A little assistance please Re: TT System, 0.21 ohms on Earth Rod.

[1shortcircuit]

Good afternoon everyone, I'm just looking for a little friendly advice if I may.

I have been to a property to price up installing an Extractor fan (via lighting circuit in Bathroom) and a FCU for a combi boiler.

Before work was due to commence I noticed that the Main Earth was completely uninsulated, exposed to touch and running across the top of a carpet before disappearing under the floor. I advised the client that this would need to be replaced as under fault conditions this could create the risk of electric shock or even a fire.

Now on further investigation I got a reading of 0.21 ohms, I was very surprised. However, I cannot locate the earth rod. Once the cable goes through the boards it disappears through the wall (beneath the lounge area) which has laminate flooring.

Now I'm going to contact Elecsa about this issue but as I do not encounter many TT Systems I would like to hear other peoples opinions.

There is NO RCD protection at all, whether it be for the circuits OR upfront.

I am of the opinion that regardless of what I do I will not better the reading by positioning a new accessible rod outside of the building.

Who else would advise that the circuits to be worked on are protected by a 30mA device and an upfront time delayed RCD? How would you protect the uninsulated main earth? trunking? Be stuffed if I'm going to try and sleeve it :lol Trunking would eliminate the touch factor but risk of fire???

Client is not wanting to spend anymore than is necessary but is about to rent the property out. What should I be advising as a MINIMUM that is not likely to be contradicted by another spark? (lol)


What are the requirements for a property being rented out with regards to the electrical installation?

Any advice will be VERY VERY much appreciated, like I said I will be contacting Elecsa for their view too.

Kind Regards.

1SC

 

[Paul.M]

Are you sure it goes to a rod mate? May be just connected to gas and water incomers!

 

[telectrix]

could even be TN=S.

 

[mickys86]

Could be a rod..... Where's E54.......

 

[1shortcircuit]

Are you sure it goes to a rod mate? May be just connected to gas and water incomers!

I did wonder this to start with but Gas and Water enter the property in the opposite direction. Not to say that it doesn't somewhere else however but without locating the termination it will remain unknown.

Thanks Tel, There appears to be no connection to the sheath for it to be TN=S :thumbsup

- - - Updated - - -

Could be a rod..... Where's E54.......

Behave

 

[Engineer54]

It's unlikely (but certainly not unheard of) that a typical UK TT system alone will give you a Ze/Ra of 0.21 ohms. Far more likely you have extremely good parallel earth paths by way of the water and or gas pipework bonding.... Which in essence is the installations Zs value...

 

[1shortcircuit]

It's unlikely (but certainly not unheard of) that a typical UK TT system alone will give you a Ze/Ra of 0.21 ohms. Far more likely you have extremely good parallel earth paths by way of the water and or gas pipework bonding.... Which in essence is the installations Zs value...

So would it be acceptable to just ensure that I protect my work by means of 30mA protection and leave the rest of it well alone? Bearing in mind there is no RCD protection on the system at all at the moment?

Thanks to your replies everyone:thumbsup

 

[Paul.M]

If the main earth conductor is not sheathed, it my be touching pipe work under the floor or touching structural steel works?

 

[richy3333]

If the customer is going to rent the property out they will have additional obligations as a landlord - well there certainly are in Scotland. That being the case they should? make the electrical installation as as safe as possible?

In this situation and on the basis that it is a TT system I think I'd be suggesting 30mA RCD protection to circuits and a 100mA S RCD upfront etc.

If they weren't renting the house out then I'd be ensuring my own work was RCD protected etc?

 

[Engineer54]

I'd first check if you have a TT system in place. Have you identified the bonding cable(s)?? So is this bare cable the rod cable or bonding cable?? If no TT system, then you'll need to advise your client.

Whether this bare cable is the Rod cable or a bonding cable it will need sorting. You could cut it at a suitable position and crimp a length of insulated cable, that you can run clipped around the walls of the lounge etc.
Always better to have RCD protection on a TT system than not and it's been a Reg requirement for many years now. It's both your calls how far you and your client are willing to go to achieve a safe installation.

As they say you can lead a horse to water, ...But... lol!!!

 

[Nik_lamb]

You could contact the supplier to confirm it is a TT system. I've never contacted them myself so don't know how long you would be waiting....

 

[1shortcircuit]

If the customer is going to rent the property out they will have additional obligations as a landlord - well there certainly are in Scotland. That being the case they should? make the electrical installation as as safe as possible?

In this situation and on the basis that it is a TT system I think I'd be suggesting 30mA RCD protection to circuits and a 100mA S RCD upfront etc.

If they weren't renting the house out then I'd be ensuring my own work was RCD protected etc?

Whilst I believe that there should be a minimum standard for rented properties I don't believe there are such obligations in England but I was hoping that someone may confirm this.

I'd first check if you have a TT system in place. Have you identified the bonding cable(s)?? So is this bare cable the rod cable or bonding cable?? If no TT system, then you'll need to advise your client.

Whether this bare cable is the Rod cable or a bonding cable it will need sorting. You could cut it at a suitable position and crimp a length of insulated cable, that you can run clipped around the walls of the lounge etc.
Always better to have RCD protection on a TT system than not and it's been a Reg requirement for many years now. It's both your calls how far you and your client are willing to go to achieve a safe installation.

As they say you can lead a horse to water, ...But... lol!!!

Thanks E54, I have identified a 10mm bond to the water in the kitchen and a piddly little shoe lace bond to the gas from the water pipe which I also advised be replaced especially as the Consumer Unit is not very far from the Gas meter anyway.

The unsheathed cable is definitely the main earth but where is runs is unknown unless the laminate floor gets lifted and there is definitely no rod visible anywhere at the front, side or rear of the property.

If I'm honest, I am quite happy to walk away from this job if the client doesn't want to do the REQUIRED work but I am just hoping to satisfy myself that what I am advising IS what is essentially necessary. 30mA protection on every circuit has already been rejected and it's been stated clearly that only the essential work will be be accepted.

My first advice was, Replace uninsulated main earth - Then discovered that the rod (?) was not accessible, bonding to gas upgraded and taken to consumer unit main earth, circuits to be worked on protected with 30mA device/s.

Once I have established exactly what is acceptable I am happy to advise client accordingly and if they are not prepared to accept this then I will walk. At least I can sleep at night knowing that my advice was sound and it was their decision not to go ahead with what is required.

Really appreciate the input:thumbsup

 

[1shortcircuit]

You could contact the supplier to confirm it is a TT system. I've never contacted them myself so don't know how long you would be waiting....

I've only done this once and the reply was "The only way we can do this is to send someone to the property and have a look". Never tried it since:thumbsup

 

[Moses]

I would leave the original "Main Earth" cable in and add a new ROD in a position where it can be inspected.

Then RCD the installation as above.

 

[Guitarist]

Have you isolated the supply and carried out an Ra reading at the main earth with the bonding disconnected? I'm not sure if you are saying that your 0.21 ohms is "as is" or from the main earth only.
At least that way you could be sure about where your earthing is coming from.

 

[Richard Burns]

If you have a Ze of 0.21 then you would not need to provide the upfront time delay RCD as you would meet disconnection times with the OCPDs.
Obviously you would need the 30mA RCD protection for your circuits (assuming spur is subsurface cable).
Regs wise the earth rod connection should be accessible, so i would try a bit more searching to find it, might be worth asking if an extension has been built and covered the rod!!. Have a wander in the garden in line with where the cable enters the lounge.
Insulating the main earth or replacing (part of) the cable would be good.

I think you have covered what is required in post 12 "

My first advice was, Replace uninsulated main earth - Then discovered that the rod (?) was not accessible, bonding to gas upgraded and taken to consumer unit main earth, circuits to be worked on protected with 30mA device/s."

For the landlords part I believe if it meets BS7671 it will meet the landlords requirement. There is this document from ESC about landlords requirements that may be useful.​

 

[Marvo]

If it's a TT system and you can't find the rod then you don't know where the 0.21ohm reading is coming from and you don't know if it's a reliable setup. I would definitely install a new rod and leave the existing earth wire connected as well after sleeving it.

That .21 reading isa bit too good to be true so I would be suspicious. I might consider putting 40A through it with a loop impedance tester and see if it's got any integrity as long as it's not connected to a gas pipe

 

[trev]

If there's another room which is not covered by laminate flooring could you not lift a few boards there and get into the crawl space underneath as there is often a way through the brickwork supporting floors which might give you access to the rod. At the very least you might be able to trace the cable a bit more.
Well when I say could YOU, i meant send your apprentice

 

[Spazz]

That really dont sound like a TT system with 0.21 ohms.
Call the DNO up and tell them the situation - it might be a cowboy TN-C-S or TN-C.
They should have a record of what is installed, if not as said above could be using a water pipe - way to tell is do a Ze test using a socket and a water pipe as the earth - if you get a lower reading than 0.21ohms then its using the water pipe - try and get as close to the origin of the water pipe as possible to get the best reading and away from the bonding clamp.

Good Luck

 

[trev]

That really dont sound like a TT system with 0.21 ohms.
Call the DNO up and tell them the situation - it might be a cowboy TN-C-S or TN-C.
They should have a record of what is installed, if not as said above could be using a water pipe - way to tell is do a Ze test using a socket and a water pipe as the earth - if you get a lower reading than 0.21ohms then its using the water pipe - try and get as close to the origin of the water pipe as possible to get the best reading and away from the bonding clamp.

Good Luck

TN-C is severely restricted in this country mate, I've never seen one in 33 years in the game.
If his measured Ze is 0.21 how is he likely to get a reading lower than this and if by some chance he did, how would that prove the installation is using the water pipe as it's method of earthing?