Vitreous Enamelled Wirewound Resistors WZO Series Datasheet

Category: Electronics, Resistors, TT Electronics PLC

TT Electronics’ WZO Series of wirewound resistors are designed to operate in harsh environments, providing high power dissipation relative to their size. They are characterized by a vitreous enamel coating that is impervious and lead-free, complying with EU Directive 2011/65/EU amended by (EU) 2015/863, also known as RoHS3. The resistors in this series are particularly suitable for protection circuits due to their overload characteristics, along with offering high stability and reliability.

Electrical Data

The WZO Series features commercial power ratings at 25°C ranging from 3.0 watts for the W21 to 14.0 watts for the W24, and resistance ranges from 0.1 ohms up to 100K ohms with tolerances of 1%, 2%, and 5%. The Temperature Coefficient of Resistance (TCR) spans from typically less than ±50 ppm/°C to a maximum of ±200 ppm/°C. The resistors also fulfill BS CECC 40-201-002, with power ratings consistent with the commercial ones and similar resistance ranges and tolerances, but with different TCR values notably ±400 and ±200 ppm/°C for resistance below and above 10 ohms, respectively.

Physical Data and Construction

The construction of these resistors involves a high purity ceramic substrate with interference fit end caps which are welded to the termination wires. The resistive element is wound around the substrate and welded to the caps before applying the vitreous enamel protective coating. The termination wires are made of nickel-plated, solder-coated copper-clad steel wire, meeting IEC 68.2.21’s strength requirements and IEC 115-1’s solderability clause. The W23s and W24s types are not supplied on tape, and lead lengths are a minimum of 30 mm. Markings on the resistors display the type reference, resistance value, and tolerance in accordance with IEC 62.

Product Ratings and Values

The limit element voltage of the resistors varies with type: from 100 volts for the W21 to 750 volts for the W24. Preferred resistance values are from the E24 series, but TT Electronics can accommodate special orders with different values. Thermal impedance is given in °C per watt from 22 to 88 depending on the resistor type.

It is important to note that TT Electronics reserves the right to change product specifications without notice and considers all the provided data accurate at the time of print. The dimensions, weight, and construction details provided are specific to the WZO series, with nominal diameters and lengths varying by resistor type.