The wire harness and designing consumer appliances
You may be designing your latest project, thinking that the wire harness is just a load of wires. Perhaps you’re focusing more on the form, function and features, which makes it easy to leave the wiring until last. It’s a common mistake to make. But it’s a mistake you can’t afford to make in the consumer appliance and electronics industry, where cost is everything.
Here's a few key points about wire harnesses to keep in mind:
- Each component of a wire harness can affect the finished product.
- Wires, connectors and coverings must be designed to perform in a specific set of environmental conditions.
- Voltage, amperage and operating temperatures must all be considered as they will affect the choices you make.
So, what are these choices and what are the right ones to make for your application? Here’s an engineer’s guide to designing your wire harness.
Wire Harness assembly
- Shorter wires do not necessarily mean lower costs. Assembly times can actually have a bigger impact on the cost if errors are made.
- One of the biggest problems with wire harnesses is the routing and bunching of wires, so it needs to be laid out in a way that the operator can’t make a mistake.
- There could be 30 or 50 terminations, so design it in a way that the operator can’t insert a terminal in the wrong place.
Wire Harness installation
- Again, the cost of wires and heat resistant wire connectors is less than the installation time so always weigh up one against the other.
- A spinal cord design typically has more wire than a spider web design but are easier to install and simpler to service.
The connectors
- The type and speed of the signal being transmitted will drive the connector choice.
- Choose a crimp-type connector if power is being sent through the assembly.
- Choose a soldered or welded connection if a high-speed signal is being transmitted.
- Consider if the final assembly is already equipped with a certain type of connector. Terminal choices will be limited.
The conductor or circuits
- The type and number of circuits or conductors included will depend on your application.
- The most versatile and widely used conductor material is copper, as it’s compatible with a wide range of coatings to slow the rate of corrosion.
- If you require more breaking strength, use copper-clad steel or copper alloys.
The coverings
A wire covering provides an extra layer of insulation and protection from abrasion, chemicals, fluids, heat, moisture, moving parts, squeaks, rattles and vibration. Flexible wire covers also act as electromagnetic protectors against interference.
Wire harness coverings include:
| Wraps comfortably around wires and smooths out surface imperfections, providing thermal and electrical insulation. Adhesive-backed tubing gives a robust seal against moisture and chemicals. | |
| Expandable or wrap sleeving is easy to install and highly flexible which enables fast wire bundling. Flexible braided wire covering made of polyethylene (PET) is popular, due to its durable and lightweight design. It’s fully flexible in any direction, even at low temperatures. | |
| Allows wires to enter and exit the covering at multiple points. Both polyamide and polyethylene are available and multiple colour choices allow for easy identification. | |
| A slit down the side makes it easy to insert wires. The slit closes after installation, which eliminates the need to heat shrink or spot tape the ends, reducing production time. Materials vary. You can use a steel braided wire loom or a split mesh wire loom. | |
| Single-coated, pressure-sensitive tapes are available with a variety of backing materials and pressure-sensitive adhesives. PVC is the most common backing material for harness tape, but other materials are available, including cloth, felt, foam and foil. Stiffness can be an issue, as tapes minimise the flexibility of the harness. |
Wire Harness - Environmental considerations
Think about every aspect of your wire harness in relation to the environment it will be exposed to.
- Can each part withstand a specific voltage or operating temperature?
- Is the connector and harness mounting designed to take the pressure of any extreme vibrations, such as on a washing machine?
- Will your harness need to contend with detergents and greases or water? Do you need to consider flammability?
The safety standard
Location is everything. Your wire harness needs to meet the safety certifications of the country or region it will be used in. Many countries have their own regulatory and safety standard agencies that enforce the examination and testing of electrical devices. Most countries use one of the following as the basis for their guidelines:
- IEC (International Electrotechnical Commission)
- CEE (International Commission for Rules for the Approval of Electrical Equipment)
- CENELEC (European Committee for Electrical Standardization)
The IPC/WHMA-A-620 Standard Revision C remains the only industry-consensus standard for Requirements and Acceptance of Cable and Wire Harness Assemblies. IPC and the Wiring Harness Manufacturer’s Association (WHMA) continue to work together to develop this significant update.
The environmental standard
You should be familiar with the three standards that limit the use of hazardous substances:
The WEEE Directive governs the disposal and recycling of electronic and electrical products when products are at the end of their usable life.
In addition to safety and environmental standards, assemblies may also need to meet industry standards based on specific performance criteria. Depending on the application, the cable assembly may need to meet criteria such as HDMI, SFP+, QSFP, TIA/EIA 568-C.2, or the assembly may need to be verified by an independent testing service such as ETL.