Rcd not tripping at 30mA

[Brooklyn101]

I am currently at college and decided to get some practise in testing my house. Its TT and everything was fine until it came to RCD testing

I have 2 Rcd on the main CU and another in the shed. Testing at 5I is well under 40ms but testing at 1I is showing >400ms

?

 

[GaryMo]

Are you testing the RCD's in isolation at source?

ie outgoing disconnected and testing directly on the outgoing terminals of the RCD.

 

[Brooklyn101]

I think I may have probed the live on the incoming side of the RCD and not the load side

would this leave me with these results?

 

[GaryMo]

No as the RCD shouldn't trip on 5xIn test.

Unless you probed the live side on the 1xIn test only?

 

[Brooklyn101]

No I tested them both the same

edit...I got the same results for all 3 RCD's

 

[Taylortwocities]

What type and rating is that RCD?
30mA, 100mA
is it a time delayed (S type?)

post a photo if you like/.

 

[Brooklyn101]

80 A
30mA
no time delay

 

[Jacobssi]

Don't RCD in a TT system have to be S type?

 

[GaryMo]

Don't RCD in a TT system have to be S type?

No.

 

[Jacobssi]

Fair enough

 

[Brooklyn101]

Can anyone tell me what they would do next to figure this one out?

 

[GaryMo]

Has one of your friends or relatives got an RCD protected consumer unit?

If so, pop along with your meter and rule out that problem.

Do the RCD's operate when you press the onboard test button?

Other than that, if you're testing the RCD in isolation and the meter is healthy then I'm stumped other than to suggest faulty RCD's. Surely not three though

 

[Brooklyn101]

Just tested on a friends CU......same result

Only had the tester a couple of months and this is the first time I have used it for a full test

Its a megger MFT1552, basically the same as we use at college, do I contact megger or the people I bought it from

 

[GaryMo]

You've definitely selected 30mA on the right hand dial?

It's the same meter as mine.
I normally clip the earth lead on the earth bar and probe the outing line terminal with the red lead. I don't use the black lead. I then use the auto RCD function which goes through 0.5xIn, 1xIn 0 then 180, 5xIn 0 then 180.

 

[Spark123]

Can you confirm you are testing the RCDs in isolation i.e. there are no circuits connected to it?

Can you borrow one from college overnight to compare?

If you do deem your Megger is faulty and it is less than a year old then your first port of call is with the place where you bought it, if they advise you to go direct to Megger then fine, Megger service is excellent.
If you go direct to Megger off your own back then you could be throwing away your rights with the retailer.