This section talks about the proper use of IDC connector in wiring up a model railroad layout.
This section is written in the from of a FAQ.
1) WHAT ARE IDC CONNECTORS?
2) HOW DO IDC CONNECTIONS WORK?
3) WHY USE IDC CONNECTORS?
4) HOW CAN I KNOW THAT IDC CONNECTORS CAB BE RELIABLE?
5) WHERE DID IDC TECHNOLOGY COME FROM?
6) WHY DO YOU HEAR STORIES OF IDC CONNECTION FAILURES?
7) WHAT ARE THE ABSOLUTE NON NEGOTIABLE IDC USAGE RULES FOR RELIABLE IDC CONNECTIONS?
8) WHAT WILL HAPPEN IF I FAIL TO FOLLOW THE RULES?
9) WHERE DO I FIND THE SPECIFIC RULES FOR A GIVEN IDC CONNECTOR?
10) SUMMARY TABLE OF 3M IDC CONNECTORS SPECIFICATIONS
11) WHAT STEPS CAN I TAKE TO MAKE SURE I HAVE RELIABLE IDC CONNECTIONS?
12) WHAT ARE THE WORKING STEPS I NEED TO DO TO MAKE A GIVEN IDC CONNECTION?
13) Where do I buy IDC connectors?
1) WHAT ARE IDC CONNECTORS?
IDC are modern precision connectors that allow single wire or a large number of wire connections to be made all at once without the need to prepare the wire prior to making the connection. Unlike all other connectors, IDC connectors are 100% based on the mechanical and material properties of the copper wire itself interacting with a precision made and designed U-hook (AKA Blade). They only work with copper wire!! As a consequence of this scientific/physics based connector technology, there are some associated strict rules involved in their usage and the failure to follow them will result in long term connection failure.
2) HOW DO IDC CONNECTIONS WORK?
IDC = Insulation Displacement Connection. The name more or less describe the process of how the connection is made. As you apply pressure to the IDC connector, a sequence of steps occur all at once. The steps are:
1) The wire insulation is moved out of the way by the TOP edge of the U-Hook (AKA blade) to allow the center of the U-Hook to come into contact with the round wire.
2) The exposed round copper wire is forced into the narrow IDC's U-Hook slot becoming mechanically deformed to fit into it as the pressure forces it down. The round wire in direct contact with the U-Hook becomes FLAT as it enters enters the slot.
3) As the flat copper wire slides down it creates a wiping action that cleans the U-Hook metal surface that is in direct contact with the copper wire.
4) AT NO TIME during the process does the U-Hook CUT the wire. The U-Hook edge is NOT sharp by design. It is actually very blunt.
5) The deformation action that flattens the copper wire inside the U-hook slot exposing internal virgin copper to the just cleaned U-Hook contact surface. The contact area is now physically larger than what can be accomplished with just a round wire and a screw.
6) The relatively soft copper wire mechanical compressive deformation properties in combination with the U-Hook compressing spring action creates a constant high pressure contact area.
7) This high pressure contact area is designed to be maintained at all times to keep it an air tight metal to metal connection.
8) The wire insulation is still in place on both sides of the U-Hook apply some pressure. Although not an air tight seal, nor is it a requirement for it to do so, it does keep other solid contaminant material out.
3) WHY USE IDC CONNECTORS?
1) Fast connections: A quick squeeze of the proper IDC crimp tool with the wire properly inserted is all you need to do to make the connection. The actual connection time is about 2 seconds. Setup time will take about 10 seconds to position the wires into the connector. The whole process from start to finish will get faster too the more you do...aka practice.
2) Reliable connections: If one is using the proper gauge (AWG), type (Solid/stranded) and material (Copper) wire in the IDC connector, the design guarantees a very reliable and low resistance connection. Its based on the science regarding the physical properties of the copper wire interacting with the precision "U-hook blade" under pressure. The resulting connection is GAS TIGHT oxygen free. In other words a pure raw metal to metal connection with no oxidation potential is made.
3) Less work: There is minimal setup and tear-down time require to make the connection. You do not need multiple tools nor do they need to be moved to the work location. There is no wire preparation required (insulation stripping, cleaning or tinning) when you get there.
4) Safer than Soldering: This benefit become obvious when you working in tight cramped quarters under the layout on wiring that is above you head. Hot solder can fall on any part of your body at any time. You do not have to breath any of the toxic fumes created by the act of soldering.
4) HOW CAN I KNOW THAT IDC CONNECTORS CAB BE RELIABLE?
Two big examples that we all come into contact every day.
1) Office "land line" telephone systems found all over the world.
2) Personal Computers.
Literally Billions of Billions of IDC connections have been made over the world in the past 50 years to make these system work and they still work today. You rely on them everyday.
In the electronics industry, WE NEVER HAVE PROBLEMS using IDC technology.
5) WHERE DID IDC TECHNOLOGY COME FROM?
The telephone industry developed it.
If you have ever seen a "telephone room" of an office, you would see rows and rows of that are called "Punch Blocks". Punch Blocks are an array of exposed U-Hooks formed in rows allowing wires to have a common connection within each row with other wires through the punch block. The "Punch Block" allowed 100's of telephone wires connections to be made quickly in office buildings and facilitate quick changes without the need for any soldering or terminal blocks. The term "Punch" refers to the special tool that rams the round "telephone wire" into the slot to create the high pressure contact. Since round telephone wire has only one standard copper wire gauge, there is no chance of using the wrong type of wire with the "Punch Block"
IDC technology exploded with the development of "Ribbon Cable" allowing up to as high as 64 wire connections to be made instantly all at once. Mainframe computers adopted it quickly. When the personal computer industry came along, its use exploded. Why? IDC technology reduces the cost of manufacturing products by reducing the time it take for a human to make all the required wiring connections. Like telephone wire, ribbon cable has standardized on one wire gauge (26AWG for the common 0.05" pitch cable).
Both the telephone and computer industry follow the standards they set for this technology and do not violate the rules.
6) WHY DO YOU HEAR STORIES OF IDC CONNECTION FAILURES?
IDC connectors HAVE VERY STRICT ABSOLUTE RULES on how they can be used. Model railroaders disregard these rules because they do not understand why they are needed. They are not aware of or respect the precision science behind how IDC technology works and its limitations. They think the connection is not anything special relative to any other connection. They may also think they are smarter than the connector manufacture recommendations (Standards) and rationalize there way out of following the standard patting themselves on the back for being so clever because they think they just saved themselves some money on wire. WRONG. The opposite is just happened when all is said and done. Unfortunately it will take a bit of time for them to figure that out and when that happens their EGO prevents them from admitting they made a mistake. It's easier to blame the IDC connectors and vent their frustration when people ask about IDC connectors.
7) WHAT ARE THE ABSOLUTE NON NEGOTIABLE IDC USAGE RULES FOR RELIABLE IDC CONNECTIONS?
Not in any specific order.
1) IDC CONNECTORS HAVE PRECISE LIMITATIONS OF THE RANGE, UPPER AND LOWER, OF COMPATIBLE WIRE GAUGES (AWG). DO NOT USE ANY SIZE OF WIRE THAT IS OUTSIDE THE RECOMMENDED RANGE FOR ANY REASON.
2) SOME IDC CONNECTORS HAVE WIRE FORMAT, STRANDED VS SOLID, LIMITATIONS. DO NOT USE SOLID WIRE IN AN IDC THAT WILL ONLY SUPPORT STRANDED WIRE IN THE LARGEST WIRE GAUGE PERMITTED.
3) IDC CONNECTORS HAVE WIRE CONDUCTOR MATERIAL LIMITATIONS. ONLY COPPER WIRE CAN BE USED. DO NOT USE ALUMINUM OR ANY OTHER NON-COPPER WIRE MATERIAL.
4) IDC CONNECTOR HAVE WIRE INSULATION MATERIAL LIMITATIONS. THEY ONLY WORK WITH WIRE THAT HAS THERMOPLASTIC BASED INSULATION.
5) IDC CONNECTORS CANNOT BE USED IN HIGH VIBRATION OR "WIRE WITH MOTION" APPLICATIONS WITHOUT PROPER STRAIN RELIEF SUPPORT. IDC CONNECTORS ARE MEANT FOR MECHANICALLY STATIC APPLICATIONS.
6) NEVER REUSE AN IDC CONNECTOR. THE COMPRESSION PROCESS INVOLVING DEFORMATION IS A ONE TIME PERMANENT PROCESS WITHIN THE U_HOOK. IT IS NOT POSSIBLE TO RE-ESTABLISH THE SAME HIGH PRESSURE CONTACT AREA WITH REPEATED USE.
8) WHAT WILL HAPPEN IF I FAIL TO FOLLOW THE RULES?
Failure to comply will result in the failure to create an air tight compression connection inside the IDC. It is not unlike having a loose screw on a screw terminal block that is supposed to make an electrical connection between two wires.
When the wire gauge is undersize you now have a ticking time bomb electrical connection that will eventually fail sometime in the future. Why? Oxygen will find its way inside and oxidize the copper wire raising it contact resistance. The connection becomes intermittent with movement of the wire as the lack of sufficient pressure allows the wire to move around inside the U-hook contact area.
When the wire gauge is oversize, the U-hook itself becomes destructively deformed. The U-hook no longer has uniform contact surface area and the wire is free to move around inside the deformed blade. There is no gas tight connection established. The connection is basically bad from the start.
TO BE CLEAR. THIS IS NOT A MATTER OF IF IT WILL FAIL. IT IS JUST A MATTER OF WHEN.
By far the most broken rule for Model Railroaders #1 above followed by #6 and then #2. For model railroaders, it means a layout who electrical performance degrades with time forcing one to redo the connections to fix it. When I hear these stories of how they had to remove all these "crappy connectors" and solder the joints I know the real problem is they did not follow the rules be intentionally or by accident.
IF YOUR NOT GOING TO FOLLOW THE RULES THEN DO NOT USE IDC CONNECTORS. SAVE YOURSELF FROM FUTURE PROBLEMS. It is more important to take the time to make reliable wire connections since wiring is part of the foundation of making your layout work. One should instead stick the the wire connection technology they now works for them be it, soldering, twist cap, barrier terminal strips, crimp lugs..ect...
9) WHERE DO I FIND THE SPECIFIC RULES FOR A GIVEN IDC CONNECTOR?
The wire compatibility information is found in the datasheet or manual that comes with the IDC connector.
3M-Scotchlok-Electrical-Run-and-Tap-Connectors
10) SUMMARY TABLE OF 3M IDC CONNECTORS SPECIFICATIONS
Below is a summary table of the wire gauge compatibility using the 3M Scotchlok Series of IDC connectors.
TAP ONLY: The connector only allows the secondary wire to enter and terminate inside.
TAP/RUN: The connector allows the secondary wire to enter one and pass through the connector exiting out the other end. You can also choose to use it just as a Tap connection with the secondary wire terminating inside.
In the above list, the 567, 562, 558 and the 905/905N are the most useful for Model Railroaders.
I cannot comment on the reliability of foreign made versions of the above IDC connectors. They may or may not be compatible with the American Wire Gauge (AWG) standard. They may be based on metric wire standards that are slightly different. You get what you pay for.
11) WHAT STEPS CAN I TAKE TO MAKE SURE I HAVE RELIABLE IDC CONNECTIONS?
Not in any order since all are equally important.
1) Having the proper compression tool. The pressure required for a solid connection is more than you think. The 3m tool is very expensive but I can tell you from experience that if you doing a large layout, the tool is worth every penny. Once it is setup correctly for the 3M connector you are using, it works faster and eliminates over compression mistakes by not damaging the connector compared to common pliers or a monkey wrench. Beside the connector looks nicer using the tool when its done.
2) Tap Connectors: Visibly inspect the wires are all the way in the connector BEFORE crimping. Test the connection after compression is complete by pulling on the tap wire. If you missed, the tap wire will come out.
3) Throw away used IDC Connectors. They are not re-usable.
4) Standardize on the wire sizes that are compatible with the IDC connector. REMOVE all incompatible wires from the layout room. Remove temptation to cheat or accidentally make a mistake.
12) WHAT ARE THE WORKING STEPS I NEED TO DO TO MAKE A GIVEN IDC CONNECTION?
1) Identify the location on the primary wire that allows the best possible secondary wire attachment.
2) Bend the cover out of the way exposing the back of the U-hook so the cover will not fight you.
3) Pry open by hand the open side of the IDC to expose the two wire slots inside.
"Tap Only connector"
4a) Identify the location of the secondary tap wire. It will be in the front (558) or in the back (567) of the connector.
4b) Insert the wire, primary or secondary, that goes to the back of the connector first.
4c) Insert the wire, primary or secondary, that goes in the front of the connector second.
4d) Inspect the Tap wire to make sure the end of the wire is visible in the "inspection window". The inspection window is the rectangular open area between the U-hook and the closed end of the tap wires slot. If you can see the end of the tap wire, you know the wire is PAST the U-hook and will make connection.
Tap/Run connection
4a) Insert primary "run" wire to the back of the connector first.
4b) Insert secondary "Tap/Run" wire in the front of the connector second. This makes the Tap/Run wire position in the slot visible to you.
4c) If your only make a tap connection, Inspect the Tap wire to make sure the end of the wire is past the U-hook and the end of the tap wire can be seen at the other end of the connector.
ALL
5) Position the jaws of the compression tool to the exposed top back of the U-Hook and the plastic underside of the connector that is directly under the U-Hook
6) Compress the U-Hook down into the IDC connector until the back of the U-hook is almost flush.
7) With a Tap connection, tug on the tap wire to make sure it has a solid connection. If you missed the U-hook, the tap wire will come out. If this happens, start over with a brand new IDC.
8) Close the cover down over the back of the U-Hook
9) Re-apply pressure a second time using the same tool. If you are using a good tool, the cover will SELF LOCK into place when sufficient pressure has been applied.
13) Where do I buy IDC connectors?
For IDC specifically, the first place to look is Mouser Electronics
Mouser: 3M IDC wire connectors.
6/20/15