When we touch the ground wire(!) on some of our power outlets, the tester lights up. Not as bright as when touching the live wire and the circuit breaker doesn't tip, but there is definitely "something". On the search for the potential cause, we opened up a few walls and found the following phenomenon: The copper wires in one of the distribution thingies are discolored. All three wire strands are affected.

enter image description here

Is that an indicator of arching? Are we getting close to the culprit? Or is there another problem present?

  • 1
    You might be on to something as you have described it, you should not have power on your ground. What made you decide to check the grounds/wires at all? Can you explain the problem you are having? To Retired Master Electrician's response belows point - if the ground was truly live, it should trip, so if it isnt, that could mean your ground is floating & hot via a bad connection or a piece of equipment you have is faulted, OR the person wiring it re-purposed the ground for something else..... please give us more details. And what kind of tester are you using and how are you using it? – noybman Sep 30 '17 at 14:31
  • @noybman Ground wires aren't wired to the breaker, neither are the neutral wires. – raterus Dec 7 '17 at 14:53
  • How much current? Hard to answer, I know, but 3 stranded cable acts like a poorly built 1:1 transformer. – Wayfaring Stranger Apr 24 '18 at 20:03

I am not sure where you live, but I have never seen that particular type of conductor connector. In answer to your first question you probably don't have a short circuit. If you did you wold have your overcurrent protection tripping or blowing if it was a fuse.

In answer to your last question, yes you have a problem with the splices. I appears they are not making a good mechanical or electrical connection. This is causing a fluctuation in your normal current flow. From what I can see is that your splices are failing. You need to go through you residence and clean and replace as many of these as you can find. I would use a standard wire nut.

  • If the screw & ring is going through a metal sleeve, that style of connection should be fine as long as it is tight, and using same metals. I agree, that's not a USA install or wire color – noybman Sep 30 '17 at 14:25
  • These are EU wire colors, so it could be anywhere on 4 continents wher the EU playbook is followed. – Harper - Reinstate Monica Sep 30 '17 at 16:04
  • @Harper correct, it's in Germany in this case. – Stephie Sep 30 '17 at 16:37
  • I've always wondered if frays sticking out of a connector was bad.... apparent-freaking-ly. - WTF on those connectors (all of which are failing), +1 – Mazura Dec 14 '19 at 7:14

When we touch the ground wire(!) on some of our power outlets, the tester lights up

That might be because you are using the cheapest (€1?) kind of tester - a screwdriver with a metal cap you have to touch.

enter image description here

Consider using a better sort of voltage tester that you can obtain relatively cheaply (€10?).

enter image description here

and the circuit breaker doesn't [trip]

A Circuit breaker only trips for high currents, those voltage testers only pass tiny currents (otherwise you'd be too dead to post a question here).

If your earth wires were really live, you'd be right to expect the circuit breakers to have tripped. Worst case is the earth wires are live and not properly connected to ground at the main distribution panel.

A better voltage tester would help you to establish the facts.

The copper wires in one of the distribution thingies ...>

A more usual name for those "distribution thingies" is "screw-terminal" "connector-block" or some variation.

... are discolored ... Is that an indicator of [arcing]?

In my (limited) experience, arcing usually produces much more pitting and blackening than is visible in your photo.

This discoloration could be a sign of overheating - though the plastic nearby seems unaffected.

However there should be no current flowing through the earth wires. That should only happen very briefly in a fault condition that quickly ends with the panel saving your house from burning down by tripping a breaker.

Usually, overheating is caused by not screwing down the connector tight enough.

Tightening the connectors ought to be sufficient - though I'd remove them and check for corrosion in the contact area. As a precaution you could replace the connectors with new ones of the same type and clip off the discoloured parts of the wires, re-trim the insulation to a suitable length and reconnect tightly.

A blue or blue-green colour can also be caused by some kinds of copper corrosion. I don't know what might have caused that in your photo.


This sounds like a ground loop and can happen if, for example, if you bridge the earth potential from different floors of one building or in some cases between buildings, for example with a LAN cable.

The term for what is happening is stray voltage and can cause discoloration / corrosion of your wiring and potentially lead to a fire.

Immediately get high quality surge protectors for your expensive electronic equipment, try and track down the cause of the ground loop and if nothing turns up get a professional to look at your breaker box.


1> If not already present Install a differential breaker (aka RCD) just after the meter -> it breaks with 30mA current leak 2> check if ground is good (use a multimetre and see if you have voltage between heater / metal pipe and live and heater and ground)

Anyway if the differential doesn't trip, it's not a leaking current.

  • Or if you want to do it Yankee style, put an 8ma RCBO on every branch circuit that goes where humans habitate or near water. – Harper - Reinstate Monica Jun 26 '18 at 14:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.