Don’t scrimp when it comes to the crimp

Im often asked by my power voyaging clients, “What do I need to know about making good crimp connections?” Fortunately, not very much.

Material selection

High quality solderless or “crimp” 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.

There are three kinds of insulation available on solderless connectors: PVC, nylon and heat-shrink. The PVC is the most common, and it 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/wire size 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 that will grow during the heating/shrinking process. Crimping tools with gently rounded dies should be used for attaching this type of solderless connector. Test the tool you intend to use.

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.

Tools

There is some debate as to which tools are the best for installing solderless terminals. Ratcheting tools apply pre-set 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 overkill. Although the ratcheting crimp is preferable for the less experienced, the conventional, non-ratcheting crimper can yield good results if attention to detail is observed. My preference is for the latter because it is nimbler, and it can fit more easily into tight spaces.

Manual or automatic strippers may be used. Either is fine provided it does not damage the conductor strands.

Follow these steps to obtain a reliable crimp:

– Ensure that the crimping tool being used is of the proper size and die configuration for the crimp needed.

– 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 entry as the wire is inserted into the connector.

– 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 terminal. 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 (optional but highly desirable) strain relief sleeve from functioning properly.

– Execute the crimp. The ratcheting mechanism should travel through a full cycle before the crimp is released. Most won’t release without completing a full cycle. 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 that 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 can 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, called “bell-mouthing”, should be evident. 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, 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 twelve-gauge crimp should be able to support 70 lb. for UL approval and 110 lb. 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, bullet, flanged spade and snap spade. Any type of quick disconnect, often a spade or bullet, 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 correctly sized 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 incorrectly sized ring will result in a poor connection and a loose fastener; the ring size must match the screw or stud size. Ring sizes range from #6 screw to 1/2”.

When properly installed, high quality solderless terminals can be expected to achieve low-resistance and long-lasting electrical connections.

For many years a full-service yard manager, Steve now works with boat builders and owners and others in the industry as Steve D’Antonio Marine Consulting. He is an ABYC-certified Master Technician and sits on that organization’s Engine and Powertrain, Electrical, and Hull Piping Project Technical Committees. He is a long-time Ocean Navigator contributor. 

Categories: Marine Technology, Power Voyaging