Model Forum / General / Railroads / September 2010

The rating of each type of connection will depend on the situation and
conditions it is used for.

Much of the wiring on a model railway is fixed, not subject to vibration
mechanical force and is never subject to disconnection and reconnection.

Mechanical connection, such as 'through insulation clips' (suitcase)
nuts and even screw terminals rely on mechanical presure and will
eventually degrade through oxidation and relaxing mechanical force.

Crimp lugs generally have greater mechanical force (provided they are
properly fitted) but spade terminals will eventually degrade contact
between spade and socket. (20 years) Disconnecting and reconnecting
the spade connection solves that problem.

Solder plus mechanical connection is still probably the best connection
for model railway purposes.

The exception is of course components/modules that will be replaced.
(eg point motors)

The most common cause of failures in modern electronics is failed
solder joints, but then most electronics have huge numbers of such
joints.

Probably rocket scientists will plump for the cut/clamp type connections
but the application's lifetime will be shorter than model railways.
Telephone infrastructurewiring mostly uses the same system, but that
relates more to the costs of instalation and much lower currents
than typical MR situations.

Greg.P.

   OK, you asked for it. A bit of background first: I've been involved
with industrial electronics, mainly motor controls (variable speed
drives), for nearly 2 decades. Prior to that I mostly worked on computer
or microprocessor-controlled equipment going back into the late '70s.
That included mainframes to PCs.
   As mentioned in my previous post, in the field I have had to replace
many connections that failed or were failing because they were getting
loose. Badly crimped lugs and insulation displacement connectors (IDCs)
make up very close to 100% of these failures. The connections that very,
very rarely seem to fail are the screw clamp type, wherein a wire is
inserted into a slot or hole and a screw is tightened clamping the wire
in place.
   IDCs work by having a metal piece with a slot, sometimes with
sharpened edges. The wire is pressed down into this slot and the metal
sides cut through the insulation making contact with the wire.
Unfortunately, as Greg mentions in his post, flexing or movement or
vibration of the wire and IDC can work the wire until it becomes loose
in this slot. A loose electrical connection - ANY electrical connection
- builds up resistance. As electrical current passes through a
resistance it generates heat; heat can cause annealing of the wire and
connector, which creates more resistance, which creates more heat, etc.
Poorly crimped ring lugs, fork lugs, butt splices and other sorts of
crimp connections can suffer the same failures.
   Overwhelmingly, the failed connections I have had to replace over
the years have carried much higher current than we typically have
flowing through our wires, track and layouts. The half amp that a modern
loco with a can motor might pull at most probably won't burn up many
connections. Intermittent operation is probably a bigger nuisance we
have to watch out for. However, on a large home or club layout with
multiple engines drawing power from one DCC booster or multiple analog
throttles using a large common transformer for power, we could pull
sufficient amperage to cause an eventual problem at a connection which
is not tight.
   What will I use on my layout once I have a satisfactory design and
can afford to get it started? As mentioned above, screw clamp terminals
have proven the most reliable in industrial applications. I have seen
these used on input and output terminals for variable speed drives
carrying hundreds of amps at up to 600 volts AC and they have rarely
failed. They are also widely used where control wiring needs to
terminate to a circuit board. I have a few hundred single terminal
blocks that can be bunched together on a piece of DIN rail to create
whatever size of terminal strip I may need. Here's a link to a photo of
this style of terminal block:
http://media.digikey.com/photos/Phoenix%20Photos/3044131.JPG?cshift_ck=null&clie
nt_id=5042

   The other type of connection that I would trust is the common screw
terminal strip that we're all familiar with, using ring or fork lugs
that are PROPERLY crimped. For this you need the right tool. Avoid
crimpers with jaws that look like a pair of parentheses (). These are
the worthless crimpers that create all of the bad crimp lugs I've had to
replace. Get a good pair that creates an indented crimp, sort of like
this:  D). The crimpers I use are made by Klein. When I crimp a wire
with these it WON'T come apart or work itself loose.
   For feeders from the bus to the track I think there's only one way
to do it: strip a short bit of the bus, wrap the feeder wire around the
bus wire a few times, and solder it. It's more time consuming than the
quicky suitcase connectors but it should give worry free, reliable
operation for decades. With a pair of wire strippers you can just cut
through the insulation without nicking or cutting the wire, and push the
insulation an inch or so back on itself, leaving a bit of bare wire to
work on.
   I hope some of you can find this information useful.

Not everyone can use normal pliers and make a neat job - my
brother-in-law
reduced a connector to something that looked like it had been through a
car shredder inside 5 minutes - admittedly it still worked ;-)