Know Your ATS Options to Keep Costs Low
Automatic Transfer Switches can be provided with a wide array of options and features. Like any customizable product, the more features included, the higher the cost will be. Contractor ratings can also drive prices exponentially high.
Below are two tips to consider when deciding on ratings and features for an application. These tips can help to ensure the switch is suited for the job, and priced within the customer’s budget.
Continuous Current Rating
The Standard expectation of an automatic transfer switch (in regards to a continuous load), is that the switch should be able to hold maximum value for three hours or more. Transfer switches differ widely from other emergency equipment in that they must continuously carry the current to critical loads, either from the normal source of the power of the emergency source. Whereas, a standby generator will typically only supply power during emergency periods.
Automatic transfer switches for generators are manufactured to meet continuous current ratings from 30-4,000 amperes. New ATS is typically capable of carrying 100% of the rated current at an ambient temperature of 40° C. Transfer switches incorporating integral overcurrent protective devices may be limited to continuous load current, no more than 80% of the switch rating. Always make sure to check standards to ensure you are complying with the current NEC codes.
Bypass Isolation ATS
Bypass Isolation Transfer switches are designed for applications where maintenance, inspection, and testing must be performed to maintain continuous power to the load. This is typically required in health care applications, critical life support systems, data centers, and other standby power applications calling for safe system maintenance without power interruptions. This option also needs to be carefully considered when planning out projects, due to the high cost associated.
Underwriters Laboratory is the prevailing authority figure when it comes to independent testing of electrical products. Underwriters Laboratory or UL classifies automatic transfer switch loads under guideline UL 1008. Underwriters Laboratory requires that all transfer switches for generators be marked to specify what type of load it is capable of handling.
The panel indicates that the switch can be used for a variety of loads. However, when dealing with an incandescent (tungsten-based filament), the total load should never exceed 30% unless the transfer switch is specifically rated to transfer a higher percentage of power to incandescent lamps. Depending on the application, a standard open transition switch is the most common type of switch specified. Other options include Service Entrance, Bypass Isolation, and Close Transition.