R1+R2 Test on outbuilding

[hutch6447]

Hi guys right I have had my head well confused by an instructor I was chatting to. Now the problem is a run to an outbuilding going through a 30Ma RCD at garage consumer unit, installation is in and works fine, now he is saying if you do the r1+r2 test at the plug sockets in the garage and join up at the main board Line & Cpc as you do then you should get a reading now I think because the continuity test is 200Ma test it will trip the RCD because the RCD is 30Ma and to get a proper r1+r2 you ave to bypass the rcd at the garage consumer unit?

Any advice would be greatfully received.

 

[SirKit Breaker]

Hi guys right I have had my head well confused by an instructor I was chatting to. Now the problem is a run to an outbuilding going through a 30Ma RCD at garage consumer unit, installation is in and works fine, now he is saying if you do the r1+r2 test at the plug sockets in the garage and join up at the main board Line & Cpc as you do then you should get a reading now I think because the continuity test is 200Ma test it will trip the RCD because the RCD is 30Ma and to get a proper r1+r2 you ave to bypass the rcd at the garage consumer unit?

Any advice would be greatfully received.

I dont like saying this, but, you have been given info that is either incorrect, you dont understand it, or both.
To be fair mate, if you are doing electrical work, then this test is a very basic task, and you should be able to do it fairly easily.

My advice, get an Electrician in to make sure it is tested properly, and more importantly, safely. If you attempt ta continuity test on a live circuit, you will get hurt, or do some damage.

Cheers..........Howard

 

[hutch6447]

yes when doing the r1+r2 test the whole installation is dead, I have been qualified as electrician in army for 12 years just doing the refresher course for civvy street what I am saying is line, cpc connected at main board you will have to bypass the rcd at the consumer unit in the garage to get an r1+r2 reading of the circuits and the run in SWA to main board.

 

[Snapester]

If the garage has a consumer unit then test the sockets to there and then get an r1+r2 of the submarine feed feeding the garage? The garage CU is classed as a submain so any circuits connect to it should be tested to there and then added to the zdb of the submain board.

 

[PC Electrics]

Yes, you are correct. If you conduct an R1+R2 test with an RCD in the circuit under test then the RCD will trip. Conduct the test in two parts each side of the RCD and add the results together. Don't forget to check the continuity across the RCD L-L and N-N to make sure there is no high resistance on the RCD contacts (had this problem a few times)

If you really are refering to carrying out r1 and r2 tests on a ring final, then disregard the above and why would you have the RCD connected in?

Watch your terminology if you are planning to ever take 2391, it's a major factor in the high failure rate.

 

[hutch6447]

Yes that has answered my question I have done the test in two separate parts anyway but doing a 200mA test on a dead circuit would still trip that RCD because reduced my test down to 15mA test and it did not trip the RCD so it was the 200mA test that was tripping it which is pretty straight forward really 200mA will trip a 30mA RCD.

Thanks for your answers mate been great help for confirmation oh I understand you about the terminology thing did my 2391 in forces just havent touched things in a while.

 

[PC Electrics]

Glad to be of assistance. Now that you are back in the "big bad world", just remember that old addage "where there's blame there's claim". It's also important for any certificates you might issue that you get your terminology spot on. If the brown stuff should ever fly (let's hope not) your competence may be called into question and your certificates and use of incorrect terminology would be the starting point.

Good luck.

 

[Sparkystu79]

Sorry, I am maybe misunderstanding but how can an rcd trip if testing on a dead circuit, and surely you're testing R1+R2 on ohms not mA?

 

[telectrix]

sounds like a bit of confusion between R1+R2 , and Zs measurements.

 

[TaffyDuck]

Well Im totally confused now.

 

[D80]

Sorry, I am maybe misunderstanding but how can an rcd trip if testing on a dead circuit, and surely you're testing R1+R2 on ohms not mA?

Doing continuity test for R1+R2 will most likely trip the RCD if testing through it, even if installation is dead.

 

[ringer]

To do the continuity test, the tester is putting 200mA into the circuit, and it is this that trips the RCD. By injecting an exact current (200mA) and measuring the volt drop over the circuit, the resistance is calculated. This, I believe, is the way that low resistance ohmmeters testers work.

 

[PC Electrics]

Sorry, I am maybe misunderstanding but how can an rcd trip if testing on a dead circuit, and surely you're testing R1+R2 on ohms not mA?

because your tester uses a current of 200mA on it's continuity setting. So if you link out L-E on one side of an RCD and test on the other 200mA will flow through the line side of the RCD and trip it. Try it!

 

[Sparkystu79]

because your tester uses a current of 200mA on it's continuity setting. So if you link out L-E on one side of an RCD and test on the other 200mA will flow through the line side of the RCD and trip it. Try it!

I will! Only reason I queried it is in 15 years I've never come across that scenario before. Every day is a school day!

 

[abuameer]

Hi there,

I am just learning and wanted to say that going on the understanding of how RCDs work, it will only trip if the neutral has a difference of more than the rated RCD (ie 30mA in this case) of the supply given to it (in this case 200mA). It shouldn't matter if the system is dead or alive, the fact that you are sending the current is making that circuit 'live' in a way. I guess it would trip if you send a test current of 50mA? Is my understanding correct?