> I actually have come to believe that the spring type wire nuts (Marettes,
> Murettes) are FAR more reliable than any other connection I have used in
the
> past.  They just have to be installed correctly.  I used to do a lot of
> electrical work (1 year between high school and college) - we used to use
> T&B Sta-Kon crimp splices.  I have since seen many of those splices fail
> over a period of 15 years or so because they became loose (copper cold
flow,
> I think).  I have not seen this happen with a wire nut - the spring
> stretches while being tightened and keeps the connection under tension.

I have to agree; in the States, each different type of wire nuts are UL
listed
(not much sure of the reliability of UL) for a certain number of wires at
various
wire gauges.  One in particular that I have used commonly was rated for 2-5
14 gauge, 2-4 12 gauge, and 2-3 10 gauge wires.  As long as the wires were
within the proper number, the wire nuts made a firm hold that could not come
loose.  (These also had the metal spring, which would hold onto the wires by
making grooves in the exposed copper.)  To insure the connection, however,
the wires were twisted together tightly using side cutters and the wire nuts
were mainly used to cover and hold the joint.  If the wires were not twisted
together beforehand, I doubt the connection would be as good.  Plus, this
was with solid copper, not stranded, which my pose a whole different
ballfield.

> Note: I have seen other brands of wire nuts without the spring - I don't
use
> them and do not know how reliable they are.

If they do not have the metal spring, the plastic threads can become warped
or stripped while twisting the nut on the joint, leaving an insecure hold.
(Imagine
trying to screw a plastic screw into a hole in a sheet of metal...)

Regards,

-- Michael