The following information is meant to provide a brief overview of the various aspects to consider when designing a wire harness or cable assembly. Since different industries and applications have unique requirements making it impractical to address all aspects, only the basic considerations will be presented.
Please contact us for specific help with your individual requirements.
Always verify that the contact/connector and wire combination will pass the quality standard you require. Many combinations, that the manufacturers state are compatible, will not pass the IPC620 standard. Notably when it comes to insulation supports. If you use IPC620 as your default quality standard, always confirm that your terminal and insulation diameter will give you an IPC620 acceptable insulation support and transition.
Neither analysis is superior from a crimp quality perspective. Crimp height was the industry standard but now pull testing is being required more often.
Crimp height measurement is a quick and reliable check that is non-destructive and can be done at any time during production without fear of damaging the parts being inspected.
Pull testing is a destructive test. It requires additional parts to be produced and pulled to destruction, generating waste in the form of unusable product and avoidable man hours. This translates to additional costs. Non-automated pull testers can be operator sensitive, creating mixed results within a given batch of parts.
A pull and release test is when a part is pulled to its minimum tension and then released. Although the purpose of this test is to avoid destroying the part, this test can cause undetectable damage and result in latent failures. If a pull and release test is a requirement, all subjected parts should be discarded after the test is complete.
Learn more about crimping basics.
Two of the most common errors we see are; using an insulation diameter (usually UL1007) in a connector that is on .100 centers, making the insulation diameter too large for this application, and terminals for multiple wire crimps not being matched for the correct total gauge or insulation diameter. Always confirm that your wire fits in the contacts and connectors.
As a rule, it’s just good practice to remove the potential for assembly errors with keys and/or polarization.
If your equipment or system has any of the following, locking connectors would be advised:
The required temperature rating of your wire and connectors needs to take into consideration the physical temperature of the system and any temperature rise due to current in a multi-conductor bundle.
The two most common flame ratings for connectors are the UL 94V-0 and UL94V-2. This is commonly confused with the temperature rating.
The 94V tests refer to how quickly a wire or connector will extinguish itself after being removed from an open flame. The actual temperature difference between the ratings, in most cases, is less than 5-10 degrees. However, the cost difference can be double.
If your wire bundle is applied around sharp metal edges or if it is in close contact with components in motion or elements that get hot, you may want to add some form of additional protection. If you have cables that move in tracks or are exposed to traffic, you may want to consider some of the more robust jacketing materials.
To tin un-terminated wires or not. If your wire is going to be soldered later, tinning is an ideal way to keep the strands together and prevent ‘bird caging’. If the wires are going to be put into terminal blocks, tinning can cause delayed failures, especially with larger gauges. In these cases, if you still require strand management, you should consider using wire ferrules or request the supplier provide a partial strip (leaving the insulation slug on the end of the wire).
Check out our wire insulation chart for assistance in determining the insulation or jacket type with the correct physical properties for your application.
The voltage that you can safely apply to any given conductor is dependent on the dielectric strength of the insulation around that conductor. In most industrial and electronic applications, PVC is the insulation of choice. If you have a high voltage application, you will need to consider using Teflon or silicone insulation. You should refer to the various UL and CSA ratings to allow for safe operating margins. For connectors and contacts, you should always stay within the manufacturer’s recommended operating range.
How much current that can be safely run through a given conductor is dependent upon many factors, but the primary issue is heat. You must take into consideration:
Copper and its derivatives are excellent conductors but readily oxidize. Plating is done to protect the base metal and reduce oxidation. Tin, Silver, and Gold… don’t mix them! Tin oxide is non-conductive.
When you mate tin to gold or silver, fretting can cause tin oxide to accumulate at the contact interface and over time degrade the performance of the connection resulting in higher resistances and heat build up.
Tin contact systems are designed with higher mating forces to provide sufficient wiping action to achieve a strong connection. Tin is easy to plate and inexpensive. It is your leading and most economical choice for general electronics applications.
Gold is an exceptional plating material (confirm that it has a nickel under plate), but it is expensive. It should be used for harsh environments, very low signal and voltage levels, high mating cycles and long product life expectancy applications.
Silver is the preeminent conductor, it has a conductive oxide. Silver is typically your best choice for high voltage, high current or RF applications.
This needs to be considered when deciding on contact plating. Signal levels below 100uA should be gold or silver. Low signal levels may not have enough energy to break through the oxide layer on a tin contact. This becomes critical when the connector is used in an environment where there may be no signal for log periods of time, allowing the tin oxide to buildup.
If the cable is external to a device, it probably needs to be shielded. Shielding issues are both electrical and mechanical. On the electrical side, you will need to determine what percentage of coverage will be adequate for your application. On the mechanical side you need to consider weight, stiffness, bend radius and bend cycles. Braids are heavy, more expensive, can make the cable stiff,and don’t usually have full coverage. Foils are light, inexpensive,and provide full coverage. However, if the cable is going to be in a high flex environment, the foil can fracture inside the jacket and ultimately result in a loss of shielding.
Check out our wire gauge chart for assistance in determining the conductor size, stranding, and material with the correct physical properties for your application.