

NT

Reply to
Tabby

Apologies, *I* missed it!

Reply to
Bob Eager

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