Earthing system - as installed in a 1940s house

[olddog]

My background is in SCADA systems - I'm not a sparks - this is why I'm taking up space on your forum with such a basic question as this :

I have become involved with a rural house built in the late 1940s

Supply is two wire, overhead from a pole mounted transformer around 300M away
Internal wiring would appear to be mostly original !

The only service entering from below ground is water. There is some evidence of earth bonding to water pipes. The attic located water tanks are made of plastic.

At the fuse boad N and E are commoned ( is this a normal arrangement in domestic houses ? )

There is no evidence of an earth spike

In the medium term a total rewire would be in order

My concern is, in the short term, is this safe ?

What, for instance, if the supply neutral wire were to be damaged ?

What is your view ? & what ( if any ) modifications would you make ?
　
Olddog

 

[Mac]

Sounds like a rewire if it is all original.Overhead cables from the pole maybe a TT system and the spike is buried somewhere,but i did hear that the DNO's were changing all TT systems to TNCS.If as you said you have an earth coming off the neutral incomer then it may have already been done but you would have to do a Ze test on it.The incoming supply is the responsibility of the DNO.Maybe a new spike needed if you can't find the old one.Hope this is of some help,don't do a lot of domestic.Hi and welcome to the forum also

 

[Eggster71]

Earth into the neutral block is PME (t-n-cs). If this is the correct earthing you won't need an earth electrode. It would be as well to check with the electric supplier if PME is actually available in that location, it's not uncommon for people to do the conversion themselves.
A Ze test will not prove either way as the earth is connected to neutral already, the problem is a PME supply is Protective Multiple Earthing and as such the supplier should have a network of earths. If this is a TT supply that has been adapted a broken neutral conductor on the supply side will also mean your earth has vanished!!!
The required main bonding for PME is 10mm copper to all incoming services, within 600mm of either the meter/ stopcock or point of entry entry to the building.
The minimum size of main earth cable is 16mm copper, if the cable there is smaller I'd suggest fitting an earth marshalling block, terminating the original earth to it and running a new 16mm to the fuse box. You can also connect your main bonding to this.

If the board have done the PME connection there should be a warning notice somewhere near, most lkely on the incomer.

 

[Spudnik]

If there are 2 separate cables coming across from the pole then as far as im aware, the earth SHOULD NOT be connected to the incmoing neutral, but an earth electrode installed for earthing arrangements.

Normally when overhead TT is converted to TNCS, a new split con is run from the pole to the in commer and the earth is then taken from the neutral from the carrier and a label positioned accordingly.

 

[olddog]

Wow !

Three great replies in three hours - I didnt expect three replies in a day - Thank you all.

Not wanting to bloat my first post with detail - here is a bit more

This house is located in southern Ireland - DNOs changing TTs to DNCSs hasnt happened

Indeed judging by the dead spiders, its years since the cover was taken off the fuse box

(For old timers like myself the wiring is a trip down memory lane
The sockets are circular by Wylex ( you can stack a small plug out of a big - unfused - plug )
The cable into the main fuse has an outer thread braid)

Ground bonding to the water pipes is by uninsulated wire ( a few strands - nothing like 10 sq ) and 'bonded' with perforated copper strip.

A local sparks remarked : shure thats the ways a lot of houses are done, isnt it working

If I came across this sort of arrangement in my day job I would demand the customer do better

Is it safe ?

I cant believe it is ( please tell me I'm wrong )

I know the long term solution ( total rewire ) but what should be done short term ?

An earth rod ? and then divert all earths to it ? should the existing E - N link be left in place ? ( I would presume not )

　
Thanks again for the replies

Olddog

 

[Spudnik]

Without seeing any pics, its difficult to say.

Ultimately its your decision but from what you have described, it would being easy to install an earth rod, fit a 30mA RCD on the existing CU tails (and hope that it doesnt trip!!), and divert the cpc's to the rod.

You could also chuck in a 10mm bonding to the water (and gas?), as a temp measure.

However, it most certainly sounds like it needs a rewire.

 

[Eggster71]

What sort of insulation's on the wiring? If it's the old black rubber then I'd rewire as soon as possible!

 

[Risteard]

TN-C-S installations in the south of Ireland also have an earth electrode.

 

[robsparky1975]

suspect the whole installation is vir(vulcanised rubber),falls to bits when touched,not uncommon to still see it about,generally on the older property with the original owner who has lived there since 40's,fuse wire i expect,wooden fusebox,probably no earth electrode,periodic inspection,do a visual first,it may be that bad that testing would be a waste of time,lights probably dont have earths,metal fittings?,if so on lights,make safe or change for plastic.more details/pictures we could help you more,went to killarney in july so if your really stuck, digs,plenty of guinness and ill come and have a look, merry xmas and welcome to the forum.

 

[olddog]

TN-C-S installations in the south of Ireland also have an earth electrode.

I'm darned if I can find an earth rod nor anything that looks like a cable running to one. Do you know approx what era this would have come in as a standard ?

Maybe original work relied on bonding to water pipes ? ( shudder - before PVC tank and misc non copper pipes were retrofitted )

Robsparkey, not that far off with your description but some of the wiring is PVC T+E, fuse box is metal clad ASEA - has provision for 3 phase ! ), all switches and AFAIK light fittings are non metallic ( but without earthing ).

Jason, No gas available in area. So have put in a heat pump. THIS, of course, is what got me looking into what I'd got myself into. Have HP and cooker on a new CU but still earthed to neutral

Agree long term total rewire required but short term what to do ?

Olddog

 

[Sintra]

I'm darned if I can find an earth rod nor anything that looks like a cable running to one. Do you know approx what era this would have come in as a standard ?

Maybe original work relied on bonding to water pipes ? ( shudder - before PVC tank and misc non copper pipes were retrofitted )

Robsparkey, not that far off with your description but some of the wiring is PVC T+E, fuse box is metal clad ASEA - has provision for 3 phase ! ), all switches and AFAIK light fittings are non metallic ( but without earthing ).

Jason, No gas available in area. So have put in a heat pump. THIS, of course, is what got me looking into what I'd got myself into. Have HP and cooker on a new CU but still earthed to neutral

Agree long term total rewire required but short term what to do ?

Olddog

Yes an electrode is also required on a TNC-S system in Rep of Ireland as these systems are not made TNC-S by the ESB but by the installation electrician so it is not in effect PME. This is called neutralisation and protects if the neutral is lost. All systems in ROI must be neutralised and electrode installed.
Completly different Regs from UK.

 

[Risteard]

I see sintra has responded already.

 

[Spudnik]

Looks like we could be following yours on the next amendment.

 

[Risteard]

Looks like we could be following yours on the next amendment.

I live in the north in BS7671 land.

 

[Sintra]

I live in the north in BS7671 land.

Me too.