boiler earth bonding

[stokecity]

when bonding at the boiler do you just cross bond the pipes or do you need to run earth cable back to the earth block at consumer unit? cheers

 

[GQuigley67]

depends on electrical installation if its up to 17th edition regs then only bonding required at gas meter and water main

as long as there is MEB(main equipotential bonding) present then cross bonding the pipework is fine, if in doubt consult a sparky

 

[stokecity]

im no spark but pretty sure its not up to 17th and been told if in doubt bond it

 

[kirkgas]

when bonding at the boiler do you just cross bond the pipes or do you need to run earth cable back to the earth block at consumer unit? cheers

although bonding is easy to do, it needs to be done by a competant person who tests it and verifies it is right (theoretically)

 

[Scoobydoo]

Depends on the setup. 10mm main bonding is required back to the MET on all water/gas/oil supplies close to where they enter the premises if they are extraneous conductive parts, ie. capable of introducing a potential.
This bonding is required regardless of whether an RCD is installed in the system (before anyone asks)
Your best bet is to consult an electrician if you are unsure.

 

[SimonJohns]

I've never really understood bonding.

The pipes are metal. The valves are metal. Usually connected together by a peice of metal

Surely theres enough metal there so that bonding isn't required.

 

[chris watkins]

im no spark but pretty sure its not up to 17th and been told if in doubt bond it

Spoken like a true spark, they bond everything.

Did you know that a plumbing apprentice now has to complete 100 + hours of electrical training as part of their level 3, more than cold water or heating !!!!!

 

[Nostrum]

It's supplementary bonding underneath a boiler, and no longer required if the circuits are RCD protected (17th edition)

SimonJohns I think it all got a bit out of hand a few years ago when everything needed bonding and 'joining up' so that you didn't have metallic objects with different potentials. Otherwise if you had hold of one and then touched another, under fault conditions you could recieve a shock as the currrent passed through you.

RCD's mean that regardless of potential, any current that is not travelling around the circuit it should be causes the RCD to trip within 40ms so there is no risk of you coming to any harm.

As ScoobyDoo says though main equipotential bonding is still required but that's a sparky's job anyway.

 

[GQuigley67]

i done electrical training as part of my apprenticeship it was mostly wiring heating systems and fault finding which i quickly forgot as i was working on commercial new builds at the time lol

 

[secret squirrel]

Interesting about the bonding, my sparks said that if you bond something that isn't done correctly in the first place your making a risk not curing it, giving the electricity somewhere to go.

Another point he babbled on about was what if someone has repaired a leak with plastic pipe (not a flexi, system 3) and not bonded between the two pieces of copper!

 

[tamz]

Hi what can you say about gas boiler bc?

The competition won't bother me

 

[Nostrum]

Interesting about the bonding, my sparks said that if you bond something that isn't done correctly in the first place your making a risk not curing it, giving the electricity somewhere to go.

Another point he babbled on about was what if someone has repaired a leak with plastic pipe (not a flexi, system 3) and not bonded between the two pieces of copper!

Water is a conductor so it's not the end of the world.

That's the idea of equipotential bonding, if everything is at the same potential, there is no where to go so to speak, as there has to be a potential difference.

A bit like joining hot and cold together. If the 2 are at the same pressure then the water won't go anywhere, if one was mains and one was tank fed, then the mains pressure would force the water up the tank fed pipe, not sure if that is a good analogy or not....

 

[Dannypipe]

Hi what can you say about gas boiler bc?

That you're a spammer.

 

[Bernie2]

Basically cable's are copper and conduct electricity, copper pipe or virtually any metal does the same. So if you get an electrical fault it can travel along any metal, until of course somebody touches it.
So you have to ensure the resistance to Earth of the metal is low, because if its higher than you, electricity being lazy would rather travel through you to Earth than down the earthing route your cross bonding has made for it.

The easiest way is get hold of an Earth Loop tester and see what the resistance to earth is. An ordinary test meter will not tell you they usually only measure continuity and do not use a high enough test current. The earth loop tester tells you how much earth fault the earthing system can take.

Incidentally you should really do an earth test on a boiler as part of an overall electrical test if you have been repairing it, you can usually use the ohms on a multi-meter for it.

 

[zzzjim]

The pipes are metal. The valves are metal. Usually connected together by a peice of metal

What about all that PTFE , found wound on Olives !

 

[Nostrum]

As already suggested though, providing the circuits are protected by an RCD, there is no longer any requirement for supplementary bonding (under boilers, sinks, baths etc)

If it's not, then it would be quicker to bond the pipework than it would be to do the tests. ideal have a metallic strip integral to the boiler which acts as supplementary bonding.

Also to test whether or not you would need to cross bond the boiler, you would need an insulation resistance tester.

 

[Scoobydoo]

Basically cable's are copper and conduct electricity, copper pipe or virtually any metal does the same. So if you get an electrical fault it can travel along any metal, until of course somebody touches it.
So you have to ensure the resistance to Earth of the metal is low, because if its higher than you, electricity being lazy would rather travel through you to Earth than down the earthing route your cross bonding has made for it.

The easiest way is get hold of an Earth Loop tester and see what the resistance to earth is. An ordinary test meter will not tell you they usually only measure continuity and do not use a high enough test current. The earth loop tester tells you how much earth fault the earthing system can take.

Incidentally you should really do an earth test on a boiler as part of an overall electrical test if you have been repairing it, you can usually use the ohms on a multi-meter for it.

An earth fault loop impedance tester will measure the resistance of the path between line voltage and earth back to the transformer, ie. the "earth fault loop", and use ohm's law to give you a fault current calculation.
Continuity between exposed and extraneous conductive parts is all you should be interested in regarding bonding to keep touch voltage below 50v in the event of a fault. A simple continuity tester will do this.
As always though, if you don't know what the readings mean, then they may as well be in a foreign language.

 

[Scoobydoo]

As already suggested though, providing the circuits are protected by an RCD, there is no longer any requirement for supplementary bonding (under boilers, sinks, baths etc)

If it's not, then it would be quicker to bond the pipework than it would be to do the tests. deal have a metallic strip integral to the boiler which acts as supplementary bonding.

Also do test whether or not you would need to cross bond the boiler, you would need an insulation resistance tester.

There are a couple of other provisions besides having an RCD which preclude the need for supplementary bonding, but generally you are correct. Whether supplementary bonding is needed, along with where, and cable sizing should really be decided by a qualified electrician.

 

[Nostrum]

Thankfully, I am able to decide all of the above then

Rather than getting into willy waving I will quote the OSG green book amendment 1 to clarify for those who are still unsure.

The purpose of supplementary bonding is to reduce voltage (potential) between various exposed conductive parts and extraneous conductive parts of a location during fault conditions (boiler pipework being an extraneous conductive part)

Where a required disconnection time cannot be achieved, supplementary bonding must be applied. (a working RCD will provide satisfactory disconnection time)

If the installation meets the requirements of BS7671:2008(2011) (17th edition amendment 1) for earthing and bonding, there is no specific requirement for supplementary bonding of:

kitchen pipes, sinks or draining boards
metallic boiler pipework
metallic furniture in kitchens
metallic pipes to wash hand basins and WC's
locations containing a bath of shower, providing the conditions of regulation 701.415.2 are met

regulation 701.415.2

supplementary equipotential bonding may be omitted where the following conditions are met

all ring final circuits of the location comply with the requirements for automatic disconnection according to regulation 411.3.2

all final ring circuits in the location have additional protection by means of an RCD

all extraneous conductive parts of the location are effectively connected to the protective equipotential bonding

Just to clarify, to test whether or not a part is extraneous you would need to carry out an insulation resistance test between it and the main earth. If the reading is over 22k ohms then the part is not deemed extraneous and therefore does not require supplementary bonding.

 

[tamz]

We are plumbers NOT electricians. It is not our concern or problem. Give your customer a bit paper or postcard saying "your electrics may be dodgy get it checked" (jobs for the boys) to discharge your duties.
Unless you are properly qualified it is not our concern so leave it alone.

 

[stokecity]

sambotc cheers

 

[Bernie2]

Insulation tests do not tell you how good the earth is just that one wire is insulted from the other and how good that insulation is. An Earth loop test tells you how much current your earth path will take. It would be point less earthing with fine wire it would burn out if you got a 230 volt 13 amp fault discharging to earth and leave your pipework still live and able to deliver a big shock for anybody touching it.

The RCD is intended to sense the current is the same voltage in both the Neutral and Positive wire in the cable. If its equal it stays open, if its more in one wire than it is in the other it shuts down because in an AC system it means the current is running to earth somewhere. But its relying on a mechanical RCD to always be working and not seized up over many years. That is why they have test buttons on them that should be tested every month or so. But who does?

It is right though, you do not have to supplementary bond providing the pipework is connected somewhere along its length to the main Earthing point and protected by an RCD. But how would you know it was connected without testing the earth and how good was the connection?

Anyway as Tamz says its not our job, but its interesting.

 

[Nostrum]

Bernie, you are getting a little bit confused I think.

An earth loop impedance tester will tell you what the resistance is for the 'loop' between live and earth and what the prospective fault current is for a particular circuit. This then allows you to calculate the disconnection time for you to confirm that the circuit protective device (fuse, circuit breaker etc) is suitable and will disconnect within the allowable time according to BS7671.

We are talking about measuring the potential difference between earth and an extraneous conductive part (pipework) and effectively the extraneous conductive part and the human body.

The metallic part can be assumed not to be an extraneous-conductive-part if the following condition is met:

Rcp> (Uo/Ib) - Ztl

where,

Rcp is the resistance between the conductive part and the MET (main earth terminal) in ohms

Uo is the nominal voltage to Earth in volts

Ib is the value of current through the body in amperes that should not be exceeded (10mA according to GN8)

Ztl is the impedance of the human body in ohms. 1000 ohms where Uo is 230 V (50 Hz) under dry or wet conditions.

Rcp > (230/0.01) - 1000 / (23000) - 1000
Rcp > 22000ohms

....so if the resistance between the MET and the part in question is above 22000ohms, it is not considered to be an extraneous-conductive part and does not require bonding.

You test this with an insulation resistance tester at 500v.

Basically if the resistence of the path to earth of the pipework is high enough, the potential difference will be so small that you will not receive a shock or that it will be so small that it is deemed not be be unsafe.

Yes it's complicated, yes it's nothing to do with the job of a plumber but, this is the correct method for testing if your pipes underneath the boiler need bonding if no RCD is present, which is why I said earlier, if there's no RCD you would be better off just doing it!

and yes I did copy and paste it from another source as I couldn't remember the equation, just the figures and how to do it!

This is why when I hear people say that electrics is easier than gas etc I disagree, there are more equations and maths involved being an electrician by far, and my brain doesn't store equations very well so I am constantly having to refer back to the books when I doing electrical, where as gas/plumbing/heating tends to stick in the brain a bit easier, although maybe that is because I started life as a gas engineer so it is second nature.

 

[tamz]

^^why it should be left to those who know how^^

It is not our concern and our only responsibility is whether a gas pipe has a 10mm bond or not and inform the customer or householder.
Now that is another one.
We (generally) have no qualifications experience equipment or knowledge of how electrics work or how to test them.
I've found gas pipes bonded to nothing (bit of cable stuck under a floor) i've found 1 that was bonded to itself (the earth wire was actually soldered to the gas pipe under the floor and tagged at the meter) so who or what is to say it is our responsibility or would we be liable if anything were to happen because we said the meb was present and (assumed) ok?
Seeing is not believing!
Has anyone ever died touching an unbonded gas pipe or appliance in everyday normal operation?
Has there ever been a case of a gas explosion cause by no earth bond?
Should we, even if we say the bond is present and correct also recommend it is properly checked because we really haven't a clue?
If we fit a heating system should we be recommending a visit from an electrician?
If you fit a speedfit fitting to a copper pipe are you then liable if anyone got a skelp?

Questions questions :smile:

 

[Nostrum]

so who or what is to say it is our responsibility or would we be liable if anything were to happen because we said the meb was present and (assumed) ok?​

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If you are part P then I would say yes, if not then no I would guess Tamz. It's the usual case of probably only finding out when the sheet hits the fan and some lawyer starts referencing law talk from the british standards. The difference being they can sit down and study them for days putting a case together whereas we all have a job to do and have to take most of it in in laymans terms so we actually get jobs done.

Has anyone ever died touching an unbonded gas pipe or appliance in everyday normal operation?
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Possibly if they were holding onto it and it was introducing a fault current

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Has there ever been a case of a gas explosion cause by no earth bond?
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That's not what it's there for and we all know that you'd need a 5-15% gas/air mix within the pipe anyway :44:​

If we fit a heating system should we be recommending a visit from an electrician?
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If in doubt I guess so. The reality is wiring itself isn't very complicated is it, a bit like painting by numbers, but testing is where things get complicated and if your signing work off then you take the responsibility that goes with it.

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If you fit a speedfit fitting to a copper pipe are you then liable if anyone got a skelp?
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Doubt it would make that much odds really as water is conductive.











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