Electricians Die

[muffking]

Remove the cutout fuse, which is it's primary purpose.

Silly question, but if the cutout fuse takes power away from the Line is there any danger between Neutral and Earth?
I only ask as I'm being brain washed (as a preventative measure) to beware of live Neutrals, although logic is telling me that occurs when there is a Line connected somewhere.

 

[John D v2.0]

Silly question, but if the cutout fuse takes power away from the Line is there any danger between Neutral and Earth?
I only ask as I'm being brain washed (as a preventative measure) to beware of live Neutrals, although logic is telling me that occurs when there is a Line connected somewhere.

In terms of bs7671 neutral is a live conductor. But in terms of the dno only live is dangerous. So you need a double pole main isolator, but the dno don't.
Maybe they trust themselves not to get polarity wrong.
If all bonding is in place on a TN-c-S then with the line isolated the dno neutral will be the same potential as all your extraneous conductive parts anyway. In a tn-s there could be a difference depending what current is flowing in the local network.

 

[JohnW2]

In terms of bs7671 neutral is a live conductor. ... So you need a double pole main isolator, but the dno don't.

That's not quite true "in terms of BS7671" ....

If all bonding is in place on a TN-c-S then with the line isolated the dno neutral will be the same potential as all your extraneous conductive parts anyway. In a tn-s there could be a difference depending what current is flowing in the local network.

That is all true but, for reasons better known to it's authors, BS7671 regards single-pole isolation as adequate with both TN-C-S and TN-S (double-pole isolation only being needed with TT). Whilst I can understand their argument (which is actually stated in BS7671) in the case of TN-C-S, I am personally not quite so comfortable about TN-S.

If/when I need isolation in which I am totally confident, I have to say that I really want to see DP isolation (not the least because 'reversed polarity' is not unknown!), regardless of whether the supply is TN or TT!

Kind Regards, John

 

[John D v2.0]

Fair enough didn't realise that, thought DP main isolator had to exist for all supplies.

 

[JohnW2]

Fair enough didn't realise that, thought DP main isolator had to exist for all supplies.

Ah, that's a bit different, and raises another inconsistency in BS7671 .... 537.1.4 requires a means of breaking the supply on load and isolation as near as practicable to the origin of an installation and then goes on to say (consistent with your comment) that a "main switch" intended to be operated by ordinary persons must be DP.

However, a couple of inches further down the page, in the section actually entitled "Isolation, 537.2.1.1 says "In a TN-S or TN-C-S system, it is not necessary to isolate or switch the neutral conductor ...."

So 'go figure'! I suppose we have to assume that what you say is actually correct, and that 537.1.4 is meant to over-ride the contradictory 537.2.1.1. I also assume that 537.2.1.1 is thinking primarily in terms of the Main Switch (or RCD incomer) in a CU, not anything which may exist upstream of the CU.

Kind Regards, John

 

[flameport]

is there any danger between Neutral and Earth?

No, and on many supplies they are the same conductor.