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| tom66:
--- Quote from: Gyro on October 10, 2022, 09:15:00 am ---P.S. * I meant to comment on this on tom66's second CU in reply #44. That PE wire coming out of the top of the second CU really ought to have a flame retardent gromet (or at least a bit of intumescent caulk around it). The hole is too big to pass regs. Seeing some of the other installs drove it clean out of my head. :D --- End quote --- Yup, it's on my list. Just forgot to order it for the day. |
| themadhippy:
--- Quote --- Metal enclosures have been mandatory for new installations since the UK 17th ed wiring regs. --- End quote --- And yet right next to our sealed metal box the network provider can chuck in there plastic box to hold there isolator. --- Quote ---I think these are a definite step backwards compared to the old twin screw terminations, --- End quote --- yea but 2 screws take longer than 1 to tighten,so productivity goes down and we aint earning our lord and masters as many shekels --- Quote ---I have similar concerns about the new-fangled 'Wiska' type maintenance free junction boxes, where the solid core wire is simply pushed under the sharp edge of a leaf spring (or lever action). Put a cable tie through the tags on the plastic box and stuff it under the floor and it becomes maintenance free. --- End quote --- Had the same concern for a few years when they first came out,but having now used them for a good few years i'd rate them as more reliable than the old "landmine"style junction box,and they certainly grab the wire better than other push terminals.plus the wiska box incorporates a decentish cable grip,something the old round jb's lack |
| Gyro:
Yes, one rule for us mortals, the DNOs don't have to comply with IEE wiring regs, they have they are a law unto themselves. --- Quote from: themadhippy on October 10, 2022, 10:42:12 am ---Had the same concern for a few years when they first came out,but having now used them for a good few years i'd rate them as more reliable than the old "landmine"style junction box,and they certainly grab the wire better than other push terminals.plus the wiska box incorporates a decentish cable grip,something the old round jb's lack --- End quote --- Yes, lack of any form of cable grip was a definite downside of the old JBs (but maybe a testament to how well the terminals gripped). The new ones are neater too and able to fit through holes (much harder to strip back the bare PEs and twist them together outside the box though >:D). I guess the decades will tell. |
| AVGresponding:
--- Quote from: Gyro on October 10, 2022, 09:15:00 am ---Yes, basically fire. Too many house fires caused by loose and overheated connections that are not contained by the plastic enclosure. Metal enclosures have been mandatory for new installations since the UK 17th ed wiring regs. There are restrictions on fire exit paths through the top and rear of the enclosure, fire retardant gromets and glands, fire retardent caulk sealing etc.* Many (most?) older UK homes have the mains feed coming in under the stairs, so have the consumer unit in the same place - directly under a wooden primary escape route! There are many videos on the subject. High drain items like high kW electric showers and EV chargers only make the problem worse. Personally I think 'cage clamp' terminals are the primary culprit, particularly on the incomming supply tails into the consumer unit. Even when tightened to the correct torque, the thick 25mm2 stranded tails will easly work loose under movement and thermal cycling. If people don't use the appropriate torque settins and torque screwdrivers, the problem is even worse. I think these are a definite step backwards compared to the old twin screw terminations, where the screws bear directly on the conductors and have 100% redundancy. --- End quote --- I think the reluctance to use twin direct screw terminations relates to the potential to shear through the conductor when overtightened, though I'll grant you this is less likely on something as big as tails. I've found the best way to get a good cage/rising clamp connection is to waggle the cable once the screw is tight, then retighten the screw. Do this two or three times and you should be golden; it's because the individual strands spread out to fill the width of the clamp. |
| Gyro:
Yes, that could be part of it, although modern consumer units still have single screw connections of cores on the Neutral and CPC bars (ok, the Neutrals are ferruled on an RCBO system, but not on an RCD board). The bars and screws have also changed from softer brass (a bit closer to the Copper hardness), to Steel - conflicting agendas I think, cost vs consistency. Pre-forming and settling the tail strands certainly helps with clamping, but the teeth (more like rounded ridges) on the cage clamps are far too shallow, and the pressure too low, to grip the strands if they 'shuffle' due to movement and thermal effects. [Edit: You're also not supposed to have exposed copper, so the tail is expected to go from round profile to rectangular in nearly no space, leading to a slightly tapered profile, it wouldn't happen going into a round hole]. |
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