Products > Test Equipment
Low R measurement on a DMM
AVGresponding:
--- Quote from: nctnico on March 27, 2023, 01:48:52 pm ---
--- Quote from: pope on March 27, 2023, 12:55:36 pm ---
--- Quote from: grumpydoc on March 27, 2023, 12:52:08 pm ---As ever, what are you trying to measure, and why?
--- End quote ---
Continuity between PE and different points of the enclosure.
--- End quote ---
AFAIK you need a special tester for that which uses high AC currents (up to tens of Amps). At least if you want to adhere to standards.
--- End quote ---
Don't know how things are on that side of the moat, but here in the UK the PAT regulations have become ISITEE regulations :palm: and high current testing of the PE is no longer required, my guess is due to the overwhelming majority of stuff not even having a PE these days, and also that so many testers are battery powered and just can't deliver the higher currents that mains powered ones used to do.
Gyro:
These days, it's permissible to use proper electrical insulation / continuity testers for limited PAT testing, but BS7671 still requires a minimum of 200mA test current for PE - enclosure continuity.
pope:
The meter I'm using is a Brymen BM869s but as it has mentioned even a 4W meter isn't suitable for this job.
Probably a hi-pot tester is the appropriate instrument for such measurements but unfortunately I can't afford one at the moment (they seem to go for over 1k) and secondly I don't feel very confident to use one as I've never done it before. AFAIK, you have to somehow discharge the DUT after the test and I have no idea how to do this. Also, although I appreciate the DIY recommendation I don't feel competent to to do it myself.
So, I was wondering whether a PAT tester would be sufficient. For some reason it's almost impossible to buy one in EU. It seems to be a UK thing. Searching around I found this one (which will set me back a bit over 500 euro) but I don't know anything about its quality and whether it makes sense to buy one. For example in a youtube video there's the following comment:
"I would love to know how this even qualifies as a PAT tester, it has a FAIL threshold of two Meg on a class one device according to the manual, yet the official threshold is one Meg. On a class two device it has a fail threshold of four Meg, when the the official threshold is two Meg, this all seems so very wrong when other testers are correctly calibrated, and this one seems to pass items other machines would fail."
https://www.firststopsafety.co.uk/product-page/memorypat-tester-with-display-and-memory
2N3055:
--- Quote from: pope on March 30, 2023, 09:26:45 am ---The meter I'm using is a Brymen BM869s but as it has mentioned even a 4W meter isn't suitable for this job.
Probably a hi-pot tester is the appropriate instrument for such measurements but unfortunately I can't afford one at the moment (they seem to go for over 1k) and secondly I don't feel very confident to use one as I've never done it before. AFAIK, you have to somehow discharge the DUT after the test and I have no idea how to do this. Also, although I appreciate the DIY recommendation I don't feel competent to to do it myself.
So, I was wondering whether a PAT tester would be sufficient. For some reason it's almost impossible to buy one in EU. It seems to be a UK thing. Searching around I found this one (which will set me back a bit over 500 euro) but I don't know anything about its quality and whether it makes sense to buy one. For example in a youtube video there's the following comment:
"I would love to know how this even qualifies as a PAT tester, it has a FAIL threshold of two Meg on a class one device according to the manual, yet the official threshold is one Meg. On a class two device it has a fail threshold of four Meg, when the the official threshold is two Meg, this all seems so very wrong when other testers are correctly calibrated, and this one seems to pass items other machines would fail."
https://www.firststopsafety.co.uk/product-page/memorypat-tester-with-display-and-memory
--- End quote ---
Are you confusing earth continuity tester (that tests that grounding wiring is low enough resistance) with an insulation meter (HI Pot that tests that insulation is proper i.e. very high resistance)?
That tester has both of these functions. It can test insulation leakage from live to ground with 500V applied, and separately with 150mA it can test that housing is connected to earthing on plug with low enough resistance..
As for insulation test, more is better .. few MΩ is already very low resistance... If instrument threshold is 4MΩ and standard is 2MΩ it means tester is more rigorous than standard, which means it errors on the safe side... Which means it will show failed on some marginal devices that would PASS on strictly calibrated devices.
Problem is that even 4 MΩ is actually very bad insulation on most devices outside industrial environments.. 100W toroidal transformers i tested recently had resistance between primary/secondary in GΩ ranges. One that was outside in damp, salty, environment for 5+years was more than 50 MΩ still...
DX1:
Please can you explain what you are trying to do?
If low resistance PE to case and do not need to test to specification and have a power supply, Set current limit on power supply to 1A, connect the points you wish to test. Then measure the voltage drop with the Brymen. Thus use Ohms law to calculate resistance. Wire it 4 wire, which means that you connect to the measuring points, not to the power supply leads or clips. You can measure the power supply current as well to improve accuracy.
--- Quote from: pope on March 30, 2023, 09:26:45 am ---The meter I'm using is a Brymen BM869s but as it has mentioned even a 4W meter isn't suitable for this job.
Probably a hi-pot tester is the appropriate instrument for such measurements but unfortunately I can't afford one at the moment (they seem to go for over 1k) and secondly I don't feel very confident to use one as I've never done it before. AFAIK, you have to somehow discharge the DUT after the test and I have no idea how to do this. Also, although I appreciate the DIY recommendation I don't feel competent to to do it myself.
So, I was wondering whether a PAT tester would be sufficient. For some reason it's almost impossible to buy one in EU. It seems to be a UK thing. Searching around I found this one (which will set me back a bit over 500 euro) but I don't know anything about its quality and whether it makes sense to buy one. For example in a youtube video there's the following comment:
"I would love to know how this even qualifies as a PAT tester, it has a FAIL threshold of two Meg on a class one device according to the manual, yet the official threshold is one Meg. On a class two device it has a fail threshold of four Meg, when the the official threshold is two Meg, this all seems so very wrong when other testers are correctly calibrated, and this one seems to pass items other machines would fail."
https://www.firststopsafety.co.uk/product-page/memorypat-tester-with-display-and-memory
--- End quote ---
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