Dry Type Distribution Transformers Buck-Boost transformers are small, single phase, dry type distribution transformers designed and shipped as insulating/isolating transformers. They have a dual voltage primary and a dual voltage secondary. These transformers can be connected for a wide range of voltage combinations. The most common use is to buck (lower) or boost (raise) the supply voltage a small amount, usually 5 to 27%. Buck-boost transformers are in compliance with NEC Article 210.9, Exception 1 when field connected as an autotransformer. The major advantages of Buck-boost transformers are their low cost, compact size and light weight. They are also more efficient and cost less than equivalent isolation transformers. When connected as an autotransformer, they can handle loads up to 20 times the nameplate rating. A buck-boost transformer is the ideal solution for changing line voltage by E77014 small amounts. When a buck-boost has the primary and secondary windings Accessories connected, per recommended instructions, it becomes an autotransformer. Now, only the secondary windings are Surge Protective Devices transforming voltage and current. The majority of the kVA Active Tracking Filters load passes directly from the supply to the load. This is the reason buck-boost transformers can supply a load with a much larger kVA rating than the nameplate indicates. Selection Steps 1. Input Line Voltage Low voltage lighting control applications Measure the supply voltage with a voltmeter. SolaHD buck-boost transformers are designed to supply power to low voltage lighting circuits, control panels or 2. Voltage Required for the Load other systems requiring 12, 16, 24, 32, or 48 Volts. When Check the load equipment to determine the voltage connected as an insulating transformer (by following the requirement. wiring diagram located after the specification tables on the inside of the transformer case), the transformers capacity 3. kVA or Ampere Rating of the Load matches the nameplate kVA rating. Find either the load kVA or the load amperage requirements. This information is listed on the SolaHD buck-boost transformers are also suited for low nameplate of the load equipment. voltage landscape lighting. They are UL Listed for outdoor service and their compact size makes them the perfect 4. Frequency solution for providing power to accent lighting applications. Electrical Connection diagrams are shown at the end of Either 50 or 60 Hz. The frequency of the transformer this section. must match the frequency of the load. Use dimmers on the output of the transformer that are 5. Number of Phases designed and rated for use with magnetic loads. We strongly Single or three phase line and load must match. recommend contacting the dimmer manufacturer for advice (A transformer cannot convert single to three phase.) on your specific lighting application. A common application is to make a single phase connection from a three phase supply by using one Certifications and Compliances phase of the three phase supply circuit. Be careful not to overload that phase of the three phase supply. For Listed buck-boost applications the supply must provide load - UL 506 kVA not just the nameplate rating of the buck-boost. - CSA C22.2 No. 66 Refer to the Selection Tables on the following pages. Visit our website at www.emerson.com or contact Technical Services at (800) 377-4384 with any questions. 246 January 2017Dry Type Distribution Transformers Three phase, buck-boost applications require two or three Using the Selection Tables transformers. Check the Quantity Required column of the 1. Determine if you are trying to Boost (raise) or Buck Three Phase Selection Tables for the exact quantity. (lower) your voltage. Select an input/output voltage combination that comes closest to matching your Fusing Buck-Boost Transformers application from the appropriate single or three phase For determining the correct size of breaker or fuse for a given charts on the following pages. range of input or output ampere ratings, refer to Section 450.4, of the National Electric Code (NEC). 2. Move across your selected input/output voltage row to the amperage or kVA rating closest to, but greater than Where an overcurrent protection device is required, the the rating required by your load. electrical connections and selection tables will reference appropriately. 3. Reading the top of the column will give you the catalog number of the exact buck-boost transformer you need. See the Specification Tables on the next page. 4. Connect the transformers according to the diagram indicated. See the Electrical Connections section at the end of this section. Connection diagrams are packed with each transformer. Overcurrent devices OC-1a and OC-1b are shown correctly installed in accordance with NEC 450.4. Locating an overcurrent device in series with the shunt winding anywhere 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.emerson.com or contact Technical Services at (800) 377-4384 with any questions. 247 January 2017