Groundwire sparked while connecting it to the main ground

[Rubendabiest]

Hi all

So, my brother bought a (new to them) house. I've been redoing the fuse boxes in the house. Today, while putting the grounds from the kitchen together the last wire made a little spark... but the differential didn't trip so is this a big problem? Something to look into? Or something to disregard? All these grounds were wired together before I worked on it for at least a few years.

Also, the Ri was too low only 25kohm could that possibly be the problem?

Located in Belgium

 

[LastManOnline]

Hi all

So, my brother bought a (new to them) house. I've been redoing the fuse boxes in the house. Today, while putting the grounds from the kitchen together the last wire made a little spark... but the differential didn't trip so is this a big problem? Something to look into? Or something to disregard? All these grounds were wired together before I worked on it for at least a few years.

Also, the Ri was too low only 25kohm could that possibly be the problem?

Located in Belgium

Firstly the "differential" (rcd) will only trip when's its rated leakage current is exceeded (30 ma). Any appliance which has intentional leakage in its design will "spark" if you disconnect or reconnect its circuit CPC but will not trip the rcd as the intentional leakage is designed to be much lower than the rcd rated tripping current. This is completely normal.
But to establish exactly what's causing the sparking it would be wise to trace exactly which circuit the sparking earth belongs to and trace exactly what it is connected to.

 

[Rubendabiest]

Alright, I'll look into it. Luckily I remember what cable it was so can't be that hard to track down.

 

[Lucien Nunes]

As above, a small spark is quite normal due to functional leakage from appliances and capacitive leakage from the cables, but really you should not disconnect any grounding cables or connections while any part of the system is energised. Even then, with the main switch off, there can be sparks between one 'version' of ground and another (e.g. between a buried metal water pipe and the electrical supply ground) due to externally-created potential differences. Especially if the supply is TN-C-S, where normal voltage drop in the earthed neutral creates local variations from 'true' ground.

So in short, a spark is not unusualy and does not always indicate a fault. Insulation of 25kΩ does indicate a fault and needs finding and correcting.

 

[LastManOnline]

Out of curiosity, what kind of supply system do you have in Belgium? TNC-S or TT?