Insulation tester HP-6688F

I had recently again problems with my Dishwasher. For some reason it was tripping the FI-main switch.  I decided to need an insulation tester to investigate this further.  A short search on internet pointed me to this HP-8866F insulation tester.

This is a fairly reasonable low cost tester with a 2500V range. This high voltage range is on most lower cost instruments not available. There is not that much information available on this instrument, but here is a review with tear-down on youtube.
The specification for this instrument is as follows (copied from the manual)

Insulation tester	2500V
Test voltage / Minimum resistance to keep voltage	250V	1MΩ
	500V	1MΩ
	1000V	2MΩ
	2500V	2MΩ
Output voltage	90 – 110% of the test voltage
Measurement range	1MΩ – 20GΩ
Resolution	0.01MΩ
Accuracy	1MΩ – 200MΩ	±(3.0%+5)
	200MΩ – 10GΩ	±(5.0%+5)
	10GΩ – 200GΩ	±(10.0%+5)
AC voltage range	1V – 750V	±(2.0%+5)
Frequency range	1V	40 – 400Hz

It is of course typical a measurement tool that you need only once a year and therefore I didn't want to spend too much on such instrument. I have bought the instrument at Komerci, but it can also be purchased on ebay, Amazon or Aliexpress.

For my purpose to find a short in the heater of the dishwasher did this instrument do a good job. However I would not depend my life on it; the professionals can better buy a Fluke or other name instrument. The voltages are a bit off and the youtube review shows quite some overshoot. Testing motors, heaters and other "passive" components will be no problem, but testing some active semiconductor circuit can be a problem.

For this blog I made a few experiments with 10 x 1MΩ resistors in series.  My small multimeter is measuring the voltage over the last resistor, which makes that it shows the measurement voltage divided by 10. This gives the following results:

Fluke		Resistance: 10.16MΩ Voltage: 2.489V
Old Multimeter		Resistance: 10.07MΩ Voltage: 0.508V Interesting difference in measurement voltage between my fluke and my old multimeter of 25 years ago.
250V		Resistance: 9.98MΩ Voltage: 208.7V (Too low!!)
500V		Resistance: 10.01MΩ Voltage: 456.9V
1000V		Resistance: 9.95MΩ Voltage: 909.9V
2500V		Resistance: 9.88MΩ Voltage: 2262V

The results are not too bad, however the voltage on the 250V range is a bit too low according to the specification.

This instrument was anyhow useful to find the short in the heater of the dishwasher.