Main earth and bonding issues

[leep82]

So today i go to a job to remove 3 x dual sockets, 1 x light switch and 1 x light fitting from a bedroom that the customer is converting into a bathroom, so that the plasterer can get in and make a start.

As i will be returning to do the job i took a look at the mains and checked out the bonding to both incoming gas and water. It is a TT system and after a little bit investigating it became clear that there is no main bond to the incoming gas.

What i could see were two 10mm2 earth cables leaving the DB. One i traced and it appears to be the main water bond the other dissapears after being clipped along the top of a piece of skirting board where it meets the arcitrave of a door. I checked with the customer and had a thourough walk around the property hoping to find an inspection point for an en earth rod, but couldnt.

When i performed a Ze at the mains ( with the main switch off ) i got a reading of around 4ohms. I then disconnected the 10mm2 water bond and performed the test again getting a reading of around 20ohms.

For anyone who has read any of my recent posts i have recently gone into self employment, and whilst i have my inspection and testing certificate, my previous experience of testing has largely been on new installations/circuits. I feel that it is still very much a learning curve and so i suppose im looking for a little guidance even reassurance that what im doing is along the right lines.

I am aware of the need to install a main bond to the gas supply, but are the tests ive done today enough to suggest that there is a reliable earth, even if it is not visible. And when it comes to filling out my test sheet should i note this down?

Any advice mich appreciated

 

[Pete999]

My advice for what it's worth, you should have checked and tested for main bonding before starting work, what was the Zs at the sockets and lights?

 

[leep82]

My advice for what it's worth, you should have checked and tested for main bonding before starting work, what was the Zs at the sockets and lights?

Even though i have only removed items and not actually installed anything yet?

 

[Wilko]

Like you, I would like to see the means of earthing (rod). Seeing it you can confirm it's mechanical condition, its label etc. Without seeing it you can't confirm it meets 542.1.2.3 which will be part of your cert. So, I'd have another real good look

 

[Pete999]

Even though i have only removed items and not actually installed anything yet?

Right OK, but presumably you have submitted a price for the work, and now you have to explain to your customer that there may be extra costs to install an earth bond to the Gas intake.
Main earth and bonding issues - http://www.electriciansforums.co.uk/threads/main-earth-and-bonding-issues.119229/#post-1246120

 

[The Ghost]

Oh yes @Pete999 is right check out the installation you are working on before starting any work as installing later you will find the problems you missed and be crying. It is a bit strange your Ze changed when you disconnected the water bond. As the Ze is disconnected from the installation so no chance of parallel earths. You did disconnect the main earth in from MET yeah?

 

[leep82]

Right OK, but presumably you have submitted a price for the work, and now you have to explain to your customer that there may be extra costs to install an earth bond to the Gas intake.
Main earth and bonding issues - http://www.electriciansforums.co.uk/threads/main-earth-and-bonding-issues.119229/#post-1246120

I had already paid a visit to the property albeit late one evening, and with no test equipment in tow. Its for a friend and i did make them aware that the price may differ if the main earthing and bonding werent upto scratch

 

[westward10]

Is it a terrace because I have found them below the ground floor floorboards. You need to physically verify the water bond continuity to eliminate it as the source of earth.

 

[Des 56]

Even though i have only removed items and not actually installed anything yet?

The earthing and bonding will only be an issue when you come to installation,the safety reasons and the regulations can or should have been explained when pricing the new works

As far as determining what needs doing

I would have disconnected the two 10mms and identified the visible water bond
Do a loop impedance on the now disconnected other 10mm and noted the reading
Shoved a temporary stake(screwdriver) in the ground and measured the resistance between that stake and the 10mm with a trailing lead,if good continuity was found it could be assumed the 10mm is connected via a (usual Builder) buried electrode,explained the requirement for it to be visible and agreed for a new rod (using that existing cable)

If the customer does not want a new rod and the loop reading is adequate,note the deviation of the lack of visibility for inspection on the certification and that the customer declined improvement

 

[marc8]

Hello Leep82
ok as you have only removed stuff not that much of a problem as long as you have made them safe.
if TT system is 4ohms with everything connected then you are not going to get a reading below this at the sockets or the lights your better of with an r1+r2 & IR test.
but I would start with the following myself.
ZE test first with switch off across L/N then PFC.
get these results & then do the loop test on what you suspect to be the earth rod.
look at the incoming supply is it a concentric cable or a pair of cables.
explain to customer about the TT system & you strongly recommend to bond the water if Metal incoming or even plastic before I get my head bitten off, check readings first if plastic to see if it needs bonding.
gas bonding or oil if they have it.
explain these will need to be done before you can do any electrical work on the bathroom.
install 100ma trip s type on mains & new earth rod or alternatively if readings are good & you can bond water & gas install a 16mm tail from consumer unit into a MET block ring up board & ask for an earth upgrade to PME.
normally free of charge I have done this years ago for customer but check readings first mainly ZE.
if not then go with new rod bonding & 100ma trip before you start the bathroom.
also so you don't have to test the whole house if you can run a new circuit for bathroom lights & install on own RCD unit then do this & issue an electrical certificate for your works.
if you can't run new feed then check IR, r1+r2 of old circuit run to a RCD fused spur above door or other location outside bathroom & treat the bathroom lights, shaver & fan as a new install from the rcd unit outside the door & then issue a new certificate.

 

[Midwest]

Some good advice offered to OP, although I feel its a bit harsh to suggest you should verify earthing & bonding at quotation stage, I do free quotations not free electrical work I look to see if everything's in place, but I ain't spending time testing it, when they are just asking for a price.

That said, I'm always cautious with TT supplies, like to see something resembling an earth rod.

Edit: have some reference in your T&C's on the subject.

 

[leep82]

Hello Leep82
ok as you have only removed stuff not that much of a problem as long as you have made them safe.
if TT system is 4ohms with everything connected then you are not going to get a reading below this at the sockets or the lights your better of with an r1+r2 & IR test.
but I would start with the following myself.
ZE test first with switch off across L/N then PFC.
get these results & then do the loop test on what you suspect to be the earth rod.
look at the incoming supply is it a concentric cable or a pair of cables.
explain to customer about the TT system & you strongly recommend to bond the water if Metal incoming or even plastic before I get my head bitten off, check readings first if plastic to see if it needs bonding.
gas bonding or oil if they have it.
explain these will need to be done before you can do any electrical work on the bathroom.
install 100ma trip s type on mains & new earth rod or alternatively if readings are good & you can bond water & gas install a 16mm tail from consumer unit into a MET block ring up board & ask for an earth upgrade to PME.
normally free of charge I have done this years ago for customer but check readings first mainly ZE.
if not then go with new rod bonding & 100ma trip before you start the bathroom.
also so you don't have to test the whole house if you can run a new circuit for bathroom lights & install on own RCD unit then do this & issue an electrical certificate for your works.
if you can't run new feed then check IR, r1+r2 of old circuit run to a RCD fused spur above door or other location outside bathroom & treat the bathroom lights, shaver & fan as a new install from the rcd unit outside the door & then issue a new certificate.

Wow lot to take in but thanks. The current DB has a 30ma RCD already in place. I performed an RCD test on this today to ensure tripping times were met and all was ok.

The customer has plans in place to have an extension built this will mean the current DB, meter and cut out will require moving. He has already informed Western Power of this, and after speaking to myself asked if he can be upgraded to a PME system. This extra work may not go ahead for a few months so in the mean time i just want to ensure the work i do is up to standard

 

[Midwest]

OP are you with a scheme?

 

[leep82]

OP are you with a scheme?

Not yet but registered with LABC as a competant person

 

[marc8]

Wow lot to take in but thanks. The current DB has a 30ma RCD already in place. I performed an RCD test on this today to ensure tripping times were met and all was ok.

The customer has plans in place to have an extension built this will mean the current DB, meter and cut out will require moving. He has already informed Western Power of this, and after speaking to myself asked if he can be upgraded to a PME system. This extra work may not go ahead for a few months so in the mean time i just want to ensure the work i do is up to standard

the first bit I have sent you will take about 30mins to determine, I would not always listen to the client about short term stuff. the day you do the work is the day it needs to conform not at a later date. get the PME before you do works & the bonding.
just suppose they don't go ahead with extension or you fall out with them & they don't want you back.
you could end up doing that work for nothing when if they use someone else because you have undertaken electrical work & left unsafe. I have been in the game a while now & I have been fooled & heard a lot of stories of this nature.

 

[Midwest]

Not yet but registered with LABC as a competant person

Cool how does that work? Interested cos I'm paying 500 squids to Elecsa

 

[leep82]

Cool how does that work? Interested cos I'm paying 500 squids to Elecsa

Ive had to send off copies of my relevant certs, 17th edition and 2391 inspection and testing. Once theyre satisifed with these i go on there register. Problem is every time i do any work that is notifiable i have to fill in a building notice form and send it off to them along with a fee of £82. The fee is payable for every notifiable job i do so being in a scheme is probably more cost effective long term. I just didnt want to lose out on any potential work in the short time whilst im not registered with a scheme

 

[Midwest]

Ive had to send off copies of my relevant certs, 17th edition and 2391 inspection and testing. Once theyre satisifed with these i go on there register. Problem is every time i do any work that is notifiable i have to fill in a building notice form and send it off to them along with a fee of £82. The fee is payable for every notifiable job i do so being in a scheme is probably more cost effective long term. I just didnt want to lose out on any potential work in the short time whilst im not registered with a scheme

Not such thing then, as a free lunch. You might wanna try Stroma at £285 (I think), although their on-line software is pants (so I'm told)

 

[Midwest]

explain to customer about the TT system & you strongly recommend to bond the water if Metal incoming or even plastic before I get my head bitten off, check readings first if plastic to see if it needs bonding.
gas bonding or oil if they have it.
explain these will need to be done before you can do any electrical work on the bathroom.
install 100ma trip s type on mains & new earth rod or alternatively if readings are good & you can bond water & gas install a 16mm tail from consumer unit into a MET block ring up board & ask for an earth upgrade to PME.
normally free of charge I have done this years ago for customer but check readings first mainly ZE.
if not then go with new rod bonding & 100ma trip before you start the bathroom.
also so you don't have to test the whole house if you can run a new circuit for bathroom lights & install on own RCD unit then do this & issue an electrical certificate for your works.

Not wishing to dis some of your advice, but struggling a tad with some.

Metal services must be bonded. Plastic services do not need bonding, and wouldn't waste my time checking them. The metal pipe work that runs from the plastic services may need bonding (528.3).

Changing from TT to TN-C-S may have a cost implication to the client which may not be necessary (although I would), and I wonder why installing 100mA S Type in this situation, would be a consideration. And OP doesn't have to test the whole installation, if he is doing an alteration or addition (minor works).

I'm always learning, so I willing to stand corrected.

 

[westward10]

Ive had to send off copies of my relevant certs, 17th edition and 2391 inspection and testing. Once theyre satisifed with these i go on there register. Problem is every time i do any work that is notifiable i have to fill in a building notice form and send it off to them along with a fee of £82. The fee is payable for every notifiable job i do so being in a scheme is probably more cost effective long term. I just didnt want to lose out on any potential work in the short time whilst im not registered with a scheme

Sent my quals off to LABC got a letter back asking if I was any good at road sweeping

 

[marc8]

Not wishing to dis some of your advice, but struggling a tad with some.

Metal services must be bonded. Plastic services do not need bonding, and wouldn't waste my time checking them. The metal pipe work that runs from the plastic services may need bonding (528.3).

Changing from TT to TN-C-S may have a cost implication to the client which may not be necessary (although I would), and I wonder why installing 100mA S Type in this situation, would be a consideration. And OP doesn't have to test the whole installation, if he is doing an alteration or addition (minor works).

I'm always learning, so I willing to stand corrected.

might have read slightly wrong with plastic pipe & not mentioning the metal part after.

changing from TT to PME or TN-C-S has always been free for me & have done quite a few

the 100ma trip S type is normally used to protect cabling in the infrastructure more important in what was 16th edition as lights ect did not require RCD protection now most circuits are 30ma protected. but I would always do a TT system with 100ma trip & the reason for s is the time delay so the 30ma will trip first if you only use 100ma without S type they can go at the same time as the 30ma & take out whole board.
me now with metal clad board cables in there unprotected I would install the 100ma trip on a TT.

testing meaning the one circuit or more if pumped shower (running of sockets) & lights running of lighting, i would want to test the whole circuit before i put an RCD at the mains hence the mention of RCD spur above the door & protecting just the work i would be installing so i don't have to test the whole circuit.

 

[Midwest]

It might be just the way your wording your replies then.

I have never been involved with costing of conversions to PME, but I've read of different responses by DNO's with regarding to charges, something to consider before going ahead with it perhaps.

Agree with you re 100mA S Type on TT supplies and A3 CU's, the OSG gives some suggestions for all supplies (3.6.3.3). There are other considerations for TT, distribution circuits for example.

Still not clear what you mean in your last paragraph. Installing a local RCD, would still need the series of tests conducted for the whole circuit, not just the piece after the RCD.

 

[The Ghost]

Still would like to know why Ze changed when you disconnected water bonding.

 

[leep82]

Still would like to know why Ze changed when you disconnected water bonding.

Parrallel paths?

 

[The Ghost]

If you did not disconnect the main earth from the MET you would have the water pipe as parrallel earth causing a misleading Ze reading

 

[westward10]

Typical TT the water bond is probably providing the earth and the connection to the electrode is probably doing no more than earthing it.

 

[leep82]

If you did not disconnect the main earth from the MET you would have the water pipe as parrallel earth causing a misleading Ze reading

My original ze test was with main bonding and main earth both connected in the MET and a reading of around 4ohms obtained. I then removed the main bonding to the incoming water performed a ze test again and got a reading of 20ohms

 

[The Ghost]

water bond is probably providing the earth

Thats very naughty then

 

[The Ghost]

So that second reading is your Ze which is ok then. I think that might be a bit of a poser then bacause the water sounds like a better earth than the main earth so it would then act as earth in fault conditions....hmmmmm

 

[leep82]

So that second reading is your Ze which is ok then.

Yes

 

[Des 56]

So that second reading is your Ze which is ok then.
Yes

and a reading of around 4ohms obtainedMy original ze test was with main bonding and main earth both connected in the MET. I then removed the main bonding to the incoming water performed a ze test again and got a reading of 20ohms

Leep82,you keep stating that you measure at the met at a time with bonds connected then disconnected

Has a loop reading been taken off the assumed 10mm cable with it actually disconnected from the consumer unit?

It seems to my reading that a Ze has always included parallel paths on each occasion if that reading has been taken at the met,it seems no assurance of any kind of electrode connection has been carried out

 

[leep82]

Leep82,you keep stating that you measure at the met at a time with bonds connected then disconnected

Has a loop reading been taken off the assumed 10mm cable with it actually disconnected from the consumer unit?

It seems to my reading that a Ze has always included parallel paths on each occasion if that reading has been taken at the met,it seems no assurance of any kind of electrode connection has been carried out

No I havnt disconnected the assumed main earth from the MET to do a Ze only the known main bond to the water. I assumed with the main bond disconnected it would in essence be a true Ze reading, what other parrallel paths could there be? The c.p.c's for the connected circuits were also in the MET at time of test. Should i have actually disconnected the assumed main earth form the MET and done a Ze test that way?

 

[SparkyChick]

You should disconnect it to be absolutely sure there are no parallel paths. Could be supplementary bonding for example which could bring the water pipe into play through some convoluted path.

I'd also be inclined to double check that the other 10mm isn't actually connected to the gas pipe. I did a job the other day two 10mm bonds, one traced to water, the other to the gas (verified by continuity) but the clamp was nowhere to be found and the cable just disappeared off somewhere.

 

[The Ghost]

Should i have actually disconnected the assumed main earth form the MET

Well really this is what I was sneakily alluding to without wishing to cause concern. So you are measuring external E ohms hence mains off and Main E disconnected from MET so you can only be measuring Ze. But clearly if its one of them MET on the board outside the DB then you can see there is nothing connected to it, it is the same really.

 

[The Ghost]

cable just disappeared off somewhere

Well I hope you found it and put it where it belongs.

 

[leep82]

You should disconnect it to be absolutely sure there are no parallel paths. Could be supplementary bonding for example which could bring the water pipe into play through some convoluted path.

I'd also be inclined to double check that the other 10mm isn't actually connected to the gas pipe. I did a job the other day two 10mm bonds, one traced to water, the other to the gas (verified by continuity) but the clamp was nowhere to be found and the cable just disappeared off somewhere.

There is definately no bond to the gas. The gas supply is visible its entire length on the outside of the building from the meter at the front

You should disconnect it to be absolutely sure there are no parallel paths. Could be supplementary bonding for example which could bring the water pipe into play through some convoluted path.

I'd also be inclined to double check that the other 10mm isn't actually connected to the gas pipe. I did a job the other day two 10mm bonds, one traced to water, the other to the gas (verified by continuity) but the clamp was nowhere to be found and the cable just disappeared off somewhere.

There is definately no bond to the gas. The gas supply runs externally down the side of the house and is visable for its entire run. It enters the property at two points the boiler and the gas hob. I checked at both points and no bonding present. I also checked in the meter enclosure before anyone asks

 

[westward10]

So that second reading is your Ze which is ok then. I think that might be a bit of a poser then bacause the water sounds like a better earth than the main earth so it would then act as earth in fault conditions....hmmmmm

This is par for the course on TT systems with metal piped services bond the gas, assuming a metal service pipe the Ze will probably be even lower.

 

[The Ghost]

This is par for the course on TT systems

Ok, so very rarely come across TT and usually arrange PME when I do. Suppose it could be interesting having a shower then when there is a fault.

 

[davesparks]

Still would like to know why Ze changed when you disconnected water bonding.

Technically Ze didn't change, he just measured a Zs and a Ze. Ze can only be measured with all bonding disconnected.