[FONT=&]Fluke 165x series MFT error codes:
Error 1, Self-Test failure. Return tester to Fluke service centre.
Error 2, Over-Temperature. Wait let tester cool down.
Error 3, Internal protection failure? Return tester to Fluke service centre.
Error 4, Fault Voltage. Check the installation, in particular, the voltage between N and E.
Error 5, Excessive Noise. Loop, RCD tests, isolate all appliances. Earth Resistance tests, move earth stakes.
Error 6, Excessive Probe Resistance. Put the stakes deeper into the soil. Tamp down the soil directly around the stakes. Pour water around the stakes but not at the earth electrode under test.
[/FONT]I'm afraid Error 5 is the bane of the Fluke user's life mate, the no-trip test method employed by Fluke is very sensitive to any electrical noise on the supply all you can do is ensure all loads isolated before testing and if you then get an Error 5 warning retest until you get a valid reading. If you cannot get a stable reading you may have to test at an alternative time when the supply is less noisy, eg. lunchtime or after-hours.
Fluke trumpet the fact that when Error 5 is shown on the display you can press the down arrow and the measured value will be displayed (pressing the up arrow returns the display to the Error 5 message) but this is one of those pointless features that manufacturers dream up, because the measured value is unreliable due to the errors introduced by the noise on the supply and therefore should not be recorded on any certification paperwork.
Error 4 is usually caused by poor contact between one (or more) test prod or crocodile clip and the test point(s) usually the N and/or E connection(s). However, if reconnection makes no difference, then the MFT may well be measuring a real fault voltage, usually between N and E, this will obviously need to be cured before the MFT will allow you test normally.