I'm talking about the bog standard things, sometimes called 'choc blocks' or terminal strips. I much prefer the ones with wire protectors, but they seem to be rare. I've found them on the Rapid website and the CPC website I've and bought some. But since they're so much better why don't all terminal blocks have wire protectors? The cost difference is minimal and they remove the danger of the screw cutting the wire.
Bill
You say the cost is minimal but its another piece you need when you make them. I've never quite understood the basis of just a screw myself as all too often it just separates stranded wire and the bloomin thing falls to bits. its The same story as terminals, which do not have any kind of washer to stop wires coming out the sides. Brian
That's why you twist the strands up before you insert the cable. The terminal should be as full as possible (with conductor).
Bill Wright used his keyboard to write :
They are horrible things to use, difficult to get the conductors in place, but even worse when they become distorted once they have been tightened.
There are (in theory) ones designed for stranded wires. They either have leaf protection springs, or a wide screw with rounded end that the wires can't squeeze out of.
The other option is to use bootlace ferrules on the strands and then you can use ones for stranded or solid core conductors. This is what I normally do for stranded conductors up to 2.5mm2.
For high current with stranded conductors, I use ones which are suitable for twice the conductor size, and make sure all the conductors are under both screws.
That I'm afraid is a definite no no. Some misguided manufacturers tinned the ends of cables when appliances were supplied plugless.
The tinning used to "flow" away from the point of pressure.
Being cheapskates my company will often provide individual JB,s for sensors etc and if the spec does not call for it, a chunk of chockstrip is the norm.
The field wiring is 1.5mm, the sensor can be a few whiskers. Taking both cables through the connector, so that each one is clamped by both screws secures things nicely. Bootlaces are fine, but if those are being used it is easier to go the whole hog and stick a few DIN terminals in the box along with a short bit of rail.
AB
Should etc, and some wire just seems to come untwisted when flattened. i guess you could tin the twisted ends but that is not always an easy thing to do in situ. Brian
:-)
I often find that some of the effects encountered with faults and design shortcomings would be near impossible to arrive at if One aimed deliberately at the "feature".
Some DIN terminals produce this effect. The cable end seems to slide outside the "box" that clamps the cable yet sits inside the plastic body. Usually in dark corners of panels where little space has been allowed between terminal and cable trunking.
Actually I find chockstrip quite good, although I avoid those with "frills" such as cable protectors like the plauge.
AB
And it encourages the wire to break at the end of the tinning.
For all these reasons I avoid choc-block type terminals wherever possible.
The other screw-down terminal idiosyncracy that annoys me is where they have a 'pad' but you can get the wire the wrong side of it so you carefully put the wire in, tighten the screw and the wire promptly falls out because it's nut under the grip.
You often find the screw cuts the wire?
The cost difference is miniscule on each individual strip, but when you make tens of millions of them a year, a fraction of a penny is thousands of pounds of lost profit on that item.
I have also noticed some "ebay" strips having a lot less metal around the screw than I'm used to, and it's not particularly brassy coloured.
Owain
I haven't had a problem.
but even worse when they become distorted once they have been
They are a use-once item surely?
Bill
Yes in hard to reach places tinned ends can squash over time, but a look at most devices supplied with no plug from back then, most were in some way tinned Any connection can and does work loose. I remember the electrician many moons ago who did this house suggested I tested and tightened all socket and lightswitch and bayonet screws about a year on from the finish of the job. many were not as tight as they had been for whatever reason. Brian
Funny you should say that. I put a 30A ring main into the bungalow some years back. Fibreglass insulation was given away, so I took full advantage.
I do think about all those JB's up there and the need to check the screws, but all that glass and the addition of six stone to yours truly is a little off putting :-(
On a plus point, the fibreglass is not too flammable, sadly a ceiling constructed from tongue & groove with umpteen layers of varnish is probably not the most ideal mounting for JB's
AB
It often cuts some of the strands. It's worse with ultra-flexible wires. Of course some makes have screws with sharp ends!
Bill
Haven't Airbus UK got a massive order in with Ebay?
Delivery post Brexit :-)
AB
They were tinned for test reasons in the factory. The instructions usually told you to cut them off and they were never the right length for a plug anyway.
Screw terminals always work loose which is why they aren't used on important things. What was the last time you saw chock blocks on aeroplane wiring?
Thank you, I will try that in future.
Bloody obvious with hindsight, I must confess I would never have thought of doing that though.
AB
Brian Gaff brought next idea :
You should never tin a conductor to insert it in a screwed terminal. The solder will settle and turn what began as a good termination, into a poor one, possibly heating up if it is carrying much current.
Brian-Gaff formulated on Monday :
It doesn't happen, if the job is done right! They come loose due to settling. Proper way - Insert cable, tighten a little, waggle the cable to settle it, tighten some more.
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