The failure to automatically transfer a building’s electrical load to an emergency generator is a nerve-racking scenario that any facility manager would prefer to avoid. For this reason, automatic transfer switches (ATS) are considered one of the most critical components of an emergency power system. This article discusses the use of “open vs. enclosed” contacts in transfer switches, and also alerts you to a basic transfer switch design feature that may not be in your current specifications, with possible negative consequences for the facility’s owner.
While most transfer switches are equipped with basic features that make them suitable for simple installations, larger or more complex projects often require additional features to meet special requirements. One such special requirement is the need to protect sensitive equipment whenever building loads are switched between two live, un-synchronized, power sources. How exactly does a proposed transfer switch execute a transfer between the normal source and the emergency source, and what effect will the transfer sequence have on the connected loads? Learn the key differences between open, delayed and closed-transition automatic transfer switches, and how to specify the right equipment.
When reviewing emergency power system designs, I am sometimes asked about 4-pole transfer switches. The typical question is “when should I use them?“, followed quickly by “why should I use them?“. Since each project is likely to have special circumstances that make a generic answer impossible, this article focuses instead on providing the basic sources of information that should allow you … Read more
How and when to apply “3-cycle rated” vs. “30-cycle rated” transfer switches should be a rather important consideration for a design engineer. A coordination study is a critical element that must go hand-in-hand with the design and specification of a safe and reliable emergency power system. Some basic definitions Interrupting ratings – the highest current at rated voltage that a device is intended … Read more