IT configured back-up genny

[LastManOnline]

I'm guessing this is in ROI and I'm aware that there is a "neutralising link" between the supplier's PEN and the local earth rod, etc. However, is it a bit like UK TN-C-S where the N & E are only ever linked in the supply cut-out,

Yes.Similar to UK

The reason for asking is the time you need to use a generator is under supply fault conditions and that could well include the open-PEN situation, so if any transfer switch could be isolating the supply PEN and line, leaving the installation on the earth rod and then the generator would also be safe under open-PEN failure of the supply.

I,ve been a supporter of this approach for a long time.This idea would (in my experience)..

..solve 100% of open PEN issues in new housing estates

..95% in rural houses

..very large numbers of urban houses.The remainder could have their metallic services rendered "harmless"by installing plastic inserts at the point they enter a home.

I should add that if I was doing this genny install in the UK ,I would feel less concerned.From reading this forum I understand that many of your TNC-S supplies are converted TNC underground supplies.I would consider those significantly safer than overhead supplies.
Secondly, I would imagine that the lead sheath ( or what remains of it after conversion to TNC-S.) would still provide a great earth rod.This should be very effective in dragging down the "touch voltage" occuring during any fault.

 

[davesparks]

I,ve been a supporter of this approach for a long time.This idea would (in my experience)..

..solve 100% of open PEN issues in new housing estates

..95% in rural houses

I too support this approach but it would not solve an open PEN, the open PEN fault would still occur.
What it would do is reduce the danger which arises as a result of the open PEN fault.

 

[LastManOnline]

I too support this approach but it would not solve an open PEN, the open PEN fault would still occur.
What it would do is reduce the danger which arises as a result of the open PEN fault.

Correct.I could have phrased that a little better.

 

[pc1966]

Its not really my area but I think most UK homes in built-up areas (i.e. underground cables) were TN-S and those are now TN-C-S (with the C-S transition at the cut-out for new builds, but potentially elsewhere in the network for older conversions). For rural I guess twin cable overheads would always be TT, but now you see the ABC (Aerial Bundle Cable) where an damage incident is likely to take out both constructors maybe those are going TN-C-S as well.

Something like this could do the generator switching you seem to want:

Here two 4-pole switches are arranged so you have either the mains or the generator, and with the "neutralising link" from the supply not connected under off-grid use. There is then a 2nd link (using the generator-side 4th pole) but never two at the one time, and with the 2nd earth rod at some reasonable distance from the supply earth rod you are always connected to a means of earthing.

If the supply switch's earth pole should fail or be fractionally slower to switch, and if the CU is all RCBO (or has an RCD incomer), you can still meet ADS as a TT arrangement no matter what.

When on-mains the generator chassis is isolated from the PEN circuit, and then earthed when in use.

There are no PEN conductors here bar the supply, all of the others may be linked, but they are not simultaneously current carrying and solely linked to the CPC network. The main gap here is there is no RCD "additional protection" on the generator feed so under UK regs it would have to be hard-wired and not on a socket (if no more than 32A).

Just for discussion as I doubt anyone makes such a configuration!

 

[LastManOnline]

Just for discussion as I doubt anyone makes such a configuration!

Think you have the nuts and bolts of a viable system there.Not allowable at this point in time to break the PEN conductor but it would,nt surprise me at all if that were to be reviewed in the not too distant future

 

[pc1966]

Think you have the nuts and bolts of a viable system there.

Thanks!

Not allowable at this point in time to break the PEN conductor but it would,nt surprise me at all if that were to be reviewed in the not too distant future

Ah, but it is not breaking the PEN conductor (which I agree is a very VERY bad thing to do). It breaks the N & E separately so at no point can a part-open contact allow the CPC to be fed from the live current via the installation.

I know there are regs in the UK about not switching the CPC but that is a fundamental requirement for any EV chargers and related open-PEN fault detection systems, however, I have not really looked in to the specifics of regulations around that.

 

[LastManOnline]

Thanks!

Ah, but it is not breaking the PEN conductor

my apologies.I was a bit hasty in looking over it.Should have known you would have paid great attenion to detail