When testing a circuit protected by RCBO, do you test at the DB or furtherst point

[Sparky8898]

Hi, I just have a few questions in regards to testing an RCBO circuit

Is there a requirement to test at either the furthest point or the DB or is it down to the testers discretion.

Do the test results differ?

What tests on a circuit will trip the RCBO when you are away from the DB. Is it just the tripping times test?

Thanks

 

[Pete999]

Hi, I just have a few questions in regards to testing an RCBO circuit

Is there a requirement to test at either the furthest point or the DB or is it down to the testers discretion.

Do the test results differ?

What tests on a circuit will trip the RCBO when you are away from the DB. Is it just the tripping times test?

Thanks

Dis the circuit from the board and test from there.

 

[Deleted account]

If you mean testing the disconnection times of the residual current device at half, one and five times rated mA then it doesn't matter where you test from on the circuit.

I personally test at the board straight into the terminals of the device for convenience and ease. Why make things difficult.

 

[Deleted member 26818]

I prefer to test at the furthest point, so as to prove that the RCD/RCBO is providing the required protection.
I understand that some MFTs can struggle with this method, so most advice is to conduct the test at the RCD/RCBO.

 

[Silly Sausage]

PP, you've agreed with Pete, then said it doesn't matter!
Test RCDs as Pete says. The test is for the device, not the circuit.

 

[Ian1981]

At the DB.
Imagine testing on your own in a large commercial installation and having to go and reset the rcd every time you test on the 0 and 180 degree cycles If testing at the furthest point.
Plus there should be no load on the circuit so it’s more convenient at the DB id say.

 

[Deleted member 26818]

PP, you've agreed with Pete, then said it doesn't matter!
Test RCDs as Pete says. The test is for the device, not the circuit.

The reason I disagree with this advice, is:
Testing at the device does not prove that the device is functioning as intended.
If sockets require RCD protection, then the only way to prove the sockets have RCD protection, is to my mind test at the sockets.
Where circuits require RCD protection, again the only way to prove those circuits have RCD protection, is to test the circuit.

 

[Silly Sausage]

The reason I disagree with this advice, is:
Testing at the device does not prove that the device is functioning as intended.
If sockets require RCD protection, then the only way to prove the sockets have RCD protection, is to my mind test at the sockets.
Where circuits require RCD protection, again the only way to prove those circuits have RCD protection, is to test the circuit.

We've all had this discussion years ago, I, for one, am not going to change my stance that the test is for the device only. Any circuit(s) connected are separate entities that should be tested in their own right. Are you going to do speed tests on every circuit that is connected to an RCD?

 

[Deleted member 26818]

We've all had this discussion years ago, I, for one, am not going to change my stance that the test is for the device only. Any circuit(s) connected are separate entities that should be tested in their own right. Are you going to do speed tests on every circuit that is connected to an RCD?

Yes this is a recurring discussion, neither of us have changed our viewpoint.
Personally, I very rarely conduct Periodic Inspections and when I do, I charge for a whole day.
So taking my time and conducting a thorough I&T is not a problem.

 

[SparkyAndGeorge]

Some RCBO terminals are too deep for the probes on certain testers though so you'll have no choice but to test somewhere else on the circuit.

 

[Flanders]

Memshiled 2 rcbos fail if you test them at the board. fit a short length of cable to them and they test ok otherwise as other have said test and board or any where on the circuit, just need to make sure all loads are disconnect when you test it .

 

[KEV 1 N]

Memshiled 2 rcbos fail if you test them at the board. fit a short length of cable to them and they test ok otherwise as other have said test and board or any where on the circuit, just need to make sure all loads are disconnect when you test it .

Yes....they are a pain in the ar*e!

 

[UNG]

I prefer to test at the furthest point, so as to prove that the RCD/RCBO is providing the required protection.

My thinking as well.
If you apply a measured current / test to any point on a circuit with RCD protection then the device should IMO operate within the devices spec

I understand that some MFTs can struggle with this method, so most advice is to conduct the test at the RCD/RCBO.

Is it that MFT struggles or is there an underlying problem with the device that is not being identified


To add to this my question would be how many of us do a ramp test on a circuit with RCD / RCBO protection

 

[Midwest]

I just think its easier to test at a socket outlet, rather than taking the lid back off a CU and struggling to push some probes onto the RCD/RCBO terminals.

My MFT has a dedicated plug lead, and an auto function for the RCD tests. Don't most MFT's have these?

 

[ipf]

Either way, for me, whichever is easier..... I had an assessor telling me it had to be done at the device....but what difference between that and circuit points, after all, you are just testing RCD operation times, as required.
Ramp testing is a separate test, altogether.

 

[45140]

The whole point of testing an RCD is to prove that if a fault occurs in the circuit then the RCD will trip. Unless you do this at the extremity you cannot be certain that there is not a fault on the circuit which results in the RCD NOT tripping.

 

[Ian1981]

The whole point of testing an RCD is to prove that if a fault occurs in the circuit then the RCD will trip. Unless you do this at the extremity you cannot be certain that there is not a fault on the circuit which results in the RCD NOT tripping.

That is what a Zs test is for , checking the valve of the earth fault loop impedance so that the protective device will disconnect the power in the required times permitted,not an rcd test.
The rcd test can be done anywhere in the circuit with loads disconnected as you are injecting a test current into the circuit to trip the device, the extremity of the circuit should have no relevance.
If in doubt then discuss with the manufacturer As I have done in the past regarding this matter.

 

[UNG]

Either way, for me, whichever is easier..... I had an assessor telling me it had to be done at the device....but what difference between that and circuit points, after all, you are just testing RCD operation times, as required.
Ramp testing is a separate test, altogether.

I think we are all aware a ramp test is a separate test that wasn't the question asked and from your reply I assume you don't ramp test any RCD's so therefore don't fully check it's function

I have found on quite a few occasions recently that RCD's / RCBO's can meet the trip times especially when testing at the device while a ramp test has indicated a trip current in excess of the specified 30mA to trip the device
So it is possible that a faulty device can meet the trip times but not within the specified 30mA tripping current

 

[ipf]

I think we are all aware a ramp test is a separate test that wasn't the question asked and from your reply I assume you don't ramp test any RCD's so therefore don't fully check it's function

What are you talking about?
I tested a car ramp last week...…..there wasn't even an RCD involved....

 

[davesparks]

The whole point of testing an RCD is to prove that if a fault occurs in the circuit then the RCD will trip. Unless you do this at the extremity you cannot be certain that there is not a fault on the circuit which results in the RCD NOT tripping.

Nonsense, the point of testing the RCD is to prove that the device itself works.
The tests carried out on the circuit are to prove the safety of the circuit. If you get to doing the RCD test and there is a fault on the circuit that prevents it tripping then you clearly haven't carried out the preceding tests correctly.

 

[Toneyz]

Test either at the D.B or circuit, it makes no difference whatever is the easiest for you. If you are using an RCD tester that does all tests in sequence and you reset trip each time you may need to isolate unplug some loads as when they start up they prevent the next test being compleated.

 

[ipf]

I think we are all aware a ramp test is a separate test that wasn't the question asked and from your reply I assume you don't ramp test any RCD's so therefore don't fully check it's function

The return dumb is for an absolutely stupid assumption.
…...as well as not being able to take a joke!

 

[UNG]

The return dumb is for an absolutely stupid assumption.
…...as well as not being able to take a joke!

I can take a joke but you clearly don't have a problem putting peoples lives at risk by trashing a serious conversation

Yes you can achieve the trip times and still leave a customer with a faulty RCD

Don't bother replying I won't see it you have disappeared from view

 

[ipf]

I can take a joke but you clearly don't have a problem putting peoples lives at risk by trashing a serious conversation

Yes you can achieve the trip times and still leave a customer with a faulty RCD

Don't bother replying I won't see it you have disappeared from view

Whether you see this or not, it seems you are one sad man……..resorting to such a serious and stupid accusation.
Nuff said.

 

[Midwest]

I think we are all aware a ramp test is a separate test that wasn't the question asked and from your reply I assume you don't ramp test any RCD's so therefore don't fully check it's function

I have found on quite a few occasions recently that RCD's / RCBO's can meet the trip times especially when testing at the device while a ramp test has indicated a trip current in excess of the specified 30mA to trip the device
So it is possible that a faulty device can meet the trip times but not within the specified 30mA tripping current

If you carry out the RCD test (e.g. BS EN 61008), for example x 1, the testing device introduces the 30mA current, for which the RCD must detect & disconnect within 300ms.
I can't see how an RCD would pass such a test, but fail because the mA would be too high, as the test current used by the test device is set at 30mA.

A ramp test will measure at what mA the RCD is tripping at. If the RCD was tripping at say 40mA, it would fail the x 1 test, surely?

 

[ipf]

If you carry out the RCD test (e.g. BS EN 61008), for example x 1, the testing device introduces the 30mA current, for which the RCD must detect & disconnect within 300ms.
I can't see how an RCD would pass such a test, but fail because the mA would be too high, as the test current used by the test device is set at 30mA.

A ramp test will measure at what mA the RCD is tripping at. If the RCD was tripping at say 40mA, it would fail the x 1 test, surely?

May be an instance. An existing RCD failed, initially. It tripped at well over on ramp. It hadn’t been tested or operated for a good while. After a few test button operations, it operated fine. Replaced anyway because it was pretty old, but it goes to show.

 

[Deleted member 26818]

Failing the X 1 test is not an issue.
The requirement is for the device to operate within 40ms when tested at a current equal to or higher than 5 times it’s rated operating current.
Assuming of course, that the RCD is intended for additional protection.

 

[Midwest]

May be an instance. An existing RCD failed, initially. It tripped at well over on ramp. It hadn’t been tested or operated for a good while. After a few test button operations, it operated fine. Replaced anyway because it was pretty old, but it goes to show.

But what I am saying is, the tester introduces 30mA (at x 1) nothing more nothing less. If the rcd is faulty and only trips at say 40mA, the test will time out and therefore the rcd will fail that part of the test?

PS the inspector would then move to the ramp test, to verify the issue. Same would go for 1/2 x test.

 

[Deleted member 26818]

But what I am saying is, the tester introduces 30mA (at x 1) nothing more nothing less. If the rcd is faulty and only trips at say 40mA, the test will time out and therefore the rcd will fail that part of the test?

PS the inspector would then move to the ramp test, to verify the issue. Same would go for 1/2 x test.

It doesn’t matter if it fails the x 1 test.
It’s the x 5 test that it has to pass.

 

[DPG]

I think Midwest is responding to the point that UNG made.

 

[Midwest]

It doesn’t matter if it fails the x 1 test.
It’s the x 5 test that it has to pass.

Take your point. I'm trying to make mine about ramp testing.

 

[UNG]

If you carry out the RCD test (e.g. BS EN 61008), for example x 1, the testing device introduces the 30mA current, for which the RCD must detect & disconnect within 300ms.
I can't see how an RCD would pass such a test, but fail because the mA would be too high, as the test current used by the test device is set at 30mA.

A ramp test will measure at what mA the RCD is tripping at. If the RCD was tripping at say 40mA, it would fail the x 1 test, surely?

I have had this issue on 3 occasions in the the last couple of years
One was a CU installed 6 months previously tested ok at install yet one of the RCD's was found to be faulty 6 months later, the other 2 were brand new CU's where one of the RCD's was not within spec at install

The first CU was found because a quick check at a socket where it had previously been ok failed to trip, tested at the CU it tripped within acceptable times both 1x and 5x although a little higher than I would normally expect decided to do a ramp test at the CU and found it tripped at 37mA I ramp tested it back at the socket but can't remember the exact figure I got but was high enough to cause concern as to whether it is acceptable just to test at the RCD
The other 2 had similar outcomes
On all occasions having contacted the manufacturers the RCD's have been replaced with no problems

It doesn’t matter if it fails the x 1 test.
It’s the x 5 test that it has to pass.

On my MFT on auto test if it fails the 1x then it fails the whole test
Given that ventricular fibrillation can occur at currents as low as 30mA I think the 1x test really matters

 

[Deleted member 26818]

From the current Regulations:
NOTE: Effectiveness is deemed to have been verified where an RCD meeting the requirements of Regulation 415.1.1 disconnects within 40 ms when tested at a current equal to or higher than five times its rated residual operating current.

You want to disagree with what it says, fine.
Take it up with the IET.

 

[Midwest]

I have had this issue on 3 occasions in the the last couple of years

The first CU was found because a quick check at a socket where it had previously been ok failed to trip, tested at the CU it tripped within acceptable times both 1x and 5x although a little higher than I would normally expect decided to do a ramp test at the CU and found it tripped at 37mA I ramp tested it back at the socket but can't remember the exact figure I got but was high enough to cause concern as to whether it is acceptable just to test at the RCD

I'll say this again, & then drop it.

At x 1 my MFT introduces a test current of 30mA (+0% to +10%.) to test an RCD. If it was testing this faulty RCD, its not going to provide it with the 37mA it needs to trip and the test would time out at 300ms, and my MFT would display an error code. I would then go on to conduct a ramp test on the RCD.

Therefore there is no need to conduct a ramp test, in normal circumstances.

 

[brianmoooore]

From the current Regulations:
NOTE: Effectiveness is deemed to have been verified where an RCD meeting the requirements of Regulation 415.1.1 disconnects within 40 ms when tested at a current equal to or higher than five times its rated residual operating current.

You want to disagree with what it says, fine.
Take it up with the IET.

Ridiculous change to the regs IMHO! A working 100mA RCD will pass as a 30mA one.

 

[tudore]

Guidance Note 3 Section 2.6.19 says testing should be at the load side of the RCD, with loads disconnected. I always strive to test at the furthest point on a circuit, as Zs is critical to correct operation, and even correct type of RCD (see Section 411). What is the point of Table 41.3 if circuit resistance can be ignored? I admit if I'm working alone on a big circuit I'll test at the board, but this is very rare as I can usually find a helper for the resets.

 

[Silly Sausage]

Guidance Note 3 Section 2.6.19 says testing should be at the load side of the RCD, with loads disconnected. I always strive to test at the furthest point on a circuit, as Zs is critical to correct operation, and even correct type of RCD (see Section 411). What is the point of Table 41.3 if circuit resistance can be ignored? I admit if I'm working alone on a big circuit I'll test at the board, but this is very rare as I can usually find a helper for the resets.

For the umpteeth time, you are testing the device, not the circuit.
Do test every circuit connected to an RCD?
And, finally, surely you have an instrument that can perform auto testing?

 

[ipf]

For the umpteeth time, you are testing the device, not the circuit.
Do test every circuit connected to an RCD?
And, finally, surely you have an instrument that can perform auto testing?

I wish they did one that does an auto reset
Now that would be an invention

 

[Midwest]

For the umpteenth time plus 1 , the all knowing all seeing IET have this little piece about RCD's; testing is at indent 5.

Inspection and testing of electrical installations: residual current devices - https://electrical.------.org/wiring-matters/issues/50/inspection-and-testing-of-electrical-installations-residual-current-devices/

How do we interpret that? Think it says something similar in GN3.

 

[Ian1981]

For the umpteenth time plus 1 , the all knowing all seeing IET have this little piece about RCD's; testing is at indent 5.

Inspection and testing of electrical installations: residual current devices - https://electrical.------.org/wiring-matters/issues/50/inspection-and-testing-of-electrical-installations-residual-current-devices/

How do we interpret that? Think it says something similar in GN3.

The way I interpreted that is that you test on the load side and that can be anywhere in the circuit covered by the rcd, be it at the CU or at the closest socket outlet or the furthest light.
Your just testing the device only and not the circuit is what the article is saying.
I always test at the CU and until the regulations say different then I always will

 

[Midwest]

The way I interpreted that is that you test on the load side and that can be anywhere in the circuit covered by the rcd, be it at the CU or at the closest socket outlet or the furthest light.
Your just testing the device only and not the circuit is what the article is saying.
I always test at the CU and until the regulations say different then I always will

Its the words 'between the line conductor of the protected circuit and the associated cpc' that confuses me. Personally, I would test the easiest quickest way, either at the CU or from somewhere on the circuit, which for me is usually the latter.

 

[Deleted member 26818]

That IET article is from 2014.

 

[telectrix]

sod the IET. i do it my way.

 

[Baddegg]

sod the IET. i do it my way.

Tel.....you got more titles than uncle Albert got medals!

 

[telectrix]

don't blame me. i didn't put them there. and it wasn't my fault the Titanic sank.

 

[littlespark]

Can I just interject into this discussion.

My rcd tester comes with 2 leads. One with 3 prongs and croc clips, the other with a regular square pin plug(top)

If we were only to test the device, there would be no need to supply the lead with the plug on.


I see it as one of the reasons we have rcd’s is to protect users when you plug in a faulty appliance, so the outlet itself should be tested.

 

[magnoliafan89]

Surely its whichever is more convenient at the time of testing surely?? Why are people so aggressive about this? If you're already in the board just check it at the device...if not just plug it in. Stop being girls about this....

 

[Deleted member 26818]

Surely its whichever is more convenient at the time of testing surely?? Why are people so aggressive about this? If you're already in the board just check it at the device...if not just plug it in. Stop being girls about this....

It’s all about why you are testing the RCD/RCBO.
If you are testing it just to see whether it works, then yes test at the most convenient point.
If you are testing to prove it provides additional protection, then test it at the point where the additional protection is required.

Not aware anyone is getting aggressive about it.

 

[magnoliafan89]

It’s all about why you are testing the RCD/RCBO.
If you are testing it just to see whether it works, then yes test at the most convenient point.
If you are testing to prove it provides additional protection, then test it at the point where the additional protection is required.

Not aware anyone is getting aggressive about it.

I personally dont see any need to test at the point. If it works at the board...its going to work in general.

 

[Deleted member 26818]

I personally dont see any need to test at the point. If it works at the board...its going to work in general.

So, if you were to test at the board and the RCD passed, then test at a socket and the RCD failed, you’d be happy?