Missing earth connection.

[E.Swain]

Hi all,
I was at a property yesterday and found a number of problems with their installation.
To name a few.

6mm radial supplying a 8.5kW shower and 3.5kW emersion heater on a 32A RCBO.

Extractor fan unfused and spured from shower in 1.5mm cable.

Isolator and light switch in zone 2.

When we finished our work and tested loop impedance we had a result of 85 Ohms (water bond was in place). When investigating we found that there was no link between the main earth of the Tns system to the consumer unit. ( pictured top left incoming earth in Henley block)

We rectified the problem and had a loop impedance of 0.57 Ohms.

The reason for my post is, since finding this I have wondered if a board is not adequately earthed would this prevent an RCD from tripping? As in if the earth is not intact will it provide a path for fault current to flow and trip the RCD?

I have only just finished my first year of training and any advice would be greatly appreciated.

 

[davesparks]

Where does the black wire coming in to the smashed Henley block come from?

 

[telectrix]

RCD does not rely on an installation earth it senses imbalance between L and N. si if a person touches a live part, the imbalance is caused by current flowing through his/her body to earth. anything over 30mA it should trip.

 

[E.Swain]

Where does the black wire coming in to the smashed Henley block come from?

TNS system. The pole transformer was only outside, 2 core cable to cut out and separate earth into the Henley block.

RCD does not rely on an installation earth it senses imbalance between L and N. si if a person touches a live part, the imbalance is caused by current flowing through his/her body to earth. anything over 30mA it should trip.

I hadn't even considered this. I had asked my boss at the time and he couldn't give me an answer. Thanks for clearing that up for me Telectrix.

 

[davesparks]

TNS system. The pole transformer was only outside, 2 core cable to cut out and separate earth into the Henley block.

Has it, and how has it, been confirmed as TNS?
I'm curious as this sounds like an unusual supply setup to me

 

[E.Swain]

Has it, and how has it, been confirmed as TNS?
I'm curious as this sounds like an unusual supply setup to me

The supply transformer was no more then 20m from the property. Cables ran over head, 1 2 core cable for live and neutral and one conductor for earth. Unless I'm mistaken this is TNS, isn't it? The earth conductor looked like a bare conductor painted black. It didn't seem to be pvc insulated.

 

[davesparks]

The supply transformer was no more then 20m from the property. Cables ran over head, 1 2 core cable for live and neutral and one conductor for earth. Unless I'm mistaken this is TNS, isn't it? The earth conductor looked like a bare conductor painted black. It didn't seem to be pvc insulated.

It does sound like TNS, just a pretty unusual way of it being supplied.