TN-C-S (PEN) RCBOs Discussion

[pc1966]

I too like to see how things are done elsewhere as every country's system is a mixture of good and bad, and largely not that planned either (i.e. often things had to follow on from past installations & standards).

The TN-C-S open PEN risk is something that looks like becoming a topic as more folk look to EV chargers. I suspect there won't be and change to TN-C-S usage by the DNO as it is widespread and cheap, but I think inevitably EV chargers will all have to be Zappi-like in protecting against open PEN risk without an earth rod, as driving in rods in urban areas is going to cause all sorts of practical issues and damaged utility cables/pipes.

The ROI practice of having rods for the TN-C-S earth locally makes a lot of sense, though I doubt that 1.2m rods are meaningfully low to help much. The discussed option in AM2 for our 18th to make it part of foundations makes more sense, as it could be well under 10 ohms that way, but that will take years (if ever) to make much difference considering it won't be retro-fitted to the majority of housing.

 

[LastManOnline]

I too like to see how things are done elsewhere as every country's system is a mixture of good and bad

"A mixture of good and bad" sums it up well. I like to start a discussion on the "bad" to explore how it might be improved.

I suspect there won't be and change to TN-C-S usage by the DNO as it is widespread and cheap.

No. Its here to stay. So with that in mind lets educate people about the shortcomings of the system and that could go a long way in mitigating the risks associated with it.

The ROI practice of having rods for the TN-C-S earth locally makes a lot of sense, though I doubt that 1.2m rods are meaningfully low to help much.

They will help in reducing touch voltage to some extent. What is unfortunate about them is that in almost every country that uses them (ROI, AUS, NZ etc) in their TNC-S supply system, there is this misunderstanding that the 4 foot rod is a "back up" under open PEN faults. This misinformation is widespread. I have encountered it in discussions with inspectors and educators. I, m a, little baffled by that.

. The discussed option in AM2 for our 18th to make it part of foundations makes more sense, as it could be well under 10 ohms that way,

Makes good sense.

 

[pc1966]

What is unfortunate about them is that in almost every country that uses them (ROI, AUS, NZ etc) in their TNC-S supply system

I think the USA has two rods, spaced apart (8 feet?) but again 4 foot deep is not going to give you any meaningfully low earth Ra value.

Historically the metal service pipes did give you a decent earth, and often backup connectivity between supply E (i.e. PEN) bonds, but they are of course all being converted to plastic.

 

[LastManOnline]

I think the USA has two rods, spaced apart (8 feet?) but again 4 foot deep is not going to give you any meaningfully low earth Ra value.

I stand to be corrected here but my recollection is that the Americans use as you correctly say, 2 rods, but I think they are longer than 4 feet. In any case I know they do a better job with their rods than we do.

Historically the metal service pipes did give you a decent earth, and often backup connectivity between supply E (i.e. PEN) bonds, but they are of course all being converted to plastic.

This has been the single most important factor in the introduction of our TNC-S system. I can appreciate that in the late 80,s when plastic started to replace metal services there was a major recession going on. There possibly was, nt the money to pay for anything other than TNC-S, the cheapest supply system available.