RCD test with socket tester

[Marius Brok]

I will start building a house, Thailand,  in October and i prepared myself to buy a socket tester already. I bought one at Aliexpress and got him in a week. I have a KMoon KKM5 Pro max. 300 Volt Cat. II. The RCD test > 30 mA. I tried him in my home in The Netherlands and found the system was OK(correct). I have a grounded system with 7 MCB's and splitted up in 2 groups 4 and 3 MCB's with each group 1 RCBO. No main switch. This is normal in houses before 1990.The RCBO's are 30 mA and 25 AMPs

Surprice the RCD test with the socket tester failed on both RCBO's. Tested on all grounded sockets present. Then I tested the RCBO's with their testbuttons onboard, both tripped.

I went to my neighbour house and the tests were OK all RCBO are tripping by the socket tester.

What can cause this failing of the test in my house????

 

[Crossy]

The only think I can think of would be if your home is wired TN-C where the neutral and earth share a conductor right to the outlet.

 

The tester works be sending a small current down the ground to create a L-N imbalance and trip the RCBO, of course if the N and E are the same wire there's no imbalance.

 

But as far as I'm aware TN-C within an installation has been illegal in most of the world for many years.

 

Pop one of the outlets off the wall and check it has all three wires. 

 

If you're worried call a local electrician, who will have the proper test kit and the knowledge of how to use it (Note to skip-readers, our OP is in the Netherlands at present). 

[Fruit Trader]

Many of these cheap quick testers do not make a earth impedance test and are satisfied with simple ground present.

The socket ground might be good enough to satisfy a ground detection circuit but not good enough to deliver the required fault test current.

 

Check the quality of ground at the socket.

[Marius Brok]

10 hours ago, Fruit Trader said:

Many of these cheap quick testers do not make a earth impedance test and are satisfied with simple ground present.

The socket ground might be good enough to satisfy a ground detection circuit but not good enough to deliver the required fault test current.

 

Check the quality of ground at the socket.

Do not forget this tester worked well in my neighbours house! Is it possible the RCBO's are worn? They are from 1981. He has increased his installation to 3 phase.

[Marius Brok]

15 hours ago, Crossy said:

The only think I can think of would be if your home is wired TN-C where the neutral and earth share a conductor right to the outlet.

 

The tester works be sending a small current down the ground to create a L-N imbalance and trip the RCBO, of course if the N and E are the same wire there's no imbalance.

 

But as far as I'm aware TN-C within an installation has been illegal in most of the world for many years.

 

Pop one of the outlets off the wall and check it has all three wires. 

 

If you're worried call a local electrician, who will have the proper test kit and the knowledge of how to use it (Note to skip-readers, our OP is in the Netherlands at present). 

Yes I have every socket wired with earth.

Yes I go consult a electrician. They are costly overhere at least €70 hr.

[Fruit Trader]

1 hour ago, Marius Brok said:

Do not forget this tester worked well in my neighbours house! Is it possible the RCBO's are worn? They are from 1981. He has increased his installation to 3 phase.

I based my theory on your ground being poor and your neighbors good which is why I suggested testing the quality of your ground before moving forward.

 

Many of these cheap testers will indicate ground OK even when the ground is poor. The RCD test button on the KMoon socket tester requires ground to pass a fault current.

 

If you are sure your ground is healthy then you must look into how much fault current is required to trip your RCD's.

 

The test buttons on the RCD usually apply a fault current inside of the operating range and indicate a healthy device. You say test button are working fine. 

[Marius Brok]

4 hours ago, Fruit Trader said:

I based my theory on your ground being poor and your neighbors good which is why I suggested testing the quality of your ground before moving forward.

 

Many of these cheap testers will indicate ground OK even when the ground is poor. The RCD test button on the KMoon socket tester requires ground to pass a fault current.

 

If you are sure your ground is healthy then you must look into how much fault current is required to trip your RCD's.

 

The test buttons on the RCD usually apply a fault current inside of the operating range and indicate a healthy device. You say test button are working fine. 

It is possible. ground can be weak because the ground water level is very low caused by very dry summers on a row. Belief it or not we suffer a heat wave on this moment with temperatures of 38 C for 2 days and continuing. A temp. record of 75 years is broken today. But I wiil contact a electrician for safety reasons, thanks.

[tjo o tjim]

Are your ground conductors full size, or are they reduced size relative to L and N?  It is possible that the tester is only passing 40-50mA under nominal circumstances, and that results in a lower current with (unanticipated) ground path resistance.

 

Also, is the voltage consistent throughout the house?

 

The other possibility is that you have a second path for the current on the ground back to the circuit’s neutral— something like a pinched neutral that is “leaking” a bit of current.  One way to test this is to plug a kettle into another outlet on the same circuit and run the tester while it is on.  

[Marius Brok]

Possible. I go test it and report back to you.

[Marius Brok]

On 7/28/2019 at 6:38 AM, Marius Brok said:

Possible. I go test it and report back to you.

The voltage is always very consistent between 227 and 230 and drops down with 2000 watt about 3 Volt.

I tested with a load of 2000Watt on 4 different circuits with ground, no tripping of my 2 RCB's when I use the testbutton on the tester.

I do not see any connection of Ground and Neutral to the bars thus no TN_C system, we have TT.

I have now borrowed a new ABB F204 A RCCB for testing. I have now 2 old see pictures.

This old ones are also 4P but the connection is for a 2P system. One N and 3 (L) lines to a separate MCB.

But the question is can I use the ABB upside down because the N is on the rightside. Old one on the left.

Have to rewire all connections if not possible. In the manual is written "The device can be fed from either the upper or lower terminals"

[tjo o tjim]

Reverse feed is fine for testing since the Neutral is disconnected. 

[Marius Brok]

1 hour ago, tjo o tjim said:

Reverse feed is fine for testing since the Neutral is disconnected. 

Not at all. Look close to the picture, there is a Busbar to the MCB neutral next to it.

[Crossy]

I think I see why your RCDs are not tripping on the tester.

 

The old unit in your photo appears to be a 500mA (0.5A) tripping current, your tester provides 30mA.

 

Does your neighbour (where the tester worked) have exactly the same 0.5A units?

 

[Marius Brok]

6 hours ago, Crossy said:

I think I see why your RCDs are not tripping on the tester.

 

The old unit in your photo appears to be a 500mA (0.5A) tripping current, your tester provides 30mA.

 

Does your neighbour (where the tester worked) have exactly the same 0.5A units?

 

That is what I need, A bright eye.

I did not see this. In my CP there are 2 RCCB one with 500 and another 30 mA. The 30 mA is used for the dry groups and the 500 for the wet groups including bathroom. Strange enough I have no earthed sockets on the 30mA groups, only lamps. I can not test indeed.

Your knowledge about the ABB RCCB of 30 mA. Can I use it upside down in the CP?

[Crossy]

2 minutes ago, Marius Brok said:

Can I use it upside down in the CP?

 

If the documentation says it can be top or bottom fed then it should work just fine upside down.

 

Odd that the higher tripping current is used in the more hazardous wet locations. I would definitely be tempted to replace it permanently with a 30mA unit.

 

[Marius Brok]

2 hours ago, Crossy said:

 

If the documentation says it can be top or bottom fed then it should work just fine upside down.

 

Odd that the higher tripping current is used in the more hazardous wet locations. I would definitely be tempted to replace it permanently with a 30mA unit.

 

Yes, I was surprised, maybe it was the standard in 1981. I am the first resident in this hous and know there is nothing changed. I is also approved by the E-company.

 

First job to do is change the 500 mA RCCB for the ABB 30 mA

 

Thanks for your input. A new succes can be written on your list.

[Crossy]

10 minutes ago, Marius Brok said:

First job to do is change the 500 mA RCCB for the ABB 30 mA

 

If the existing 30mA one is only on lighting and is physically identical I'd be tempted to just swap the two for a cost-effective fix ????

 

That said the beasties are approaching 40 years old, maybe time to replace anyway.

 

[Marius Brok]

9 minutes ago, Crossy said:

 

If the existing 30mA one is only on lighting and is physically identical I'd be tempted to just swap the two for a cost-effective fix ????

 

That said the beasties are approaching 40 years old, maybe time to replace anyway.

 

Yes, I buy them at Amazon.de. Only €35. Other shops up to € 120

[Marius Brok]

22 hours ago, Crossy said:

 

If the existing 30mA one is only on lighting and is physically identical I'd be tempted to just swap the two for a cost-effective fix ????

 

That said the beasties are approaching 40 years old, maybe time to replace anyway.

 

Mission accomplished. Changed RCCB to ABB 30 mA and RCB tester works.

Ordered one more to change the old one.