clamp meter

[assegayer]

hi guys just a quick question. going to invest in a clamp meter was just wondering whether a clamp meter like this one would be able to measure any current on the earth line for rcd faults in mA



http://m.screwfix.com/p/kewtech-kt2...l&gclid=COCNvZSUmMgCFUSNGwodBN0IWg&kpid=23318

 

[Richard Burns]

Unfortunately that meter does not have the resolution required for measuring earth leakage in mA.
The meter has two ranges 400A and 40A.
The screen shows four digits in either case so the 400A range can show from 000.1A to 399.9A the resolution being only 0.1A which is 100mA.
On the 40A range the display can show from 00.01A to 39.99A this is a resolution of 0.01A which is 10mA and this is not enough to be accurate for earth leakage.
Also notice in the specification that the accuracy is 2.5% +- 6 digit, this would mean that on the 40A range measuring an actual 50mA current which would display as 0.05 if accurate could actually display any value from -0.01 to 0.11 as the last digit can vary by 6 places.
so even thought the accuracy would only be 2.5% the variance in the reading could be as much as 110% at the low levels of measurement.

In order to measure the earth leakage current you would need a specific earth leakage clamp meter that can give you a better resolution, really you are looking to be close to accurate when measuring 0.1mA or 100µA. but you may be OK with 1mA resolution but it will not be ideal.
You may also be able to use these as a general clamp meter as some of them can do ranges up to 100A as well which should be enough for most domestic purposes.
Perhaps have a look at the range available on test meter here.

 

[assegayer]

Unfortunately that meter does not have the resolution required for measuring earth leakage in mA.
The meter has two ranges 400A and 40A.
The screen shows four digits in either case so the 400A range can show from 000.1A to 399.9A the resolution being only 0.1A which is 100mA.
On the 40A range the display can show from 00.01A to 39.99A this is a resolution of 0.01A which is 10mA and this is not enough to be accurate for earth leakage.
Also notice in the specification that the accuracy is 2.5% +- 6 digit, this would mean that on the 40A range measuring an actual 50mA current which would display as 0.05 if accurate could actually display any value from -0.01 to 0.11 as the last digit can vary by 6 places.
so even thought the accuracy would only be 2.5% the variance in the reading could be as much as 110% at the low levels of measurement.

In order to measure the earth leakage current you would need a specific earth leakage clamp meter that can give you a better resolution, really you are looking to be close to accurate when measuring 0.1mA or 100µA. but you may be OK with 1mA resolution but it will not be ideal.
You may also be able to use these as a general clamp meter as some of them can do ranges up to 100A as well which should be enough for most domestic purposes.
Perhaps have a look at the range available on test meter here.

really appreciate your thorough response Richard, would you be able to recomend me one that can detect voltage and continuity with the leakage at 1 ma....i was hopeing not to spend more then 80 to 100 quid

 

[Marvo]

I use one of these as my day to day leakage tester even though it's not actively marketed as one for some reason. I have several earth leakage clamp meters but I've found this one to be one of the most accurate even at <5mA and the flexible clamp is a godsend, it means it's really convenient to use especially when you're trying to get it around the L+N supply wires simultaneously. It's Chauvin Arnoux which are one of my favorite tester brands, they do a larger diameter version as well for an extra 13 quid, it's small and portable and has great specs. It's a few quid over your budget but I'd say it was good value for money if you can find the extra.

 

[Richard Burns]

Marvo's one looks quite good, resolution of 1mA is acceptable.

Not sure how to say this well, but you are looking for a high precision instrument, if you want to measure 0.1mA, and these are expensive.
I can totally understand that you want to avoid spending too much but sometimes you are stuck with spending far too much money on something that can be useful to the job at hand.

Any meter you can get that will measure accurately to that level of current will be out of budget range and if you want to have multifunction voltage and resistance as well the cost will go on up.

Probably for a starting meter so that you can get the hang of measuring current and gain an idea of earth leakage and be able to measure resistance and voltage whilst being aware that such a meter may not be totally accurate it may be best to go for one of the small hand held multimeters.
The UNI-T 210E has all the functions you want: a.c. and d.c. voltage, a.c. and also d.c. current (rare), resistance and continuity. It also measures capacitance. The maximum resolution is 1mA but this figure will be slightly variable. However at less than £35 it would be an adequate starting meter and a useful handy meter in many cases.

 

[Paul.M]

Fantastic posts Mr Burns (yet again), keep up the good work.


Assegayer, try phoning or send a PM to Test-Meter. Tell them your budget and what you require and they will bend over backwards to get you the correct clamp meter. Ask for Chris and tell him that your a Trainee on this forum, you will get 5% discount just for being a member... also say Paul M sent you, you may get a 10% increase on the discounted price lol. only joking.



These guys are great, really know how to treat their customers. Give them a buzz and see if they can sort you out. I've been using them for 3-4 years now, I buy all my test equipment from them and calibration every year.