Bonding....

[NozSpark]

It's sort of the same question that you might have about bonding an external gas service that goes under a suspended floor straight outside and then back into a rear kitchen...

Where does the service enter the property?

 

[Southcoast2015]

OK,,, so another option might be to replace all the speedfit elbows, tees etc with brass fittings and bond at a more accessible place

To access these would mean pulling apart just as much of the place as running the cable in plus really I think all you'd be doing then is creating more pipe work that could create a potential difference.

At least at the moment it's all in sections that are isolated from one another.

It's sort of the same question that you might have about bonding an external gas service that goes under a suspended floor straight outside and then back into a rear kitchen...

Where does the service enter the property?

It would have originally be the kitchen at the rear of the property but it has a large extension on the back now so it's now the middle of the house.

 

[Doc Hudson]

How much of the property is RCD protected. Can you access the property when it is empty, only you there. I may be curious just to simulate a fault from the nearest supply to the pipework, using my RCD tester with L & N from nearest socket and the earth lead on the pipe work. Verify how quick the RCD trips and at what current. That may help you make up your mind.

Doc H.

 

[steptoe]

OK, so having read most of this,

seems the OP is continually reading that the purpose of bonding is to ensure a good earth path in the event that you touch a live part while touching the water main,

maybe you should re-familiarise yourself with the requirements for bonding,

that is not its sole purpose,

still, imho, it requires bonding,

to not bond is a deviation from the regs, and should be noted as such,

or,

get in writing that the owner does NOT want the work doing, and state such on certificate along with a copy of the owners statement.

it was always drilled into me as an apprentice that

cost or inconvenience is no reason not to apply all safety measures required

or words to that effect.

 

[binky]

if I thought safety was being compromised I would totally agree with your last point, but as it happens it is highly unliklely to compromise safety in the current installation. Should the house be modiifed then that might change. It would be good practice to leave  a note on the CU ( on the sticky lables normally provided) to make the situation clear to anyone working here in the future. Hopefully then they would consider what they are doing and the need for a bond.

It's sort of the same question that you might have about bonding an external gas service that goes under a suspended floor straight outside and then back into a rear kitchen...

Where does the service enter the property?

but the point is, is the extranuos earth path linked to the main earth terminal? within 600mm is an attempt to standardise the location of a bonding point, to make it easier to find and inspect. The actual requirment is to negate a potentially fatal situation. If you bonded 20m into the house, as long as the resistance to earth is less than required it still works to create the 50V touch voltage which is the ultimate aim of the bonding.

 

[Essex1]

OK, so having read most of this,

seems the OP is continually reading that the purpose of bonding is to ensure a good earth path in the event that you touch a live part while touching the water main,

maybe you should re-familiarise yourself with the requirements for bonding,

that is not its sole purpose,

still, imho, it requires bonding,

to not bond is a deviation from the regs, and should be noted as such,

or,

get in writing that the owner does NOT want the work doing, and state such on certificate along with a copy of the owners statement.

it was always drilled into me as an apprentice that

cost or inconvenience is no reason not to apply all safety measures required

or words to that effect.

You can not just note deviations on the certificate and think it is ok. Deviations are only permitted if it provides the same degree of safety as specified in BS7671. You cannot just not do something and note it on the cert. If the customer does not want a part of the job done that is vital to the safety of the user then walk away from the job. Do not staple a letter to the cert and think that is you covered. It is neither correct or ethical.

 

[Southcoast2015]

How much of the property is RCD protected. Can you access the property when it is empty, only you there. I may be curious just to simulate a fault from the nearest supply to the pipework, using my RCD tester with L & N from nearest socket and the earth lead on the pipe work. Verify how quick the RCD trips and at what current. That may help you make up your mind.

Doc H.

Board is split load - all sockets, kitchen and shower is RCD protected.

 

[binky]

You can not just note deviations on the certificate and think it is ok. Deviations are only permitted if it provides the same degree of safety as specified in BS7671. You cannot just not do something and note it on the cert. If the customer does not want a part of the job done that is vital to the safety of the user then walk away from the job. Do not staple a letter to the cert and think that is you covered. It is neither correct or ethical.

so you would leave a broken socket hanging off the wall with exposed conductors because there is a debatable water bond?

bit different if installing a new kitchen. Its buired somwhere in guidlines that you don't have to turn work away becuase the customer is skint, but you do need to tell them what is wrong. Rental is different as is commercial, but domestic has its own unique issues. I wouldn't install / alter circuits under a dodgy condition domestic or not, that is wrong.

 

[Essex1]

so you would leave a broken socket hanging off the wall with exposed conductors because there is a debatable water bond?

bit different if installing a new kitchen. Its buired somwhere in guidlines that you don't have to turn work away becuase the customer is skint, but you do need to tell them what is wrong. Rental is different as is commercial, but domestic has its own unique issues. I wouldn't install / alter circuits under a dodgy condition domestic or not, that is wrong.

Of course not. The risk of the broken socket is far greater. Make safe then walk away. I am talking only if the customer refuses point blank. It would not cost much to clip an earth around the skirting to get a bond. So money really is not an issue. Preference is the issue here.

 

[binky]

running bonds behind skirting can be a tidy option. Customers who can afford, but refuse to pay are worth walking from, they are asking you to legally be responsible for them being tight - generally sh!te customers anyway.

 

[Rob_the_rich]

I would describe the plastic couplers as having  a very high resistance rather than being insulated - I got called to the bath of doom becuase of a 'popping noise' ie the electric was occasionally arcing through the water.

The whole point of bonding is to bring all extrenuos earth paths to a safe touch voltage under fault conditions, which on a re-wireable fuse is 5secs (in theory). This means if you were touching a radiator with good earth path and a faulty appliance the potential difference between good earth path and appliance is less than 50V and subsequent fault current flowing through you is insufficent to kill. Now if you can't touch incoming water supply and faulty appliance, you are 'safe', and if high resistances exist on all pipework over about 500 ohms, then a/ bonding stopcock is useless, b/ current flow would in the region of 48mA at 500Ohm, less if higher resistance exists.

Shouldn't that be 0.48A (240V/500ohms)?

Definitely agree that plastic fittings should be considered as high resistance. Southcoast2015 seems to think that a plastic fitting means no continuity, but may be underestimating the effect of water in the pipe.

Pure water has very low conductance (and therefore high resistivity), tap water resistivity can vary greatly depending on how many dissolved ions are in it, so will change from region to region eg dissolved chalk on the south coast.

Paul Cook says here http://www.plasticpipesgroup.com/media/1036/earthbonding.pdf that a meter of tap water (from Leatherhead) in 15mm plastic pipe has a resistance of 100,000 ohms. The distance between the copper pipe ends in a plastic fitting is about 1cm, so the resistance of a plastic fitting is about 1000 ohms. This would give 0.24 amps @ 240V

If the distance between the pipe ends is less, the resistance would be less.

 

[Tony S]

[SIZE=medium]Funny how I could use water cooled cables for 4000A @660V and still have 15mA instantaneous earth fault protection.[/SIZE]

 

[roys]

Funny how I could use water cooled cables for 4000A @660V and still have 15mA instantaneous earth fault protection.

Yeah but was that de-ionised water?

 

[Tony S]

Yeah but was that de-ionised water?

[SIZE=medium]Treated water from Severn Trent.[/SIZE]

[SIZE=medium]The fun and games start with the length of “insulated” pipe required between the earthed copper water feeds and the live copper conductors.[/SIZE]

[SIZE=medium]If the section is too short it will lead to electrolysis that then leads to furred connections and restricted cooling water flow. The alarm system goes berserk on over temperature.[/SIZE]

 

[Southcoast2015]

I don't think anything - the incoming water pipe has no continuity to the other 2 sections that I could access after the plastic fittings and obviously the pipe is full of water.

 

[IzzyS]

To test an existing in-service installation, I turn off the main switch (safe isolation etc), then disconnect the main earthing conductor and test between that and the suspected extraneous-conductive-part.   This removes fortuitous paths, such as a cpc connection to the immersion heater in a copper hot water cylinder, the gas or oil pipe bond, or the central heating boiler cpc.

It's not a true test of the pipe alone, as for example, a heating boiler sitting on a wet concrete floor can introduce earth potential.

However, if it the overall result >23kOhms then the part under test is not considered to be an e-c-p and no bonding is required (See GN8), anything less then bonding is required.

 

[binky]

Shouldn't that be 0.48A (240V/500ohms)?

Definitely agree that plastic fittings should be considered as high resistance. Southcoast2015 seems to think that a plastic fitting means no continuity, but may be underestimating the effect of water in the pipe.

Pure water has very low conductance (and therefore high resistivity), tap water resistivity can vary greatly depending on how many dissolved ions are in it, so will change from region to region eg dissolved chalk on the south coast.

Paul Cook says here http://www.plasticpipesgroup.com/media/1036/earthbonding.pdf that a meter of tap water (from Leatherhead) in 15mm plastic pipe has a resistance of 100,000 ohms. The distance between the copper pipe ends in a plastic fitting is about 1cm, so the resistance of a plastic fitting is about 1000 ohms. This would give 0.24 amps @ 240V

If the distance between the pipe ends is less, the resistance would be less.

ok poor calculation late at night - my bad.

chances are thus place has numerous plastic elbows. Southy has tested pipework and found very high resistance / no continuity. so question is does 6ft of pipe as it enters the building need bonding when it is boxed in and effectively out of any equipotential zones. My opinion is that a bond would add nothing to the safety of the premises, ergo is unnecessary, but customer should be advised that it would be a good idea. According to CIS I shouldn't use a ladder over 6ft, I've worked safely off ladders to install, for example, a bathroom fan wall vent for years. It's done carefully! In doing this I am choosing to ignore recommendations, I see ignoring bonding the stopcock and 6ft of pipe as a similar thing in this case - it's sa case of not blindly following dogma to me and applying common sense where it can be demonstrated sense should prevail, especially as it is backed up by testing.

 

[pewter]

What box?

What stop cock?

no stop cock accessable.

email the detail to the electric police so they can send Bodie and Doyle electrical police round to turn them over for not having an accessable stop cock that is correctly bonded.

 

[Southcoast2015]

What I think I'm going to do is eliminate all parallel earth paths and test again - With a bit of luck it may even test as not an extraneous conductive part.

If it measures <22-23K then I'll strongly advise it's done which may be more practical next time they do the above tiled bathroom floor or if for some reason they take down their ceilings.

I just know there is no way I'd even entertain pulling my house to pieces for something that is going to do very little.

The pipe does have multiple elbows and joiners all in plastic, pipe downstairs are boxed in, they have Tee pieces under upstairs floor boards, one tee's off for kitchen sink (drops back down in Kitchen), the other is tee'd for a plastic shower pump which is hidden in floor cavity, then the main pipe continues (still inside the wall) up to shower where another tee piece has been added  and plastic pipe supplies the shower itself, then the pipe goes up to loft to supply boiler - unless you pull up tiles in bathroom and then the floor boards you can't even reach any of the pipe.

 

[binky]

sounds sensible to me