meters not accurate below 0.01 ohms

[peterhardacher]

After previous thread on here regarding. Max Zs when getting to the bigger fuses 400 amp + max ZS is below reading range of meter R1R2 0.01 ohms I have told this to my boss who is not giving me no feedback now I. Am the only tester on site no one else to ask really. Now I really would like to know the procedures other testers follow and or equipment used for these situations . As I want to make sure my work practices are what the standards require and equipment I test is safe and correct testing equipment procedures been followed so I can be certain that when I have tested it its safe to use or in the other case could be unsafe the last thing I want is anyone getting hurt

 

[telectrix]

a thread was psted some time ago, suggesting a resistance was used in series with 1 lead. then subtract that resistance value from your reading.

 

[peterhardacher]

The scale on the meter is only 0.00 so even if u done that and had a 0.02 resistance lead your readout won't register cos it's smaller than 0.01 ie 0.096 for a 400 amp thanks for ure input though its got me thinking

 

[Guitarist]

If you are solely responsible for this testing, but are not sure exactly what procedures to follow, can I suggest that you ask your boss to sign you up for a refresher course to give you the confidence to test what is required of you. The instructors will also help you decide if new equipment is needed, and you can stop worrying.

 

[peterhardacher]

I am competent and not worried I am just trying to get input from other electrical testers there is nothing hard about what am doing and going in a refresher purely to ask the question I have asked now is is not nesrcery . And as u are aware 2391 is a course designed round the house bashing industry . I think the question I have asked is a valid and responsible one as I don't remember covering fuses etc outside the scope of the regs . All I am doing is asking other industrial electricians for there input as I am on my own here if I was not I would ask one of the old boys as we do in our industry as one person does not know the ansure to everything , and guitarist do u know the ansure to what am asking I don t think u do instead u make a sarcastic comment instead to try make ya self seem clever guess u know it all . That is what is wrong with are industry these days we should be helping each other out as sparks and union brothers but guess my way of thinking is one of the few

 

[peterhardacher]

When I said what procedures to follow I was not talking bout how to test I was talking if your Meter does not allow a acurate test ie calculation and like the first reply to my thread some guys use a resistance on the meters hope the first post was not misleading in what I was asking about testing is not the problem the meter itself is and after u have reported this to management they say its fine I would like to go back into the office next time with some valid points for my argument

 

[telectrix]

i can't see what the need to measure <0.01Ω

 

[peterhardacher]

Max ZS on a 400 amp fuse for a 5 s disconnection time is 0.096 and higher fuses are. Lower

 

[Guitarist]

I am competent and not worried I am just trying to get input from other electrical testers there is nothing hard about what am doing and going in a refresher purely to ask the question I have asked now is is not nesrcery . And as u are aware 2391 is a course designed round the house bashing industry . I think the question I have asked is a valid and responsible one as I don't remember covering fuses etc outside the scope of the regs . All I am doing is asking other industrial electricians for there input as I am on my own here if I was not I would ask one of the old boys as we do in our industry as one person does not know the ansure to everything , and guitarist do u know the ansure to what am asking I don t think u do instead u make a sarcastic comment instead to try make ya self seem clever guess u know it all . That is what is wrong with are industry these days we should be helping each other out as sparks and union brothers but guess my way of thinking is one of the few

That was just rude, and totally unnecessary! I wasn't trying to be clever or put you down. It's replies like this which make me feel like I don't want to bother helping anyone. Maybe look at yourself before moaning about others not helping.

 

[peterhardacher]

Well suggesting some one goes back to college is a Help full ansure ???? If u feel it is I would be glad u don t reply on anything am not being rude one bit usually the lads on here are helpfull and knowledgable , and do u know the ansure cos that would be help full cos s lot of experienced sparks don t should we all go back to college . It's type of testing lot of people don t. Come across not in commercial or house bashing its heavey industrial petrochemical

 

[telectrix]

to be fair though, your OP was not that clear. at first glance it appeared that you were unsure of your testing procedure.

 

[peterhardacher]

Yeah I know should have been more clearer hope my other posts cleared this up a bit don t want to come across as bein a --- but just bit at the comment I think this is a good forum and I will offer advise when I can cos I have had some good advise myself . Which brings me back to the orginal question lol guess I will have to get on Internet tomorrow do some research and contact suppliers of test equip

 

[telectrix]

does make you wonder, though, why these values are called for when there's no means to measure them. perhaps there' are meters available at stupid prices that will have a resolution low enough.

 

[peterhardacher]

I know yeah there has got to be or maybe by calc ?? I will know more after this weekend research haha then I can be in a position to refuse to test or note down on test sheet instrument won t test as u know ya signing a legal binding document and if anything did happen the first question they would ask why you signed it ok dangerous territory lol

 

[telectrix]

one way would be to measure the cable/s with a tape measure, then calculate the resistance from the mΩ/m tables.

 

[Knobhead]

The guys at Test Meters (sponsors) gave me the phone number of a company that hires equipment.
I’ll try and find it for you.

 

[Spark_shark]

You could use a ductor, which measure milli/micro ohms, but as mentioned earlier, there very expensive

 

[Knobhead]

Electrical Test Equipment

Look for Ductors

 

[peterhardacher]

Cheers

 

[Knobhead]

Megger DLRO200 Digital Microhmmeter | Hire | Inlec

 

[peterhardacher]

That's very helpfull thanks tony these are expensive wonder how much to buy ? This is a great starting point for me even though my firm should be telling me this not other way round lol but knowledge is power and if they want my signature they need to provide the correct equipment for me to do my job

 

[Knobhead]

I’ve had access to a ductor at all the companies I’ve worked for. It’s an invaluable bit of kit.

 

[peterhardacher]

There only 3500 haha

 

[Bobster]

The megger ltw 425 on that site is the loop tester i use which measures down to 0.001ohm. Only £379 an that's without discount.

 

[ian.settle1]

Max ZS on a 400 amp fuse for a 5 s disconnection time is 0.096 and higher fuses are. Lower

Which is 9.6 times higher than 0.01

 

[peterhardacher]

I ment 0.1 ohm haha this is the reason I post on here cos its good to chat to other guys bout these things and to get ya mistakes pointed out lol ( no o es perfect ) . I be honest I had not heard of this it was a another of the lads to mention this which has lead me to do some research and start asking some questions

 

[peterhardacher]

Am I totally mis informed about this 0.1 ohm accuracy thing ?? Has any one else heard of this

 

[Sintra]

OP have a look at the attached file.

https://www.dropbox.com/s/tlgl6xsxunrwzf8/Megger Low Resistance Testing.pdf

 

[peterhardacher]

Thanks some useful information there

 

[vaughant]

My megger meter went to 4dp,would have been fine for the job.
think it's a megger 286 from memory,were about £500 a few years back.

 

[Engineer54]

My megger meter went to 4dp,would have been fine for the job.
think it's a megger 286 from memory,were about £500 a few years back.

I think you may be right, and sounds like the unit we have used on past projects. But i can't remember the actual model number either!! lol!!

 

[Engineer54]

I'm not seeing much of a point in using a Ductor tester to measure Ze to be honest, you would need much more information than the values measured with this device. You'd need some very long test leads too in most circumstances, and a fair bit of calculation if you do happen to be in possession of all the other relevant information!!

I use these testers to determine contact resistances of say Switchboard buss bar joints, contact resistances of ACB/GCB and larger MCCB breakers etc, and basically anything that has a sizable and/or critical site made joint/connection and the like!! Like Tony, i wouldn't be without a decent Ductor test kit during testing/commissioning sub-stations and the like!!

 

[Knobhead]

I had an electricians mate, his job was to run out the 70mm test leads.

 

[jams88]

A ductor tester might be much more accurate for measuring lower resistance ..

 

[Knobhead]

Please stop digging up old topics.