--- title: 2-Wire vs. 4-Wire Terminal Connection for Resistance Testing | Triad Magnetics description: Learn the difference between 2-wire and 4-wire resistance measurement and how we measure resistance at Triad Magnetics. image: https://info.triadmagnetics.com/hubfs/4wireschematic.png --- x [![Triad Magnetics](https://www.triadmagnetics.com/wp-content/uploads/logo.png "Triad Magnetics")](https://www.triadmagnetics.com) ![Exit](https://www.triadmagnetics.com/wp-content/themes/triadmagnetics-default/img/ico-exit.svg)![Exit](https://www.triadmagnetics.com/wp-content/themes/triadmagnetics-default/img/ico-exit.svg) ##### Search by: ![Info icon](https://www.triadmagnetics.com/wp-content/uploads/text.png "Info icon") Use this search to find a product based on its specifications. 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Manufacutring Locations - [Philippines](https://www.triadmagnetics.com/location/philippines/) - [USA](https://www.triadmagnetics.com/location/usa/) ![Certified to ISO 9001:2015](https://info.triadmagnetics.com/hubfs/ISO9001_Hor-1.jpg "Certified to ISO 9001:2015") Search [RFQ](https://info.triadmagnetics.com/lp-request-quote?__hstc=51647990.0ccaf6aa0dc1330f366743a266e2ffb3.1698833525884.1698833525884.1698833525884.1&__hssc=51647990.1.1698833525885&__hsfp=200288785)   # 2-Wire vs. 4-Wire Terminal Connection for Resistance Testing Posted by [Bill Dull](https://info.triadmagnetics.com/blog/author/bill-dull) | January 8, 2025 [0 Comments](https://info.triadmagnetics.com/blog/2-wire-vs-4-wire-terminal-connection-for-resistance-testing#comments-listing) - [Tweet](https://twitter.com/share) Precision digital multimeters (DMMs) and source measurement units (SMUs) offer two methods of measuring resistance: 2-wire resistance measurement and 4-wire resistance measurement. However, these techniques are not interchangeable because their readings vary in accuracy. While a small margin of error is acceptable for certain applications, other applications require greater accuracy to prevent serious issues, like [energy loss](https://info.triadmagnetics.com/blog/how-losses-affect-your-transformers-performance) or overheating.  DMMs typically measure resistance using a constant-current method. This technique sources a constant current to the device under test (DUT) and measures the voltage. Resistance can then be calculated and displayed using the known current and measured voltage. However, you'll need to understand how each process works before you can identify the best testing method for your device. In this article, we'll discuss 2-wire and 4-wire resistance measurement and how we measure resistance at Triad Magnetics.  ## 2-Wire Measurements  In the 2-wire testing method, two wires connect the device under test to the measurement equipment. This technique is the simplest way to measure resistance. The voltage measurement is done in the DMM, with the lead wire resistance included in the reading.  ![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXfyIzIJEtuqdaMHTSTtL1b0aDjK42GXOehs9WmzKdG3OuaBaTRTQNt5os6DveR5H99CFN_DyILIltyl6VP6kbT5Uqau1T_1wzFbmxIYispxF2127BXsd_OQpBsrXslT1jUd-qmHXw?key=9hDDo5UUVXF5ZIeTqR8_Jg) While the 2-wire resistance measurement method is fast and easy, it is not perfectly accurate since the wires themselves have some resistance, which is included in the measurement results. The voltmeter not only measures the voltage drop across the device under test but the test lead wires as well. This small degree of error might be acceptable for higher resistance measures, but it creates a more serious concern when measuring low resistances. It is possible to adjust out the lead resistance, but you will need to recalculate the [DCR](https://info.triadmagnetics.com/blog/impedance-vs-dcr-what-is-the-difference) each time.  ## 4-Wire Measurements  With 4-wire measurements, the voltmeter features four leads instead of two. Two of these leads, called force wires, send current to the DUT while the other two, known as sense wires, connect to the voltmeter. Since voltage is measured at the device under test, the resistance of the leads is excluded from the measurement.  ![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXci0rVHSo_xrQdZWBHfSfB0Y4M5Lc_wbRFAwBswoOcn6SvipBgqJI6K2r6DdlIkbnwqqC0gpDXZCP6an3SjcOP4U7ltLXtBKSAYTbn3QrAAXZD4VSacXR_kxKT4cEiaqIyw_Dm1?key=9hDDo5UUVXF5ZIeTqR8_Jg) The 4-wire resistance measurement method is more precise, as it eliminates the variance that results from the power source and ohmmeter sharing a connection. When the current path is separated from the voltage measurement like this, it's possible to obtain a more accurate measurement. This is very important when taking low-resistance measurements, such as anything below 10 ohms. At Triad Magnetics, we test everything using the 4-wire measurement technique to ensure the highest accuracy, quality, and reliability. While 4-wire testing is a standard option in specialized benchtop testing equipment, it is uncommon in handheld multimeters. Our experienced team uses the most sensitive and advanced technology to achieve more accurate measurements.  ### Applications of 4-Wire Measurements  The greater accuracy of 4-wire measurements results in safer and more reliable devices that adhere to even the most rigorous industry standards. Some of the most common applications for this type of resistance testing include:  - **50-60 Hz applications**: Distribution power or pad-mounted transformers - **5 kVA or higher**: These applications have low winding resistances - **Air coils**: Inductors without ferrous cores - **Power conversion**: Switchmode power supplies - **Large transformers**: Larger components tend to have lower resistances, which can be measured accurately by 4-wire resistance measurements ![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXc6tMSSV3whdzpFDWcnD_MLfopKwA--tlKtzLtM9DqKd2QhOKPcLzjmA51MztjVmXTsznLadGHixrNgab_xzYu3fCLMVIS4-iIrC-CgqUjpEZWmt-w9BcqP2NezpOwzjAgOk_GIfw?key=9hDDo5UUVXF5ZIeTqR8_Jg) ## Contact Triad Magnetics to Learn More  While 2-wire measurements are simple to perform, many applications require a greater degree of accuracy. At Triad Magnetics, we obtain precision readings using the 4-wire measurement technique on every device we test. This approach ensures that the part will perform as expected without excessive power loss or overheating. We conduct all testing, design, and prototyping operations from our Perris, California facility, overseen by our experienced design engineers. Since 1943, Triad Magnetics’ innovative magnetics technology has powered industrial, commercial, and consumer electronics. We are committed to continuously building upon this legacy by offering customers extensive design and engineering support. Get started today by [requesting a quote](https://info.triadmagnetics.com/lp-request-quote) or [contacting our team](https://info.triadmagnetics.com/lp-contact-us). 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