Need to install an earth rod for a domestic property (no existing earth at all!). Can anyone help me with information regarding depths required, sizing of earthing conductor, means of protection and anything else i may need to know (this is my first time!). Also can I test using a Ze figure rather than buying a dedicated tester?
earth electrodde
- Thread starter cedric
- Start date
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aim for a Earth loop impedance of less then 100 ohms and protect the entire installation with a 100mA RCD (preferably a type s)
pundle said:
Why?
Earthing conductor depends upon the csa of the tails but to be safe use 16mm cable. Use a time delayed RCD for main incomer. Yes you can use the Ze obtained from a standard ELI tester. anything above 100 Ohms is regarded as possibly unstable but if in doubt add another rod and connect them in tandem. V= IxR V <50volts I=100mA you do the math.
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TT installations must be protected by 100mA RCD, Time delayed so that if the 30mA RCD you have protecting your sockets trips it will not take out the entire installation. Circuits must be arranged to prevent inconvenience if one circuit trips.
If you cannot achieve 100 ohms with the rod it is better to screw another rod on to it and drive them both deeper. You can get rods like this at your disty.
If you have a second rod, and it is too close to the first, you will not improve the impedance that much. Cant remember off hand but I think the distance of the second rod must be greater than 4 times the length of the first??
Use the thickest rod. They come in a number of csas.
you need to fit a proper cover over the end of the rod that has a proper warning notice. Cover the connection of the earth cable to the rod in vaseline.
Whacking it in can be hard with a sledge or something. After a few struggles I bought an SDS adaptor with a ½" square end and fitted a suitable sized hex nut socket on it. Put your SDS drill on hammer and it'll drive in nice and easily (straight too).
Qedelec - Got an issue with your suggestion of 16mm main bonding on TT. Its not necessary, have a look at the regs & OSG. 6mm is just fine. It is only going to carry 100MA before the RCD trips, after all.
If you have a second rod, and it is too close to the first, you will not improve the impedance that much. Cant remember off hand but I think the distance of the second rod must be greater than 4 times the length of the first??
Use the thickest rod. They come in a number of csas.
you need to fit a proper cover over the end of the rod that has a proper warning notice. Cover the connection of the earth cable to the rod in vaseline.
Whacking it in can be hard with a sledge or something. After a few struggles I bought an SDS adaptor with a ½" square end and fitted a suitable sized hex nut socket on it. Put your SDS drill on hammer and it'll drive in nice and easily (straight too).
Qedelec - Got an issue with your suggestion of 16mm main bonding on TT. Its not necessary, have a look at the regs & OSG. 6mm is just fine. It is only going to carry 100MA before the RCD trips, after all.
Correction Tay I meant to say 10mm. Yes I know OSG says 6mm but have you noticed how each successive edition of the regs goes up anothe notch lol.
Its gonna be fun meeting the latest ammendment "All sockets must me RCD protected" Deep joy.
Its gonna be fun meeting the latest ammendment "All sockets must me RCD protected" Deep joy.
For a TT system where the efli is greater than 1 ohm (p163 osg):
Burried:
25mm² unprotected
16mm² protected against corrosion
2.5mm² protected against corrosion and mechanical damage (seems rather small though imo)
Not burried
4mm² unprotected
4mm² protected against corrosion
2.5mm² protected against corrosion and mechanical damage
Burried:
25mm² unprotected
16mm² protected against corrosion
2.5mm² protected against corrosion and mechanical damage (seems rather small though imo)
Not burried
4mm² unprotected
4mm² protected against corrosion
2.5mm² protected against corrosion and mechanical damage
I use 10.0mm² bonding onTTs, then it's there ready for when a PME upgrade becomes available 
I'd think 2.5mm should take 240A for long enough to take out a RCD, especially given that it should be starting from coldSpark123 said:
anyone fancy calculating the adibatic for the trip time of a type S rcd, a starting temp of room temperature, the limiting temp of PVC insulation and an EFLI of 1 ohm?
Realistically however protecting against mechanical damage is probablly more trouble and expense than just using the larger cables.
Sorry Qedelec, but there is no requirement for a TD 100mA RCD on its own. No quibble with your argument for using one (with 30mA on sockets etc), but this comes up as a common point on this forum and people are told that they must have one. Only if two RCDs are used and then to provide discrimination (as you suggest) do the regs call for TD.
To the OP ; being pragmatic with the rod - try to locate where land does not dry out. Not uncommon to find them in lean to outhouses where the soil is dry as a bone and Ze is over the moon.
HTH
V
To the OP ; being pragmatic with the rod - try to locate where land does not dry out. Not uncommon to find them in lean to outhouses where the soil is dry as a bone and Ze is over the moon.
HTH
V
Yeah but if you only have one RCD protecting the whole installation then this does not comply with the regs either
RF Lighting said:I use 10.0mm² bonding onTTs, then it's there ready for when a PME upgrade becomes available
Yes but why do that. Your 10mm² will go to the earth spike.
If/when PME comes along you'll be connecting from the MET to the service head & it will need to be 16mm² then.
Or am I missing something?
No, sorry. I was referring to the MEBs to incomming services (water, gas, oil etc)
Not the main earth from the electrode.
I was replying to part of the thread that I thought (maybe incorrectly) refferd to MEBs on a TT system.
Not the main earth from the electrode.
I was replying to part of the thread that I thought (maybe incorrectly) refferd to MEBs on a TT system.
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