The term **20-R** (or **20R**) in electronic components is most commonly a standardized code used to indicate a specific resistance value or a specific series of surge protection devices. ### 1. Resistance Value: The "R" Notation In the world of resistors, the letter **"R"** is used as a decimal point and a multiplier for Ohms ($\Omega$). This system prevents errors when reading small decimal points on tiny components. | Code | Value in Ohms | Meaning | | :--- | :--- | :--- | | **20R** | $20\ \Omega$ | The "R" acts as the decimal at the end ($20.0$). | | **R20** | $0.20\ \Omega$ | The "R" acts as a leading decimal. | | **2R0** | $2.0\ \Omega$ | The "R" acts as the decimal point. | --- ### 2. Common Component Types Depending on the context of your circuit, a "20-R" part usually refers to one of the following: #### A. Fixed Resistors (SMD or Axial) * **SMD (Surface Mount):** You will see "20R" or "200" (where the last digit is the multiplier) printed on small black chips. These are used for current limiting in LED circuits or as termination resistors. * **Power Resistors:** Often found in ceramic housings (e.g., 5W 20R J). These are used to dissipate heat in power supplies. #### B. NTC Thermistors (Inrush Current Limiters) Many NTC (Negative Temperature Coefficient) parts use a "20D" or "20R" naming convention. * **Function:** They have a high resistance ($20\ \Omega$) when cold to prevent a massive surge of electricity when you first turn a device on. * **Behavior:** As they heat up from the current, their resistance drops significantly to allow normal operation. #### C. Metal Oxide Varistors (MOV) Some manufacturers use "20" to denote the diameter of the disc (20mm) and "R" to denote a specific series or tolerance. These are used for **overvoltage protection**. --- ### 3. Technical Specifications to Check If you are looking for a replacement part labeled "20-R," you must verify these three parameters: 1. **Tolerance:** Usually denoted by a letter after the value (e.g., **20R J** = 5% tolerance, **20R F** = 1% tolerance). 2. **Power Rating:** Measured in Watts (W). A 1/4W resistor cannot replace a 5W resistor even if they are both 20 Ohms. 3. **Package Size:** For SMD parts, check the footprint (e.g., 0805, 1206, or 2512). ---