Accurate earth loop impedance testers or MF tester recommendations for industrial type installations/supplies

CF52 said:

I do not feel my older Megger 1741+ is particularly accurate. When I compare readings to a colleagues modern Metrel touch screen style multifunction tester the impedance readings he obtains are significantly lower.

It does not answer the question, but I assume that both of you have a regular (annual) calibration check. Megger claims an accuracy of ± 5% to the nearest 10 mΩ.

Why do you feel that your MFT is less accurate than your chum's Metrel?

Chris Pearson said:

It does not answer the question, but I assume that both of you have a regular (annual) calibration check. Megger claims an accuracy of ± 5% to the nearest 10 mΩ.

Overall service error of ± 10 % ± 2 digits, though, on loop test, I believe ... and not uncommon for a general MFT?

Given the  ± 2 digits, and resolution of 0.01 Ω, any readings that would come in below about 0.05 Ω (equivalent to about 4.6 kA prospective fault current) are effectively indistinguishable with such an instrument.

This is the problem with general MFTs used with high prospective fault current supplies.

gkenyon said:

This is the problem with general MFTs used with high prospective fault current supplies.

Quite so. I fear that the original question has not been answered. I would say a specialist EFLI tester, but which manufacturer, and which model?

The description of a '4-Wire Impedance Test' in the Megger booklet I mentioned would suggest something like the Megger NIM1000 Impedance Meter.

• https://www.megger.com/en-gb/products/nim1000 

It uses a test current of up to 1000A, has a measurement resolution of 1 mΩ gives the measurement results as Z Ω / R Ω / X Ω.

However, with a price tag around £8k its purchase and use is probably only economical for DNOs and similar.

I have no connection with Megger other than as a user of their products and services.

- Ross

you do need to ask how often you need that sort of measurement rig. Unless the answer is 'daily' then hiring one in, either with or without the skilled subcontractor to operate it, is probably the way forward.

Much like buying your own telehandler, cherry picker or crane.... which is also rarely owned outright, except perhaps for Bob the builder who seems to own a lot of plant that is mostly underused. But that is a fictional  kids TV programme.

Mike.

you do need to ask how often you need that sort of measurement rig. Unless the answer is 'daily' then hiring one in, either with or without the skilled subcontractor to operate it, is probably the way forward.

Much like buying your own telehandler, cherry picker or crane.... which is also rarely owned outright, except perhaps for Bob the builder who seems to own a lot of plant that is mostly underused. But that is a fictional  kids TV programme.

Mike.