Exporting the earth?

[antimatter]

@telectrix

i was only joking

 

[telectrix]

The key point being that you know that you have a choice on the installation method.

exactly. beauty is in the eye of the installer.

 

[SimpleSimon]

The key point being that you know that you have a choice on the installation method.

I think that was a subpoint. The main point being is that he's old.

 

[IQ Electrical]

Perhaps best if I don't ask you to define 'old' Simon?

 

[SimpleSimon]

I'll just leave it on Im young enough to still take meaning on the saying "Respect your elders"

 

[telectrix]

I'll just leave it on Im young enough to still take meaning on the saying "Respect your elders"

right attitude. but then again, us older ones have to respect the younger generation for it is they that will select our nursing homes.

 

[IQ Electrical]

Your diplomacy knows no bounds!

 

[telectrix]

i studied under adolph

 

[Dave_]

TNC-S is considered a lot less dangerous now with concentric supply cables, where the PEN conductor surrounds the line conductors like the armour but as a copper core, thus making it impossible to cut through the PEN conductor (i.e. digger bucket) without creating a short circuit and ensuring disconnection of the DNO´s protective device back in the substation. Not sure how many underground TNC-S supply cables are concentric though!!! Anybody know??

 

[SimpleSimon]

right attitude. but then again, us older ones have to respect the younger generation for it is they that will select our nursing homes.

True. It's also us who'll push your wheelchairs down the hill when you get a bit narky!

 

[IQ Electrical]

The general opinion of the various DNO's is that a loss of the PEN does not happen and they have sophisticated monitoring devices in place. There was a report by the IEC some time ago that basically concluded that 'the incidence of a break of the neutral conductor in low voltage systems is so low as to not deserve any consideration'.

 

[telectrix]

True. It's also us who'll push your wheelchairs down the hill when you get a bit narky!

i'm over the hill already, but shove my wheelchair down further and find out what walking sticks are really for. LOL.

 

[antimatter]

TNC-S is considered a lot less dangerous now with concentric supply cables, where the PEN conductor surrounds the line conductors like the armour but as a copper core, thus making it impossible to cut through the PEN conductor (i.e. digger bucket) without creating a short circuit and ensuring disconnection of the DNO´s protective device back in the substation. Not sure how many underground TNC-S supply cables are concentric though!!! Anybody know??

New supplies, i have some concentric here i got off a jointer when i was meter fitting, also got a few lucy cutouts, the concentric for those that don't know is copper outer core (neutral and earth) with a solid aluminium core in the middle (line conductor).

 

[Engineer54]

the following post is meant to be read in the spirit it is posted.

having been in the trade for a while, when the height of accuracy of resistance measurement was an AVO 7, with a bit of good eyesight you could just about get an accuracy of 1 and a bit ohms, not the zillionth of an ohm we read to now, a caclculator was a slip stickmade by thornton's who now make chocolate, and the only digital equipment was a red led watch, on some boffins drawing board, sketched in pencil, it was usual to TT outbuildings, as most installs were TT anyway . nowadays we have a choice. i only export the earth if the outbuilding has no extraneous metal conductive parts. the dangers inherent having been expained on this thread better than i can. so far nobody has been electrocuted on one of my installs, so i will continue as an old fossil until my legs give way, or goverment increase pensions to a level wherein i can live in the style to which i am accustomed.

I too am from your era, and i still have my old AVO 8. ...lol!!!

The difference between a TT system then and now, is that most of the younger sparks of today will rely on an RCD device for ground fault protection with a TT system. Whereas in our day the sparks had only the rod(s) to give them that protection. So now days, they just whack a rod in the ground and if it's under 200ohms it's a good-un!!! I bet that if you look around at some of these newly installed rods, most will be right by the side of the building wall too. The very last place to drive a rod!! ...Why, because that's where all the building rubble is going to be. I also bet that a good number of those rods have been cut short because they ''Have'' hit in-passable rubble, so the chances of gaining a decent Ra is even further diminished!!!

Most of the newer installations generally also rely on a single rod, whereas in my day, if a high reading was present on the initial rod a second rod was driven. It wasn't that uncommon in the past, to see 3 driven rods, especially in unfavourable ground conditions/locations... The other thing is, ...how many modern day sparks know how to maintain a TT system?? How many know of chemical conditioning, what chemicals to use, and some of there drawbacks, ....or know about conductive mortars and when and how to use them?? Very few would be my guess!!! Now days, almost total reliance is given over to an RCD, ....which although very good, are prone to failure. Then that rod with an Ra of 200ohms isn't going to operate any protective device in a
time that will give any meaningful protection....

Installing a ''Good'' TT system requires both skill and experience, and money too, if it's to be installed properly. It's not just a case of whacking a rod in the ground and hoping for the best ...lol!!!

 

[Engineer54]

The general opinion of the various DNO's is that a loss of the PEN does not happen and they have sophisticated monitoring devices in place. There was a report by the IEC some time ago that basically concluded that 'the incidence of a break of the neutral conductor in low voltage systems is so low as to not deserve any consideration'.

I couldn't agree more with you IQ, I have a friend that has spent the whole of his working life with the leccy board and DNO company. He is now a regional manager. He has only known of 2 such cases, both of which were tripped out on there protection relays before any detrimental affects had time to establish within the fault area. Yet you always get those that will tel you they know of many such incidents..... Basically it's all down to hearsay, and scaremongery. If the system was anywhere near as dangerous as some would have you believe, it would NOT be a part of ours and many others countries supply distribution system.