Pass / Fail PAT Testers (Go / No-Go Testers)

Pass / Fail PAT checker

Some PAT testers are sold as “single button” or pass / fail instruments. They are designed to be simple to use and usually give a green “pass” or red “fail” without showing the actual measured values.

This sounds convenient, but it removes the most important part of PAT testing: being able to judge whether a result is sensible for the appliance and cable length. A tester that only shows pass/fail can hide borderline results, give misleading passes, and make it difficult to demonstrate that testing has been carried out correctly.


The Main Problem: Earth Continuity Limits

This is one of the reasons pass/fail testers are so limited: the correct earth continuity limit is (0.1 + R)Ω, where R is the resistance of the supply cable. Without the measured value you can’t make a proper allowance for cable length and CSA. See our earth continuity limit guide and calculator.


For background on the limits and how they’re applied, see our IET Code of Practice guide.

For example:

  • A typical appliance with a short 1m flex might have a maximum limit only slightly above 0.1Ω.
  • A long extension lead can legitimately measure much higher due to the cable resistance alone.

A true PAT tester that displays readings lets you compensate for lead resistance. A pass/fail tester usually can’t do this properly, so manufacturers often set the pass limit to a “one-size-fits-all” value that is higher than it should be for many appliances.


“Some portable appliance test instruments with go/no-go indication may fail a cable connected appliances with earth continuity resistance exceeding 0.1Ω. If it is not possible to reprogramme the appliance test instrument it will be necessary for a measurement of the actual resistance to be made with another instrument." - IET Code of Practice.

Insulation Testing Can Be a Compromise Too

Insulation resistance testing should normally be carried out at 500 V DC, but some equipment (particularly older or more sensitive items) may require a reduced test at 250 V DC. With many pass/fail testers you don’t have proper control of the test voltage, and some models use “in-between” voltages or simplified methods.

When the instrument doesn’t display the measured insulation value (only pass/fail), it’s much harder to spot deterioration over time or identify results that “pass” but are still poor compared to previous records. This is also why good records should include the measured values, not just “Pass” or “Fail”. In fact, not recording the measured readings is in our top five PAT testing mistakes. See our common PAT testing mistakes article.

So Are Pass / Fail Testers Ever Useful?

In limited situations, a go/no-go tester can be used as a basic screening tool provided you understand its limitations and have access to a tester that provides measured readings when needed. If you’re responsible for workplace electrical safety, or you test commercially, you will usually be better served by a tester that displays values.

What We Recommend Instead

If you’re buying a PAT tester, choose a model that displays the actual readings (earth continuity, insulation resistance, leakage where applicable) as well as showing pass/fail. That way:

  • You can allow correctly for different cable lengths.
  • You can identify borderline results and investigate properly.
  • Your records can include measured values, which helps demonstrate due diligence.

It’s also worth remembering that a “pass” result is only meaningful when the test has been set up correctly and the right test has been selected for the equipment type.

Good training helps you understand what each test is actually proving, when results can be misleading, and how to interpret readings rather than relying on a simple green light. Our PAT testing courses cover correct test selection, correct use of instruments, and interpretation of results.