ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Interesting Fault

Today I came across an interesting fault and I havnt figured out yet what it could be. Any advice or ideas greatly appreciated.

The main breaker from the poco is 63A. I have a panel monofase (1 fase+N). There are 2 RCDs. The main one is 300mA which covers the whole panel and the 2nd one is 30mA which covers bathrooms, washing machine and central heating boiler (which rund on gas).

The main breaker from the poco is on. When I measure between fase and Neutral I get 0 Volt, between fase and earth=224V, between Neutral and earth 224V! The Neutral is not broken.
If I push the test button on the main RCD 300mA, then it jumps.
When I disconnect the 2nd RCD 30mA, then all the other circuits work fine.
I measure between fase and Neutral I get 224 Volt, between fase and earth=224V, between Neutral and earth 0V (as it should be).
When I reconnect, the problem comes back.
After having reconnected I turn off all the breakers which are under RCD30mA, turn on the RCD and turn all the breakers back on and low and behold, everything works fine!

There are 2 things which maybe I should mention:
1, Both RCDs are 40A whereas the main breaker is 63A, so they should have been 63A as well.
2, There were different issues with the central heating boiler (which is under RCD 30mA).
Could it have to do with the boiler?

For me it's a riddle. If any of you has any logical clear explanation, please let me know.

To me that sounds like the Neutral has somehow become a phase... and since it's the same phase you measure 224V to ground but 0V between the wires. How that could have happened... sounds like it's time for an isolation resistance test.

If that would be the case, then it would have to make a short and the poco breaker should switch off. But it didn't.

Is this a TT system? Has the earth wire somehow been disconnected from the earth electrode? An phase-earth leak (or direct short circuit) after the 30 mA RCD would not be noticed by the RCD if there is no connection to the earth electrode. It would go away when you switch off this RCD or the breakers under it. It sounds odd though, as one would expect some connection through appliances.

Yes, C-H it's a TT system. The earth wire was very well connected to the earth in the panel as well as in the cellar, where it's connected to the earth electrode! This building was built in 1998, so all sockets have a earth connection and all connections are neat and tidy according to the actual norms.

Are these double pole breakers? Where are you reading the voltages?

Yes, Gideonr, they are double pole breakers. The voltage was measured after the PoCos breaker and after the first RCD 300mA

Eli,
It sounds to me like Phase and Neutral have been transposed (swapped).
Call the PoCo.

No, They were'nt transposed because when I reconnected, then the readings were correct. Between Neutral and earth= 0 V , Between phase and earth 230V. It is a very strange story. The meter which I use is a Fluke, so I wouldn't say that its a meter fault.

[This message has been edited by Belgian (edited 05-22-2005).]

My feeling is that one of the breakers may be faulty, possibly one of the poles gone, or its not snapping open. The oddness of it all suggests there may be more than one fault here. Are you quite sure about the earth integrity, e.g. are you getting volts to the boiler pipework?