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I have never seen a wire nut used in the UK, but they seem to be very common in the USA, why?

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Don't know much about UK wiring, but if I'm not mistaken you guys use aluminium wire more, right? If that's the case, I don't think aluminium wire works well with wire nuts. Or it could just be an artifact; since they didn't use wire nuts with old aluminium wire, they found a different way and continue to use it today. –  Tester101 Nov 16 '11 at 15:00
    
@Tester101, I have never seen aluminium wire used in UK house wiring. However it is used for overhead cables etc as part of the grid. –  Walker Nov 16 '11 at 15:38
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Part of it may be that most sockets (and switches) in the UK have space for 3 wires to be fixed in each terminal. –  Walker Nov 16 '11 at 18:08
    
Just out of curiosity, what do you use in the UK instead of wire-nuts? –  Tester101 Nov 16 '11 at 18:08
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@Tester101: I'm in very Eastern Europe and I don't remember ever seeing wire nuts in action. The typical way to connect wires is to either twist them and wrap in insulation tape or use connectors with screws. –  sharptooth Nov 17 '11 at 7:34
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7 Answers

up vote 12 down vote accepted

One possible reason provided by Ideal Industries in This article

Although very much the connector of choice in North America, the twist-on wire connector remains a largely untapped resource in the UK electrical market. Unfortunately many electricians still associate them with the poor-quality ‘screw-it’ wire nuts from the 1970s; manufactured from ceramic, these had a tendency to crack very easily and expose the wires, leading to safety hazards.

Though it looks like Ideal is still trying to tap UK twist-on wire connector market, with the new Twister® PRO (which to me looks just like a regular wire nut, aside from it being multicolored).

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Those ceramic wire nuts were crap. You find them in older installations here in the US. Their modern equivalents are the plastic ones with plastic threads that come with cheap fixtures. Quality Wire Nuts have either a hard or soft shell with a conical spiral spring that threads itself on and binds the wires together tightly. They're color coded for size of conductor and number of conductors they can contain. –  Fiasco Labs Sep 18 '12 at 15:04
    
@FiascoLabs What years were the ceramic ones in use? I've found modern plastic + spring ones from early/mid-80s work. The mid-40s work I've seen uses soldered and wrapped splices. –  Jeremy W. Sherman Sep 18 '12 at 21:45
    
The ceramic nuts I came across must have been out of the 50's, I'd guess, post WWII and kind of rare actually. I lived in a house that had a guest-house outbuilding with the old tube'n insulator wiring with Western Union splices and the remains of Gutta Percha insulation where it had baked one too many summers and started to flake off. Easy to see why people were afraid of rural electrification in the early days. –  Fiasco Labs Sep 19 '12 at 3:03
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Tester101 addressed your "why not in the UK?" question. As to the "why in the USA?", I believe it's because wire nuts are easy to use, cheap, and occupy little space in the box.

Even an amateur can create a good splice with wire nuts. They don't need to learn to pretwist or anything: just line the wires up, jam 'em in, and twist like your life depends on it (hint: it might). Then hold the nut and give each wire a tug to make sure the nut grabbed it good. Got it wrong? Try again, no muss, no fuss. Really mangled things? Cut the ends off, strip a bit more, and try again. It's a lot more forgiving and reliable than any similarly cheap alternative.

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You're actually supposed to pretwist the wires, even when using wire nuts. –  Tester101 Sep 19 '12 at 10:38
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@Tester101 The instructions supplied with the nuts do not specify pretwisting. And IIRC UL standards require the nuts to make a solid splice without pretwisting, as well. –  Jeremy W. Sherman Sep 19 '12 at 14:24
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I've gotten good solid splices out of "hold 'em parallel and twist it on" with 4 12 AWG conductors. All I can think is trying to pretwist those would be an exercise in frustration. –  Jeremy W. Sherman Sep 19 '12 at 14:25
    
@JeremyW.Sherman - that's when a good pair of linesman's pliers come in handy! –  geerlingguy Jan 21 '13 at 2:00
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@geerlingguy You actually need two pairs if you want to pretwist heavier wires, one to clamp them at the base of the splice and the other to spin the ends around. I've found when splicing 3 or 4 (or more) wires, it's easiest to pretwist or use push-in connectors, because getting the wire nut to actually grab and twist all the wires into a solid splice without pretwisting them is very frustrating. –  Jeremy W. Sherman Jan 21 '13 at 3:49
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Not sure about "why not" in UK (although Tester101 seems to have a good explanation [as always]), but there is a trend in US, at least in the DIY community to use the new side-by-side connectors

wire connector

The overall connection is wider, but I find it easier to flex the bundle toward the back of the box, especially when there are three or four wires. Also, there is tactile feedback that the connection of each wire is solid and less chance that one of the wires has a loose connection as it might in a twisted bundle.

Finally, it generally needs less of a stripped lead, which is helpful if you need to snip the end for a new connection. Sometimes cutting the twisted lead leaves a pretty short wire to work with.

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These are starting to be used in the UK as well –  Walker Sep 19 '12 at 14:22
    
Just ran into these (made by Wago) the other day provided with some recessed cans for splicing. I had to look close, check the model, and look up the instructions. They aren't well labeled on the connector, but they include a strip gauge and a hole at the end for testing liveness with a probe. Pretty nifty. –  Jeremy W. Sherman Sep 19 '12 at 14:27
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Building Regulations Part P in UK does not specifically ban or recommend using screw terminals in the UK. It goes to mention, that during joing wires they should be joined in the terminal of a switch/contact or to use appropriately certified equipment that is relevant to the job!

There is also an a section for old building compliance that may be encountered during renovations and they show some bad and good ways of doing certain things but do not mention anything about joining wires.

  • I have noticed that in every electrical installation i work with in the UK there are always block connectors used. I even took apart some old lighting made in Birmingham in 1990 that used ceramic block connectors for joining 220V to ballasts.

  • When I did some electrical certifications in South Africa, examples of connecting wires used plastic block connectors. But, allot of light fittings I installed; for example ceiling fans - were supplied with screw nut thingies and I just used those. But other halogen type lights had block connectors.

  • It is interesting though that during a short period in Poland - most of the wiring i worked with (in pre-WWII buildings) they used some sort of soviet ceramic screw caps and connectors were scarce. Today however.. You can only buy plastic block connectors and those screw things are frowned upon. You cant even buy them at the whole sellers, just eBay if you desperate.

I have never seen any regulation banning the use of those connectors- But in my own experience I ALWAYS questioned how long will that wire actually last screwed in freely like that? And i preffered to use block connectors for piece of mind!

If you interested in more building regulations please click here (UK)

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They are also common in Belgium, if that adds anything. I found the old ceramic ones in my house and have used the modern quality ones for wiring lighting circuits very effectively. Simple to use and the house has not burnt down yet after 5 years so appear to be safe.

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Twist-on connectors

The Wikipedia article on twist-on connectors suggests they were outlawed in the UK 50 years ago. No references are given. It is suggested that 50 years ago the ("Scruit" brand) twist-on connectors were made of ceramic and were liable to crack and expose the wires.

UK Electricians are a conservative group. Vendors of novel products have to go to considerable length to persuade them that their products meet the relevant legislation.

An Ideal Industries Inc. catalogue says

Conforming to BS EN 60998 Twister® wire connectors fully comply with BS 7671:2008 (17th Edition Wiring Regulations).

However, it isn't uncommon to see strenuous efforts on the part of manufacturers to persuade UK electricians that novel products meet regulations. E.g. Wagobox and Ezybond earth fasteners Some of these novel products more or less disappear from the market within a few years, others succeed.


Screw-terminal-blocks

In the UK, electricians almost invariably use screw-terminals.

UK connectors
ruler is marked in cm with mm subdivisions

The white translucent screw-connector block in the foreground is a typical example. This one is rated for 5A. Other sizes are available for different current ratings.

An electrician left behind the other connectors in this picture. I suspect they were used for temporary connections during installation. I've not seen any in a completed installation (but I'm only a householder not an electrician, so have very limited experience)

The "Marr No.1" connectors at back right look superficially similar to US wire-nuts but are very different. The metal insert is removed and a grub nut is used to clamp the wires, then the plastic insulator is screwed over the connection.

The "Legrand 10mm2" connectors at top left may be for higher current ratings. Note that the plate that presses on the wires is arranged so as not to exert any twisting force on the conductors. Perhaps this avoids damaging stranded conductors. It certainly prevents the conductors being pressed to one side of the screw and therefore not being securely clamped in place.

An obvious advantage of these connectors is that the wires can be removed intact and should usually not need trimming before reconnection. I have the impression that in the US, wire-nut connections are often removed by cutting the wires, which may leave progressively less and less wire available in the junction-box or back-box for remaking connections.

When more than two wires are to be joined, a slightly different type of screw-connector is used:

Example junction box

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240 Volts everywhere has something to do with it - not a good idea to have wires twisted together. Can't have receptacles or wall switches in bathrooms either.

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Another answer states that they're common in Belgium, which uses the same line voltage as the UK. –  Niall C. Dec 31 '13 at 5:34
    
Rob, can you elaborate a little bit more? Not sure I follow. –  Edwin Jan 2 at 8:15
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