Loss of neutral

gkenyon:

AdrianWint:

So, taking this discussion in a slightly different direction....


What would be the general consensus/opinion about using a 4 pole REC isolator to disconnect (for a single phase domestic installation) the phase, neutral & also disconnect the water & gas bonds away from the network earth/neutral conductor? I'm thinking perhaps use two of two of the poles to switch two 25mm^2 conductors connecting the MET to the network earth/neutral to give some redundancy against a failed switch contact.


Over to the floor....

Removing the main bonding  won't achieve anything at all in an installation with internal conductive service pipes. The pipes throughout the installation would still import PEN voltage from other installations.


In addition, even if adjacent consumers had the same protective provision, metal service pipes "in the street" could still pick up risen PEN voltage from the street.


I think it would be better for the SMART meter system to alert the DNO to the fact they may have a problem in a particular area so they can investigate. In a single-phase installation, the meter won't know whether it's a supply line conductor issue, supply transformer or tap issue, or a broken PEN conductor, but the DNO can build up a picture based on the voltages reported by meters from single phase installations on different phases, to determine which of these it might be.

Metal service pipes are so last century.


My water pipe is plastic, and presumably has been since the house was built.  My gas pipe is now plastic too, since the supply was re-laid.


I don't suppose I would have any problem isolating my house from the neighbours.


Bring back the VOELCB, I say!

AJJewsbury:

But would it not stop diverted neutral currents flowing in my bonding?

If I've pictured it correctly, L & N are disconnected, as are main bonds - but the main earthing conductor is still connected to the DNO's earth terminal - and hence the c.p.c.s to any equipment that happens to be in contact with metallic pipework (boilers, pumps and so on). So the diverted N currents will still flow, just now all through 1.0mm² or even 0.75mm² c.p.c.s rather than mostly through 10mm² bonding conductors. Given that diverted N currents (especially in a broken PEN situation) can be many tens possibly even hundreds of amps, I think I'd prefer to keep the 10mm² connected...

   - Andy.

Maybe I phrased it poorly ... I was thinking of the MET & everything connected to it (bonding, circuit cpcs etc) being disconnected.


I agree with your point... dropping the bonding but leaving the 0.75mm^2 cpc of the central heating pump etc connected would jjust make the situation even worse. I'm envisaging complete disconnection from the DNO network.... L, N and main earthing conductor.

Zoomup:

You could just alter the pipe work in your installation, and ensure that it is all plastic,  so that main equipotential bonding is not required. The gas main up to the house would be plastic in most cases, and just internal gas pipes would be metal.

 

This is a huge assumption. There are many 1000's of properties out there with one, or both, water and gas services in metal. My own house still has both in metal - gas is the big issue because the internal piping still has to be metal. Whilst a lot of the internal water pipework has been replaced with plastic, a lot of the central heating is still metal, and still very serviceable.


Whilst the mains in the street have possibly been replaced, what we don't know is how far the joints are to earthing for the PME ...


Other premises will have different issues - for example, premises that require LPS there's just no way of getting away from conductive stuff connected to the ground.


I'm definitely an advocate of the approach of using the smart meter system, and it's a great idea - it's just that I think it would be better if the DNO were to be alerted to the issue, especially single-phase installations, to avoid nuisance-trips.

gkenyon:

Zoomup:

You could just alter the pipe work in your installation, and ensure that it is all plastic,  so that main equipotential bonding is not required. The gas main up to the house would be plastic in most cases, and just internal gas pipes would be meta


Other premises will have different issues - for example, premises that require LPS there's just no way of getting away from conductive stuff connected to the ground.


 

Oh, I think there is. I work in many 1970s houses, and even they have a main black plastic water pipe entering the house.


If needed we can install non electrically conducting inserts in metal water pipes where they enter the building if the pipe is metal.


There will be houses with metal gas, oil  and water pipes entering the building of course.


In this part of the woods we have many householders that rely upon oil fired boilers. The oil pipe from the garden tank, which is sometimes plastic or metal, is raised off the ground on blocks. The metal pipe can be plastic covered. Electrical testing would be required to determine if the plastic covered oil pipe from garden tank to house boiler is an extraneous conductive part.


I come across old mains gas installations with a final lead pipe connection at the meter position. I would not like that semi-flexible lead pipe section to carry large fault currents and get hot then melt.


Many mains gas pipes that supply houses are yellow coloured plastic underground but convert to metal pipes internally. Electrical testing would be required to determine if the internal metal pipes are extraneous conductive parts and could carry diverted neutral currents, otherwise they may just be exposed conductive parts.


411.3.1.2.


Perhaps TN-S supplies offer a partial solution.




Z.