Tony Williams wrote:
In article ,
Andy Dingley wrote:


I would be cautious about crimps, unless the blurb
actually said the word 'solid'.


Crimps are relatively non-fussy about stranded vs. colid core
cable. For most combinations the same crimp terminal can be used,
although the ideal crimping force is slightly different.


Bare copper is a reactive metal, subject to long term
oxidation, or verdigris, or other chemical attack.
To make a reliable crimp joint onto bare copper needs
something that first of all cuts through any oxidation
that may be there, and then makes a gas-tight connection.

This needs a heavy gauge crimp, with sharp serrations
down the bore, used with the correct tool.

How then are screw terminals acceptable? Normally these are just the
means of fixing the wire into the terminal - not the main conductor. A
screw point is not terribly big, so I wouldn't expect it to remove a
significant amount of oxidation when screwed up - especially if two
wires are present (eg. ring main in back of socket, where the screws
tend to be smaller than, say a junction box). Much of the main contact
is by the surrounding metal in the terminal - which doesn't have any
means of removing oxidation etc. Then there's the secondary problem of
the screws coming lose over time and the fact that a round wire doesn't
perfectly fill a square hole, so not all the copper wire is in contact
with the terminal (made worse when running a spur from a ring where you
have 3 wires in a termainal).

I agree that in most case, you'll probably find that a standard crimp
doesn't cover the oxidation issue - but I don't believe many other
common fixings (other than soldering) make much, if any, attempt at
doing his either. At least with crimps you have a better mechanical
joint than screws, practically all the external surface of the wire is
in contact with the crimp - and I'd doubt the electrical joint was
significantly worse than a screw terminal. Based on that, a crimp joint
seems better, or am I missing anything?

D