Just For General Discussion.. Tt High(Ish) Zs, Gas Man/electrician & The Invisible Rod....?

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SPECIAL LOCATION

SPECIAL LOCATION

Trailer Boy - Electrician.
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I just thought I'd chuck this into the pot for a bit of general discussion....

Job last week...

customer rang to say the gas man servicing the boiler reported a very high earth reading...!

Could I come and check it out please???

So I visit the next day,  Heres what I found...

1/ Gas mans report says High resistance earth (greater than 200ohms)

2/ Supply overhead TT. Whole installation protected by front end 30ma RCD.

CU is in cupboard in kitchen.

(RCD all tested working OK)

3/ A.N. Other electrician has done some minor kitchen alterations in 2009..

Cable runs from CU to kitchen will be negligible <10m.

Zs on his(/her) minor works certs is 442ohms..

No other comments or observations on cert

4/ 2 x nice newish bonding wires to Gas & Water probably installed during 2009 kitchen work. 

5/ I De-energise whole installation, Disconnect 2x bonding wires off..

Do Zdb at incoming tails & CU earth bar..

get 390ohms earth loop impedance at CU.

6/ Continuity test between each bonding wire open circuit and electrical earth is <5ohms.

7/ Absolutely NO visible signs of any earth rod anywhere..

No earth wires labeled up to indicate which is the main earth..

a couple of 6mm earth wires are terminated in CU..

but no idea where they go or what they do....

8/ The property is "old" customer thinks 100ish years...

(so maybe original earth was via water pipe?????)

So........

Points for open thoughts and opinions....

a) TT with working 30ma RCD Max permissible Ra 1667ohms...

Should the gas man be concerned with greater than 200ohms...?????

b) With no easily identifiable means of earthing (hidden rod or maybe water pipe)..

Should the 2009 electrician have verified this prior to doing his work???

Reg 131.8 red book Bs7671:2008..!!

c) 2009 test reading was <27% of max permissible.. 

2013 reading <24% of max permissible..

4 year period no more than 3% variation of max permissable value.. 

stable or unstable earth re greater than 200 ohms?????

d) Have either the Gas Man or the 2009 Electrician being negligent / over zealous in their duty of care and competent work ??

Discuss???????????????

Guinness

 
Well I can add to this thread.........

BG are changing the old cast gas main & feeders to all properties along our road (including mine), all properties are wired as over head TT & I know a fair few havent had the earthing sorted over the years so are relying on the gas (or water in a few cases) as the means of earthing, gas meters are beside the leccy meters under the stairs.

I'm waiting for someone from BG to notify us that the earthing arrangements might need looking at & I suspect it will not come until they send in the BG bloke to reset the boilers/heating.

Must drop some more cards round the road .................... special offer on earth rod's this month :innocent

 
My view 2009 Electrician should have verified earth and earth rod as part of his 2009 work.

BG, enough said, I once had BT doing the same on a large house that wanted a small phone system installed by BT, they requested a power point which we installed, guy turns up and refuses to connect system to our power point saying Zs too high, it was a TT supply.

Had to explain in detail to his manager the supply type, who replied our instruction is that it must be below 1.15 ohms and it's not.

I gave up and told him to call the NIC, they returned the next day and plugged the equipment in.

 
 
I think personally the 2009 sparks should have tried to get a better earth. It depends on ground but generally you should be able to get it a lot lower than that on a rod. I would be very worried as to why the main bonds are not bringing readings down 100 year old properties generally have metal services are they not extraneous. If I relied on my water pipe copper I would get around 3 ohms. Ze. 

 
Could you not have disconnected the other earths and see which one "was" the actual earthing conductor?

I'll have to think on this one, a little.

I believe that the value "should" be lower, but, at the two points in time it is comparable, thus stable.

Do you think the ground conditions would be similar at the time of measurement, i.e. similar time of year, or season?

 
My Initially thoughts before I got to site were....

It is just a case of Gas man having a paddy because he doesn't understand TT earths....

and all he knows is its greater than 200..   Probably by a plug-in tester with a pass/fail LED!

 

But after seeing the 2009 sparky's MWC ..

he obviously knows Earth is around 400ohm....

BUT....

makes NO comments or observations about it...

Even though the model MWC in the regs has a box for Earthing arrangments...

AND asks for comments about the adequacy of earthing and bonding arrangements..!

If I had have been doing the previous 2009 work...

my initial step would have been to locate the earth rod...

Check for any high res joint or simialr....

as The supply is blatantly overhead two wire TT..

and the installation SHOULD have a rod somewhere!!

There may be a rod buried outside somewhere.. 

or internally under a floor...   Dunno!!!

But..

on general consideration..

I think the 2009 spark has shown MORE incompetence than the 2013 Gas Man!

I just wonder if the 2009 spark was a "kitchen fitter" spark..

as the work done was just sockets & lights in the kitchen!

My assessment of the current situation is:-

There is NO immediate danger..

As 30ma RCD is fully working and 400ohm+/-20ohm has been stable for at least 4 years... 

BUT without an identifiable earth rod there is a potential danger as we don't no how the installation IS earthed..

I have advised customer to get an earth rod installed ASAP and provided a written quote for the work..

If I get asked to install a rod...

I will tell you what difference it makes when installed!!!

Both the Gas Man & 2009 Sparks have shown a level of incompetence..

BUT.. IMHO the 2009 Spark should have known better...and looked  into the earth arrangments..

In which case the Gas Man would never have found an earth >200ohms!!

Guinness

:popcorn

 
pot and kettle comes to mind 

so you have left the installation the same way as the 2009 sparky 

 
Adrian said:
pot and kettle comes to mind 

so you have left the installation the same way as the 2009 sparky 
Click to expand...
Lack of understanding of the differences between...

"Inspection work" and

"Alterations work" and

"Contractual obligations" and

"Guidance for good practice in wiring regulations"

and how they all balance together comes to mind...

to explain...

As with any form of inspection and testing;  be it a full PIR or just a small part of an installation..

Inspection is purely 'an inspection of the integrity of some part of an installation with a report given on its condition to the client'.

Providing there are NO immediate dangers then no essential improvement or disconnection work is required...

However when doing any additions or alterations to an installation (as per 2009 spark)..

To comply with good practice in BS7671 then there is a duty to verify the condition of the supply and its earthing and bonding.... 

BEFORE commencing any alteration work!

I was asked to inspect the earth condition following the gas mans concerns..

1 hours labour was agreed with the customer for this purpose..

The inspection was done and paid for and my observations given verbally and in writing....

For any remedial work needed the customer may wish to get various prices for the job from other contractors and select whoever they choose to do the work..... 

They are under NO obligation to pay me my rates just because I have said I think the best solution is to fit a new rod! 

I was only requested to inspect & test the earth... NOT carry out any alterations.

This is the subtle difference between...

Inspections/Alterations/Agreed contract of work/BS7671 good practice.

.

 
Sorry Special 

My mistake I answered this post from memory over the day I should of reread it in full  as you clearly stated you had advised the customer

 
Adrian said:
Sorry Special 

My mistake I answered this post from memory over the day I should of reread it in full  as you clearly stated you had advised the customer
Click to expand...
:Salute

Guinness

:Applaud

No problem sir!

Always easy to miss-read..

or forget to read parts of a thread on forums!

:)

 
Just a quick update re this thread..

I had a phone message today asking me to do the work installing a new earth rod...

(I guess end of month... customers salary now in the bank!!!)

hopefully sometime during the next two weeks should be able to slot it in..

then I will post back what difference a new earth rod makes to the installation!!! 

Guinness

 
The 2009 spark should of verified the earthing arrangement and it's condition upon obtaining his reading and at the very least had a go at finding the rod and checking for a high res joint then notify the customer of the issue and quote accordingly to rectify the issue, end of the day up until now he was the last "competent" person to work on this install so it's his duty to leave it in a safe and serviceable condition and as he didn't verify the earthing arrangement or locate the phantom rod he hasn't don't that so he's an incompetent clown that needs beaten with a rather large stick

As for the gas man, We'll done to him for knowing that a TT system should ideally be under 200ohms but if he's taking it upon himself to take earth readings and become the worlds leading authority on 7671 then he should of set about doing what the customer called you in to do instead of treating it like the end of the world, a little knowledge is just as bad as no knowledge but in this story he's not as incompetent as mr 2009 spark

Comparing your readings whatever is earthing the installation seems to be stable even if it is on the high side and the RCD is at the front of the installation and in good working order so like you've said although it's an issue there's no immediate danger there but as the location and identity of the rod can't be confirmed there's potential for danger there which you've highlighted in the requested report and the customer is taking action to rectify this and do something that should of been done 4 years ago

So in conclusion the spark from 2009 gets the prize for total incompetence as all of this should of been done then, as said previous in the thread I wouldn't be surprised if he was a kitchen fitter with a part pee course under his belt

As for the gas man he needs to wind his neck in and stop the scare tactics to try and secure work for BG, when were BG gas men appointed as the national electricity police?

 
Ok...

Just a quick recap...

Beginning of November customer had rung to say the gas man servicing the boiler reported a very high earth reading could I check it out.  (Gas mans report says High resistance earth greater than 200ohms)

Supply overhead TT. Whole installation protected by front end 30ma RCD.

A.N. Other electrician did minor kitchen alterations in 2009..

Zs on minor works certs is 442ohms..  No other comments or observations on cert

De-energise installation, Disconnect bonding wires Zdb at incoming tails & CU earth bar, 

get 390ohms earth loop impedance at CU.

Absolutely NO visible signs of any earth rod anywhere.. No earth wires labeled up to indicate which is the main earth..  The property is "old" customer thinks 100ish years... so maybe original earth was via water pipe, but customer did say water board had replaced some pipes with plastic in the not do distance past?

So I had advised customer its best to get a earth rod fitted, left a quote for the work...

So they agree price and I popped back the other day..

They now have this outside near the back door with approx 5 or 6m of 16mm from CU to standard 1m Rod. 

NEW ROD.jpg

(p.s. it does have the lid on.. not left open!! :slap   )

So you are ALL now reading with excitement and anticipation to see what the measurements are now....???

shall I tell????

:innocent

OK then....

Before connecting the new rod up I did another Loop impedance at the CU..

All bonding still in place... 

477ohms  ..  (gone up a bit!)

So Earth loop down the new new rod on its own isolated from the installation

86ohms...

All looks a lot more healthy to me..

With rod connected back onto installation all bonding in place Zs at a local socket in kitchen 69ohms..

So hopefully when the gas man comes back to do his boiler service his little plug-in tester wont show greater then 200ohms fail!!! 

My conclusions:-

1/ The installation has not had a proper means of earthing for years...

(originally probably via water pipe pre 1966)

2/ The gas man was actually correct with his quick plug-in tester and advising customer to have earth looked at.

3/ The previous electrician during kitchen alterations, should have investigated further and installed a proper means of earthing.  OR at least put some observations or comments on his cert?

4/ The previous certificate customer showed me was a Red NICEIC approved contractors cert... 

possibly the bloke doing the kitchen work was an employee just told to get in do the job and get out and on to the next job.. 

But even if he didn't comment the QS should have noted the high Zs and asked a few questions.?

Not sure if this scenario is a result of electrical incompetence or just the "cut-costs-back-to-the-minimum" culture of, with a do the job on a shoestring budget with no time or money to allow for other probable investigations that are quite common and likely on a lot of installations.

Or a bit of both?
 
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