Electrician advised against just updating the fuse box

[bernardgreen]

Maybe someone who works for a DNO could tell us how often

That would be useful information. Provided it was accurate when identifying the reason for the incident.

 

[JohnW2]

That would be useful information. Provided it was accurate when identifying the reason for the incident.

It would be useful information even if it did not identify (accurately or otherwise) the 'reason for the incident'.

I may be wrong, but I suspect that 'melting bonding conductors', due to any reason/cause, is incredibly rare.

Kind Regards, John

 

[EFLImpudence]

Maybe there should be a decision to bond or not to bond depending on the impedance of the extraneous pipework.

There is.

Over 23kΩ is generally accepted as not requiring bonding depending on the actual voltage.

You may use a higher figure if you wish but then you enter the realm of unnecessary and unwanted hazardous earthing - probably not a problem with a water pipe connected to CPCs.

 

[JohnW2]

There is. Over 23kΩ is generally accepted as not requiring bonding depending on the actual voltage.

Indeed, but that's because it is then essentially regarded as not being an extraneous-c-p.

Bernard is talking of the other extreme - i.e. as I understand it, he is suggesting that one should be able to decide not no bond if the impedance to earth were less than, say, 1Ω - which would seemingly be crazy, even if it did eliminate the (I would think incredibly tiny) risk of bonding conductors melting!

Kind Regards, John

 

[EFLImpudence]

Indeed, but that's because it is then essentially regarded as not being an extraneous-c-p.

Indeed.

Bernard is talking of the other extreme - i.e. as I understand it, he is suggesting that one should be able to decide not no bond if the impedance to earth were less than, say, 1Ω - which would seemingly be crazy, even if it did eliminate the (I would think incredibly tiny) risk of bonding conductors melting!

I thought that's why they had to be 10mm².
Shouldn't the argument be for larger conductors (if thought necessary) not the omission of Bonding?

 

[JohnW2]

I thought that's why they had to be 10mm².

I'm sure it is.

Shouldn't the argument be for larger conductors (if thought necessary) not the omission of Bonding?

I would say that it obviously should, and that the omission of bonding would be just crazy.

One thing which is probably being overlooked is that, in the event of a broken neutral, very high currents would only flow through bonding conductors to earth (as their 'return path') if a lot of high-current loads were 'switched on' in the affected part of the network. In that situation, those loads would represent a very low impedance, such that, unless it were extremely low, the impedance of the return path via the extraneous-c-p would substantially limit the current - quite possibly enough to eliminate any 'danger' to the bonding conductors. Furthermore, the VD is that 'return path' would probably be sufficiently high that a lot of the connected loads would cease to function (properly, or at all) and therefore might well be switched off.

Kind Regards, John

 

[SimonH2]

... in the event of a broken neutral, very high currents would only flow through bonding conductors to earth (as their 'return path') if a lot of high-current loads were 'switched on' in the affected part of the network.

And also, there has to be an imbalanced load - eg all the houses on L1 putting their cookers on, while all the rest have gone out and left everything switched off. Rather unlikely ?