TT system main bonding CSA?

[davesparks]

If you are rewiring the property, why not just stick 10mm bonding in and a 16mm main earthing conductor. either reposition the earth rod and see if you get a better Ra value or add another until you get a better value, If I was rewiring the property I would be inclined to install my own rod anyway as for all you know the rod that's already been installed could of been cut down in size as hit hard ground etc when it was installed.

Because that would be a waste of time and money if only 6mm is required, you might as well install 2.5mm for lighting and 16mm for cooker supplies if you are going to use that logic .

Why are you talking of installing a rod in the singular? That won't achieve anything useful, at least 2 electrodes made up of at least 2 rods coupled together would be a good starting point.

 

[Deleted member 9648]

Because that would be a waste of time and money if only 6mm is required, you might as well install 2.5mm for lighting and 16mm for cooker supplies if you are going to use that logic .

Why are you talking of installing a rod in the singular? That won't achieve anything useful, at least 2 electrodes made up of at least 2 rods coupled together would be a good starting point.

If there is a possibilty of a PME conversion at some point it would definately be worth upgrading now though.

 

[Leesparkykent]

Because that would be a waste of time and money if only 6mm is required, you might as well install 2.5mm for lighting and 16mm for cooker supplies if you are going to use that logic .Why are you talking of installing a rod in the singular? That won't achieve anything useful, at least 2 electrodes made up of at least 2 rods coupled together would be a good starting point.

Because if its a rewire, surely the whole purpose of a rewire is to rewire the whole property and no leave in the existing.And I installed a single rod a few weeks ago and got a value of 15ohms so what would be the point if installing another rod in this case?

 

[7029 dave]

http://www.westernpower.co.uk/Connections/Information-for-Electrical-Installers.aspx

 

[Falcon Flyer]

Ooops, I appeared to have stirred a hornets nest.

I've fitted the installation with 30Ma RCBO's to all circuits, but so far I've left the main 100Ma RCD in the installation.

To comment on another post, about putting TWO earth rods in, I was told in no uncertain terms that this was a highly dangerous practice, and any fault going to earth would go to both rods and this would cause a dangerous potential difference, possibly resulting in a fatal shock to anyone standing near the rods at the time. The example given at the time was grazing cattle during an electrical storm, with the lighting taking the path of least resistance through the animal, rather than along the ground?

I have to confess, that I remember a figure of 200 ohms being a realistic maximum on a customer supplied rod, and any higher readings than that "required investigation"

 

[davesparks]

Because if its a rewire, surely the whole purpose of a rewire is to rewire the whole property and no leave in the existing.And I installed a single rod a few weeks ago and got a value of 15ohms so what would be the point if installing another rod in this case?

The point of installing multiple rods is to achieve good depth and ensure stability.
The ground is generally pretty wet at the moment so your 15ohms will rapidly disappear in the summer if it is based entirely on the moisture content of the topsoil.

 

[davesparks]

Ooops, I appeared to have stirred a hornets nest.

I've fitted the installation with 30Ma RCBO's to all circuits, but so far I've left the main 100Ma RCD in the installation.

To comment on another post, about putting TWO earth rods in, I was told in no uncertain terms that this was a highly dangerous practice, and any fault going to earth would go to both rods and this would cause a dangerous potential difference, possibly resulting in a fatal shock to anyone standing near the rods at the time. The example given at the time was grazing cattle during an electrical storm, with the lighting taking the path of least resistance through the animal, rather than along the ground?

I have to confess, that I remember a figure of 200 ohms being a realistic maximum on a customer supplied rod, and any higher readings than that "required investigation"

Were they SPSN RCBOs or are they the standard SP RCBOs which are commonly available?

Was the person who told you that 2 rods is dangerous certified as insane or something? The whole country would be in serious trouble if this was the case!

Every DNO supplied earth will have many many rods connected in parallel!

 

[Deleted member 9648]

Ooops, I appeared to have stirred a hornets nest.

I've fitted the installation with 30Ma RCBO's to all circuits, but so far I've left the main 100Ma RCD in the installation.

To comment on another post, about putting TWO earth rods in, I was told in no uncertain terms that this was a highly dangerous practice, and any fault going to earth would go to both rods and this would cause a dangerous potential difference, possibly resulting in a fatal shock to anyone standing near the rods at the time. The example given at the time was grazing cattle during an electrical storm, with the lighting taking the path of least resistance through the animal, rather than along the ground?

I have to confess, that I remember a figure of 200 ohms being a realistic maximum on a customer supplied rod, and any higher readings than that "required investigation"

The 100ma RCD needs to be S type in order to achieve discrimination. If you have installed SP RCBO's then you will need to keep the up front S type as SP RCBO's are not recommended for TT systems.

 

[davesparks]

If there is a possibilty of a PME conversion at some point it would definately be worth upgrading now though.

Then get PME installed now whilst it is being rewired!

 

[Deleted member 9648]

Then get PME installed now whilst it is being rewired!

If it's available.....YES!

 

[davesparks]

And if it's not available then install it as a TT

 

[richy3333]

BS7430 suggests a maximum of 100 ohms. I guess? the 21 ohm value is something specified in ESQCR. So is that for the DNO?

 

[shanky887614]

surely if your hitting 180 ohms regularly then your using twigs?

are you using the rods that can be extended about 16mm ish thick (1/2" is 12.5 so around 16mm for 5/8 off the top of my head)


(got myself confused converting lol, im more used to 6/8 razors)

 

[davesparks]

Not installed many earth rods then shanky? Lol

1/2" is closer to 13mm and 5/8 is more like 16mm

 

[shanky887614]

Not installed many earth rods then shanky? Lol

1/2" is closer to 13mm and 5/8 is more like 16mm

good point two inch holesaw is 51mm XD my bad 1"=25mm