test & inspect tripping when doing zs on not trip

[junior-sparky]

Hey all,

I'm playing with my new Metrel mi3000 and using my parents house as a quinea pig.

So if you see in the pic it has the main/rcd switch as a cutout and when trying to measure the zs my little Metrel trips it every time (tried on non trip and normal).

I have my R1+R2 and ze so can calculate zs but would just like your thoughts.

When I did an Rcd test at 100ma it trips at 28ms.

 

[Deleted member 9648]

You get the odd one that will trip every time on a 'no trip' test....I had one yesterday. Might be a sign that there is excessive earth leakage due to a low IR,or a 'tired' RCD,or just one of those things that you just have to accept and move on.

 

[junior-sparky]

I think given the age of it I think it's given up but it gets the tick for 28ms trip time.

 

[SPARTYKUS]

Hello chap

Is the rest of the house disconnected when you did the test

 

[junior-sparky]

Spartykus I did not disconnect the rest of the house. I've probably done something wrong but didnt believe everything else have to be disconnected?

thanks in advance.

 

[Richard Burns]

If you have all the house circuits live when you are testing Zs on no trip setting then if there is already about 90mA leakage from the existing installation the additional current that the tester uses would push the RCD into tripping.

Have you tested the RCD for the current at which it trips (ramp test) it may be that it is tripping at, say, 55 mA instead of the 100mA.

 

[PEG]

...Too slow again...as^^,try testing the RCD fully disconnected,to give a true value of its' tripping current,then,move on to find out what,if anything,is adding to its' threshold. Top-marks to playing with your device in order to get familiar with it. It will be those hours that enable you to use confidently,and interpret results effectively.As a kid,my folks sat around in the dark a lot during my frequent "safety tests"...:stooge_curly:

 

[Plonker 3]

You were doing it as a 3 wire test werent you?

 

[SPARTYKUS]

Hi junior-sparky

sorry for delay in replying but nothing to add as Mr Burns /PEG have said the required words

 

[telectrix]

Hi junior-sparky

sorry for delay in replying but nothing to add as Mr Burns /PEG have said the required words

Amen...

 

[junior-sparky]

Hello All,

i was doing this using the 3 pin plug adaptor.

i had a little play again today and the RCD tripped at 110ma again at 28ms, well it said 110ma.


another question please... As I'm having issues getting a measured zs i calculated it. Ring final for whole house.

R1 0.50
R2 084
ze 0.10

zs total - 1.44 not good.

These are type 2 bs 3871 push fuses and max zs is 0.87 using the rule of thunmb.

I'm still learning but i know this is not good, would increasing the main earthing from the 6mm to 16mm make the difference or am i way off the right trail?

thank you

 

[junior-sparky]

...Too slow again...as^^,try testing the RCD fully disconnected,to give a true value of its' tripping current,then,move on to find out what,if anything,is adding to its' threshold. Top-marks to playing with your device in order to get familiar with it. It will be those hours that enable you to use confidently,and interpret results effectively.As a kid,my folks sat around in the dark a lot during my frequent "safety tests"...:stooge_curly:

look after your tools they look after you, and play of course.

 

[Andy78]

Are 0.5 and 0.84 your end to end readings for your ring final conductors ?
If so then these are your r1 and r2, and you need to look up again how you obtain R1+R2 for a ring final.

 

[junior-sparky]

now i feel stupid, taxi for me.

0.31 was my R1+R2, i feel stupid.

 

[junior-sparky]

i overlooked it so much.

 

[junior-sparky]

Thanks for your help