TT system sub main design

[Engineer54]

That's not an Ra value is it?? Perhaps i should have asked for the existing Ze value!! lol!!

 

[Markblox]

OK, I give in! I'll put in a new rod and pit, the existing one has no inspection pit anyway.

 

[rattlehead85]

Thanks for the quick replies, the garage is detached and only three meters away the supply circuit is to be buried and will only be about 6m long. The SWA will not run through insulation save for about 60mm.
rattlehead, are you saying the 100mA S type will cover the sub main and I should use a 60898 cb in a way separate from the 30mA part of DB1?

Yes Mate.
All this 'do you don't you add an extra rod' is splitting hairs really. Personally i would do it mainly to try and further reduce down the Zdb value in the garage. Also by adding an extra rod you are not relying on connecting the earthing conductor from the house to the shed and using that as a combined earthing and bonding conductor. Bare in mind if you use only the rod from the house supply you would need to run your bonds from the garage back to the M.E.T within the house or ensure your earthing conductor is big enough to use as a combined earthing and bonding conductor.

 

[Markblox]

All this 'do you don't you add an extra rod' is splitting hairs really. Personally i would do it mainly to try and further reduce down the Zdb value in the garage. Also by adding an extra rod you are not relying on connecting the earthing conductor from the house to the shed and using that as a combined earthing and bonding conductor. Bare in mind if you use only the rod from the house supply you would need to run your bonds from the garage back to the M.E.T within the house or ensure your earthing conductor is big enough to use as a combined earthing and bonding conductor.

Thanks, I was feeling a bit bullied there for a moment. It is only a small part of the question, well actually it wasn't any part of the original question, I do like to make it correct though and as the existing rod hasn't got an earth pit I think I will put it in. As far as PFC not being Ra, no it's not but it is quite easy to divide by the voltage which makes the Ra 115 ohms-ie less than 200


Read more: http://www.electriciansforums.net/e...t-system-sub-main-design-2.html#ixzz2L4vUDRaZ

 

[telectrix]

you can put in 10 rods if you want. secret is to go deep with 1 or 2, then measure Ra or Ze. additional rods may reduce the value. aim for <10 ohms. ( yes 10, not niceic 100, not IET 200, but 10 or less. )

 

[Guitarist]

Ask the local power network operator if you can have it PME'd to begin with. Many are doing so free of charge now.

Just one more time incase you missed it....

 

[Engineer54]

All this 'do you don't you add an extra rod' is splitting hairs really. Personally i would do it mainly to try and further reduce down the Zdb value in the garage. Also by adding an extra rod you are not relying on connecting the earthing conductor from the house to the shed and using that as a combined earthing and bonding conductor. Bare in mind if you use only the rod from the house supply you would need to run your bonds from the garage back to the M.E.T within the house or ensure your earthing conductor is big enough to use as a combined earthing and bonding conductor.

Thanks, I was feeling a bit bullied there for a moment. It is only a small part of the question, well actually it wasn't any part of the original question, I do like to make it correct though and as the existing rod hasn't got an earth pit I think I will put it in. As far as PFC not being Ra, no it's not but it is quite easy to divide by the voltage which makes the Ra 115 ohms-ie less than 200

No-ones trying to bully you here!! 115 ohms is pretty much a waste of time, and if what your now planning to do includes a new additional rod, will make perfect sense too!! Use 2 X 5/8'' rods coupled together to give you 2.4m of depth to your rod position...
Now how am i to know how you tested this existing rod, and what voltage to use, the fake 230 volts or the real 240 volts?? lol!!

Have you thought about making enquires to the local DNO to find out if a PME connection is available from your service head, as has been suggested above?? Which will give you a far superior domestic earth connection than a TT system can provide...

 

[Knobhead]

Must be nice to live somewhere where you can drive a 2.4M rod in without there being a resounding clang as it hits bedrock at 500mm. Trust me to always live at the top of a hill (I have a fear of drowning).

 

[shocking_eg]

Prospective earth fault is 2A

LOL

heavily relying on RCD's then

 

[jaydee81]

Must be nice to live somewhere where you can drive a 2.4M rod in without there being a resounding clang as it hits bedrock at 500mm. Trust me to always live at the top of a hill (I have a fear of drowning).

know what you mean did however manage to drive a 2.4m rod in at a job in the middle of dartmoor the other day and got Ra of 22 ohms

 

[Engineer54]

Must be nice to live somewhere where you can drive a 2.4M rod in without there being a resounding clang as it hits bedrock at 500mm. Trust me to always live at the top of a hill (I have a fear of drowning).

Can't really say i've ever had too much of a problem, when i've driven rods in the ground myself in the UK and in Cyprus for myself and friends and some were straight 3m rods!! There's an awful lot of fractured limestone in Cyprus as well, which makes things a little more difficult at times!!