TT earth rod need to be visually verified?

[odigi]

Hi all,

just did my first PIR on a TT system and found an earthing conductor heading from the MET, under the floorboards and into the ground away from the ccu towards the house. Ze gave me 3.9 ohms.

Question is: do i need to visually verify connection to a rod (if there is one!)?

thanks

odigi

 

[IQ Electrical]

Is it going to a gas pipe or a central heating pipe under the floor?

You don't know and 3.9 Ohms is an extremely low reading for an earth electrode.

If I can't verify the means of earthing, let alone see if there's a secure connection with a BS 951 clamp, it's a code 2 on my report.

 

[odigi]

Thanks

The wooden floor is raised a foot above the ground level. The earth conductor disappears into the ground level. I put a code 2 also. Also, the upstairs flat is using the same conductor - didn't see a problem with this,but is there?

 

[IQ Electrical]

Thanks

The wooden floor is raised a foot above the ground level. The earth conductor disappears into the ground level. I put a code 2 also. Also, the upstairs flat is using the same conductor - didn't see a problem with this,but is there?

Is it a separate installation?

 

[odigi]

Yes it has its own distribution and cut out fuse

 

[Engineer54]

Yes it has its own distribution and cut out fuse

Then you have your answer odigi!!!

 

[odigi]

I see, should I advise moving the isolator, meter upstairs also? what if the upstairs refuse to get their own earth? should i connect as i found and note on PIR?

 

[Engineer54]

I see, should I advise moving the isolator, meter upstairs also? what if the upstairs refuse to get their own earth? should i connect as i found and note on PIR?

You asked if there was a problem with this arrangement, there clearly IS!! What you do to to correct the situation is totally down to you and your customer. It's no good getting upset, because you don't like the asnswer mate....

 

[odigi]

Wasn't aware that I said I didn't like the answer. I only continued to ask what could be put on PIR if anything at all.

 

[Engineer54]

Sorry, i misread your post then mate...

First things first then, have you checked all possible accessible places where connection is possible to extraneous pipework in this flat?? Is it not possible to undertake installing/driving in your own rods for this installation?? As it stands at the moment, your customer is getting a code 2, and maybe a code 1 for this unverified earthing/bonding source if left in it's present situation.

As for this shared connection with another flat, ...have you tried talking to these neighbours, explaining the situation?? Maybe by quoting a competitive price for rectifying the situation!! Think you need to talk to both parties together, before deciding on a course of action

 

[odigi]

Oh I think I see how you read it now! I wasn't being sarci those where genuine questions :!

thanks for your advice - I was hoping to drive one rod but as you suggest I could quote for two. But the question is still: if they say no, should reconnect them to the downstairs or leave them disconnected? I would see this as leaving an installation worse than i found it, albeit not the installation I started on!

 

[vitoboy]

yes i agree ..advise for a new rod in a good place for your customer....advise the other flat on the situation if you can...quote them...of course..for a new rod also...but other wise its up to the customer what they do...
i find if its an option then the other party will just ignore it..
had one with no earth at all...still didnt want it sorted.that was few years ago and still like it now....we can only try

 

[Engineer54]

Though you would in effect be disconnecting a connection, albeit of unknown origin, you wouldn't i hope disconnect this cable from the neighbours installation without informing them before hand, there-by giving them prior notice, to either make there own arrangements, or to employ yourself to make the necessary rectifications.

This is a PIR job your doing at the moment i understand, so in all honesty you could just record your findings and leave it at that, with recommendations. The problem comes if your customer wants you to rectify their installation. It's then that you would have to disconnect that unknown earthing/bonding source from the upstairs flat installation....

 

[vitoboy]

but 54
why will he have to disconnect the other flat?
just put in new for your customer and leave the other flat as is.

 

[Engineer54]

Because no-one knows if this is a bonding connection or a rod connection, ...at 4ohms it is more likely to be a bonding connection. Now you can't leave a main bonding connection from one properties installation that's also a part of another totally independent installation.

 

[odigi]

never occurred to me to leave the earthing for upstairs and advise a new rod for downstairs - makes sense now! nice cup of tea with both parties if they decide to rectify. cheers for help with this

 

[odigi]

As long as I don't disconnect it when the time comes. And inform them what I 'assume' is there i.e. bonding

 

[Engineer54]

Bit of wishful thinking there odigi, that earthing cable that disappears under the floor is much more likely to be connected to a gas or water pipe in the downstairs flat than any earth rod...

 

[Engineer54]

Can't have a bonding connection for one property, that's located in another property, .....and it's Still inaccessible!!!

 

[odigi]

true, but as said earlier they have the last say

 

[domestic spark]

had a similar problem last week, TT system 6mm green, going off somewhere, looked for earth electrode nothing, front/back, under slabs plant pots, in bushes, couldnt find it anywhere,
ZE of 0.30ohms pefc of 609a

hmmm, taking main earth from pipework. had no way of lifting boards upstairs, but 6mm green went up through the ceiling and along the house. MUST have gone to central heating pipe(s)

 

[domestic spark]

havent really dealt with TT though. always TN-CS OR TN-S

 

[Golden_Boy]

When I bought this house it was 2 flats, each with its own concentric overhead feed ( from diffrent supply poles ), cutout ,meter and fusebox. BUT a shared earth rod. Its all one house now but there are still flats up and down my road with exactly the same setup.

 

[Engineer54]

When I bought this house it was 2 flats, each with its own concentric overhead feed ( from diffrent supply poles ), cutout ,meter and fusebox. BUT a shared earth rod. Its all one house now but there are still flats up and down my road with exactly the same setup.

What are you saying here, ....are you saying that this arrangement is OK then??

 

[Golden_Boy]

What are you saying here, ....are you saying that this arrangement is OK then??

Not at all. Just that it was how things where here when I bought the property, and was like that for ages before I made a big house out of the 2 flats, then of course I only have one of everything. Still the same rod though ( Ze 14.7 Ohms )

 

[Engineer54]

That's a good value Ra you have there for a single rod. What sort of soil type do you have there a clay type soil or a sort of marshy land soil?? I reckon if you supplement your existing rod with another you stand a very good chance of a single figure value...

 

[domestic spark]

Engineer, the good book says earth rod ok no greater ZE of 200ohms. However i would be happy with a rod reading that high, and i want what's safest for customer, what max value would you expect or accept. You seem extremely clued up on TT systems. Thanks I'n advance

 

[IQ Electrical]

Engineer, the good book says earth rod ok no greater ZE of 200ohms. However i would be happy with a rod reading that high, and i want what's safest for customer, what max value would you expect or accept. You seem extremely clued up on TT systems. Thanks I'n advance

200 Ohms is an excellent reading-remember that your actual maximum is 1667 Ohms and the 200 Ohms figure is to allow a massive margin for soil drying and freezing etc.

A deeply driven earth electrode with an Ra of 400 Ohms will be far more stable and effective than a shallow driven electrode with an Ra of 100 Ohms because the freezing/drying effects do not penetrate the ground past the first 300mm or so.

You have to understand the purpose of the electrode when looking at Ra values, there is absolutely no point in trying to achieve TN system impedance/resistance readings on a TT system and even if you did get down that low, can you imagine trying to explain your theory of stability?

 

[vitoboy]

wire it
my nic inspector told me just this week that he would accept a tt system with a 450 ohm plus ze.
that is being in a problem area and having taken steps to try and improve ..ie adding another rod.
i can say i was amazed by this...but happy....loads of my jobs have 300-500 ohm earth stakes

 

[Engineer54]

The reasoning behind my philosophy (which i totally stand behind) on having as low a Ra value as possible, is that the lower you can get that value, the better chance you have of forcing a protective device to trip, even if it is outside the required disconnection times. Your not going to achieve that with a single 1.2 3/8'' rod bunged in the ground i might add!! lol!!

So yes, an Ra of 200 ohm is very good (tongue in cheek ...lol!!) , but ONLY while an RCD device is functional!!! Totally useless without that RCD protection. And we should all know, that RCDs aren't the most reliable bits of kit at the present time, you only have to look at the threads in these forums, ...almost every day there is at least one thread or another complaining about failing RCD devices... I'd hate to totally rely on a RCD for my families protection, well i just wouldn't, full stop!!

Another of my hang-ups with TT systems, is the lack of understanding of what makes a good, or stable TT system. Most TT systems these days rely on a single 1.2m 3/8'' rod, bunged in the ground where ever it's easiest to drive it, and normally right by the side of an outside wall where all the old building rubble is normally found!!!

There are many ways of getting a TT system in a ''stable'' state and keeping it that way, not always practicable in domestic installations i might add!!! Which is why they should be considered as a last choice of earthing an installation, it is always better to have a TT systems supply PME'd if it is available on your DNO's local network....

IQ, ...I personally know of domestic TT systems in parts of Essex that by careful placing, 2 x 3m 3/4'' rods (extended) achieve an Ra equal or bettering a standard TN-S earthing arrangement, and that is stable year round without any soil conditioning, i jest not!! I'm sure that there are other areas in the UK, where similar results can be attained..