Cheapest and reliable enough clamp for AC leaks

[ThunderZed]

Hi all, this is my first post and I'm a very noob! 
I've got a problem with current leakages in an old house. Light is turned off by anti-electrical shock switch whenever AC leakages go over 30mA and I suspect there's more than just one leakage. I can't afford enough money to buy a good AC clamp to detect low currents and my budget is only 60$. In my scenario I just need a clamp that can detect AC down to 10mA. I guess I don't need anything more accurate, I mean the worst scenario could be 3 points of leakage of 10mA each one.

A friend of mine has bought an ACM92 clamp and it can detect AC down to 2.0mA so it's my best candidate for now.
I searched anyway within this forum and found out that is the uni-t UT210E the most suggested cheap clamp for low AC measurement, isn't it? It's within my budget but when I see all its other functions (V, Ohm, etc) I wonder what's its "real value" only to measure low AC compared to the ACM92 and I'd like to listen to your opinions about that. Another question: I saw you can hack this clamp's bandwidth, could it be an advantage for me in my scenario?
Finally I'd like you to add this Zoyi-Zotek VC902 to this comparison because I saw there're a lot of you using zotek instruments so I'd give a chance to this VC902.

I'd be glad to listen to your suggestions within my budget and for my goal. Thanks in advance.

[Gyro]

Hi, welcome to the forum. 

Yes, the UT210E is certainly the best documented (and potentially cheapest?) on the forum. It's pretty much a known entity.

Beware of the headline specifications of the Zoyi-Zotek VC902 . Although it looks extremely (suspiciously) sensitive on its current ranges, a look at the front panel shows that the uA ranges are on the sockets and not the clamp.  It looks as if the clamp part is AC amps (600A range?) only. Almost certainly not what you want.

I have absolutely no knowledge of the ACM92, I don't see a manufacturer name. If your friend has one, then you would be best advised to play with that and check it out for yourself. It may be a clone of the UT210 (it's possible to mod the UT210 to 6000 count with an eeprom mod), or based on another chip. It's not an issue for AC current sensing, but for DC, the influence of the Earth's magnetic field is a limitation on ultimate resolution, or at least repeatability.

[WattsThat]

It is very easy to increase the sensitivity of low cost clamp-on meters. You simply increase the turns count passing through the clamp jaws. You can make a ten or twenty turn coil of the appropriate gauge wire terminated with a screw cage terminal block. You put the wire in which you want to measure the current in series with the coil, put the clamp-on meter jaws through the center of the coil and you’ve now increased the meter reading by the turns count.

Have 10 millamps and 10 turns ? The meter will read 0.1 amps or 100 milliamps. 20 turns with 10 mA and the meter will read 0.2 amps.

The bottom line is you don’t need a super accurate, expensive meter. Sure, it’s easier but if it’s something you’ll only do once, why waste the money? Use some science, it’s free.

[Grandchuck]

Also, welcome to the forum. 

I just tried my UT210E at 50Hz and the minimum detectable is about 6 mA.  And yes, adding turns works well but might not be convenient.

[Brumby]

And yes, adding turns works well but might not be convenient.

Convenience is a function of your access to a single current carrying conductor - and that could be a problem from the outset.  Just to clarify (in case you may not be aware) clamp meters work on the magnetic field generated by current flow.

If you have both current carrying conductors (live and neutral) passing through the jaws, you will have equal current in opposite directions which will result in the magnetic fields cancelling out .... giving a meter reading of zero.  You have to have only one conductor passing through the jaws.

This is how putting one conductor through the jaws several times (ie looping it) gives you higher readings ... because the current is running in the same direction, the magnetic fields add together.  If you want to check plug-in appliances, you can easily make an "extension" lead which has a free conductor and give that conductor enough length to do a number of turns.


So to get the correct current in this example, you divide the displayed value by 5.  Using the 30.00A value displayed in this image, the actual current flowing through the wire would be 6.00A.

Change the number of loops and you change the number you divide by.

[Alti]

Light is turned off by anti-electrical shock switch whenever AC leakages go over 30mA and I suspect there's more than just one leakage.

This device is called residual current circuit breaker RCCB. It is very hard to find a wiring leakage because the leakage varies with phase of the Moon. I doubt you could find it in other way than by isolating parts of the circuitry one by one. If you hope to use single pole MCBs for that then this is not possible.

Mind that wiring leakage finding and repair is justified only when the wiring is well maintained and in a good condition. It is  unlikely to fix leakages in abused or worn out installation.

[electr_peter]

New AC leakage clamps start at ~$100. eBay has some range ac leakage clamp (for example, ETCR6600 model). These have specialized jaws for low current only.
As mentioned above, regular clamps may not resolve small current differences without winding multiple turns around the clamp.

Another measurement option would be to use DMM current range spliced into earth wire. Careful setup with covered cables/measurement box should be used to reduce risk. Not recommended for beginners.

[ThunderZed]

Hi all,

This is the 30mA switch I refered to
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I saw the "trick" of loops to get a measure of low currents with these clamps but it will be quite hard due to my outset. This is the first main box where the wires begin and where I'll have to start my search:


As you suggested I'll discard Zoyi-Zotek VC902 but now I want to be sure about the ut210e's "minimum detectable AC value" so I've just asked this question on its official thread, I hope someone will answer because it's fundamental for my goal. For now I keep ACM92 in my candidates list, I'm going to contact my friend (the acm92's owner) to ask him to send me some photos of the inside of this instrument and I'll show you here, if he'll accept to open his new "boy"

eBay has some range ac leakage clamp (for example, ETCR6600 model). These have specialized jaws for low current only.

Price is my real problem! As someone said above, I need this clamp only for this job, I don't think I'll use it in my future and "science" (WattsThat's quote) can't help me this time for the reason I wrote above (too narrow spaces).
Anyway I'd like you to tell me your opinion about this SZBJ BM2060 for 73.2$ (above my budget), which falls in the leakage clamps category. Here's the only specs sheet I found on it ("20mA  0.01mA  ±(1.5%+5").

leakage varies with phase of the Moon

Amazing! Can you post some link to study this relationship?

by isolating parts of the circuitry one by one

It was my first idea but I think it's economically better (and faster) to get a cheap clamp than N (maybe 7-10) switches to solve my problem in an electrical system like mine: there's only one switch for all the wires for now.

PS - sorry for the pics but I couldn't resize them

[Alti]

I think you should go with UT210E, it has the resolution of 1mA at 2A range, 2%. Finding 5mA or 10mA should not be a problem, I just tried it with 5mA AC, indicates 4mA. And it has really compact clamps. It is CAT III 300V which in your situation is a perfect tool. I think it fits your $60 budget.

The "switch" on the picture is not a switch but RCBO wich is an integrated RCCB and 2-pole MCB in one package. And because of that RCBO you won't be able to isolate smaller parts of circuitry because there are no MCBs downstream. Looks like rebranded Legrand.

BTW, do you have a coax entangled in this spaghetti?

[electr_peter]

eBay has some range ac leakage clamp (for example, ETCR6600 model). These have specialized jaws for low current only.

Price is my real problem! As someone said above, I need this clamp only for this job, I don't think I'll use it in my future and "science" (WattsThat's quote) can't help me this time for the reason I wrote above (too narrow spaces).
Anyway I'd like you to tell me your opinion about this SZBJ BM2060 for 73.2$ (above my budget), which falls in the leakage clamps category. Here's the only specs sheet I found on it ("20mA  0.01mA  ±(1.5%+5").

SZBJ BM2060 will do just fine for your application - enough ranges and resolution. With 0.01mA resolution you will have more confidence in measurements than semi guessing with 1mA resolution.
It has similar specs and construction to other specialized meters like ETCR6600. Jaws actually have small metal fingers/plates that mesh together, take care to not damage that.

[ThunderZed]

First of all sorry for my very bad tech english I called "switches" devices with different functions, thanks for the correct names.
My very first idea was to put one RCBO for each line inside that "spaghetti" box so I'd have been suddenly sure what the "culprit" were but it was too expensive. Then I thought to use simple MCBs turning OFF only one of them and check if the RCBO switched off or not but it'd has taken too much time. So the cheap clamp solution came.

About u210e.
I know you've already told me the minimum AC value it can measure but I'd like you to look at this pic taken from a forum [see attach_1] and the forumers say: 1) this clamp is not reliable enough measuring only one lead on 2A scale; 2) if looping the wire 10 times this clamp measures 20 times the real value. Consider that I asked them if this clamp will be good enough for my specific goal in my scenario.
Your comments and explanations on this will be fine

Finally and just for completeness, I want to show you this interesting real comparison between BM2060 and fluke 8808A by a final buyer (M***) on the feedback section [see attach_2]
Ok, we have to trust he was "honest" and his photo is real

[Gyro]

About u210e.
I know you've already told me the minimum AC value it can measure but I'd like you to look at this pic taken from a forum [see attach_1] and the forumers say: 1) this clamp is not reliable enough measuring only one lead on 2A scale; 2) if looping the wire 10 times this clamp measures 20 times the real value. Consider that I asked them if this clamp will be good enough for my specific goal in my scenario.
Your comments and explanations on this will be fine

The big attraction of the UT210 for most people here is that it has a Hall-effect sensor and is therefore capable of measuring DC current as well as AC. For such a low cost Hall-effect clamp, its sensitivity is very good.

For AC only, the clamp will be a current transformer type. It is much easier to make these for lower currents, a simple matter of turns ratio. Circuit sensitivity and noise are still ultimate limiting factors (together with how accurately the jaws close - the main problem for the UT210 as they are plastic faced to avoid DC saturation), but the designer doesn't need to worry about circuit DC offsets, which are a big issue for the Hall ones.

For your specific AC requirement, you should be looking for the current transformer type - being very careful to check that the lowest current ranges still use the jaws and not probe leads.

Just one note though, low levels of DC Current offset are becoming more common on modern mains wiring, cause by things like LED lighting dimmers and EV chargers in the house. Probably not something to worry about at the moment, and in any case you would have to pay much more for a solution that can reliably measure such low DC currents with high accuracy.

[Alti]

I think you are not looking for <1mA leakage, main selling point of BM2060. Every piece of wire there has some leakage, every grounded equipment, which is normal, just ignore it. You need to find a big leakage that appeared recently and trips RCD and for that a 0.01mA equipment gives no or very little advantage when compared to 1mA meter. And if you find some suspicious circuit you need to monitor more precisely for a weekend, you can add a pair of wires wrapped around 210E, lets say seven times. IMHO.

Light is turned off by anti-electrical shock switch whenever AC leakages go over 30mA

BTW, this Bticino RCBO gives no indication what has made it trip (it includes 4 tripping mechanisms inside) and at the same time you do not own clamp meter. Then how did you get to the conclusion this is the leakage current that trips it?

[ThunderZed]

For your specific AC requirement, you should be looking for the current transformer type - being very careful to check that the lowest current ranges still use the jaws and not probe leads.

I guess this is a very interesting point in my case, so how to check it out? Of course you already know that for the u210e so it's a sure information here but how for other clamps especially the not-known chinese ones? Is it necessary to open them and look by your eyes their current transformer type?
Btw my friend (acm92's owner) refused to open it, he said he's no time to do that... ok, no xmas wishes for him this year

I think you are not looking for <1mA leakage

Of course the point is not to measure <1mA but to be sure that all this chinese cheap stuff *really* can measure down to 10mA for my goal. Due to that I posted the u210e at work from that other forum and asked you your opinion, but if you ensure me this tool is "good enough" for my goal in my scenario it's ok for me I just guess some of them are built "worse", I mean they've a higher tolerance, so I think it's definitely a question of luck as well on a large scale of sold cheap instruments.

this Bticino RCBO gives no indication what has made it trip

I'm sure it's a leakage matter because the house's owner (a relation of mine) said the trips (right word?) occur only when it's raining hard and for long time especially when rain falls inclined (not straight). My bet is the leakage relays in one of the outside lamps so last week I dismantled almost everything outside the house: all those lamps on the external walls, the neon lamp and the 2 power outlets. Yesterday it rained quite hard but no trip occurred and now... my fingers are crossed, I mean my strategy is to wait with much patience: if another trip occurs I'll buy the clamp, if not I won't buy it.
What do you think about that? Do you agree with my strategy?

[Alti]

the trips (right word?) occur only when it's raining hard and for long time especially when rain falls inclined (not straight).

No, no, no. It is not rain, it is the phase of the Moon. 

Did you consider what if there is actually no leakage there but just an intermittent short in between L and N? Sure, my experience also tells me leakage is more probable, but you never know with this type of RCBO. Next time instal a proper RCCB followed by set of MCBs. It is cheaper, more flexible and at the same time easier in maintenance.

One more thing to consider in tracking down leakage is that it is intermittent. I had two nasty situations with leakage where I live, both came from heater element (one was from a washing machine and one was from cooking top). This leakage was ramping up quite fast so this was tough to measure. And of course it disappeared just after heater element cooled down. So - does the BM2060 have the option to remember max leakage value and auto-off disabling?  If so, it could be a serious advantage when compared to 210E which does not remember max value (but has auto-off disabling). I can imagine you could clamp such BM2060 so that it runs 24/7 and monitors leakage. Once the RCBO trips you could just take a look at what was the max value. Can BM2060 do that? Does it have decent battery life? Like 50 hours? This could be a very useful feature.

[ThunderZed]

just an intermittent short in between L and N?

Do you mean:
1. the rain gets into the old building ceiling
2. reaches the plastic electric pipes that can be broken in some point
3. gets into them
4. flows on until reaches some wire that is tore up (L-N)?
If I've understood what you meant I agree with you and it will be hard to check and find. What do you suggest me?
I don't know anything about the BM2060 so just put it away from all this.

Next time instal a proper RCCB followed by set of MCBs

Let's naming. I "tell" you how the italian switches I know work and you'll name them in you language so I'll understand you better:
- "magneto-termico" switch: it has a "magnetic" part that makes it trip if a short circuit happens and a "termic" part that makes it trip when a current overload occurs;
- "differenziale" switch: it registers the difference between the incoming current and the outgoing one (L-N) and trips if this delta is equal or more than its value, in other words it's for leakages;
- magneto-termico differenziale switch, as the bticino in that house: it's a combo of the previous two switches.
I assumed MCB = magneto-termico and RCBO = magneto-termico differenziale, right?
How do you name them in EN?

Btw There's another problem with the old washing machine in that house: the bticino trips almost every time the machine washes at max temperature.. but this is another story and doesn't deal with rain.

It is not rain, it is the phase of the Moon

I'll sing "Put the blame on Moon, boy"

[Alti]

Do you mean (..) What do you suggest me?

I just point out that the whole story might end up in finding no leakage because there wasn't any. Just be aware of consequences of installing this type of RCBO - it protects but does not show what tripped it. If that is L-N short then the leakage meter is going to show 0.0 .

I "tell" you how the italian switches I know work and you'll name them in you language so I'll understand you better

Just use names from wikipedia EN. So MCB (miniature circuit breaker), RCCB(residual current circuit breaker) and RCBO (residual current circuit breaker with overload ...), I think these names are well established in EU (?). Also be aware that you can also buy a disconnector, isolator and a switch. Definitely don't mix switch and circuit breaker names - these are different devices.

[ThunderZed]

I've just looked at bticino switches' tech sheets and found out the EN acronyms so now I can say:
- magnetotermico = MCB;
- differenziale = RCCB;
- megnetotermico differenziale = RCBO
Here we go. I think I can check for sure the cause of trips (short circuit or leakage) if I install a MCB in series with the bticino RCBO and after it so if the new MCB trips then the cause is a short circuit for sure, else if the MCB doesn't trip but the RCBO does then the cause is a leakage for sure.
Do you agree?

[Alti]

Do you agree?

That is not as easy as you propose. This is called selectivity (or discrimination) and is quite tough to do that reliably in between two MCBs (or two RCBOs or MCB and RCBO). It is doable and sometimes you get some hints about discrimination provided by manufacturer of a specific gear but it always relies on some specific range of loop impedances (L-N or L-PE loops) which are most likely unknown in your case.

Sorry that there is no simple answer to deal with RCBO and all this situation. I guess you have to take the chance, assume this is leakage and see how this goes further. As I mentioned, my experience tells me leakage (L-PE or N-PE) is more likely than L-N short, but you never know till you find the cause.

[ThunderZed]

I've just looked at the bticino RCBO's tech sheet and the manufacturer put a "yellow indicator" that rises up in its little front window whenever the switches trips due to a leakage. Today I was "lucky" because I was there and it rained very hard, the RCBO tripped and the yellow indicator appeared. I was so happy of that but then I read yours:

it always relies on some specific range of loop impedances (L-N or L-PE loops) which are most likely unknown in your case.

I'm sure you refered to my yellow indicator when you said "sometimes you get some hints about discrimination provided by manufacturer" so now the question is: can't I be sure it's a leakage with this hint? Moreover: can I check something out about those loop impedances?

[Alti]

Today I was "lucky" because I was there and it rained very hard, the RCBO tripped and the yellow indicator appeared.

Wow, that is great, they included indicator. Ok, so now you can be quite sure this was leakage! Now the next step is to find it.

Forget the idea about connecting MCB in series of RCBO, find the leakage.

[Gyro]

First, check which outside light or outside socket is full of water, then work inwards. 

[ThunderZed]

I've just told my friend (acm92's owner) the "current transformer type" matter about his clamp, I mean

For your specific AC requirement, you should be looking for the current transformer type - being very careful to check that the lowest current ranges still use the jaws and not probe leads.

and he answered the ACM91 (which he's got too) has this characteristic as you can read here:

uA uses the probe inputs
[...]
Clamp, used for DC and AC current measurement, except uA

Anyway he says it can measure down do 11mA so it's not good for my goal.
Definitely I think the ACM92 will be my first choice.