Question - with an earth rod install why can the supply board not simply provide the earth from the neutral like they do on modern installs?
Thanks.
Thanks.
Earthing
- Thread starter dmcclymont
- Start date
Sponsored Links
Because if the neutral is not tied to physical earth along the supply, then there could be a potential between neutral and the ground you stand on, which would mean you could get a shock from a class 1 applience which isn't faulty.
Also, TN-C-S lost neutrals arn't nice, so the the power company need to be sure the neutral isn't lost, caused by big trucks, fallen trees etc easily, think they also have to crimp instead of bolt it as well.
The power companies are converting a lot of TT systems to TT-C-S, but you can't just take a TT system and connect the earth as if it was TT-C-S for the reasons above
Also, TN-C-S lost neutrals arn't nice, so the the power company need to be sure the neutral isn't lost, caused by big trucks, fallen trees etc easily, think they also have to crimp instead of bolt it as well.
The power companies are converting a lot of TT systems to TT-C-S, but you can't just take a TT system and connect the earth as if it was TT-C-S for the reasons above
From what you say I doubt overhead will ever get that system then ??
Sponsored Links
TT-C-S??Adam_151 said:
The reason it can be done in some places and not others is simply the quality of the suppliers overhead cables - if it goes on singles, then the neutral must be the lower of the two cables, and there must be no joints in the combined neutral-earth wire, that rely on a single bolt, and there should be a minimum number of grounding pints in the installation to make it qualify as "PME".
Even so, there are a few lost neutral accidents per year.
Many older supplies were laid in during the postwar period and simply don't meet these criteria, and unless they are restrung, which is a process likely to take years, (there are plenty of fused neutral pre 1936 mains cut outs still in use for heaven's sake - these gusy dont move fast) and installtions connected to these can only be treated as TT.
There are also situations where PME is considered too dangerous, even if the supply integrity is not i doubt, usually where you odnt want to hold neutral and stand on true earth, - supplies building sites, caravans with a metal body, outdoor sockets generally and some kinds of farm machinary for example - so some sites are refused a PME connection on principle, as this sort of use is considered likely.
The other dangerous situation, where TT is prefferred, is when th ehig fault currents it causes can be dangerous, such as petrol stations, oil refineries etc.
Hope that helps.
Even so, there are a few lost neutral accidents per year.
Many older supplies were laid in during the postwar period and simply don't meet these criteria, and unless they are restrung, which is a process likely to take years, (there are plenty of fused neutral pre 1936 mains cut outs still in use for heaven's sake - these gusy dont move fast) and installtions connected to these can only be treated as TT.
There are also situations where PME is considered too dangerous, even if the supply integrity is not i doubt, usually where you odnt want to hold neutral and stand on true earth, - supplies building sites, caravans with a metal body, outdoor sockets generally and some kinds of farm machinary for example - so some sites are refused a PME connection on principle, as this sort of use is considered likely.
The other dangerous situation, where TT is prefferred, is when th ehig fault currents it causes can be dangerous, such as petrol stations, oil refineries etc.
Hope that helps.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
