March 14, 2024

Cable Tester vs Digital Multimeter_Choosing the Right Tool for RJ45 Pass Through Connectors_1

Digital multimeter (DMM)

Digital multimeter is a common household item. On emergency, yes, you can use a Digital multimeter (DMM) to check Ethernet cables, but it's essential to understand its limitations and the specific scenarios where it's useful.

Here's how you can use a DMM for Ethernet cable testing:

  1. Continuity Testing:
  • Set your DMM to the continuity or resistance mode.
  • Connect one probe to one end of the Ethernet cable's conductor (either the wire or the connector pin).
  • Connect the other probe to the corresponding conductor at the opposite end.
  • If the DMM shows low resistance (close to zero ohms), it indicates that the conductor is continuous and properly connected.


  1. Checking for Shorts:
  • Shorts occur when two conductors are unintentionally connected.
  • Use the continuity mode to check for shorts between different pairs of wires within the Ethernet cable.
  • If the DMM beeps or shows low resistance, there's a short circuit.


  1. Verifying Wire Pairs:
  • Ethernet cables have four twisted pairs of wires (eight conductors).
  • Use the DMM to verify that each pair is correctly connected:
  • Pair 1: White with blue stripe (T568A) or white with green stripe (T568B) and blue (T568A) or green (T568B).
  • Pair 2: White with orange stripe and orange.
  • Pair 3: White with green stripe (T568A) or white with blue stripe (T568B) and green (T568A) or blue (T568B).
  • Pair 4: White with brown stripe and brown.
  • Measure the resistance between the corresponding wires in each pair.


  1. Measuring Voltage:
  • While not commonly used for Ethernet cable testing, you can measure voltage using the DMM.
  • Connect one probe to the conductor (wire or pin) and the other probe to the ground (shield or connector shell).
  • Ensure that no power is applied to the cable during this test.


However, keep in mind the following limitations: 

  • Signal Integrity: A DMM cannot verify signal integrity or data transmission quality. It only checks continuity and basic connectivity.
  • Complex Issues: For more complex issues (such as intermittent connections or signal degradation), a dedicated cable tester or network analyzer is more suitable.
  • Specific Tools: While a DMM is versatile, using a dedicated cable tester designed for Ethernet cables is often more efficient.

In summary, a digital multimeter can serve as a basic tool for initial cable checks, but for thorough Ethernet cable testing, consider investing in a purpose-built cable tester or network diagnostic tool .

  Cable Tester vs Digital Multimeter_Choosing the Right Tool for RJ45 Pass Through Connectors

Cable tester a modern wonder

When using a cable tester to test an Ethernet cable, we are primarily checking for the following:



  • We verify that all the wires within the cable are properly connected from one end to the other.
  • If there is a break or disconnection in any of the wires, the cable tester will indicate it.
  • Ensuring continuity is crucial for reliable data transmission.

Correct Wiring Order:

  • Ethernet cables have specific wire pairs (such as T568A or T568B) that must be correctly aligned.
  • The cable tester confirms that the wires are in the proper order, preventing issues like reversed pairs.

Shorts or Cross-Talk:

  • Shorts occur when two wires touch or are unintentionally connected.
  • Cross-talk refers to interference between adjacent wire pairs.
  • The cable tester detects any shorts or cross-talk, which can impact signal quality.

Pin-to-Pin Mapping:

  • It ensures that each pin on one end of the cable corresponds to the correct pin on the other end.
  • Incorrect pin mapping can lead to communication problems between devices.

LED Indicators:

  • Most cable testers have LEDs that light up to indicate successful connections or issues.
  • These indicators help technicians quickly identify problems during cable installation or troubleshooting.

Remember that cable testers are essential tools for initial cable checks, but for more detailed diagnostics and troubleshooting, additional tools like multimeters or network analyzers may be necessary.