Cable calculation

[Simon Burton]

So you are a DIYer?

What makes you say that

 

[Andy78]

No but in terms of over current in a domestic dwelling ive seen a db have 100amp main switchbwith and the main head bein 60amp fuse, the fuse in the main head would blow before rhe main switch would trip. Which is incorrect but why is this done.

I think this is the clincher. Get someone competent on this job mate.

 

[Simon Burton]

So you are a DIYer?

What makes you say that

The main switch wouldn’t trip mate......

Yes wouldnt, typo my bad

 

[Simon Burton]

I think this is the clincher. Get someone competent on this job mate.

Typo- main switch wouldnt trip,

 

[Nigel]

What makes you say that

The fact that you don’t know the function of a CU main switch.

 

[Nigel]

Not allowed to export the earth. Think about it, if you loose your neutral on the main, youve also lost your earth, so anybout building ect will not be earthed

Why are you not allowed to export the earth?

 

[Simon Burton]

Typo- main switch wouldnt trip,

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.

 

[Simon Burton]

Why are you not allowed to export the earth?

For the reasons ive just said it in the regs mate

 

[Deleted member 26818]

The main switch wouldn’t trip, just the same as your light switch won’t trip.
You have to manually operate them.

 

[Nigel]

For the reasons ive just said it in the regs mate

What Reg are you referring to?

 

[Nigel]

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.

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?

 

[Simon Burton]

What Reg are you referring to?

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]

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.

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

 

[Nigel]

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.

You are incorrect.

 

[Deleted member 26818]

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.