RWR71SR249FSBSL Vishay Dale 0.249Ω 2W Wirewound Resistor

ElecSuppliers Part Number GuideAug 22, 2026

RWR71SR249FSBSL is a Vishay Dale RWR71S series wirewound resistor designed for applications that require low resistance, relatively high power handling and stable operation under demanding conditions. The component has a nominal resistance of 0.249 Ω, a tolerance of ±1% and a rated power of 2 W.

Unlike ordinary signal resistors, this type of low-value wirewound resistor is commonly used where the resistance itself is part of a power or current-related function. Its axial construction also provides a different mechanical and thermal profile from modern surface-mount current-sensing resistors.

RWR71SR249FSBSL Key Specifications

RWR71SR249FSBSL has a resistance value of 0.249 Ω with a ±1% tolerance. Its rated power is 2 W and it uses a two-terminal axial package.

The resistor belongs to the RWR71S military series and is specified for operation from approximately -55°C to +250°C. Its temperature coefficient is approximately ±650 ppm/°C.

The component uses wirewound construction and is designed with military and moisture-resistant characteristics.

0.249Ω Low-Value Resistor

The 0.249 Ω resistance value is significantly lower than that of conventional general-purpose resistors.

Low-value resistors are often selected when the designer needs to create a controlled voltage drop or measure current through a circuit. Because even a small resistance can produce a measurable voltage at higher currents, such components can be useful in power-control and current-monitoring applications.

For example, at 1 A, a 0.249 Ω resistor produces approximately 249 mV of voltage drop and dissipates approximately 0.249 W.

At 2 A, the voltage drop increases to approximately 498 mV and power dissipation reaches almost 1 W.

This illustrates why the 2 W power rating of RWR71SR249FSBSL is important when the resistor is used in higher-current circuits.

RWR71S Military Wirewound Resistor

RWR71SR249FSBSL belongs to the RWR71S family of military wirewound resistors.

The RWR series is associated with MIL-PRF-39007 requirements and includes multiple resistance values, tolerance options, failure-rate grades and packaging configurations.

The RWR71S construction is intended for demanding applications where environmental reliability and predictable electrical performance are important.

For military or high-reliability equipment, the complete ordering code should be maintained because individual suffixes can identify important characteristics such as tolerance, failure-rate grade and packaging.

RWR71SR249FSBSL Power Rating

The 2 W power rating allows RWR71SR249FSBSL to handle considerably more power than small signal resistors.

Because the resistance is only 0.249 Ω, the resistor can carry relatively high current before reaching its rated power. However, power dissipation increases according to the square of the current.

The relationship can be expressed as:

P = I²R

With a resistance of 0.249 Ω, increasing current from 1 A to 2 A increases power dissipation by a factor of four.

For continuous operation, engineers should therefore consider the actual current, ambient temperature and resistor temperature rather than relying only on the nominal 2 W rating.

Wirewound Construction

RWR71SR249FSBSL uses wirewound resistor technology.

A wirewound resistor is manufactured by winding resistive wire around an insulating core. This construction allows relatively low resistance values to be produced while providing good power-handling capability.

Wirewound resistors are particularly useful in applications where a resistor must dissipate more power than a typical small thick-film resistor.

One consideration is that wirewound construction can introduce inductance. Whether this matters depends on the circuit frequency and application. For DC, low-frequency power and current-sensing applications, the resistance and power characteristics are generally more important.

RWR71SR249FSBSL Temperature Performance

The specified operating temperature range extends from approximately -55°C to +250°C.

This wide temperature range makes the resistor suitable for applications exposed to significant environmental temperature changes.

The temperature coefficient is approximately ±650 ppm/°C. Because the resistance value is very low, even relatively small changes in resistance can influence the measured voltage when the resistor is used for current sensing.

For precision current measurement, engineers should therefore consider the resistor's temperature coefficient together with self-heating and the thermal characteristics of the PCB or assembly.

Military and Moisture-Resistant Design

RWR71SR249FSBSL is part of the RWR military resistor family and incorporates moisture-resistant characteristics.

This is relevant for equipment that may operate in demanding environments where humidity and temperature cycling can affect component reliability.

The combination of wirewound construction, environmental resistance and military-oriented specifications makes the RWR71S family different from standard commercial low-value resistors.

For equipment requiring formal qualification, designers should verify the specific procurement and qualification requirements of the project rather than assuming that every visually similar resistor provides the same level of compliance.

RWR71SR249FSBSL Applications

RWR71SR249FSBSL can be used in power electronics, current monitoring, protection circuits, control equipment and high-reliability electronic systems.

Typical functions include current sensing, current limiting, load resistance and controlled voltage-drop applications.

Its 0.249 Ω value can be useful where a specific low resistance is required rather than a standard value such as 0.22 Ω or 0.27 Ω.

The 1% tolerance also provides tighter resistance control than many general-purpose power resistors with wider tolerances.

Axial Package

RWR71SR249FSBSL uses an axial through-hole package measuring approximately 4.75 mm in diameter and 20.62 mm in length.

The relatively large body provides room for heat dissipation and is consistent with the component's 2 W power rating.

The through-hole construction also provides strong mechanical connections, which can be useful in equipment subject to vibration or mechanical stress.

When installing the resistor on a PCB, designers should provide adequate clearance from heat-sensitive components and allow sufficient space for the resistor body and leads.

RWR71SR249FSBSL Replacement

When selecting a replacement, the 0.249 Ω resistance value and ±1% tolerance should be matched first.

The 2 W power rating, temperature range, temperature coefficient and wirewound construction are also important.

A surface-mount current-sense resistor with the same 0.249 Ω resistance is not automatically an equivalent replacement. Differences in power rating, thermal performance, package construction and parasitic characteristics can affect the circuit.

For military or high-reliability equipment, the relevant qualification and failure-rate characteristics should also be considered.

RWR71SR249FSBSL Part Number Structure

The RWR71 series uses a structured part-number system in which different sections identify the model, resistance value, tolerance, failure-rate grade and packaging.

For RWR71SR249FSBSL, the RWR71S portion identifies the resistor family and construction, while R249 represents the 0.249 Ω resistance value. The F indicates ±1% tolerance.

The remaining suffix characters identify additional ordering characteristics and packaging.

This makes it important to use the complete part number when searching for the component, especially when sourcing military-grade resistors with specific packaging or qualification requirements.

RWR71SR249FSBSL for Low-Resistance Applications

RWR71SR249FSBSL combines a 0.249 Ω resistance, ±1% tolerance and 2 W power rating in a rugged axial wirewound package.

Its low resistance makes it particularly relevant to current-related circuits, while the RWR71S military construction provides characteristics intended for demanding applications.

For new designs, engineers should calculate actual power dissipation from the expected current and evaluate temperature rise under real operating conditions. For replacement applications, matching the complete resistance, power, tolerance, temperature and mechanical specifications is essential.