Bonding ..again !

[Evans Electric]

Just reading in the   NICEIC Connections magazine    Q &A s   

Summed up , no need to bond pipework  that enters the building   insulated  then changes to  copper .  Thats what they say .

To old Pharts like me  ...THAT  WAS ONE OF  THE REASONS  WE BONDED IT ....    to allow the mains to be PME   ALL metallics  had to be bonded  .

With this NOT bonding it  I imagine a  faulty cable  under the floor,   exposed live  touching the pipework ,  the pipework is stand alone  without Earth  potential so becomes live .

MCB does not operate because its not a short ....RCD does not operate ..UNTIL ...a person makes a  circuit between live & earth .    

That not good surely ?     RCDs are NOT tested  at the recomended times     

 

[Sidney]

The caveat of testing to see if extraneous seems to be missing.

The pipework would normally be directly or indirectly connected at the boiler manifold and in turn the CPC of the boiler supply circuit ergo it wouldn't need bonding as connection could be confirmed by testing.

However is that 1.5mm CPC suitable for use as a bonding conductor?

 

[ProDave]

Lets go back to the old practice of a little earth clip on the bottom of each radiator and an earth wire to each radiator.

And who was it had to bond a metal door stop screwed to the ground once?

And an earth on the metal tag provided on a steel or cast iron bath, and stainless steel kitchen sink.

 

[Sidewinder]

...

With this NOT bonding it  I imagine a  faulty cable  under the floor,   exposed live  touching the pipework ,  the pipework is stand alone  without Earth  potential so becomes live .

MCB does not operate because its not a short ....RCD does not operate ..UNTIL ...a person makes a  circuit between live & earth .    

...

This scenario requires earthing, not bonding.

Cables are supposed to be adequately separated from mechanical services

Conductors need adequate mechanical protection.

How did this cable become damaged in any case, and get into contact with the pipework?

 

[Evans Electric]

How did this cable become damaged in any case, and get into contact with the pipework?

I've seen it quite a few times ,  plumber shoves his pipe under the floor ...damages a cable ..  or rodent chews the PVC off  .... bare conductor is touching the free standing pipe   .   Or he does some soldering & melts the cables . 

The pipework would normally be directly or indirectly connected at the boiler manifold and in turn the CPC of the boiler supply circuit ergo it wouldn't need bonding as connection could be confirmed by testing.

There is no boiler  ..say . 

You may have noticed that I find in difficult to make the transition from  being told we MUST bond ALL  metal pipework  with 6mm  G/Y   ,  Gas & water ,  sinktops MUST be bonded .    If this is not carried out  the Electricity Board  will refuse to connect the  installation .   You have to create a  Faraday Cage  because  a phase reversal on the  PME supply  could have disastrous results. 

Followed by , Oooops we dropped a clanger ,  all bonding is now 10mm  .

And today ....Oh don't bother , the RCDs will cover everything . 

Just being Devil's Advocate here. 

 

[Sidewinder]

Just being Devil's Advocate here. 

So am I!

So, we have to now allow for others to maliciously damage wiring by their incompetence and not do anything about it?

I get where you are coming from, I think, but, there is more to it than that.

The idea of bonding is not to detect a fault.

Bonding is to limit the touch potential in the event of a fault, it is to keep any metalwork that could be an extraneous-conductive-part at the same potential throughout the equipotential zone in the event of a fault.

It is the job of earthing to limit the duration of the fault.

 

[Evans Electric]

So  ... if the water pipes were bonded ( in 10mm )   to the MET  as they call it  , this fault would have tripped an MCB as a dead short  ...and not just sat there  with 240V on it  , waiting for someone to jump in the bath perhaps. ?  

But as they are saying  not to bond or earth  floating metalwork  ....I just don't get the change in thinking ,  The Faraday Cage chucked  'art the winda .  

 

[phil d]

Lets go back to the old practice of a little earth clip on the bottom of each radiator and an earth wire to each radiator.

And who was it had to bond a metal door stop screwed to the ground once?

And an earth on the metal tag provided on a steel or cast iron bath, and stainless steel kitchen sink.

You forgot about aluminium window frames, oh wait, didn't that end with a dead window cleaner?

 

[ProDave]

Have you ever been in a house with a failed PEN on the PME supply?

I have once, It was really weird, nothing seemed to be live, yet everything must have floated up to pretty much L potential. The Faraday cage effect.  That was in an old house with all solid copper pipe and earth bonding in place.

Now how would that have been if the in coming water main had a plastic section and so was deemed not to be extraneous and not need bonding?

Would YOU be happy that the pipework could now end up at a different potential to everything else?  Say the unbonded copper pipe was sitting in a puddle under the floor?

 

[steptoe]

Have you ever been in a house with a failed PEN on the PME supply?

I have once, It was really weird, nothing seemed to be live, yet everything must have floated up to pretty much L potential. The Faraday cage effect.  That was in an old house with all solid copper pipe and earth bonding in place.

Now how would that have been if the in coming water main had a plastic section and so was deemed not to be extraneous and not need bonding?

Would YOU be happy that the pipework could now end up at a different potential to everything else?  Say the unbonded copper pipe was sitting in a puddle under the floor?

I got called to a job once that turned out to be reverse polarity on a TNCS

they had pulled the fuse to do something and couldnt understand how the 'workman' still got a shock

DNO were out within an hour of me phoning them

that was a scary situation, NO overcurrent protection whatsoever for the installation

what would earthed pipes have done in that situation.?  DISCUSS

 

[Sidewinder]

...Say the unbonded copper pipe was sitting in a puddle under the floor?

In which case it must be bonded.

One thing that a LOT of people miss is that if a metallic service such as a water pipe leaves the equipotential zone and then re-enters the equipotential zone at another point, it must be bonded at that point too.

So if a pipe goes under a ground floor, then up again, it must be bonded where it re-enters.

 

[Evans Electric]

I have never heard  that  mentioned ,   since bonding was introduced  TBH . :C  

 

[kerching]

I have never heard  that  mentioned ,   since bonding was introduced  TBH . :C  

I have....didn't we discuss it on here years ago?

some industrial units that were formed out of a common steel frame but services kept ducking underground ?

i think,it  Was 15th update course I went on where it was suggested we drill bottom flange of a wet Rad and fit a nut and bolt....then those little rad clamps came out.

also at same time there were some PLASTIC BS951 clamps!.....seriously, possibly by Erico, came in a yellow plastic bag. Looked like hose/washing machine ratcheting pipe clamp

and they still make them!!!!!!!

 

[Tony S]

In which case it must be bonded.

One thing that a LOT of people miss is that if a metallic service such as a water pipe leaves the equipotential zone and then re-enters the equipotential zone at another point, it must be bonded at that point too.

So if a pipe goes under a ground floor, then up again, it must be bonded where it re-enters.

I’ve known about it but not in a domestic scenario. Our works gas mains would be bonded at each entry point to the plants LV MET.

MET? I don’t think anyone could say where one ended and another began, they were all linked by the 11kV system.

 

[SPECIAL LOCATION]

In which case it must be bonded.

One thing that a LOT of people miss is that if a metallic service such as a water pipe leaves the equipotential zone and then re-enters the equipotential zone at another point, it must be bonded at that point too.

So if a pipe goes under a ground floor, then up again, it must be bonded where it re-enters.

I have never heard  that  mentioned ,   since bonding was introduced  TBH . :C  

It has been mentioned in the OSG since 2011..

ie.  Buried internal metallic pipe work re-appearing is mentioned in section 4 Earthing & bonding...

Pg 48 in the current Blue book..

Pg 44 in previous Yellow book

Pg 40 in the Green 17th Ed Amd 1 2011 OSG....

Basically saying it should be considered extraneous, the same just as incoming service pipes therefore requires bonding.

Guinness

 

[sprocketflup]

Can you guys recommend me some further reading? Im missing something 

The scenario of a pipe going into the ground and reappearing somewhere else in the house, in reality how much potential difference are we likely to see between two areas of the same house?

 

[Sidewinder]

Look at GN8 & GN5 as a start.

 

[binky]

@Evans Electric the requirement to bond metallic pipework  enetering an equipotential zone ie house, was always to  negate the potential to have differing earth potentials within the same building. ie DNO earth versus what is effectively a very large earth rod. Hence under fault conditions, all extranuous conductive parts within said equipotential zone would be at the same touch voltage, and that touch voltage should not exceed 50V. 

 

[Tony S]

OK I’ll put this in to a personal situation.

To get gas to the boiler and fire in my house I had to go under the solid kitchen floor with the main household gas pipe. The pipe was layed in a sand filled trench with a bitumen topping, continuous copper pipe throughout. Bonding at the gas meter was 7/064 (16mm), should I have bonded the copper pipe again at the point it re-immerged from the floor?

 

[Sidewinder]

OK I’ll put this in to a personal situation.

To get gas to the boiler and fire in my house I had to go under the solid kitchen floor with the main household gas pipe. The pipe was layed in a sand filled trench with a bitumen topping, continuous copper pipe throughout. Bonding at the gas meter was 7/064 (16mm), should I have bonded the copper pipe again at the point it re-immerged from the floor?

Strictly speaking bs 7671 requires that the pipe is bonded at every point of entry into the equipotential zone.

So it should have been bonded.