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Its not an issue of trust. The calculations speak for themselves. No issue. It's also not about being indifferent about resources. No issue. But speaking from a perspective where I have been using what I might term"British " T&E for most of my career and" Irish" T&E just recently. Obviously I am obliged to use it. But I see it as a trade off. A larger earth allows longer runs due to reduced FLI and volt drop. Touch voltages will be reduced. I have to say I, m also delighted to see the back of all those calculations we had to make for test reports due to the difference in the CSA of L and E in T&EBecause some countries like to waste the rapidly dwindling natural resources of this planet.
Or maybe they just don't trust the people installing the cables to understand the relatively simple calculations required.
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[automerge]1594415772[/automerge]Basically you are very unlikely to have an earth rod with an Ra below a couple of ohms, more likely tens of ohms, so under fault conditions the maximum current is in the tens to low hundred Ampere range and for a fraction of a second for the breaker to clear it that is OK. Also most TT installations have an incomer RCD that trips at levels of 100mA to 300mA usually.
So basically you won't see a large enough I2t to overload a 2.5mm conductor.
Having said that, personally I would not use anything below 4mm in that case for mechanical strength even for the protected cases.
Its not an issue of trust. The calculations speak for themselves. No issue. It's also not about being indifferent about resources. No issue. But speaking from a perspective where I have been using what I might term"British " T&E for most of my career and" Irish" T&E just recently. Obviously I am obliged to use it. But I see it as a trade off. A larger earth allows longer runs due to reduced FLI and volt drop. Touch voltages will be reduced. I have to say I, m also delighted to see the back of all those calculations we had to make for test reports due to the difference in the CSA of L and E in T&E
[automerge]1594414439[/automerge]
Basically you are very unlikely to have an earth rod with an Ra below a couple of ohms, more likely tens of ohms, so under fault conditions the maximum current is in the tens to low hundred Ampere range and for a fraction of a second for the breaker to clear it that is OK. Also most TT installations have an incomer RCD that trips at levels of 100mA to 300mA usually.
So basically you won't see a large enough I2t to overload a 2.5mm conductor.
Having said that, personally I would not use anything below 4mm in that case for mechanical strength even for the protected cases.
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I have seen the minimum size cable for an earth rod go from 2.5 to 4mm to 6mm to 10mm for domestic installations, over the years. Why the change? Soil resistance is still exactly the same as it was decades agbviously the requirement for greater protection through mechanical strength. the current flow under fault conditions remains determined by the rod res (on a good day a 100 ohms?). So under the worst fault conditions there will be max 2 to 3 amps flowing which of course means a 2.5mm is electrically fine (but mechanically not, according to the (our) regs).Basically you are very unlikely to have an earth rod with an Ra below a couple of ohms, more likely tens of ohms, so under fault conditions the maximum current is in the tens to low hundred Ampere range and for a fraction of a second for the breaker to clear it that is OK. Also most TT installations have an incomer RCD that trips at levels of 100mA to 300mA usually.
So basically you won't see a large enough I2t to overload a 2.5mm conductor.
Having said that, personally I would not use anything below 4mm in that case for mechanical strength even for the protected cases.
I also think that it would unusual to find a, TT Supply system nowadays that does, nt incorporate rcd, s. Though they do exist.
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