TT / RCD testing

[Smart Sparks]

Hi there
Just a little advice required on RCD testing:
I did some Minor Works the other day and obtained thefollowing RCD test readings –
TT system
100amp 30mA RCD protecting the CCU.
Circuit tested was a 32a ring final circuit with 32aovercurrent protection MCB type b.
0 degress
X 0.5 = no trip
X 1 = 29.5ms
X 5 = 9ms

180 degrees
X 0.5 = no trip
X 1 = 18ms
X 5 = 16ms

I was expecting similar readings on the 180 degree test compared to the0 degrees test. Can someone shed any light on the difference between the 0& 180 degree test and whether these readings look normal?.

I assumed the difference is the stage of the waveform the test is takenat?.

Overall ELI at the socket under test was 29.5 ohms

Also I noticed the Main Earth to the installation is 10mm, although thecable is buried without mechanical protection?, having looked at table 54.1(p159) it would appear the cable should be 16mm. I assume even though the ELIis ok the cable should really be replaced?.

Your thoughts and advice would be appreciated

Regards
Smart Sparks

 

[plugsandsparks]

was anything plugged into the load when it was being tested ?
Did you take several readings ?
It wouldn't worry me as you take the highest reading anyway which is fine.

 

[spark 68]

As P&S ^^^ above,

This is perfectly normal and are typical readings, the way I understand it is that some RCD's are more sensitive on one half cycle than the other, maybe be some other posters can confirm this, or expand on the reasons why.

 

[IQ Electrical]

As P&S ^^^ above,

This is perfectly normal and are typical readings, the way I understand it is that some RCD's are more sensitive on one half cycle than the other, maybe be some other posters can confirm this, or expand on the reasons why.

That's it exactly

 

[SirKit Breaker]

As all of the above. Repeat the tests 10 times and you will get 10 different results. It complies with 415.1.1 Job done.

Cheers.........Howard

 

[telectrix]

main earthing conductor on a TTsystem is minimum 6mm if not mechanically protected. no need for 16mm

 

[Smart Sparks]

Thanks for the feedback.

It is possible something was plugged in, i assume that can have an effect then.

I feel better now i know the resuits sound ok. i am a little confused on the earth size as the table in the regs states 16mm in table 54.1. Just out of interest where does the 6mm come from?.

 

[IQ Electrical]

Thanks for the feedback.

It is possible something was plugged in, i assume that can have an effect then.

I feel better now i know the resuits sound ok. i am a little confused on the earth size as the table in the regs states 16mm in table 54.1. Just out of interest where does the 6mm come from?.

I believe the minimum size is 16mm buried without mechanical protection.

 

[telectrix]

my bad. missed the "buried". most read post fully before replying.:disguise:

 

[Smart Sparks]

Thanks all for your feedback, appreciate it.