leakage clamp meter accuracy

[Sadsyndrome]

hello.
I'm using leakage clamp meter to investigate nuisance tripping in my house. It is a MULTICOMP PRO MP780050 that I bought early 2021. However, once I bought it the nuisance tripping stopped, so I put it down to damp in garage at the time. This looks just like the Dilog6518 (just without dilog badge).
house is mid 1980s with wylex board 6 off mcbs with 30ma RCD protecting them all.

2 years later...
Grill has tripped rcd a couple of times in recent weeks (including last night). So I thought I'd use clamp meter to investigate, clamping meter over L-N meter tails dangling meter vertically.

results were:
10mA leakage initially
with kettle 48mA!
with kettle and grill 114mA!!

30mA RCD didn't trip in the test? It did trip when I pressed RCD test button.

q1
How accurate are these clamp meters? am I correct in letting meter dangle vertically from tails, as holding meter horizontally did seem to change reading significantly, also clamping main earthing conductor gave significantly lower reading.

q2
what is approximate, normal baseline leakage in house with no heating elements in circuit (e.g. fridge, CH, TV, broadband router, led lights etc.)?

q3
why didn't rcd trip during my test. even assuming meter readings weren't accurate 114mA does seem very high.

q4
any ideas how I can roughly assess meter accuracy? I guess warranty is expired now

I was going to replace board to Hagar with rcbo per circuit. I think I need to get to bottom of this issue first though.

thanks

 

[DPG]

I would check the manual for that model first. See if it is accurate at those levels. Many aren't, and the readings you are seeing may be meaningless. Once you have determined that you can move forward.

 

[Sadsyndrome]

I would check the manual for that model first. See if it is accurate at those levels. Many aren't, and the readings you are seeing may be meaningless. Once you have determined that you can move forward.

thx yes I just re-checked I must have looked at that when I bought it in feb 2021 as I remembered the manual it says ×- 5% with 100microamps resolution on 20ma setting. I just saw a review on YouTube which shows same symptoms as me I guess I can't send it back after 2 years aggggggh at least I didn't buy the dilog one which looks exactly the same but cost over £150 (phew, dodged a bullret there)

 

[DPG]

thx yes I just re-checked I must have looked at that when I bought it in feb 2021 as I remembered the manual it says ×- 5% with 100microamps resolution on 20ma setting. I just saw a review on YouTube which shows same symptoms as me I guess I can't send it back after 2 years aggggggh at least I didn't buy the dilog one which looks exactly the same but cost over £150 (phew, dodged a bullret there)

There was a good thread on here a while ago about reasonably priced clamp meters that will measure down to single mA levels. Might be worth having a search.

 

[timhoward]

house is mid 1980s with wylex board 6 off mcbs with 30ma RCD protecting them all.

Before jumping to any conclusions I'd get the RCD tested. I'd only bet 50-50 on a main switch RCD that is 40 years old working exactly as intended. I've also had a few that were clearly stuck and didn't turn back on after manually turned off!

I was going to replace board to Hagar with rcbo per circuit. I think I need to get to bottom of this issue first though.

Before a board change, IR tests are essential which will highlight if there are issues or not.

In terms of a leakage clamp meter the TEK 775 is fairly cheap and hasn't given me cause for complaint yet (I've owned one for 2 years now)

Also worth noting that element faults can be transient and the earth leakage can get worse the longer the element is on.

 

[pc1966]

What you are measuring might not be actual leakage. If you have a N-E fault on a non-RCD circuit (if RCD'd it should just trip) then some of the return current might be going via the CPC (Earth cable) and so you see an imbalance on L-N that appears that way.

I have the DiLOG look-alike and it works acceptably well, I was seeing a few mA to 10mA total on my flat doing the same thing.

Any RCD or RCBO that fails the self-test is VERY suspect and needs to be properly tested and probably replaced. You can have odd N-E faults giving just enough current in one way to oppose the self-test imbalance and so stop tripping, but most likely by a large margin is it has failed.

A grill or oven element tripping a RCD is not too unusual, sometimes it is just moisture that can be cleared by repeated running to hot, but other times it is a real fault that is needing a new element. But...your odd total installation leakage points to a N-E fault, so getting that checked and (if present) fixed first would be my starting point as large loads (like a grill or oven) are more likely to cause odd trips on N-E faults elsewhere.

TL;DR - check for N-E faults first and then look at RCD tests, etc.

 

[Sadsyndrome]

Before jumping to any conclusions I'd get the RCD tested. I'd only bet 50-50 on a main switch RCD that is 40 years old working exactly as intended. I've also had a few that were clearly stuck and didn't turn back on after manually turned off!


Before a board change, IR tests are essential which will highlight if there are issues or not.

In terms of a leakage clamp meter the TEK 775 is fairly cheap and hasn't given me cause for complaint yet (I've owned one for 2 years now)

Also worth noting that element faults can be transient and the earth leakage can get worse the longer the element is on.

Thx
Yes I agree about testing before replacing cu. At the moment I’m not suspecting the rcd as it does trip sporadically ( last two times coinciding with grill turning on) so I’m guessing cumulative leakage given everything is on one rcd.

It was only the fact that I thought I’d do a quick check on leakage current as I had tool available that I stumbled across the fact the clamp meter was giving odd readings. Unfortunately I haven’t got an mft or dedicated IR tester (the price is horrendous) I was going to get my neighbour to test eventually as he is proper qualified with correct test equipment etc. I just wanted to sort out any issues beforehand… I was a spark once upon a time and I don’t want to take the pi&s

 

[Sadsyndrome]

What you are measuring might not be actual leakage. If you have a N-E fault on a non-RCD circuit (if RCD'd it should just trip) then some of the return current might be going via the CPC (Earth cable) and so you see an imbalance on L-N that appears that way.

I have the DiLOG look-alike and it works acceptably well, I was seeing a few mA to 10mA total on my flat doing the same thing.

Any RCD or RCBO that fails the self-test is VERY suspect and needs to be properly tested and probably replaced. You can have odd N-E faults giving just enough current in one way to oppose the self-test imbalance and so stop tripping, but most likely by a large margin is it has failed.

A grill or oven element tripping a RCD is not too unusual, sometimes it is just moisture that can be cleared by repeated running to hot, but other times it is a real fault that is needing a new element. But...your odd total installation leakage points to a N-E fault, so getting that checked and (if present) fixed first would be my starting point as large loads (like a grill or oven) are more likely to cause odd trips on N-E faults elsewhere.

TL;DR - check for N-E faults first and then look at RCD tests, etc.

Sorry my bad wording. What I meant to say was rcd didn’t trip when I was monitoring high levels of leakage current on the clamp meter. The Test button definitely tripped the RCD Also every circuit passes through RCD so a N-E would trip RCD I think?

I had another go and it seems the problem is the two 16mm tails in the test meter clamp give various readings dependent upon their position in the clamp loop. Clamping the main protective conductor gives a more stable reading of just over 10ma.
The DiLog one that looks exactly the same is almost 4 times the cost of the one I bought. Btw not eBay purchase , I got it from cpc