Don’t Scrimp When It Comes To The Crimp - PassageMaker

Don’t Scrimp When It Comes To The Crimp

Readers frequently ask, “What do I need to know about making good crimp connections?” Fortunately, not very much.
Author:
Publish date:
101909002

MATERIAL SELECTION

High-quality connectors start with high-quality materials. When a connector is manufactured, a die stamps it repeatedly. This helps to cut and form the metal, but it also work hardens it. Work hardened metal is brittle and difficult to form. As a result, it is not preferable for crimping. Annealing returns the copper to a softer, more malleable state. The barrel portion of a quality connector appears seamless. This is because it is actually welded or brazed together. This means that it can be crimped at any point around the barrel without bursting, while the inside portion of this barrel has serrations that are designed to cut into and grab hold of the wire as the crimp is made. This forms a good mechanical, as well as electrical, bond. Once the connector is stamped, cut, and annealed, it is then tin-plated, yielding superior corrosion protection.

 The looks of a proper connection.

The looks of a proper connection.

There are three kinds of insulation available on solderless connectors; PVC, nylon, and heat shrink. The PVC tends to be more brittle and likely to crack if over crimped. This can lead to a short or crossed circuit. Nylon insulation is much more durable. It is very difficult to pierce or remove, and as a result, is more desirable. It is distinguishable from the PVC by its translucent, as opposed to opaque, color (although it utilizes the same familiar red, blue and yellow color coding). Heat shrink insulation is similar in appearance to nylon except it is somewhat suppler. Care should be exercised in crimping it, as it is not difficult to create small holes while crimping, which will grow during the heating/shrinking process. Crimping tools with gently rounded dies should be used for attaching this type of solderless connector.

To assist in wire entry, the mouth of the connector should be tapered or funnel shaped. With this, the wire strands are less likely to peel back as the connector is placed on them. Once the conductors are safely tucked into the crimp, the extension leading from the funnel is also crimped around the wire's insulation. This insulation crimp is typically constructed of brass and it serves as a strain relief aid. It is especially useful in areas of movement and vibration, i.e., just about everywhere aboard.

062309011

TOOLS

There is some debate as to which tools are the best for crimping. Ratcheting tools apply preset pressure, making them attractive for those who undertake electrical work infrequently. This is the only type of tool that is approved for aviation use by the FAA. For the purposes of the cruiser, however, it’s bulky and may be over kill. Although the ratcheting crimp is preferable, the conventional, non-ratcheting crimper can yield good results if attention to detail is observed. My preference is for the latter.

Manual or automatic strippers maybe used. Either are fine provided they do not damage the conductor strands.

Follow these steps to obtain a reliable crimp.

  • Insure that the crimping tool being used is of the proper size and die configuration for the crimp being used.
  • Strip the wire. This should be done without damaging any of the strands. The strands should remain straight and uniform. Any strands exceeding the diameter of the conductor will catch on the crimp as it is inserted.
  • If using a ratcheting tool place the crimp in the tool. Be sure it is in the proper die station, red, blue or yellow. If using a non-ratcheting tool it will be easier to place the crimp over the wire first, then carry out the crimp.
  • Insert the wire into the crimp. The conductor should be flush with the flange end of the crimp barrel. Uninsulated wire should not protrude from the rear end of the conductor, as this will prevent the strain relief sleeve from functioning properly.
  • Execute the crimp. The ratcheting mechanism should travel through a full cycle before the crimp is released. Remember, if using a non-ratcheting crimping tool, enough pressure must be applied to break down the oxides that are present on the inside of the connector, and so the serrations can imbed themselves into the wire strands slightly. This area of the crimp must be gas tight. If gas, in the form of air, is present, then corrosion will follow. Alternatively, over crimping will elongate and weaken the wire strands. This will create a mechanically weak connection that will have higher than acceptable resistance. If the tool being used does not simultaneously crimp the strain relief sleeve, this must be crimped separately.
  • Release the crimp and inspect. The wire should be held firmly and a slight expansion of the flange end of the barrel should be evident. This is called "bell mouthing." This indicates that the crimp pressure was applied at the proper distance from the end of the barrel. Using moderate force, you should not be able to pull the crimp terminal off the wire, if you can then the terminal is defective or it was not properly compressed. In order to receive approval from UL Labs, or the military, crimp connectors must meet a variety of specifications, not the least of which is tensile strength. For example, a 12-gauge crimp should be able to support 70 lbs. for UL approval, and 110 lbs. for Milspec approval, which is more than the average adult can exert using his or her fingers.

A quality crimp connector should possess the following features:

  • At least a UL, but preferably a Federal Government Spec (Mil-T-7928) approval.
  • Annealed copper construction.
  • Tin plating.
  • A smooth, burr free, edge.
  • Insulation that is not easily dislodged from the connector.
  • A UL or Mil tensile strength rating.
  • The most reliable styles of solderless connectors for marine use are; butt, ring, flanged spade and snap spade. Any type of quick disconnect, often referred to as a spade, while under some circumstances acceptable, is less than ideal.

When selecting a solderless connector never cut back conductor strands to fit a connector. Use the correct size connector for the wire; Red -AWG 18-22, Blue-AWG 16-14, Yellow-AWG 10-12. The sizes of the rings on ring connectors are equally as important. Using the incorrect sized ring will often result in a poor connection and loose fastener. Ring sizes range from number 6 screw to 1/2 inch.

The life of properly installed, high quality solderless connectors, used in conjunction with tinned marine grade wire, can be measured in decades.

Related