RQA Series Ceramic Encased Wire Wound Resistors

What are the RQA Series Ceramic Encased Wire Wound Resistors?

The RQA is a ceramic encased Wire Wound resistor — a construction type commonly referred to as a cement resistor — designed for continuous power dissipation in industrial environments where standard silicone-coated axial resistors would be exposed to temperatures, humidity levels or mechanical stresses beyond their reliable operating limits. The Wire Wound resistive element is assembled by winding a resistance wire onto a ceramic rod or fibre glass core, with the lead terminations welded or crimped to tin-plated end caps. The completed assembly is then placed into a ceramic boat and the cavity is filled with high-temperature, fire-retardant cement, which is fired to produce a rigid, monolithic enclosure around the element.

The fired ceramic casing is the defining feature of the RQA series. It is produced from aluminium oxide and silicon dioxide compounds that are inherently non-flammable and will not melt, deform or ignite even under severe overload conditions. The sealed enclosure provides excellent resistance to moisture ingress and withstands exposure to common industrial cleaning solvents, ensuring that resistance stability is maintained over time in humid or chemically challenging environments. The rigid casing also gives the assembly outstanding mechanical robustness: it resists the cracking and delamination failures that can occur with epoxy or resin coatings under sustained vibration, making the RQA well suited to machinery, vehicles and other installations subject to continuous mechanical stress.

The RQA series is rated at 5W, 10W and 20W with a resistance range of 0.1Ω to 100kΩ. Two tolerance grades are offered — ±5% and ±10% — and two TCR grades are available depending on the alloy wire used: ±260ppm/°C for the GC and CC copper-nickel and nickel-chromium wire types, and ±400ppm/°C for the MO wire type used in low-ohmic-value variants. The operating temperature range is −55°C to +155°C, and rated power is based on continuous full load at 70°C ambient, with derating required at higher ambient temperatures. Maximum working voltage is defined by the square root of the product of rated power and resistance value. Dielectric withstanding voltage is AC 500V for one minute.

Short-time overload performance is rated at 2.5 times the rated continuous working voltage for five seconds, with a resistance change limit of ±(5% + 0.05Ω). Long-term load life testing confirms resistance stability within ±5% after 1,000 hours under rated power at 70°C on a 1.5-hour on, 0.5-hour off cycle. Humidity load life testing under the same duty cycle at 40°C and 90 to 95% relative humidity also holds within ±5%. Temperature cycling across five cycles between −55°C and +155°C results in a resistance change of no more than ±(2% + 0.05Ω). Resistance values are selected from the E24 series, and the component is marked by printing on the ceramic casing body. The RQA is supplied in axial leaded format suitable for through-hole PCB mounting and panel installation.

Model: RQA
Resistor type: Wire wound
Description: Ceramic encased
Power Rating: 5W~20W
Resistance (Ω): 0.1~100k
Tolerance (%): ±5, ±10
TCR (ppm/C): 260, 400

Model: RQL
Resistor type: Wire wound
Description: Ceramic encased
Power Rating: 10W~40W
Resistance (Ω): 0.3~100k
Tolerance (%): ±5, ±10
TCR (ppm/C): 260, 400

Model: RQR
RResistor type: Wire wound
Description: Ceramic encased
Power Rating: 2W~12W
Resistance (Ω): 0.1~75k
Tolerance (%): ±5, ±10
TCR (ppm/C): 260, 400

Model: RQR15~40
Resistor type: Wire wound
Description: Ceramic encased
Power Rating: 15W~40W
Resistance (Ω): 0.01~54k
Tolerance (%): ±0.5, ±1, ±2, ±5, ±10
TCR (ppm/C): 260 (max.)

Model: RQB
Resistor type: Wire wound
Description: Ceramic encased
Power Rating: 5W~20W
Resistance (Ω): 0.1~100k
Tolerance (%): ±5, ±10
TCR (ppm/C): 260, 400