Test leads are more than a means to connect your digital multimeter (DMM) to the unit under test; they’re an integral part of measurement safety. Poorly made, worn, or under-rated test leads can cause inaccurate readings and may pose a serious shock or electrocution hazard if you touch live wires that the meter has read, assuming they’ve been de-energized.
Here are some guidelines to ensure leads are safe to use in test measurement:
- Look for high quality leads made of good materials
- Leads made from poor quality, dissimilar materials can affect the readings recorded on the DMM.
- Be sure to use the leads that are rated for the appropriate category and voltage level
- Confirm that both the DMM and test leads are rated for the appropriate category and voltage level.
- The CAT rating on the leads should match or exceed the category of the DMM, and the two together are appropriately rated for the job.
- Ensure exposed metal matches the energy potential of a given measurement
- The higher the CAT rating, the less exposed metal is allowed at the tip of the test lead.
- Use retractable probes, probe tip covers or probes with shorter tips to avoid an inadvertent short.
- Inspect the leads
- Check to make sure insulation is not nicked or cracked and that there are no signs of gaps or cracks between the insulated wire and the molded banana plugs or probes at each end.
- Test the leads
- Conduct an ohms measurement to confirm leads are electrically reliable and able to carry a signal.
- To “ohm out” your leads, place your DMM in the resistance function, plug the leads into the meter and touch the probe tips together red to black. The meter should read about .5 ohms or less for good quality test leads.
Regardless of the quality of your multimeter, it’s only as good as the test leads you use with it. Taking a few minutes up front to confirm the leads you’re using are reliable and appropriately rated for the job are essential to ensure your electrical measurement safety.
For more information on Electrical Safety, see our online course available at the Fluke eLearning Center.