Short answer
Earthing lets a faulty appliance carry its current away to earth, so the RCD or the breaker switches off. In modern homes that goes via an earth electrode in the ground or via the grid operator's connection. Earthing to the water pipe has not been allowed for a long time, certainly not now that it is plastic. Whether the earth is sound is shown by a measurement.
Who this article is for Anyone who wants to understand what that green and yellow wire is for. Measuring and installing is work for an installer.
What earthing does
All metal parts you can touch, from a washing machine casing to a metal light fitting, are connected to earth. If a live wire inside an appliance touches the casing, that current runs away to earth instead of through you when you touch it.
That escaping current is exactly what the RCD measures. Without earth there is no path, nothing is measured, and the casing stays live until someone touches it.
Earthing and RCD work together. One without the other is half a protection.
Where the earth comes from
In the Netherlands there are two common situations:
Own earth electrode. A copper rod or a conductor in the ground by the home, connected to the earth bar in the meter cupboard. Common for homes outside the village or town centre and in new builds.
Earth via the grid operator. With some connections the earth comes along with the cable from the street.
What you have can be seen in the meter cupboard and measured. Assuming what it is, is not a good idea.
The water pipe is no longer an earth
In the past, earthing to the metal water pipe was common. That has not been allowed for decades, for two reasons: in many streets the water main has been replaced with plastic, and parts of it are renewed during renovations without anyone thinking about the electrics.
If you see the green and yellow wire running to a water pipe, that is a reason to have it measured.
How you know whether it is sound
By measuring. Two measurements count:
Measure, do not assume. Especially after a renovation.
Earth electrode resistance. How well the earth electrode makes contact with the ground. The lower, the better. In dry sandy soil it can rise considerably in summer; that is why I prefer not to measure only after a wet week.
Continuity. Does the earth actually run through to every socket and every hard-wired appliance? An earth bar that is perfectly connected means nothing if the earth core in the loft was once cut.
I also test the RCD with an instrument that measures the actual trip current and time, not just with the test button.
What goes wrong if the earth is not right
- the RCD does not switch off on a fault, because no leakage current flows
- metal parts can become live
- surge protection does not work, because it discharges to earth
- with solar panels and EV chargers the protection does not work as intended
What a measurement produces and what such a report looks like is covered under the NEN 3140 inspection. For private customers I do the same measurements, just without the business-style report around them.
From my own work
At a home in Nuth the earth wire was neatly connected, but to a section of water pipe that had been replaced with plastic during a renovation ten years earlier. Earthed on paper, in reality connected to nothing. An earth electrode was put in and the installation was retested. I come across this more often than you would think.
When to call an electrician
- You do not know whether your home has a sound earth
- The earth wire is on a water pipe
- There has been a renovation in which pipework was replaced
- You want certainty recorded in a test report
I measure the earth electrode resistance and record it. Request a quote.
Frequently asked questions
Can my earthing be on the water pipe?
No, that has not been allowed for a long time. Certainly not now that water pipes are often plastic: then in reality there is no earthing.
How do I know whether my earthing is good?
By measuring: the earth electrode resistance and the continuity to every point. Assuming it is fine is exactly where it goes wrong.
Does an RCD work without earthing?
When you touch a faulty appliance, it only switches off once current is flowing through you. Earthing and RCD belong together.
Further reading
Is my meter cupboard still safe? 10 things you can see yourself
Ten things you can see yourself without unscrewing anything. If you recognise three or more, it is time for a chat.
How old is my installation really: these are the signs
Cloth-covered wiring, no RCD, screw-in fuses and unearthed two-pin sockets: each feature tells you something about the year it was built and the risk.
Type A, type B or type F RCD: which do you need
Type A is the standard. Type B only where DC leakage can occur, and that is less often than sellers say. Saves hundreds of euros.
Questions and comments
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