Conforming to the applicable standards for circuit protection is a critical aspect of any new electrical or electronic product’s design. Ensuring those standards are incorporated into each stage of the design process is essential to moving a product from concept to certification efficiently. Occasionally, however, for some fledgling engineering teams at startup companies, the understanding of just how to do that may come only after an unsuccessful first attempt to get their product certified. Going literally back to the drawing board or CAD system is a hard and expensive way to learn that lesson.
Design projects begin with a development specification that describes every function and feature in the device, as well as its operating environment. Input and output signals, power conditioning, noise filtering, circuit protection, ground loops, voltage levels, qualified parts lists, cost, size, weight, and much more are all detailed in this specification. By the time a working prototype is complete, the original development spec has been replaced by a product design specification, which contains the requirements for a real, practical working product.
Figure 1. PICO 259-UL913 Series Intrinsically Safe Fuse.
When the project is nearing completion and the products are in the pre-production stage, a conformance spec becomes part of the product spec. The conformance spec ensures that the product can survive its environment, perform its intended functions, provides the level of reliability and safety the product spec requires, and meets all government, safety, and industry standards.
From specs to standards and back again
Some companies encourage their design engineers to help develop or modify the industry standards that thread through all these specifications, supporting them in their efforts to become members of professional societies and join the technical committees and working groups that develop standards related to their products. This offers a variety of advantages to design engineers and their employers. For example, by contributing their own experience to the development of new standards, engineers can help to ensure the safety and reliability of the next generation of products for users, operators, and maintenance people. Given that a typical committee brings together engineers from different companies that are in the same business, the committee can draw from a wider base of experience, leading to the development of standards that better reflect industry needs. Engineers who participate in standards development are also better equipped to help their companies or organizations meet the challenges new standards pose while they help keep the standards current with evolving technologies.
Littelfuse, for example, sends a representative to IEEE to ensure that the requirements for protecting circuits are uniform within the industry for a particular science (i.e., silicon solid-state circuits) and that the test procedures needed to ensure conformity are reasonable and sufficient. Engineers often also assist standards organizations such as UL, CSA, IEC, and DOE in writing test procedures that accomplish the same goals as the professional societies.
In the case of circuit protection, the process for developing a standard for the circuit protection device is largely independent of the products’ use. That is, the product may be used in communication equipment, lighting, vehicles, instruments, aircraft, weapons, factory controllers, small or large appliances, or myriad other applications. Circuit protection devices are needed for all of these applications, and the major difference among them is the magnitude and duration of a hazardous event from external sources. These events include overvoltage, overcurrent, electrostatic discharge, surge currents and voltages, and short circuits. Protection devices are essential in power and signal circuits, input-output connectors, power supplies, voltage sources, generators, motors, and circuitry of every kind.
As a standards engineer, I’ve helped customers understand which standards apply in terms of both the application itself and the geographical location for which it is designed, as well as offering guidance on how to meet those standards. For example, a circuit protection product that is certified for use in a foreign country may not be acceptable for use in the US because it doesn’t comply with the relevant UL safety standard.