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

[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.