A ubiquitous three-LED outlet checker cannot detect that. This leads to return current flowing through ground rather than through the neutral wire, resulting in a multitude of functional problems in addition to being a safety issue. More often than desired, ground and neutral wires are reversed in either facility wiring or in the internal wiring of the equipment itself. In places where grounding is done for purposes other than safety (for example, ESD/EMI) and where there are no voltage-carrying conductors, grounding wires can be selected based on other criteria (see further on in this article). Must all grounding wires inside the tool be as thick as the power wires that enter it? Not necessarily. A ubiquitous AWG18 green wire just won’t do. If your power cable utilizes AWG12 (or 2mm diameter) power wires, you cannot have ground wires that are thinner than that. How conductive should a ground path be in order to trigger the circuit breaker? There are several varying standards and guidelines on this subject, but the essential answer is that the ground path should be at least as conductive as either the live or neutral paths. The ground path must have a low enough impedance to allow a high current sufficient to trigger the circuit breaker.For all this to work, these conditions must be met:Īll operator-accessible conductors must be grounded 1 and If all operator-accessible metal parts are properly grounded, an energized loose wire that touches such a part effectively short-circuits any live voltages to ground, and the resulting excessive current triggers the circuit breaker to cut power to the tool. Here is where grounding comes to the rescue. The operator can easily be electrocuted simply by touching such a part. Now this metal part, such as the enclosure, is under high voltage. If a live wire inside such a machine or tool gets loose for whatever reason, it can touch and energize (that is, supply voltage to) a metal part to which an operator has access. Each of these tools takes its power from AC mains, meaning that typically anywhere from 100VAC to 440VAC enters the equipment. So why is grounding a safety element? As an example, let us consider a typical piece of industrial equipment, such as an integrated circuit (IC) handler, or surface mounted technology (SMT) pick-and-place machine (or any other tool that you are familiar with). In this article, we will just scratch the surface and touch on the basics. I strongly recommend that those who deal with such subjects take an electrical safety course, make friends with factory’s licensed electricians, or join a factory safety committee. The whole purpose of this section is to bring electrical safety to the attention of ESD and EMI specialists at factories and tool designers who otherwise may not be aware that grounding is a safety item. This article is far from a comprehensive safety guide, and it doesn’t cover every important safety point. Too many specialists in ESD and EMI are not professionally trained in electrical safety. This article does not cover PCB grounding (there are plenty of excellent articles on this subject) and portable tools with double insulation that do not have grounding. While this and other magazines have published detailed articles on one or more of these subjects, this article combines them all to assist equipment users and tool makers in understanding what is important and how to achieve optimal ground performance. There are several key aspects of grounding, including safety, electrostatic discharge (ESD), electromagnetic interference (EMI), and signal integrity. This article focuses on a path less traveled, grounding on a system level, that is grounding of the equipment in actual use at the factories. There are plenty of quality articles on specific subjects in In Compliance Magazine and in other publications, largely on grounding on a printed circuit board (PCB) level. Grounding is the most fundamental property of all types of electrical equipment. Is Your System Well Grounded? Consider These Points in Effective Grounding
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |