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Sourcing Electrical Connectors
Power entry connectors vary widely, depending on intended application.
By Brian Jones, Technical Engineer, Marketing, Schurter Inc., Santa Rosa, CA
Selecting the right connector involves careful planning and knowledge of the application requirements. The basic criteria for selecting a connector for either standard or medical applications are the same, except when it comes to leakage current in the filter, type of integrated fuseholder required, and the exposure to liquids in the environment where the connector is to be used.
Among the general selection criteria, the most important factor is to determine the functionality that is required — whether it is a pre-wired multifunctional Power Entry Module (PEM) or several single components. In addition to minimizing the cost of the components, several other things must be considered:
Safety aspects (reduction of touchable live parts).
Handling and logistic costs.
Advantage of a single complete component with approved functionality vs. multiple components needing separate approvals.
Functions required — filter, fuses, switches (illumination), shielding, circuit breaker, inlet, outlet.
Technical know-how and access to resources for primary circuit design (dealing with creepage and/or clearance distances vs. focusing on core competence and functionality of the product.
IP Rating — the degree of protection against solid objects and liquids. Depending on the application, this could be a major consideration in the design selection process.
Secondly, the operating conditions must be considered, since they may restrict the selection that's made — such as a fuseholder. Operating conditions play a major role in selecting the right connector to suit the application.
Domestic or worldwide use: voltage, current.
Operating temperature affects the selection of fuse, fuseholder, and filter and de-ratings must be considered.
Inrush current affects the selection of the switch.
Environmental elements such as temperature, humidity, dust, and water must be considered in selecting a connector (IP protection). A power entry module with seal protection to the chassis and inlet to cord connector may be required.
Medical Connector Criteria
Criteria for medical connector selection will probably include EMC filters, while leakage current (touch current) is a key factor. In general, medical appliances allow a touch current of 100µA. Depending on the stray capacitance of the whole system, different filters can be selected, which differ in leakage current. Schurter offers two different types with 5µA or 80µA touch current according to requirements outlined in IEC 60601-1. Medical filters with an 80µA rating are for use in applications with indirect patient contact, and the versions with a 5µA rating are for use in applications with direct patient contact. Less leakage current causes a lower common mode, (asymmetrical) attenuation. It's important to make the correct compromise here.
Another relevant point for medical applications is the selection of the fuseholder. Schurter offers "extra-safe" fuseholders that can be only removed with the aid of a tool. Some products require that the power cord be removed from the connector before the fuseholder can be removed from the module. These "extra-safe" features are in addition to the already observed IEC 60127-6 shock safety standards. In medical applications cord retaining clamps are often used as well. These clamps protect against unintended disconnection of the mains plug from the appliance.
When filters are used, it is necessary to ensure an optimal electrical contact (also high frequency wise) between the filter and the chassis. This is essential for shielding and filtering efficiency. In the case of plastic chassis, consider using metal coating.
Schurter provides services to support customer applications by measuring the disturbances in our own lab. Customers can send their appliances to us for design-in recommendations. A pre-compliance test report that guarantees passing of EMC test for conducted disturbances is provided. A wide variety of customer-specific filters are also offered on request — with solutions for enhanced withstand voltages, higher X-capacitor values with up to 6dB more attenuation.
There are many types of connectors and the information presented here is meant to provide a few tips for product selection. They are general guidelines to apply when the task of designing in a new component arises — whether a standard or medical device. Regardless of the application, these points must be taken into consideration, which taken together with careful planning and engineering expertise, can result in a highly functional, safe, reliable and cost-effective product design solution.
Contact: Schurter Inc., 447 Aviation Blvd., Santa Rosa, CA 95403
800-848-2600 or 707-636-3000 fax: 707-636-3033 E-mail: firstname.lastname@example.org Web:
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