Type WR Wirewound Resistors - 1 to 32 Amps APPLICATION Type WR Wirewound Resistor Powerohm's Type WR Wirewound Resistors are de- signed for low current applications ranging from 1.0 to 32.0 amps continuous, and resistance values ranging between 250.0 and 0.25 ohms, respectively. Units have a rated temperature rise of 375ºC above ambient temperature, which is in accordance with NEMA stan- dards. These units can be used for any type of AC or DC power application, including motor control, dynamic braking, neutral grounding and load testing. The corrosion resistant Type WR resistor will withstand considerable shock and vibration, qualifying it for use in most harsh ELECTRICAL CHARACTERISTICS environments. VOLTAGE INSULATION: A standard coil is insulated for 1000 volts. Standard resistor assemblies are also BASIC CONSTRUCTION insulated for 1000 volts. Additional stages of insulation can be added to cater for applications exceeding 5000 The Type WR resistor unit consists of a high quality alloy volts. wire coil supported by a spirally-grooved insulating core. The spring-shaped element is attached to either end of RESISTANCE TOLERANCE: The standard tolerance for a the core by rigid stainless steel terminals. This design type WR unit is + 10%. Tolerances as low as + 3% are offers sound mechanical strength, and the ability to available. package a large amount of active element in a small area. COEFFICIENT OF RESISTIVITY: Depending on the spe- The open-type construction is the key to the efficient cific unit, the resistance will increase between 3% and 6% cooling ability of the unit. Unlike enamel or ceramic after reaching the maximum operating temperature of 375ºC coated resistors which tend to "trap" the heat, the Type above a 40ºC ambient. WR resistor allows the element to come in direct contact with the cool ambient air. This unique design allows AMBIENT TEMPERATURE: Standard ratings are based on rapid, natural convection cooling of the resistive element. maximum ambient temperatures of 40ºC. Derate current rating 95% for 50ºC ambient, 90% for 75ºC ambient and 85% Our resistors feature stainless steel element and termi- for 100ºC ambient. nals. The terminals are designed to allow the use of flat bus bars for coil-to-coil connections when the resistors EFFECTS OF ALTITUDE: The published electrical ratings are mounted in our standard selection of enclosures. Our are applicable for altitudes of 6000 feet or less. Contact terminals and bus bars are fabricated from rolled stain- factory for deration factors above 6000 feet. less steel strip which insures smooth, rounded edges and eliminates any personnel hazard caused from sharp burrs. CUSTOM DESIGNS The insulating core is produced from a porcelain-type Powerohm offers a complete selection of standard size ceramic material which offers good mechanical strength coils with various resistance and current ratings. We and excellent thermal shock resistance. specialize in custom sizes, and can manufacture coils with any resistance rating ranging between 0.25 and 250.0 ohms at no additional charge. 5713 13th Street Katy, Texas 77493 POWEROHM Phone: (281) 391-6800, Fax: (281) 391-6810 Ω Please visit our website at www.powerohm.com RESISTORS, INC. Type WR Electrical Ratings of Standard Size Coils RATINGS: The electrical ratings below are the maximum for coils mounted in free air. The maximum power rating will be reduced if multiple coils are installed close together or in an enclosure that restricts ventilation. It is recommended that the factory assist you with such applications, but for approximation purposes, resistor coils mounted in a well ventilated enclosure can be rated at 90% and in an unventilated enclosure at about 80% of their continuous amp rating. CUSTOM SIZES: Please note that this table contains only the most common size resistor coils. Any resistance value between 0.25 and 250.0 ohms is available. FIXED TAPS: For design versatility, individual units are available with multiple fixed taps. ELECTRICAL RATINGS FOR CONTINUOUS AND INTERMITTANT DUTY CYCLES AMP RATINGS BASED ON NEMA CLASSIFICATION NUMBERS RESIS- PART TANCE CLASS 90 CLASS 170 CLASS 160 CLASS 150 CLASS 130 ON 15 SEC. ON 15 SEC. ON 15 SEC. ON 10 SEC. NUMBER OHMS WATTS CONTINUOUS OFF 15 SEC. OFF 30 SEC. OFF 45 SEC. OFF 70 SEC. WR25 0.25 256 32.0 39.0 45.0 51.0 76.0 WR30 0.30 288 31.0 37.0 43.0 49.0 74.0 WR35 0.35 294 29.0 35.0 40.0 46.0 69.0 WR50 0.50 365 27.0 33.0 38.0 43.0 65.0 WR70 0.70 339 22.0 27.0 31.0 35.0 53.0 WR100 1.00 324 18.0 22.0 25.0 29.0 44.0 WR150 1.50 338 15.0 18.0 21.0 24.0 34.0 WR200 2.00 338 13.0 15.9 18.9 20.9 29.5 WR250 2.50 360 12.0 14.2 16.2 19.1 27.5 WR350 3.50 386 10.5 12.1 13.9 16.2 22.0 WR400 4.00 400 10.0 11.5 13.2 15.4 21.0 WR450 4.50 381 9.2 10.7 12.3 13.5 20.0 WR500 5.00 361 8.5 10.4 12.4 13.0 19.3 WR550 5.50 352 8.0 10.2 11.6 12.7 17.5 WR600 6.00 347 7.6 9.8 10.8 11.9 16.7 WR700 7.00 373 7.3 8.9 9.8 10.5 15.0 WR850 8.50 417 7.0 8.2 9.2 9.7 14.2 WR1000 10.00 384 6.2 7.2 7.7 8.1 11.9 WR1200 12.00 404 5.8 7.1 7.4 7.7 11.4 WR1500 15.00 421 5.3 5.9 6.2 6.9 9.8 WR2000 20.00 423 4.6 5.4 5.8 5.7 8.1 WR2700 27.00 350 3.6 4.4 4.4 5.0 6.5 WR3600 36.00 324 3.0 3.7 4.1 4.4 5.9 WR4500 45.00 281 2.5 3.2 3.3 3.6 4.6 WR6200 62.00 248 2.0 2.5 2.7 2.9 3.7 WR8000 80.00 259 1.8 2.2 2.4 2.5 3.3 WR10000 100.00 256 1.6 2.0 2.1 2.2 2.9 WR12500 125.00 245 1.4 1.7 1.8 1.9 2.5 WR15000 150.00 254 1.3 1.6 1.7 1.8 2.3 WR17500 175.00 252 1.2 1.5 1.6 1.7 2.1 WR20000 200.00 242 1.1 1.3 1.4 1.5 1.9 WR25000 250.00 250 1.0 1.2 1.3 1.4 1.8 Type WR Coil Dimensions & Tap Options DIMENSIONS AND WEIGHT OF STANDARD SIZE COILS AVERAGE WEIGHT: 1.1 lbs per single coil DIMENSIONS: 3/8" DIA. 2-1/2" 2" 7-1/4" Note: Terminals are supplied with 10-24 stainless steel hardware. ADDING FIXED TERMINALS TO TYPE WR WIREWOUND RESISTORS Type WR Wirewound Resistors are furnished with two rigid end terminals which are clamped at either end on the ceramic core. Additional fixed taps consist of a steel band clamped directly around the coiled element. Numerous tap configurations are available, however, fixed terminals are limited to a spacing no closer than every two turns and a maximum of four fixed taps per coil. - For example, the part number for a 373 watt, SPECIFY PART NUMBERS AS FOLLOWS: 7.0 ohm coil with 2 taps at 1/5 spacing is WR700-2E. Part Number Number of Taps Spacing (See Table) Examples of WR wirewound Resistors with ADDITIONAL TAPS & SPACING CHART additional taps: FRACTIONAL SUFFIX WR100-1B SPACING LETTER (1 TAP @ 1/2 SPACING) 1/2 B 1/3 C 1/4 D 1/5 E WR100-4E WR100-3D WR100-2C (4 TAPS @ 1/5 SPACING) (3 TAPS @ 1/4 SPACING) (2 TAPS @ 1/3 SPACING) Type WR Mounting Bracket Options and Dimensions Type WR Wirewound Resistors are available fully assembled on open-style brackets. This open-style construction consists of resistors installed on mill galvanized brackets complete with stainless steel bus bars. - For example, the part number for a 373 watt, 7.0 SPECIFY PART NUMBERS AS FOLLOWS: ohm coil mounted on brackets is 1WR700-B1. Number of Coils in Assembly Standard assemblies of 2 or more coils include Part Number series jumpers. Add "-N" to eliminate jumpers and "-P" for parallel jumpers. Bracket Identification B1 BRACKET ASSEMBLY OPTIONS AND DIMENSIONS 1 Coil - B1 Bracket Assembly 2 Coil - B1 Bracket Assembly Example Part Number: 1WR700-B1 Example Part Number: 2WR700-B1 3-1/2" 3-1/2" 7/16" DIA. 15-3/4" 8-1/2" 16-3/4" 2" 9-1/2" 2" B2 BRACKET ASSEMBLY OPTIONS AND DIMENSIONS 2 Coil - B2 Bracket Assembly 4 Coil - B2 Bracket Assembly Example Part Number: 2WR700-B2 Example Part Number: 4WR700-B2 6" 6" 7/16" DIA. 15-3/4" 8-1/2" 16-3/4" 3" 9-1/2" 3" B3 BRACKET ASSEMBLY OPTIONS AND DIMENSIONS 6 Coil - B3 Bracket Assembly 3 Coil - B3 Bracket Assembly Example Part Number: 6WR700-B3 Example Part Number: 3WR700-B3 9" 9" 7/16" DIA. 15-3/4" 8-1/2" 16-3/4" 3" 3" 9-1/2" 24 HOUR EMERGENCY SERVICE (800) 838-4694