The problem with forums is that you never know if the people posting comments are doing so for purely malicious reasons!
I work for IDEAL INDUSTRIES the world's largest manufacturer of wiring connectors (twist-on, push-in, crimps, etc) and have been one of the guys promoting twist-on wire connectors in the UK. I know that I am setting myself up by joining this forum, but I'd like to set a few things straight:-
1). Firstly, I cannot tell if this particular connector is manufactured by IDEAL or not. Unfortunately our connectors (like Wago) have been knocked-off by numerous Asian suppliers and quite often the quality of these connectors is poor. All IDEAL's connectors are manufactured to the highest quality standards in our US factories and if this is an IDEAL wire connector we would like it back so that a full investigation into why it melted can take place.
2). In my career I have seen quite a few burnt connectors. In the main these have been terminal blocks, but I have also seen heat damage to most types of connector in the market. Loose connections, connectors used with wrong size wiring, broken wires, fine stranded wire inserted into push-in's can all cause overheating or arcing. In N. America and internationally, IDEAL sells billions of twist-on wire connectors per year and in the 11 years that I have worked for the company I am not aware of a single fire caused by one of our connectors. Installed properly, modern twist-on wire connectors are one of the safest ways of joining wires.
3). IDEAL's twist-on connectors fully conform to EN 60998-1:2004 and EN 60998-2-4:2005. These are the connecting device standards that all wiring connectors have to meet for CE requirements. In the case of IDEAL's connectors we also put all our connectors through full 3rd party certification which provides independant proof of compliance. By complying with these standards our connectors fully meet the requirements of BS 7671:2008 (17th Edition).
4). Before marketing twist-on wire connectors in the UK we worked with both the Electrical Safety Council and the NICEIC. Both bodies are happy for electricians to use twist-on wire connectors in the UK, providing they are installed in accordance with current regulations i.e. inside an enclosure where required.
5). In the 9 months that we have been selling these connectors, numerous electricians, several large contractors, housing associations and district councils have installed these connectors without incidence. They are nothing like the old ceramic Scruit connectors of the past, mainly due to the conical square edged spring that is welded inside the plastic connector cap. This spring grips the wires and does not relax over time.
We know that twist-on connectors are Marmite, so we are happy for electricians to use our 32A rated push-in connectors or the new SpliceLine in-line push-in connector instead. Twist-on's do however offer some advantages over other connectors e.g. higher current rating, IP55 rating on some models, accept solid and stranded wire and are reuseable. Thanks.