Prolonged exposure to extreme conditions can tax the performance of connectors and assemblies. Designers need to grasp environmental ratings, and the level of the protection they will provide.
BY STEVE LOYAL
Power, signal and data connectors are being installed outdoors at an ever increasing rate in telecom applications, such as those associated with WiMAX and LTE wireless broadband technologies. In many cases, there is also a shift from copper to fiberoptic cabling. In all cases, long-term outdoor exposure places significant demands on the connectors and cable assemblies selected. Easy to install, highly reliable, and maintenance free connectors are required in these applications.
Various environmental rating standards come into play when specifying outdoor communications connectors, such as those published by ANSI, TIA, IEC, IEEE, and Telcordia. Many of these organizations reference IEC 60529 environmental protection for outdoor connectors?specifically IP65 and IP67 for water and dust protection. What does that mean in terms of the protection provided, and how are connectors tested to make sure they really provide that level of protection? Designers need the answers to these and related questions to get the right connectors for outdoor communications equipment, or even indoor equipment that faces severe conditions.
An infrastructure evolution
A shift in system design is taking place that drastically changes the connectivity in base station architectures. Older architectures use heavy copper conductor cable between base stations and amplifiers, and between the amplifiers and passive antennas. Figure 1 shows the infrastructure evolution for 3G cellular architectures. The left image depicts a standard configuration, which includes the base station with amplifier, roof reinforcement due to size and weight, coax feeder cable to connect the base station to the masthead amplifier, and a coax jumper to the antenna. Typically, one high-power cable supplies power to the base station.
 FIGURE 1. Base stations have been deployed on rooftops (l), inside buildings (c), and now remotely (r) as part of a distributed architecture. |
The next phase of the 3G evolution (center, in Figure 1) has seen the base station inside the building, connected to a remote radio head on the roof by a fiberoptic/low-power cable. Now, we are beginning to see a distributed architecture with a base station server remotely located from the antenna site, and the antenna assembly with a built-in radio system. This assembly is also connected to the base station server with a fiber and low-power cable; however, the server can be several kilometers away.
Standards for the use of fiberoptic connectors are still in development. For example, the TIA TR-41.8.1 Fiber Optic Task Group is developing a fiber connector performance annex (Annex A) for the next revision of the Commercial Cabling Standard, TIA-568B. Draft Annex A lists TIA-defined Fiber Optic Test Procedures (FOTPs) that connectors must pass. These FOTPs instruct connector vendors in the methods that must be followed when performing optical, mechanical, and environmental tests.
In addition to affecting remote radio heads and antenna assemblies, the standards can also affect a wide range of other equipment types and their connectivity, including:
- Baseband indoor units;
- Wireless access points (WiFi, WiMAX, etc.);
- Data interfaces;
- RFID systems;
- Ethernet systems (W-LANs, security systems, etc.);
- Femto cell equipment.
Another trend is the shift to hybrid connectors that combine data and power connections; these reduce the number of individual connectors, are more cost-effective, and often improve reliability. Hybrid connectors must also be tested according to the pertinent standards.
Design considerations
In harsh environments, suitable interfaces and connectors for signal and power are absolute requirements. Designers must ensure reliable connections for each device that goes to market. Connector materials and designs must contend with a wide range of conditions that change frequently and rapidly. Typically, materials are chosen to ensure optimal functionality of connections for 15 years or longer. Base materials, special coatings, mating interface configurations, and reliable seal designs are all carefully considered when choosing a connector for outdoor use.
To assure reliable electrical, mechanical, and environmental performance, the designer’s starting point is a review of pertinent standards. Currently, connector designers most commonly use the IEC 60529 standard for environmental protection, particularly IP65, and IP67 levels of protection.
IP (Ingress Progress) two-digit codes in accordance with IEC 60529 are defined below. The first character indicates the degree of protection against the ingress of solid foreign objects. First character definitions are:
- - Non-protected;
- - Protected against solid foreign objects of 50 mm diameter and greater;
- - Protected against solid foreign objects of 12.5 mm diameter and greater;
- - Protected against solid foreign objects of 2.5 mm diameter and greater;
- - Protected against solid foreign objects of 1.0 mm diameter and greater;
- - Dust-protected;
- - Dust-tight.
The second character indicates the degree of protection against the ingress of water with harmful effects:
- - Non-protected;
- - Protected against vertically falling water drops;
- - Protected against vertically falling water drops as the enclosure is tilted 15°;
- - Protected against spraying water;
- - Protected against splashing water;
- - Protected against water jetting;
- - Protected against powerful water jetting;
- - Protected against temporary immersion (1 m, 30 minutes);
- - Protected against continuous immersion (1 m, >30 minutes).
Outdoor telecom connectors should have a classification of IP65 or better, meaning that the connections are protected against falling or driving rain. Some manufacturers, however, may only specify a specific part of a connector assembly, such as the cable entry seal. Obviously, it’s better to have an entire assembly tested and certified.
Harsh weather conditions can involve a wide range of temperatures, frost, snow, continuous rainfall, dust, extended exposure to sunshine, and periods of dry weather, all of which have an effect on materials and handling. These conditions must be taken into consideration during connector design. Additional consideration should be given to ease of connector mating under severe field conditions.
Moreover, connectors must be tested realistically to assure they meet ingress protection requirements. Generally, realistic simulation of actual field conditions requires sophisticated test equipment in a lab dedicated to that purpose. Testing facilities and protocols must include mechanical and electrical testing under various climatic conditions.
Many of the published standards do not define specific test conditions since equipment applications vary greatly. This means that connector suppliers must often design and test for worst-case scenarios, or test according to customer specifications.
Crucial questions
When evaluating connectors for harsh environments, the following questions should elicit the appropriate answers for the equipment being designed:
- Are the connector designs and their testing pertinent to the equipment application, such as fixed outdoor, mobile, or other specific uses?
Different equipment types use different connectors, such as coax or fiber for signal, RJ-45 for Ethernet-related datacom, and various arrangements for power connections. Depending on the manufacturer, individual cables and connectors could be used, but the use of hybrid cables and connectors that combine signal and power (Figure 2) is growing because of reduced size, weight, and cost.
 FIGURE 2. Examples of hybrid connectors: power and fiberoptic (l), and RJ-45 and power (r). |
Connector manufacturers who standardize on a few basic connector housing designs across a broad range of connection types make life easier for OEMs and users. By concentrating on standardized designs, a connector manufacturer can afford to carry out an extensive set of environmental and performance tests that apply to many types of connection. The customer is assured of reliable designs while gaining the benefits of common parts and reduced inventories. Table 1 shows an example of a test procedure available for an OEM or user to consider when choosing connector solutions.
 TABLE 1. Typical set of tests conducted on outdoor communications connectors. |
- How easy is it to assemble connectors to different cable types?
Clearly, outdoor communication connectors must accommodate a wide range of cables, with provisions for different types of conductors, insulation, EMI (electromagnetic interference) protection, and grounding methods. In the absence of standardized connector designs, cable assembly can be a hassle. Ideally, OEMs and users would like the same assembly methods across a variety of conductor types and sizes without special tools, or with a common set of tools. Easy assembly is particularly important when terminating conductors in the connector contacts, which in some designs can be problematic. Typical termination technologies include crimping, axial screw terminals, and insulation displacement types. Whatever the technology, the connector manufacturer should strive for easy assembly.
Of course, shielding is necessary to prevent EMI from entering or radiating from a copper conductor cable. This also is important internally when power and signal carriers are mixed in hybrid cables and connectors. Again, ease of assembly is a key factor in assuring good shield grounding at the connector hood and housing. Typically, signal lines in the cables are well shielded; for example, shielded twisted pairs in the case of Ethernet. It becomes a non-issue in the case of fiber- optic cabling, but when it is, keep in mind that shielding effectiveness is only as good as the weakest link in the cable/connector assembly.
- What materials are used in the connector designs?
The proper selection of connector housing material is critical to ensure the long-term durability of outdoor connectors. In many cases, an OEM or user can judge the viability of a connector in a harsh environment by knowing the materials used in its construction. Depending on the application, enclosures made of polyamide or polycarbonate plastics are acceptable, while others require a metal housing (typically, plated zinc die castings).
Special attention must also be given to materials used for seals and cable clamps. Ozone and UV radiation can seriously degrade the elasticity of seal materials. When exposed to extreme sunlight or other weather conditions, many materials become brittle, meaning reliable sealing is no longer guaranteed. Assessing material characteristics must be an integral part of the test regimen before that material becomes part of a manufacturer’s connector product portfolio.
Teamwork counts
For demanding cable/connector applications, the most successful ones come about because the supplier and customer worked closely together. With healthy give and take, they select the most appropriate combination of physical design, construction materials, and testing that simulates actual field conditions.
In the long run, this teamwork usually results in the most cost- effective solution.
STEVE LOYAL is business development manager/device connectivity solutions at HARTING North America (steve.loyal@harting.com).
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