Floating Earth on Whole House - Normal?

[FiscoKing]

Hi,

Is it normal for a residential PME earth system to 'float' 4-5V AC above real ground?

I'm measuring the 4-5V with a high impedance Volt meter. Red probe to metalwork on an earthed appliance, and the black probe held in my hand. When I touch the appliance with my hand the 5V AC drops to 0.

Every appliance in the house is like this. Wall sockets, fitted kitchen cookers etc.

I wondered if there was a break in the earth cable going back to the consumer unit, so I tried the same experiment again probing the earth rail inside the consumer unit and got the same result.

I then wondered if there was a break in the earth cable going back to the DNO fuse carrier, so I tried the same experiment again at the fuse carrier as there's a bit of exposed eath cable poking out, and I get the same result.

I get that there might be some voltage on an earth connection to real ground as all cables have resistance, so if any current flows there will be a voltage drop, but the fact that the voltage drops to nothing when touched means the earth system is floating.

DNO fuse carrier has a 'PME System Earthing Terminal' skicker on it.

Is this normal?

Thanks.

 

[endecotp]

Is it normal for a residential PME earth system to 'float' 4-5V AC above real ground?

What do you mean by "real ground"?

I'm measuring the 4-5V with a high impedance Volt meter. Red probe to metalwork on an earthed appliance, and the black probe held in my hand.

Are you imagining that your hand is the "real ground"? What kind of shoes are you wearing?

Suggestion: bury a metal object in the ground, and pour a bucket of water over it. Now measure the voltage between that and your appliance metalwork.

 

[JohnW2]

What do you mean by "real ground"? .... Are you imagining that your hand is the "real ground"? What kind of shoes are you wearing? .... Suggestion: bury a metal object in the ground, and pour a bucket of water over it. Now measure the voltage between that and your appliance metalwork.

Indeed so - but, as the OP might discover if he did all that, to have a 4-5 volt potential difference between a TN-C-S 'earth' and 'true earth' would be far from unusual, and nothing to be concerned about, wouldn't it?

 

[flameport]

I'm measuring the 4-5V with a high impedance Volt meter. Red probe to metalwork on an earthed appliance, and the black probe held in my hand. When I touch the appliance with my hand the 5V AC drops to 0.

You are seeing a tiny amount of capacitive coupling between your body and the earthed metal.
This goes away when you touch the metal, because you and the metal are then at the same voltage as they are connected together.

Is it normal for a residential PME earth system to 'float' 4-5V AC above real ground?

There is usually a small voltage difference due to voltage drop on the combined N&E conductor which supplies the building.
This is unrelated to what you are doing.

 

[JohnW2]

You are seeing a tiny amount of capacitive coupling between your body and the earthed metal.

The capacitive coupling is presumably between his body and something 'live' (rather than the 'earthed metal') ...

This goes away when you touch the metal, because you and the metal are then at the same voltage as they are connected together.

Indeed so - but it presumably would not have been there in the first place had the capacitive coupling been between his body and the earthed metal.

 

[Harry Bloomfield]

I'm measuring the 4-5V with a high impedance Volt meter. Red probe to metalwork on an earthed appliance, and the black probe held in my hand. When I touch the appliance with my hand the 5V AC drops to 0.

You are not measuring voltage on the earthed metalwork, rather you are measuring the voltage induced in your body, against the earth.