I need to know what conductor size I must use to meet 17th edition. I found a table at
The installation is: tails 25mm^2 earthing TN-S No RCD Main bond conductor length 12m Install age: early 1980s
Can someone explain the columns?
thanks, NT
silly me should have checked the wiki!
Not surprised - the text cites the wrong table just to confuse is seems.
Try this one:
Look at 25 in the left column, and then read off 10 from the rightmost.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D\
=A0 =A0 =A0 =A0|
=A0 =A0 =A0 =A0|
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D/
My supply has the earth supply clamped from the around the outer sheath of the main cable from the street. What is that? TN-S?
Thanks to all you replies to my electrical other posts.
Yes. And the Ze figure should be
Thanks. Pardon my ignorance, what is Ze?
Ze - External earth loop impedance. If you do not know about Ze or have the equipment to measure it do not worry. Do not try to measure with a standard multimeter! I mentioned it because it is of course possible that although connected in your house, there has at some time in the past been a repair in the street that has changed the cable type so that in reality your earth is connected to nothing much. Regards Bruce
Bruce, thanks. Are you saying there is no earthing? I assumed the earth was the metal sheath around the L&N coming in from the street.
You me worried.
Sorry, I am not trying to confuse or worry you, just being a bit pedantic in my reply.
As I tried to say, the simple answer to your question is YES it is TN-S.
However I was just pointing out that it is more complex than that to say you have a properly functioning TN-S earth. It is probably fine, but takes specialist equipment to check. Are you asking out of interest or because you have concerns about your installation?
Regards Bruce
Yup, sounds like TN-S. The metal sheath of the cable should be joined to earth and the neutral point on the transformer at the substation.
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