Two wires into a crimp connector?

Wunja

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Connections to my switch panel are made by screwing a washer down onto the bared cable end. I'm considering using crimped eyes instead, but some of the connections have two wired attached. There isn't enough room to get two crimps on to the connection.
Is it acceptable to go up a size of crimp and push both wires into it?
If it makes any difference, I'm using a ratchet crimping tool (best tool buy 2009!)
Many thanks for your opinions.
 

RivalRedwing

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I do, but I take good care to ensure that both wire ends are well in to the crimp (ie just visble at the terminal end). Also depends on what I am connecting - don't cheat a fuse or breaker
 

grumpy_o_g

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It's not best practice for a couple of reasons but you get a perfectly good electrical connection if you do it right.

Tape the two wires together about 1/4" back from the insulation ending. and tape again about 1" behind that. This is to stop the two wires pulling apart and vibrating against each other, which is the biggest risk.

Wearing clean grease-free gloves or with a clean cloth twist the wires individually and then twist the two cores together. Don't twist the cores together too tightly. They shouldn't be under strain and trying to pull apart.

Ideally you should then tin the conductor making sure it penetrates through to the two cores. Trim the conductor to the right length and then crimp.

Aside from the two cables vibrating against each other and creating a stress point the other issue is that it's very difficult to seal the crimp collar against the insulator - this means that moisture wicks up the conductor and causes oxidisation. The best idea is to use some kind of silica gel or PRC that sets flexible. Use this to create a seal between the two cables and put a heatshrink tube over the whole lot.

Having said that, two wires shoved in a terminal block will often last for ten years or more so you could say this is all over-kill. The thing is to make sure the wires are well twisted together before crimping but not under any strain and then make sure they are taped together and well supported but don't have any spots where they are vibrating hard against a fixed point (hope that makes sense).
 
D

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Jump From The Panel To New Rail Post or Connector

I had a similar problem with no further space on the rail. My solution was to add another rail and use one of the posts to jump the power across between the rails. Then I used the correct sized crimp on the new rail's post.

I know its probably not the same i.e. a rail / strip with connections, but you may be able to jump from your switch panel connection with a single wire to a new connection / post where you can connect both wires together.

The back of my switch panel is very tight and the boat was rewired professionally quite a few years ago. There are some double wires made up to a single crimp. The only connection issue I have had, was the double wire single crimp join. It was the gas detector circuit and the wires had loosened with the panel door opening and closing, I assume.

I only found out when I tested the gas alarm with an unlit lighter!
 

Allan

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I used to wire and later inspect military hardware to MOD standards. At that time it was forbidden to twist wires before putting them into crimps. More than one wire in a crimp was also forbidden. Personally, habit stops me twisting wires but I'm happy to put two wires in one crimp as long as it is the right size. The point about taping the wires together above seems good to me. The key thing is to reduce stress, in particular adjacent to the crimp.
Allan
 

ghostlymoron

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I'm sure from an electrical contact point of view that 2 wires in a crimp is OK but it's far better practice to stick to 1 and, as has already been said, it makes for a much neater installation to have each wire properly terminated to a fixed terminal block and labelled so you know what's what.
I don't always practise what I preach though.
 

Porthandbuoy

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2 into 1 is common practice in industry where you are perhaps running a common negative down every other connection in a row of terminals. As long as you don't remove any of the copper strands you'll be okay. As mentioned above, chafe and strain relief on a boat are essential.

I don't agree with twisting the cores together and then tinning them. That would form a solid mass that the crimp would crush; possibly leading to broken strands and a weak, short-lived connection. Use tinned multi-core cable, twist the two cores together yes, but don't solder them.
 

Bru

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2 into 1 is common practice in industry where you are perhaps running a common negative down every other connection in a row of terminals. .
Not anywhere I've ever worked it hasn't been :eek:

It's an absolute no-no as far as I'm concerned. The crimp connector cannot form a proper crimp around the conductor cores if two wires are inserted and although, with care, you'll get a connection it will be more prone to fatigue failure etc.

Using an oversize connector and inserting two conductors into it is a sure fire recipe for a mechaniclly poor crimp as well. The two conductors will move to a side by side position within the connector as you apply force on the crimping tool and thus the oversize connector will not be fully crimped down onto the conductors which will then be liable to pull out of the connector at some future date.

I don't agree with twisting the cores together and then tinning them. That would form a solid mass that the crimp would crush; possibly leading to broken strands and a weak, short-lived connection. Use tinned multi-core cable, twist the two cores together yes, but don't solder them.
Agree with you about tinning conductors. It seems to be a modern obsession to do so and again it was absolutely not the done thing when I was trained as an electrical wireman. It inevitably produces a stress point where the conductor will ultimately fail. And as you rightly point out, it means the crimp connector is crushing a solid lump of solder and wire instead of the deformable copper conductors it was designed to be used on.

Crimp connectors are wonderful things used correctly but if you abuse them ....
 

Bassplayer

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Agree ^^. Also, if you use heat shrink connectors or heat shrink the cables to the connector it makes for a more secure and stress relieved connection (can I say stress relief on here??)
 

Ubergeekian

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It's an absolute no-no as far as I'm concerned. The crimp connector cannot form a proper crimp around the conductor cores if two wires are inserted ...
How does the crimp connector know it has two wires going into it and not a single thicker one with the same total size?

Agree with you about tinning conductors. It seems to be a modern obsession to do so and again it was absolutely not the done thing when I was trained as an electrical wireman. It inevitably produces a stress point where the conductor will ultimately fail. And as you rightly point out, it means the crimp connector is crushing a solid lump of solder and wire instead of the deformable copper conductors it was designed to be used on.
Aluminium crimp connectors form a cold welded bond with copper conductors - I doubt if you'd get that with tinned conductors.
 

mitiempo

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I wouldn't put 2 wires in the same connector. Possibly not a great connection and it won't be watertight with heatshrink. I would use one connector for each wire and the screw terminal will hold both to the fuse or breaker.

The connectors Slycat linked to don't apply as the poster has screw connections.
 

grumpy_o_g

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At that time it was forbidden to twist wires before putting them into crimps.
Interesting as it was absolutely de-rigeur and what we were all taught in the 70's and 80's in the RAF. Can't speak for the Army but the RN aircraft mech's were certainly taught the same.
 

grumpy_o_g

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Using an oversize connector and inserting two conductors into it is a sure fire recipe for a mechaniclly poor crimp as well. The two conductors will move to a side by side position within the connector as you apply force on the crimping tool and thus the oversize connector will not be fully crimped down onto the conductors which will then be liable to pull out of the connector at some future date.
That's why you twist and then tin the conductors and bind and support the cables. It's not perfect but we're talking about the best way to do something less than ideal here.

Agree with you about tinning conductors. It seems to be a modern obsession to do so and again it was absolutely not the done thing when I was trained as an electrical wireman. It inevitably produces a stress point where the conductor will ultimately fail. And as you rightly point out, it means the crimp connector is crushing a solid lump of solder and wire instead of the deformable copper conductors it was designed to be used on.
I keep hearing this about a stress point being formed when you tin conductors. If you tin the the cable properly then you have a stress point just inside the insulation where the insulation provides some rigidity and stress relief. If you don't tin the conductor you still have a stress point but this time it's where the conductor exits the crimp. Even if the crimp is of a type that clamps the insulation as well there's still a hard point and there always will be. I've seen a lot more badly supported un-tinned crimps fail than tinned.

As for tinning producing a solid lump of solder, yes it should do if done right. If you are using proper crimping tools the crimp (which is harder than the solder but softer than the conductor) will then produce a more or less homogeneous mass with the solder, which also be deformed. If you tin then you are crimping a single deformable piece of cable in effect. If you don't tin then you are crimping down on to multiple strands laid over each other. These strands can slip far more easily as they take up a new position over time no matter how hard you crimp down.

We pulled quite a few crimps apart in training to prove this and every time the tinned crimp was stronger than the un-tinned one.
 

Allan

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Interesting as it was absolutely de-rigeur and what we were all taught in the 70's and 80's in the RAF. Can't speak for the Army but the RN aircraft mech's were certainly taught the same.
When I read your post, I remembered a previous thread in which exactly the same was said. It surprised me at the time and still does. Please don't think I am doubting you, I certainly am not. How strange is it that we were sending items to all three services which were made to one standard and any work done in the field was done to a different standard? Having worked with MOD stuff for many some years (1975-1987), I'm not that surprised!
Allan
 

wot

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In total agreement with Brigantia. A correctly formed crimp using the specified crimp & tooling for the cable size provides mechanical strength as well as a good electrical connection.
A good explanation of what happens during the crimping process is provided here:http://www.cableaccessories.com/home/free-crimping-guide.
Some of the comments here are, in my opinion frankly wrong and that some practices, such a putting two cables into one crimp are "common in industry" would cause me to question the standards being applied with that industry.
Some of the other practices:
Twisting of cable: - The only permitted 'twisting' of the cable was to restore the lay of the cable if it had become disturbed during the operation of stripping the insulation.
Tinning:- Absolute no-no. The deformation of the cable during the crimping procedure is designed such that the conductors are deformed in a controlled, designed manner. Introducing a modification to the process such as tinning the conductors brings extra material into a process which was designed without that extra material.

Frankly, some of the practices mentioned here would have been an instant fail on the wiring module of my Leading Hands Course and certainly would not have been approved by any Fleet Air Arm Radio Trade Supervisor that I've ever worked for or with.
 

grumpy_o_g

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When I read your post, I remembered a previous thread in which exactly the same was said. It surprised me at the time and still does. Please don't think I am doubting you, I certainly am not. How strange is it that we were sending items to all three services which were made to one standard and any work done in the field was done to a different standard? Having worked with MOD stuff for many some years (1975-1987), I'm not that surprised!
Allan
1976 to 1978 so almost identical timeframe. You're right - we shouldn't be surprised. I do know the ground trades and the heavier stuff had different rules though. The only time I saw anything different was when it came in from the manufacturer though.
 

Allan

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1976 to 1978 so almost identical timeframe. You're right - we shouldn't be surprised. I do know the ground trades and the heavier stuff had different rules though. The only time I saw anything different was when it came in from the manufacturer though.
Interesting that WOT was taught not to twist wires before they go into crimps. By twisting, do you mean restoring the lay? That is what we were taught.
Allan
PS We were the manufacturer.
 
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grumpy_o_g

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In total agreement with Brigantia. A correctly formed crimp using the specified crimp & tooling for the cable size provides mechanical strength as well as a good electrical connection.
A good explanation of what happens during the crimping process is provided here:http://www.cableaccessories.com/home/free-crimping-guide.
Some of the comments here are, in my opinion frankly wrong and that some practices, such a putting two cables into one crimp are "common in industry" would cause me to question the standards being applied with that industry.
Some of the other practices:
Twisting of cable: - The only permitted 'twisting' of the cable was to restore the lay of the cable if it had become disturbed during the operation of stripping the insulation.
Tinning:- Absolute no-no. The deformation of the cable during the crimping procedure is designed such that the conductors are deformed in a controlled, designed manner. Introducing a modification to the process such as tinning the conductors brings extra material into a process which was designed without that extra material.

Frankly, some of the practices mentioned here would have been an instant fail on the wiring module of my Leading Hands Course and certainly would not have been approved by any Fleet Air Arm Radio Trade Supervisor that I've ever worked for or with.
Damned good job you didn't get near any of my aircraft then - you would have been thrown off them :):) Having worked alongside matelots on a few occasions we were surprised to find that we did do exactly the same thing. Certainly mechs on the Harriers I worked with were happy tinnng cables - in fact they came from the manufacturer like that on most connections (the cables, not the the matelots). As Alant said though, different people were taught different things it seems.

As for which is better the fact that no-one can agree suggests there's not that much difference either way From my perspective, if you are tinning the conductor properly then there's almost no difference in thickness and the solder merely fills in the gaps between the strands - and the crimp is merely a piece of deformable metal and doesn't flow significantly in between the strands, which should also deform but only will if you're using a very good crimping tool. Even with a good high pressure crimping tool with a stop that's been set up properly, cut a crimp open that has been tinned and one that hasn't and see which you feel has the better look to it. Then try pulling them apart first and see which one gives way under the least tension as well. The tinned crimp is stronger and looks better in cross-section (though you can't see any noticeable difference in conductivity or resistance). I agree twisting is normally merely to restore the lay of the cable but that's a bit tricky when you're talking about putting two cables into one crimp where I would definitely twist the cables together and tin them. Nobody would put two wires into one crimp on an aircraft unless doing battle repairs but we're not talking about a fast jet and, done well, there's no reason to shudder. It'll survive as long as many other parts of the wiring on the boat and not pose any risk. I wouldn't do it unless there was no alternative (and it's unlikely there's not) but it's not a great deal. I'd far rather see two well-supported cables going into a well-made single crimp than two unsupported cables going on to individual crimps.

Now, do you prefer Rocna's or CQR's? :D:D
 
D

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Fleet Air Arm and other military experienced electricians; is a Harrier (or any plane) wired up using the type of Halfordesque crimps that I use on my boat? Could it be that tinned cable ends and crimps on planes are special crimps for the tinned application? Are all crimps equal!
 
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