250 Ohm Resistor Color Code: 4-Band & 5-Band Reference

If you are holding a 250 ohm resistor, the color code depends on the tolerance band format. For a standard 4-band resistor, the colors are Red-Green-Brown-Gold (25 × 10 = 250Ω, ±5%). For a precision 5-band resistor, the colors are Red-Green-Black-Black-Brown (250 × 1 = 250Ω, ±1%).

Unlike common E12/E24 values (which jump from 240Ω to 270Ω), 250Ω is a specialized value. You will almost exclusively encounter it as a 1% or 0.1% precision metal film resistor used as a shunt in industrial 4-20mA current loops, or as a custom wirewound power resistor. Below is the complete breakdown of how to read, verify, and apply these specific bands on the bench.

The 250 Ohm Resistor Color Code Reference Table

The following spec-sheet table breaks down the exact band assignments for both 4-band and 5-band formats. Always orient the resistor so the tolerance band (Gold, Silver, or Brown) is on the far right before reading left-to-right.

Decoding the Bands and the 'Rows People Get Wrong'

Reading a resistor color code seems straightforward until you are squinting at a 1/4W component under poor bench lighting. The math for 250Ω is simple: the first two digits (2 and 5) are multiplied by 10 (Brown in a 4-band system) or the third digit is zero and multiplied by 1 (Black and Black in a 5-band system).

In industrial electronics, a 250Ω precision shunt resistor is the standard component for converting a 4-20mA current loop into a 1-5V voltage signal for an ADC or PLC input. By Ohm's Law (V = I × R), 4mA × 250Ω = 1V, and 20mA × 250Ω = 5V. Because this application demands high accuracy, you will almost always be reading the 5-band (1%) or even 6-band (adding a temperature coefficient) variant in control panels.

Rows People Get Wrong

• Confusing the 4-Band Multiplier: Technicians frequently misread the Brown multiplier band as Red. Brown is ×10 (yielding 250Ω), while Red is ×100 (yielding 2500Ω or 2.5kΩ). If your PLC analog input is reading 10 times higher than expected, you grabbed a 2.5kΩ resistor.
• Misidentifying 5-Band Zeroes: In the 5-band format, the third band is Black (0) and the fourth band is Black (×1). Beginners often collapse this, reading Red-Green-Black as 25Ω and ignoring the fourth band. Always count the physical bands on the body before assigning values.
• The 'Gold on the Left' Trap: If you see a Gold or Silver band on the left side, you are holding the resistor backwards. Gold and Silver are exclusively tolerance (and occasionally temperature coefficient) indicators and can never represent a significant digit or a fractional multiplier on the left side.
• E-Series Availability Confusion: 250Ω is not a standard E12 or E24 value. If you are scavenging from a standard kit and measure 249Ω (Red-Green-White-Black-Brown), that is the E96 standard equivalent. In a 4-20mA loop, 249Ω will yield 0.996V to 4.98V, which is well within the acceptable calibration range for modern 12-bit ADCs.

Standards Context: IEC 60062 vs. Regional Wiring Codes

A common point of confusion for hobbyists transitioning into industrial or residential electrical work is the assumption that component color codes change by region, much like mains wiring. This is false. Resistor color codes are universally governed by the IEC 60062 standard. There is no 'US-only' or 'old UK' resistor code; a Red-Green-Brown resistor is 250Ω in Tokyo, London, and Chicago.

However, because bench technicians and electricians often cross over between PCB repair and mains wiring, confusing component bands with wire insulation colors is a dangerous mistake. Below is a comparison table to keep your mental models separate and ensure you never apply IEC component logic to NEC mains wiring.

Rule of thumb: If you are looking at a small cylindrical component with wire leads, use IEC 60062. If you are pulling NM-B cable or THHN through conduit, use your local electrical code (NEC in the US, BS 7671 in the UK).

Faded Markings, In-Circuit Measurement, and Safe Interpretation

When a 250Ω shunt resistor in a 4-20mA loop fails, it is usually due to an overcurrent event (e.g., a shorted sensor wiring 24V directly across the shunt, dissipating P = V²/R = 576²/250 = 2.3W on a 1/4W rated part). When this happens, the paint and color bands will blister, fade, or burn off entirely.

Safe Interpretation of Damaged Components

1. Visual Inspection: If the bands are illegible but the body is intact, check the material. Carbon composition resistors tend to absorb moisture and drift lower in value over decades. Metal film resistors (the standard for 250Ω shunts) almost always drift higher or fail completely open when subjected to thermal overload.
2. The Multimeter Test: Set your DMM to the lowest resistance range that exceeds 250Ω (usually the 2kΩ or 20kΩ scale). Short the probes to note your lead resistance (typically 0.1Ω to 0.3Ω) and subtract it from your final reading for maximum accuracy on low-value shunts.
3. Replacement Protocol: If a 250Ω shunt is burnt, do not simply replace it and power up. A burnt shunt indicates a downstream fault. Verify the 4-20mA sensor wiring for shorts, and check if the PLC's internal protection diodes have been compromised before installing a fresh 250Ω (or 249Ω E96) 1% metal film resistor.

For further reading on designing robust current loops and selecting the correct shunt tolerances, refer to application notes from major semiconductor manufacturers like Analog Devices on 4-20mA loop design. Understanding the physical and electrical context of the 250Ω value ensures you aren't just reading colors, but actually diagnosing the system.