New Circuit to 17th?

[Apache]

However in this case the earthing is not common as the outbuilding is TT'd, and there are no services - so there are no bonding issues that affect the new circuit. I suppose there is an arguement that if you are holding a water pipe made live by external influence whilst attacking the SWA with a metal handled machette then you might be at risk! Well it could happen to anyone......

Not if supplimentary bonding is adequate :^O

 

[steptoe]

Just supposing that its a TNCS system with 6mm bonds rather than 10mm. In an inspection this would come in as a code 4 - not to current regs. The inspection would not insist on upgrading. So installing a new circuit that will not be dependant on the bonding? Electrically the risk is next to nothing otherwise the safety council would insist on insufficient bonding as a code 2 - but it's not the current regs! I can see all points of view - but the safest bet could lose you the job on price!

good point, just supposing it is a TNCS system and you loose the neutral incomer to the house, you get a Neutral Line fault in the outhouse,

EVERYTHING in the house will go 230 cos you got NO MAIN BOND to take it to EARTH.

 

[davetheglitz]

good point, just supposing it is a TNCS system and you loose the neutral incomer to the house, you get a Neutral Line fault in the outhouse, EVERYTHING in the house will go 230 cos you got NO MAIN BOND to take it to EARTH.

Don't you just hate TNCS!

Bear with me on this one - I'm thinking on the hoof so I might drop a googly!

In the case you are putting forward the fuse would go at either the house CU or at the outhouse CU. The same situation could occur within the house as well.Hence the fault would be removed.

Hang on I get it! Not a fault, but anything taking current would leave your earth at 230v! This would apply to anything on the system that takes current.

However if the bonding was undersized to say the 15th the system would be protected, as virtually no current is being taken.

 

[professional]

Not the same thing, is it?The bonding affects the whole installation. The broken socket affects that circuit.

Even a MWC asks if the bonding is correct.

It is not acceptable to put an X in response, on anything other than a PIR.

n.b. If the LV fan was fed off the circuit the socket was on, and the "broken" (define?) socket affected your readings - then I`d answer "yes"

In what way would lack of bonding affect the additional circuit since it supplies a remote building on a TT system? - I am simply saying that the regs are not always logical, relying on the `do as we suggest` approach rather than a more measured, analytical methodology.

 

[SPECIAL LOCATION]

from post#10

So no part of an installation can be safe unless the entire installation is safe?

An LV fan in the bathroom is not safe because there is a broken socket in the dining room?

from post #24

In what way would lack of bonding affect the additional circuit since it supplies a remote building on a TT system? - I am simply saying that the regs are not always logical' date=' relying on the `do as we suggest` approach rather than a more measured, analytical methodology.[/quote']Morning Pro..

you seem to be missing one fundamental point...

the Protective equipotential bond (e.g. as per 411.3.1.2)

must be applied to each building where an installation serves more than one building.

As the bonding would generally be considered as part of the installation SUPPLY AT ORIGIN characteristics.. {earth type & bonding}

not an individual circuit characteristic..

So at the point where the feed to the external building joins the original building at that point it is within the equipotential zone of the supplying building!

thus logically you cannot say I will choose to apply bonding rules to some circuits leaving the main CU but NOT others from the same CU???

 

[professional]

My concern is that quoting the regs should not be seen as a substitute for logical reasoning. Too many people rely on the on-site guide etc. without any real understanding of the principles underpinning the design criteria.

I fully appreciate that the additional circuit will originate from within the ebz but as you would not be exporting the earth I cannot see the logic of automatically requiring installation/upgrading of the bonding which will be no discernible advantage to the work being carried out. I feel that alot of work that we do is more for the benefit of sparks who follow us than the customer directly - this is fine in a perfect world where we all work to the same standards, but when you are pricing against people who couldn`t really care less, will be signing for nothing (policing of Part P? err - what policing), you can only walk away from so many jobs before your business becomes unviable.

In no way do I condone unsafe work - but until we DO all price and install to the same standards (and under the same degree of effective regulation) the pressures will always be there.

 

[SPECIAL LOCATION]

My concern is that quoting the regs should not be seen as a substitute for logical reasoning. Too many people rely on the on-site guide etc. without any real understanding of the principles underpinning the design criteria.I fully appreciate that the additional circuit will originate from within the ebz but as you would not be exporting the earth I cannot see the logic of automatically requiring installation/upgrading of the bonding which will be no discernible advantage to the work being carried out........

I understand your point Prof'..

I was just highlighting the difference between two situations..

i.e. your earlier post LACK of bonding. -VS - current post UPGRADING of the bonding

(existing older SMALLER CSA bonding present as opposed to none at all).

The competent spark does have a responsibility to ensure earthing & bonding are adequate..

and to use the regs to back up their reasoning..

We need to be clear so that any yung/less competent persons reading these posts don't say...

oh I don't need to check bonding cuz I am working in an outbuilding!

IHMO.

NO bonding = need to do!!!!

Smaller size bonding = Note as a deviation advise customer and/or Recommend & quote as appropriate.

Which is logical reasoning and not just quoting regs..

and you need a reasonable understanding of the regs to have a safe approach to logical assessment of whats is Urgently needed and what you recommend the customer looks at having done at their earliest suitable convenience.

I think fundamentally we are saying the same thing here..

[install absent bonding / upgrading old bonding? :| ]

just on some of the posts a quick read could leave some with a wrong conclusion..

so hopefully we are all clear as mud now!!

unless I've just gone and dropped another big brown smelly lump in the cesspool of forum interweb world! :_|Blushing

 

[binky]

Just supposing that its a TNCS system with 6mm bonds rather than 10mm. In an inspection this would come in as a code 4 - not to current regs. The inspection would not insist on upgrading. So installing a new circuit that will not be dependant on the bonding? Electrically the risk is next to nothing otherwise the safety council would insist on insufficient bonding as a code 2 - but it's not the current regs! I can see all points of view - but the safest bet could lose you the job on price!

Better to lose the job??? You can justify undersize main earth bond by use of the adiabatic equation ie you will need to calculate cable size for that particular installation based on measurement of Ze etc. (never had a fail yet, which begs the question why are bonds so big?). Never tried to apply this to MEB, which has got me thinking for the rest of the day. But the overall emphasis in the regs is update installations as you proceed with work, hence MEB and Main Earth appear on certificates, and I would proceed down this tack.

You could always quote for earths upgrade as highly recomended additonal safety work. Kind of gives customer feeling that you are a safe installer and gives you the edge over competition (doesn't always work).

If the customer chooses not to have it done then notify it on cert - as much as I agree with KME and others above, there's also nothing in regs to say you can force customers to update ( how else can you do repairs to 14th edition installations), it's your judgement under these circumstances as to whether to proceed with job or not.

 

[steptoe]

Better to lose the job??? You can justify undersize main earth bond by use of the adiabatic equation ie you will need to calculate cable size for that particular installation based on measurement of Ze etc. (never had a fail yet, which begs the question why are bonds so big?). Never tried to apply this to MEB, which has got me thinking for the rest of the day. But the overall emphasis in the regs is update installations as you proceed with work, hence MEB and Main Earth appear on certificates, and I would proceed down this tack.You could always quote for earths upgrade as highly recomended additonal safety work. Kind of gives customer feeling that you are a safe installer and gives you the edge over competition (doesn't always work).

If the customer chooses not to have it done then notify it on cert - as much as I agree with KME and others above, there's also nothing in regs to say you can force customers to update ( how else can you do repairs to 14th edition installations), it's your judgement under these circumstances as to whether to proceed with job or not.

cos on a PME/TNCS you need main bonds/earth conductor big enough to not only carry your fault, but your neighbours as well.

multiple earthing, as the name suggests is a shared multiple spiked earthing system.

as for not worrying to much about earthing arrangements, how would that poster feel(sorry cant remember who? Blushing ) if the DNO didnt bother spiking the mid point of their transformer to earth?

 

[professional]

as for not worrying to much about earthing arrangements, how would that poster feel(sorry cant remember who? Blushing ) if the DNO didnt bother spiking the mid point of their transformer to earth?

I thought the point was that they had to so that we didn`t?

 

[steptoe]

I thought the point was that they had to so that we didn`t?

thats what PME is tho, us providing a good enough earth path for a multiple fault(multiple earth!) to find its way back to source fast enough so as to trip/knock out the overcurrent device in use, so its up to us to keep our end of the deal and provide adequate earthing within the premises to allow this to happen, otherwise the DNO have the option of withdrawing their provision for earth, how would you feel about TT every property you work at?

 

[professional]

It could well be safer for a start.

I`ve never liked the idea of a combined earth / neutral

 

[SPECIAL LOCATION]

I would like opinions on this one please! My understanding is that new circuits should be fully compliant with the latest edition of the regs.

If you were to supply a remote outbuilding via an MCB on an existing CU, via an isolator, in 2 core SWA to a TT'd outbuilding with a 30mA RCD board and no additional services, is it necessary to ensure that bonding is up to the latest regs at the CU? My gut and head are fighting over this one! Customer has had several quotes - none have mentioned anyting about bonding.

Hope you can help

Dave

Eh up Dave...

back to your initial point..

Here is the NICEIC guidance re-bonding, omitted or undersized / departures....

Departures from the requirements of BS 7671 in existing protective equipotential main and supplementary bonding

Where existing main or supplementary bonding is to be used to meet the altered circumstances arising from an addition or alteration to an installation, it is essential to correct any deficiencies in the protective bonding which would result in a degree of safety less than that afforded by compliance with BS 7671. Alternatively, new protective bonding must be provided.

Only where both of the following conditions are met may a decision be made that it is unnecessary to correct a departure from the requirements of BS 7671 in the existing protective bonding:

The designer responsible for the addition or alteration, having given special consideration to the departure, is of the opinion that the resulting degree of safety will not be less than would be obtained by compliance with BS 7671,

and

The departure is to be noted in the Electrical Installation Certificate, Domestic Electrical Installation Certificate or, where applicable, Minor Electrical Installation Works Certificate covering the addition or alteration. A note must be made both in the section of the certificate that deals with departures from BS 7671 in the work covered by the certificate (Regulation 120.1), and in the section that deals with comments on the existing installation (Regulation 633.2).

Where Protective Multiple Earthing (PME) conditions apply

 

[davetheglitz]

Wow! You guys are brill! SL - superb! Great info! Basically putting a spin on this it's cover your **** and show the way that you are thinking on the cert. Virtually anything goes if you can justify it!!! Cannot understand the NICEIC logic though. Surely main bonding is to cover the one in a milllion fault of external volage being introduced onto a metalic service. The logic that we judge existing bonding effectiveness by lack of burning smacks of not understanding what it's all about - but I suppose this is the advice from the experts!

 

[binky]

. The logic that we judge existing bonding effectiveness by lack of burning smacks of not understanding what it's all about - but I suppose this is the advice from the experts!

Anyone ever seen burn't bonds????? (other than plumbers handiwork:^ O)

 

[SPECIAL LOCATION]

Anyone ever seen burn't bonds????? (other than plumbers handiwork:^ O)

Applaud SmileyApplaud SmileyApplaud Smiley

Guiness Drink

 

[professional]

Anyone ever seen burn't bonds????? (other than plumbers handiwork:^ O)

Well said that man!Applaud Smiley

 

[norv]

Anyone ever seen burn't bonds????? (other than plumbers handiwork)

Fair play.

I got an NIC assessment coming up this month. Definatley got a few issues to discuss with the rep

Anyone got any questions they want me to ask. I'll give him a list

 

[steptoe]

guys, this all comes down to one issue,

do you want to comply with BS7671?

or do you simply want to ensure your work is safe?

if its the former,then you MUST do what the big red book says

if its the latter,,,,

then use your intellegengce and experience.

end off,

really dunno why people keep asking questions then when they get an answer they quote the book, if you have already read it and want to go by it then why ask?????