ProMbrooke:

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ProMbrooke:

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ProMbrooke:

gkenyon:

When PME was introduced, we were still in the "post-war" period.


Now we are in a position where, in existing urban areas, PME is here to stay.


I understand some DNOs are offering TN-S for new-build - of course, there is a slight cost increase for the extra core.


With TN-S, you only need one failure after broken PE, on circuits where RCDs are not used. Where RCDs are used, I thought you said you weren't happy with reliance on the RCD?


Your point regarding earthing is very valid ... for all system types. The impact on the effectiveness of main bonding due to the change to plastic service pipes can't be underestimated. I have measured the effective combined earth electrode resistance of my water supply pipe, which is still lead from the street, and it's well under 4 ohms.


How should we deal with that? Germany insist on foundation earth electrodes, which achieve a similar result ... but that idea keeps being shot down here in the UK. I'd like to see some alternative approaches considered. Don't forget, the loss of plastic service piping is not a fault of the DNO, it's a result of health & safety (replacement of corroding metal gas mains for plastic) and public health (replacement of iron and lead water pipes for plastic) and far outside the DNO's control.

Two failures for TN-S without RCD, Three failures with RCD. RCDs aren't 100% reliable, hence why I advocate a foundation of low loop impedance and rapid disconnection. 

So what happens when I am outside in the garden and I get a shock on an old non R.C.D. supplied socket, due to a fault with an appliance or appliance flex, if I am in contact with 240 Volts mains. Let's say 5 Amps is flowing through my body. Will the 13 Amp plug fuse blow and save my life?


Z.

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Thats where CPCs come in, in that they would cause the fuse or MCB to open in 0.2 seconds or less.

Not if the cable is just two core they wouldn't. Or if the appliance is all insulated=Class 2.


Z.

Right, where you would have a double insulated tool, which is not capable of becoming live ie made of plastic. 

And if the appliance flex is damaged but unnoticed. Perhaps insulation chewed through by mice or the appliance mechanically damaged by poor rough handling. If I come into contact with a live core or part then there is no protection by a C.P.C.


Z.

ProMbrooke:

Zoomup:

ProMbrooke:

Zoomup:

ProMbrooke:

gkenyon:

When PME was introduced, we were still in the "post-war" period.


Now we are in a position where, in existing urban areas, PME is here to stay.


I understand some DNOs are offering TN-S for new-build - of course, there is a slight cost increase for the extra core.


With TN-S, you only need one failure after broken PE, on circuits where RCDs are not used. Where RCDs are used, I thought you said you weren't happy with reliance on the RCD?


Your point regarding earthing is very valid ... for all system types. The impact on the effectiveness of main bonding due to the change to plastic service pipes can't be underestimated. I have measured the effective combined earth electrode resistance of my water supply pipe, which is still lead from the street, and it's well under 4 ohms.


How should we deal with that? Germany insist on foundation earth electrodes, which achieve a similar result ... but that idea keeps being shot down here in the UK. I'd like to see some alternative approaches considered. Don't forget, the loss of plastic service piping is not a fault of the DNO, it's a result of health & safety (replacement of corroding metal gas mains for plastic) and public health (replacement of iron and lead water pipes for plastic) and far outside the DNO's control.

Two failures for TN-S without RCD, Three failures with RCD. RCDs aren't 100% reliable, hence why I advocate a foundation of low loop impedance and rapid disconnection. 

So what happens when I am outside in the garden and I get a shock on an old non R.C.D. supplied socket, due to a fault with an appliance or appliance flex, if I am in contact with 240 Volts mains. Let's say 5 Amps is flowing through my body. Will the 13 Amp plug fuse blow and save my life?


Z.

.

Thats where CPCs come in, in that they would cause the fuse or MCB to open in 0.2 seconds or less.

Not if the cable is just two core they wouldn't. Or if the appliance is all insulated=Class 2.


Z.

Right, where you would have a double insulated tool, which is not capable of becoming live ie made of plastic. 

And if the appliance flex is damaged but unnoticed. Perhaps insulation chewed through by mice or the appliance mechanically damaged by poor rough handling. If I come into contact with a live core or part then there is no protection by a C.P.C.


Z.