Cable calculation

Simon Burton said:
So why is this done out there, having main switch on the board rated higher than the fise in the head, it dont make sense the fuse in the head would alway blow first.
Click to expand...

Do you not think it a good idea to have a switch rated equal or higher to the current that could be drawn through it?
 
essex said:
What Reg are you referring to?
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Under the Electricity safety, quality and continuity regulations 2002 you cannot use a suppliers earth to an out building, on a TNC-S Earthing arrangement, so the detached garage effectively becomes a TT installation with an earth electrode installed in the ground.
 
Simon Burton said:
Under the Electricity safety, quality and continuity regulations 2002 you cannot use a suppliers earth to an out building, on a TNC-S Earthing arrangement, so the detached garage effectively becomes a TT installation with an earth electrode installed in the ground.
Click to expand...
Ok lets say you exported the earth on a tncs to an outbuilding, and then lets say you lost your neutral at the main incoming, if you had a live to earth or neutral short, every thing connected to earth would become live under fault conditions, hence why you need to rod and not export form the main earth to exterior building ect
 
There are a couple of reasons why you would not export a PME earth.
One could be if the exterior of the outbuilding is metal, and the other is if there are extraneous conductive-parts which would require bonding.
At the end of the day, it boils down to cost.
Is it cheaper to run a 3 core 10mm2 armour or a 2 core armour and install an earth rod.
 
Simon Burton said:
Ok lets say you exported the earth on a tncs to an outbuilding, and then lets say you lost your neutral at the main incoming, if you had a live to earth or neutral short, every thing connected to earth would become live under fault conditions, hence why you need to rod and not export form the main earth to exterior building ect
Click to expand...

So why is it matter if it is an outbuilding or not? That would still happen in a building that is not an outbuilding.
 
spinlondon said:
TN-C-S is where the DNO supply is TN-C but is presented to the customer as TN-S.
Click to expand...

What?

A TN-C-S is where the earth is taken from the PEN within the installation.

A TN-C is where the same connection is made outside of the installation.
 
A TN-C system has a combined neutral/earth on the service side and throughout the consumers installation, very unusual.
 
As far as I am aware, the ESQCR prohibits the use of TN-C within an installation connected to the public network.
As such any connection to the PEN conductor is made outside of the installation.
 
If either of you two actually want to look at the Regs, you will note that TN-C is where all of the system uses a PEN conductor and TN-C-S is where a PEN conductor is used only in part of the system.
Where TN-C-S is used the part of the system that uses a PEN conductor is on the supply network.

This is really basic stuff.
I’m not surprised someone who believes a 100A switch will trip doesn’t understand, but I am suprised at Essex.
 
spinlondon said:
If either of you two actually want to look at the Regs, you will note that TN-C is where all of the system uses a PEN conductor and TN-C-S is where a PEN conductor is used only in part of the system.
Where TN-C-S is used the part of the system that uses a PEN conductor is on the supply network.

This is really basic stuff.
I’m not surprised someone who believes a 100A switch will trip doesn’t understand, but I am suprised at Essex.
Click to expand...
I see where your coming from but lets say you loose your pen conductor at the very source from the transformer. Not at the point at which you make it a tncs when connecting your earth. But the very source. If that pen conductor goes down, where is your mean of earth?
 
No you cannot use a PEN conductor, just the same as you cannot use a PEN conductor in your house.
Doesn’t necessarily mean TT is the only option.

What really matters, is whether PME can be used.
In some circumstances it can be used, though it would be advisable to install an earthed metallic grid in the ground where livestock are to be kept.
 
spinlondon said:
No you cannot use a PEN conductor, just the same as you cannot use a PEN conductor in your house.
Doesn’t necessarily mean TT is the only option.

What really matters, is whether PME can be used.
In some circumstances it can be used, though it would be advisable to install an earthed metallic grid in the ground where livestock are to be kept.
Click to expand...
I agree PME is the way to go, like you say especially if livestock can come into contact with the installation
 
spinlondon said:
If either of you two actually want to look at the Regs, you will note that TN-C is where all of the system uses a PEN conductor and TN-C-S is where a PEN conductor is used only in part of the system.
Where TN-C-S is used the part of the system that uses a PEN conductor is on the supply network.

This is really basic stuff.
I’m not surprised someone who believes a 100A switch will trip doesn’t understand, but I am suprised at Essex.
Click to expand...

A picture to help you.

46A9DBF5-18B0-45F7-8CB3-1D21A9C10495.jpeg
 
westward10 said:
You are not using TN-C because the neutral and cpc are separate through the consumers installation.
Click to expand...

The third letter means how the earth and neutral are linked at the transformer.

T = earth
N = Neutral
C = Combined.

This is true of both a TN-C and a TN-C-S. the S is for ‘seperate’ as the earth is then seperated from the neutral within the installation.
 

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Simon Burton

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