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Buck–Boost Transformers

Three phase, buck-boost ap pli ca tions require two or three trans form ers. Check the “Quantity Required” column of the Three Phase Se lec tion Tables for the exact quantity. Using the Selection Tables 1. Determine if you are trying to Boost (raise) or Buck (lower) your voltage. Select an input/output voltage com bi na tion that comes closest to match ing your application from the appropriate single or three phase charts on the following pages.2. Move across your selected input/output voltage row to the amperage or KVA rating closest to, but Fusing Buck-Boost Transformers For determining the correct size of breaker or fuse for a given range of input or output ampere ratings, refer to Section 450-4, of the National Electric Code (NEC).“ 450-4, Autotransformers 600 Volts, Nominal or Less. (a) Overcurrent Protection. Each au totrans form er 600 volts, nominal or less shall be protected by an in di vid u al overcurrent device installed in series with each un ground ed input conductor. Such overcurrent device shall be rated or set at not more than 125 percent of the rated full-load input current of the auto- transformer. An overcurrent device shall not be installed in series with the shunt winding ...”.“ ...Exception. Where the rated input current of an autotransformer 9 amperes or more and 125 percent of this current does not correspond to a standard rating of a fuse or non-adjustable circuit breaker, the next higher standard rating described in Section 240-6 shall be per- mit ted. Where the rated input current is less than 9 am-peres, an overcurrent device rated or set at no more than 167 percent of the input current shall be per mit ted...”. greater than the rating re quired by your load.3. Reading the top of the column will give you the catalog number of the exact buck-boost trans form er you need. See the Speci cation Tables on the next page.4. Connect the transformers according to the di a gram indicated. See the Electrical Connections section at the end of this chapter. Connection diagrams are packed with each transformer.
Overcurrent devices OC-1a and OC-1b are shown cor rect ly installed in accordance with 450-4. Locating an overcurrent device in series with the shunt winding any where between A and B is not permitted. The shunt winding is the winding common to both the input and the output circuits. Visit our website at www.solaheviduty.com or contact 214
Technical Services at (800) 377-4384 with any ques tions.