Discuss When testing a circuit protected by RCBO, do you test at the DB or furtherst point in the Commercial Electrical Advice area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Reaction score
0
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
 
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.
 
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.
 
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.
 
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.
 
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?
 
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.
 
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!:mad:
 
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
 
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?
 
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.
 
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.
 
Last edited:
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
 
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.
 

Reply to When testing a circuit protected by RCBO, do you test at the DB or furtherst point in the Commercial Electrical Advice area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock