88V8 wrote:Cars used to have j-boxes with screw terminals.
But since yonks, they have crimps and push-ons.
I see the telephone people now use crimps.
It seems domestic electrics are behind the times.
Yes but slowly catching up. For quite some time now we are not allowed to use screw terminals in junction boxes that are effectively inaccessible. We have to use "maintenance-free" connectors: crimps, push-fits, or sprung levers. These re-tension themselves.
88V8 wrote:We had a new CU last year, all RCBOS in a metal case with drop-shut door. Previously it was plastic with a fall-open door. So at least that's better. But when I was in there adding a circuit, I noticed that some of the screws are already not very tight, and I know they were tight when fitted because I checked.
Yes the metal consumer units were brought in to contain, for 30 minutes, the fires caused by the drop in quality of the switchgear terminals. A case of addressing the symptom rather than the problem. The screw terminals work loose. In my experience the first re-tensioning needs to be done after about an hour of tightening up. Maybe another go after a week or so and that should hold for quite some time.
If one tightens up the terminals to the torque settings specified for the busbar screws and for the circuit breaker cages they seem very slack. You can usually get a couple more turns on them afterwards!
It is difficult to imagine anything other than screw terminals for switchgear but in the old days there used to be two screws per connexion. They were much better. With every wiggle of a wire a screw terminal stands a good chance of the strands re-settling beneath it and so making it slack. The double screw terminals of yesteryear meant that the first held the strands more or less steady while the strands in the second didn't move as much.
88V8 wrote:When I think on this, and the number of j-boxes in house and garage some of which are hidden, it is slightly perturbing.
During the periodic inspections (every 10 years for domestic; five years for rental) it would be desirable to open up all enclosures and check the tightness of the terminals. This is not part of the remit of a periodic inspection though and would take more time than most clients would be willing to finance.
Chris