Potted Cable: How To Create This Cable Protection

Car wire harnesses undergo various stresses and exposures that can damage or corrode the electrical connection. But potted cable give these connections a lifeline by providing strain relief and chemical/environmental protection.

Let’s define this cable, its benefits, and how to create one in a few steps. Read on to learn more!

What Is a Potted Cable?

Before defining this cable, let’s look at the backpotting process. Potting or backpotting in electronics refers to filling electronic assemblies using a gelatinous material.

This filling solidifies to protect the wires from vibrations, shock, moisture, corrosive liquids, etc.

The process first involves placing the assembly inside a pot (mold) and pouring the gelatinous material to fill the cavity.

Therefore, a potted cable is an electrical wire with its connector(s) filled with this insulating liquid compound. But at the time of use, this compound is in solid form.

Wires attached to a connector before wiring (note the cavity and walls around it)

You can use this potting technology on PCBs with components installed via surface-moun t technology.

But in this application, you must use compounds with a low glass transition temperature, such as silicone and polyurethane.

Using high Tg compounds can break the solder bonds due to solder fatigue. This compound shrinks as a rigid solid over a broad temperature range, creating enough force to break the solder bonds.

However, transparent conformal coating is better than potting in circuit boards. It is lighter and easier to repair, test, and inspect.

Why Use Cable Connector Backpotting

Potted cables feature solid seals on the rear of the cable connectors with the following benefits.

Strain Relief

The primary benefit of backpotting is to provide additional holding force to the wires. These cables usually have crimped or soldered joints to the contacts. The solidified block covering the wires creates a firm footing that provides strain relief for the wires.

Wire connectors with rear fillable cavities

Therefore, pulling the wires is less likely to remove the wire strands from the contacts. Also, it is less likely to draw the contacts from the connector housing.

Environmental Protection

Besides mechanical protection, backpotting seals the wire-contact joint from moisture and dirt on the outer side. Remember, most connectors have gaskets or seals that protect the inner joint from the elements after mating. But the outer section remains exposed.

A close-up image of a car wire harness with multiple connectors

Backpotting covers this rear section, creating surface-to-surface coverage. This design is critical for external wire harness joints exposed to the elements.

Chemical Resistance

The solid seal can also protect the wires from chemicals in the vehicle. These include solvents, oils, fluids, and corrosive liquids.

Enhanced Reliability and Durability

Mechanical protection (strain relief) combined with moisture, dirt, and chemical resistance makes potted cables more stable, reliable, and durable.

The minimized movement near the joint reduces wear, making the wires, insulation, and joints last longer.

Better Thermal Performance

Some of these potting materials give excellent heat dissipation properties, quickly evacuating the heat generated by the wires.

Easily Customizable

The potting process requires a pot, cavity, or mold to pour the liquid epoxy-like material. Therefore, you can adapt the potting process to fit any connector shape or size.

Car stereo wire connectors

Using a gelatinous material also simplifies the installation process. And you can apply the material to any vehicle wire harness connector.

Reduced EMI

While some potting materials give better thermal performance, others help reduce electromagnetic interference. If signal integrity is critical in the wire harness and connector, use potting materials that provide EMI shielding.

Potted vs. Encapsulated Cable

An alternative to potting is encapsulation. Some people use the terms interchangeably because both involve pouring a liquid resin material over the electrical joint. But they are different.

Potting involves pouring the resin material into the pot mold and covering the components or devices.

However, encapsulation involves immersing the device in the resin compound. Therefore, the process applies a protective coat around the exterior of the entire component. This connection is ideal for electrical joints that you’ll submerge in water.

Typical Backpotting Materials

Some of the tried and tested materials include the following.

Stycast 2651MM (with catalyst 9)
Robnor Resins PX439XS/BK
Stycast 2651 (with catalyst 11)
Epoxies 50-3122RBK

Clear resin material in a cup

How To Create a Potted Cable

These backpotting materials or resins are like glue. So, it would be best if you began by having a clean working area inside the pot or cavity. And if you don’t have a retaining wall, create it first to surround the working area.

This wall can be temporary if not part of the connector or mold. For instance, you can use masking tape.

A roll of masking tape

Also, consider the crimp contact design. If open, you might be unable to retain the backpotting liquid behind the connector.

And before you embark on the process, use an external fixture to keep the connector steady. A simple option is to mate the connector to its opposite end.

The goal is to keep the contacts aligned in the housing to remain straight when pouring the resin.

Fixing the contacts at an angle can increase wear or insertion force, leading to an early failure.

Backpotting Steps

Once set, follow these steps to create your potted cable.

Step 1: Mix the Epoxy Compounds

Most backpotting epoxy compounds come in two parts that require mixing to initiate the hardening process.

Check the mixing instructions and the drying time before starting the process.

Mix the resin and hardener slowly to minimize trapping air bubbles.

Epoxy compounds in different cups with varying colors

Step 2: Load the Mixed Compounds in a Syringe

Load this mixture into a dispensing system with an appropriate nozzle size for application, such as a syringe. Remember, the liquid is thick and challenging to push out if the nozzle is tiny.

Step 3: Dispense the Compound

Dispense the epoxy via the syringe to the mold and fill the volume to the required level.

Step 4: De-Gas the Fluid

Although unnecessary, you can place the filled cavity in a vacuum environment to pull out any trapped air bubbles.

Step 5: Let It Set

Let the gelatinous material solidify or cure in the cavity. You can place the device in a warm environment to hasten the curing period.

Step 6: Inspect the Potted Cable

After setting, check the complete potted cable to ensure the contacts and everything else is okay.

Wrap Up

Potted cables are essential in safeguarding exposed electrical connectors, especially vehicle wiring. Creating them is simple, provided you follow the steps above and the manufacturer’s guidelines.