Technique: wire preparation for a terminal block
Zak
I am referring to a terminal strip like this.
http://www.ledlight.dk/images/samlemuffe400x320.jpg
It may be 3 amp or 5 amp or something similar to that sort of low
capacity.
The wire may be anything from wire which is thinner than bell wire
up to approx 13 amp mains flex (1.5 mm^2).
-----------------------------------
The QUESTION is this .... If you were using a terminal strip to
connect some wires then how would you prepare the ends of the wire
going into the terminal strip? It seems that there are few
satisfactory ways.
-----------------------------------
You can just strip back the insulation, twist if multi stranded,
insert and screw down. However there is always a risk that some
of the multi strands might break if the screw is tightened too
much.
However if the wire is quite fine then you may have to fold the
are wire back on itself. Maybe do that several times. But that
does not come out cleanly unless the retaining screw is almost
taken out.
You can add thickness to a fine wire by soldering/tinning the end
of the wire before it goes in. But this adds a lot of fragility
because where the solder ends is the point where the wire is
likely to bend if it is moved around in use.
I've even seen people sticking in *insulated* wire and tightening
the screw until it met the copper. This could work rather nicely
but only if you can get the depth just right. It seems to me that
chance plays far too large a part here.
The way I would love to do it is to get some sort of crimping tool
and put a small brass collar over the wire and squeeze the collar
on securely. The brass would be tough enough to resist the screw
doing any real damage.
What do you find is the best?
Sjouke Burry
> Back to basics here guys.
>
> I am referring to a terminal strip like this.
> http://www.ledlight.dk/images/samlemuffe400x320.jpg
> It may be 3 amp or 5 amp or something similar to that sort of low
> capacity.
>
> The way I would love to do it is to get some sort of crimping tool
> and put a small brass collar over the wire and squeeze the collar
> on securely. The brass would be tough enough to resist the screw
> doing any real damage.
>
> What do you find is the best?
I bought an assortemnt of sleeves and a crimping tool,
to instrument cars,etc.
Not only it solves the fraying/breaking wire problem,
those sleeves also retain a little bit of the isolation ,
so that even if you have to move about the strip/circuit
quite a lot ,wires do not tend to disconnect,and things
look a lot more professional.
You have 2 type of sleeves, metal only, or a small piece
of coloured plastic extra.
The last ones give most protection.
(And you get coulour coding thrown it for free).
Arfa Daily
"Sjouke Burry" <burrynu...@ppllaanneett.nnlll> wrote in message
news:4419d505$0$2031$ba62...@text.nova.planet.nl...
That would be my favoured way of terminating the wires, as well. I seem to
think that I've seen these things referred to in a catalogue, as " bootlace
ferrules ". I'm never in favour of tinning wires prior to securing in a
screwed terminal, for two reasons. First is the oxide layer that readily
forms on the surface of solder, which may lead to a resistive joint in time.
Second is creep of the soft solder, which over time leads to a loose screw.
How many mains plugs have you opened, and found that the manufacturer
pre-tinned leads, are virtually falling out of the plug pins, with the
screws so loose, you could undo them with your fingers ?
Arfa
cra...@electropar.co.nz
the industry here). Would also try and use screw terminal blocks with
built-in leaves that protect the screw head from the wire. Much
better, especially if you want to redo the connection a few times.
I would never try and terminate soldered wires in a screw terminal
block (it just isn't good practice).
Chris Jones
I agree totally that soldered wires should not be put into any sort of screw
terminal. I have learnt that the hard way: A long time ago I wired a lot
of screw terminals after first soldering the ends of the wire, and a few
years later I found that the terminals were loose and in some cases the
wires had fallen out. If the wires were carrying current, they could get
hot and start a fire. If they were for earthing etc. this could also be
dangerous. I had to rewire the whole lot, without the solder.
I wonder if this will be the same with lead-free solder. I would rather not
try it on anything important.
By the way you can buy screw terminals which have a flat piece of metal that
clamps down on the wire instead of the screw itself. This avoids damage to
the wire but the terminals cost a bit more. I would suggest buying the
better terminals if this sort of thing interests you.
If you use crimp-on ferrules, make sure you have a really good crimp tool,
because I have seen wires fall out of poorly crimped terminals. The one
common characteristic of all good crimp tools, it seems to me, is that they
cost at least a week's wages to buy.
Chris
elect...@electrician.com
built-in leaves that protect the screw head from the wire. Much
better, especially if you want to redo the connection a few times.>
That is the way it is done. This is a very efficient and common
practice in the Control Industry.
Ralph Mowery
"Zak" <du...@nomail.invalid> wrote in message
news:Xns9788D386...@66.250.146.159...
Either just strip the wire and insert it or use some hollow pins on the end
of the wires.
http://www.chromate.com/AgentCatalogWeb/Section%2020.pdf
And look on page 24 for them. YOu should also get their crimping tool.
I have seen and used thousands of the pins at work. Everything from a # 22
or so wire for a 4 to 20 ma circuit to larger wires.
Some RTDs came in (probably 200 or more) with the same type of connectors.
They had very small wire and were just put under the screws. On the other
side we used the hollow pins or just the bare wire under the screws.
sQuick
"Zak" <du...@nomail.invalid> wrote in message
news:Xns9788D386...@66.250.146.159...
use bootlace ferrule type crimps, and use the correct size connector
strip for the size of cable you are using.
From the fact that you are quoting 1.5mm2 cable I would guess you
are in the UK....All the main wholesalers stock ferrules and the correct
crimping tools.
sQuick..
Roy L. Fuchs
>Back to basics here guys.
>
>I am referring to a terminal strip like this.
>http://www.ledlight.dk/images/samlemuffe400x320.jpg
>It may be 3 amp or 5 amp or something similar to that sort of low
>capacity.
>
>The wire may be anything from wire which is thinner than bell wire
>up to approx 13 amp mains flex (1.5 mm^2).
No, the wire may NOT be in that range (thinner than bell wire). The
terminal strip you show has a minimum wire size acceptance as well as
a maximum.
>
>-----------------------------------
>The QUESTION is this .... If you were using a terminal strip to
>connect some wires then how would you prepare the ends of the wire
>going into the terminal strip? It seems that there are few
>satisfactory ways.
>-----------------------------------
That should read "There are few satisfactory ways".
>You can just strip back the insulation, twist if multi stranded,
>insert and screw down.
If you strip it correctly, it will retain its original twist. Also,
shear cutting should be used, NOT some lame pinch type snips.
> However there is always a risk that some
>of the multi strands might break if the screw is tightened too
>much.
Shouldn't be.
>However if the wire is quite fine then you may have to fold the
>are wire back on itself.
Bad practice, and likely that the wire is below the minimum spec for
the connector block.
> Maybe do that several times. But that
>does not come out cleanly unless the retaining screw is almost
>taken out.
Bad practice. Should not be done... at all.
>You can add thickness to a fine wire by soldering/tinning the end
>of the wire before it goes in.
Such terminal strips are not meant to accept tinned ends of stranded
wires. That is out of spec.
> But this adds a lot of fragility
>because where the solder ends is the point where the wire is
>likely to bend if it is moved around in use.
There is also a solder "creep" issue to worry about, and it is a
significant issue.
http://en.wikipedia.org/wiki/Creep
>I've even seen people sticking in *insulated* wire and tightening
>the screw until it met the copper. This could work rather nicely
>but only if you can get the depth just right. It seems to me that
>chance plays far too large a part here.
The instance for having insulator in the screw to wire interface is
too high. This is another practice that should be avoided.
>The way I would love to do it is to get some sort of crimping tool
>and put a small brass collar over the wire and squeeze the collar
>on securely. The brass would be tough enough to resist the screw
>doing any real damage.
Yes, brass creeps even less than copper, and far less than solder.
In this case, one MAY use a smaller than spec'd wire size as well.
The tin plated crimp section of a cut off ring terminal (minus any
insulation) would also be a good candidate for this procedure.
>
>What do you find is the best?
The right size solid wire is a straight insertion and clamp. The
right size stranded wire with large gauge strands is a simple insert
and clamp as well. Finer strands works, but starts to lean toward
your last solution.
One should never apply a tinned stranded wire end in a screw clamp
type terminal due to creepage issues.
Roy L. Fuchs
snip
>I would never try and terminate soldered wires in a screw terminal
>block (it just isn't good practice).
My prior argument in another thread in this group has been
reinforced. I am redeemed!
Screw all the idiots that said it was OK too!
Rheilly Phoull
From my view which has been formed over many years, use crimp lugs that
capture the insulation inside the coloured pvc sleeve. I have had long
periods of replacing bootlace sleeves that would appear to be a good system
but in practice dont work out. It maybe they were not properly installed but
IMHO they just are not reliable in the long run. Also as mentioned
previously the connectors with the crush tab are a better proposition and
are the "norm" for commercial installations. If possible use crimp lugs with
flat sections that go into the connector strip. The professional crimpers
made for each particular size of lug (Making a hexagonal compression) are
the best but of course are expensive. It all depends where you are in the
standard of installation :-)
--
Regards ......... Rheilly Phoull
Ben Miller
news:3ock12t58k14f4d9j...@4ax.com...
Snipped excellent response..
I agreed with you in the last thread, and I agree now. When you need
reliability, use the correct size wire, apply it per the terminal strip
manufacturer's recommendations, and don't use jury-rigged methods such as
folding, soldering, etc.
I would point out to the OP that the terminal strip shown is a cheap type,
which looks like the one Radio Shack sells for experimenters. It will work
fine if the wire size is large enough. As others have mentioned, a better
device with a clamping plate will accomodate a wider range of wire types and
sizes, and might meet the requirements without the questionable methods.
This is pretty much the norm for industrial control terminals.
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com
Franc Zabkar
<arfa....@ntlworld.com> put finger to keyboard and composed:
FWIW, the Australian Wiring Rules prohibit the use of tinned wire in
screw terminals for much the same reasons that you have outlined.
- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.