Design of heavy-duty connectors must specify parameters such as clearance, creepage, degree of pollution, and rated impulse voltage.
By John B. Moore
High-pin-count electrical interconnects not only offer space savings, but ease of assembly, installation, and maintenance, all in response to the need for machinery with increased sig-naling, control, communication, and modularity. A high-density connector is a connector with many contacts in a small space (see Fig. 1). High-density connectors offer design flexibility by enabling maximum connection capability in the least amount of space.
 FIGURE 1. A typical high-density Han connector from Germany is known as the "HARTING standard" in English. |
High density is a relative term. For example, a connector contact pair is much denser than a terminal block installation with one wire in and one wire out. Terminal blocks take up much more space for the same amount of contacts. A quantity of 72 terminal blocks, each 7 mm wide and mounted on a DIN rail, creates a footprint that is 20" × 1.5". In contrast, a standard 72-pin insert is approxi-mately 3.33" × 1.34".
Common terminations for rectangular connectors include screw-type, crimp, and cage clamp. Solder connections are not used for rectangular connectors. In crimp-type terminations, the contact is crimped to the conductor and held in place by spring collars mounted on the contacts or spring shoulders on the insert. Bulky termination components such as screws are not necessary, so crimp terminations are ideal for maximum-density rectangular connectors. Smaller components translate into cost savings because designers can use smaller enclosures for mounting terminations. Further, the use of robust hoods and housings to connect the mating sides of rectangular connectors sometimes eliminates the need for separate enclosures.
When designing an electrical system, one of the first factors to consider is voltage. Rated working voltage is specified by the manufacturer in accordance with VDE 0627 or VDE 0110. For example, Underwriters Lab has tested HARTING Norm (Han) connectors at 600 V for industrial use, allowing usage in U.S. industrial environments that are normally 480 V and in Canada where the voltage is 575 V. Rated impulse voltage specifies the capability of a component's insulation to withstand transient overvoltages.
Another early factor for consideration is the amount of current the system will be expected to handle on a constant basis and to withstand in case of an overcurrent. The working or operating current is the current carried by each pin on a permanent basis and passing simultaneously through all contacts that are connected to the largest possible conductors—without exceeding the upper temperature limit.
Han connectors use solid, screw-machine turned contacts from bar stock. They are not stamped and formed. Although assigned and tested to an operating current rating, the current ratings on Han contacts have been de-rated approximately 20%. The current-carrying capacity is limited by the thermal properties of materials used for inserts as well as by the insulating materials. These components have a maximum temperature rating that should not be exceeded. The working current rating of the Han 'E' type contact is 16 A. This rating has been lowered or corrected from test results by external factors that further limit the current-carrying capacity—for instance, the connectable wire gauge or an unequal dispersion of current. Transient current-carrying capacity is the ability of a contact to carry high-current loads for short intervals, such as those experienced at motor start-up. The Han screw-machined contacts are relatively unaffected by short overloads when compared to stamped and formed types.
 FIGURE 2. Clearance and creepage are factors that must be considered in the design process of industrial high-density connectors. |
Two important design factors for high-density connectors are clearance and creepage (see Fig. 2). Clearance is the shortest distance through the air between two conductive elements and is determined by surge voltage withstand levels. Creepage is the shortage distance across the surface of an insulating material between two conductive elements. Creepage distances are dependent on rated voltage, the degree of pollution, and the characteristics of the insulating material.
A typical rating on a Han insert is as follows: 16 A, 600 V, 6 kV 3 where 16 A is the current rating, 600 V is the working voltage rating, 6 kV is the rated im-pulse voltage and 3 is the degree of pollution as defined by DIN VDE 0110-1 and IEC 60 664-1.
Degree of pollution
"Degree of pollution" (based on IEC 0110 and IEC 60664-1) plays a key role because any pollution or contamination may give rise to conductivity that, in combination with moisture, may affect the insulating properties of the surface on which it is deposited.Four degrees of pollution exist with degree 1 being the driest with no conductive pollution occurring. Air-conditioned, clean, dry rooms are good examples of this environment.
Degree 2 describes areas where only non-conductive pollution occurs, except for occasional condensation causing temporary conduction (for example, sales rooms, fine mechanic workshops, laboratories, test labs, and medical rooms).
Degree 3 describes areas where conductive pollution occurs, or where condensation causes conduction in dry pollution. Industrial and agricultural plants, unheated storage rooms, workshops, and boiler rooms are examples.
Degree 4 conditions include persistent conductivity due to conductive dust, rain, or snow. Outdoor and open-air locations are examples.
Voltage and current ratings are assigned to connectors based in part on their performance in these different environments. Higher pollution areas have lower ratings. For example, a connector rated for degree of pollution 3 is approved by the manufacturer for use in conductive pollution conditions.
 FIGURE 3. Rectangular high-density connectors with straight rows of pins (left) are easier to line up and lock than circular connectors (right). |
High-density rectangular connectors are often compared to Mil/Spec circular connectors. Han connectors were designed 50 years ago in Europe and provided a modern, reliable connector to an electrical industry that was rebuilding. The circular connector was designed about the same time in the United States and was used for military purposes. Later, U.S. industry incorporated the circular Mil/Spec connector for its proven reliability. Because of this, two different sets of standards emerged for these industrial connectors.
Pick a shape
In terms of manufacturing, the circular connector is more difficult to assemble. A circular connector has contact locations in a circular pattern and it is often times difficult to identify the correct location. As pin counts increase, it is more likely that a contact will end up in the wrong location.
Rectangular connectors, on the other hand, are pin-and-socket type connectors with straight rows and columns of pins and sockets. The straight rows make it simple to identify the correct location for pin insertion. The male and female inserts fit into a hood and housing. The hood is generally on the cable side and the housing is generally on the bulkhead or side of a cabinet or machine.
Han connectors lock the mating hoods and housings together with levers that rotate over pins and are either locked or not—with no in-between. Circular connectors use bayonet or threaded connections that can be either not quite locked into place in the case with bayonet types, or cross-threaded.
Finally, the density of a rectangular industrial connector can be as high as 216 pins and configurations can include both high-current contacts (to 100 A) with low-current (10 A) contacts in the same connector body. Circular connectors are limited in the combinations offered.
Demands for high-density connectors are increasing across many industrial markets for many different types of machinery. For example, injection-molding plastics machinery uses high-density connectors as interconnects to the hot runner systems that are used to control flow, temperature, and pressure. Many points of control are necessary in this critical area of machinery.
Metal working machines use high-density connectors for quick disconnects between modular parts of the machine. This reduces the time it takes to break a machine down for maintenance and when the machine is moved often in highly flexible manufacturing facilities.
The industrial rectangular connector will continue to offer a well designed solution for meeting high pin-count applications.
JOHN B. MOORE is a market development manager at HARTING, Inc. of North America, 1370 Bowes Road, Elgin, IL 60123. Tel: (847) 741-1500; email: john.moore@harting.com.
