FEL Vedlegg 1

Metalliske rørsystemer skal ikke være benyttet som jordelektrode. Slike systemer (hovedvannledninger, hovedrør for sentralvarmeanlegg, rørsystemer for brennbare væsker eller gasser og lignende) skal tilkoples jordingsanlegget via utjevningsforbindelser.

Når det gjelder avløpsrør av isolerende materiale, skal det dersom farlige potensialforskjeller kan oppstå mellom avløp og andre ledende deler, anordnes tilfredsstillende elektrisk ledende forbindelse til innsiden av avløpsrøret eller til sluk. Slik utjevningsforbindelse er ikke påkrevd dersom det kan sannsynliggjøres at fare ikke kan oppstå. I TN-system kan det antas at slik fare normalt ikke oppstår.

The IT-nett is a Norwegian, Albanian and HV distribution system, as I'm sure you know. In this system, you are required to either ground the inside of the soil pipe, because all the dirt that builds up over time can become conductive. You then have a potential difference between equipment with an earth failure and the drain.

It's a lot easier to put in a tjømemuffe than to earth all the drains one by one.

The discussion if it's neccesary with RCDs on every circuit is another discussion :)

Tusen takk! :)

Since posting I also read some more info, including the reason being a possibility of conductive layer forming in the drain pipes as you say. Hmmm that is news to me! :) We don't have IT in the UK (except special cases) but a lot of TT and this is never considered. Hard to imagine this conductive layer reaching all the way up to the drain grate (my 30 year old drains seem pretty clean from my investigation so far), but I guess it can happen in a worst case scenario.

I think I know what a Tjømemuffe is now (or Ola-stubben, jordingsrør) but, correct me if I am wrong, this needs to go close to the origin of my drain pipes before it branches to the different drains in the house (much like main bonding of incoming water, gas pipes etc should be at the origin also). For me this must be somewhere out of reach under the basement!

I think therefore I have no choice but to supplementary bond drain grates as I renovate. I found a well circulated SINTEF article about the best way to do it and it isn't too troublesome putting a cable in the tile adhesive above the membrane. In fact I'll cut a small groove/channel in the concrete screed before I apply the liquid membrane so I don't have to worry about the height of the earth cable.

Necessary with RCDs - yes I'm sure that could be a long discussion! :) I guess the conservative position is an RCD may not work so better to have extra barriers. I can certainly understand being conservative with an IT network where, for example, your neighbor could create a standing first earth fault that is not automatically disconnected, etc etc. Better safe than sorry.

On the subject of IT nett - I would have expected to see a local earth electrode/rod but have distributed earth in the supply cable. Is this perhaps so the network owner (Lyse) can monitor for first fault, or is it entirely possible a first fault within a distribution can stand until noticed by an electrican/home owner? Just curious.

Thanks again.

You are correct - tjømemuffe is a piece of tube with a layer of conductive material on the inside and a wire poking out of it :)

https://www.ahlsell.no/33/vvs-teknisk-produkter/avlopsror-og-deler/rustfrie-ror/2250372/https://www.ahlsell.no/33/vvs-teknisk-produkter/avlopsror-og-deler/rustfrie-ror/2250443/

I guess it's called a Tjømemuffe because of the first company that produced them.

Normally the supply company don't connect their end of the earth wire, at least not in my area. Since your house was built in 1988, it may be possible that the water supply pipe is used as your earth electrode. This was legal until 1991.

The supply company sends around people to measure for earth leak currents regularly, and unless they have some automatic system to monitor it, thats the only way to detect a standing earth fault in an IT nett.

Thanks for the links for the jordingsrør. The instructions say it should be installed after the last drain as I thought so this is not accessible for me. So I am stuck with earthing drain grates individually I believe!

Interesting I didn't consider that possibility about the earthing of my house. The supply cable armour is terminated into a 16mm2 earth cable which goes to my main earth terminal in the cabinet. The earth cable to the incoming water pipe in the basement is only 6 or 10mm2. So it looks like the supply cable is supposed to be the main earth.

When my test equipment arrives from UK I guess I can measure earth fault impedence Ze via the supply cable or water pipe and find out.

Takk