I'm confused. If it's TT, how the separation between the TT and TN system achieved? Or is it just an additional electrode? Is that a corner of a car I see touching the feeder pillar door in the second picture?
- Andy.
That was the point of my post AJ. The separation between the two earthing systems is almost impossible in these types of situations. So why bother? Why dismiss a perfectly good TNCS earthing arrangement in favour of a dubious TT arrangement.
I commissioned 4 similar systems this week, all displaying the same issues. Contractors are banging in electrodes and claiming that the requirements of a TN system as set out in 722.411.4.1 do not need to be met. That would seem to be an imprudent tack to take. So the thrust of my post was to suggest that in built-up areas TTing is not a feasible solution. Even if it is at the time of installation, things can change to thwart it.
As Sparkingchip points out, there is no point in putting O-pen protection on the TT side. So if we are to comply with BS7671 and the COP, we are limited to those indents under the above mentioned regulation only one of which I would accept as a contender, that being the system devised by the MyEnergi crowd.
I am sorry I mentioned the fence, totally deflected from my point.
I didn’t realise you could pick up location from the photos I posted. I will have to ask the moderator for advice on how to avoid that.
That was the point of my post AJ. The separation between the two earthing systems is almost impossible in these types of situations. So why bother? Why dismiss a perfectly good TNCS earthing arrangement in favour of a dubious TT arrangement.
I commissioned 4 similar systems this week, all displaying the same issues. Contractors are banging in electrodes and claiming that the requirements of a TN system as set out in 722.411.4.1 do not need to be met. That would seem to be an imprudent tack to take. So the thrust of my post was to suggest that in built-up areas TTing is not a feasible solution. Even if it is at the time of installation, things can change to thwart it.
As Sparkingchip points out, there is no point in putting O-pen protection on the TT side. So if we are to comply with BS7671 and the COP, we are limited to those indents under the above mentioned regulation only one of which I would accept as a contender, that being the system devised by the MyEnergi crowd.
I am sorry I mentioned the fence, totally deflected from my point.
I didn’t realise you could pick up location from the photos I posted. I will have to ask the moderator for advice on how to avoid that.
err I do not think so. There are two groups of objects fed by the substation.
Those using the dno electrodes and supply neutral for earthing, (those may be PME) and those that use a local electrode (TT). The latter group are far safer to touch if you are standing on the ground, as whatever happens the thing you can touch remains more or less at the same voltage as your feet (except for very short times limited by ADS). Ideally you'd like not to be able to make good contact to one of each at the same time, but if you did, it would be no worse than bridging between say a PME lamp post and the bare earth or a non electrical item such in the ground such as a metal gate post.
During certain fault conditions there are voltage gradients along the earth between various items acting as electrodes, and the resistances you see allow you to estimate the currents that flow while that happens, but it is not sinister, it is just a consequence of living on a moderately conducting planet
Mike
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