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Bathroom earth bonding
Bathroom has hot and cold water pipes, electric towel rail and an
electric shower, what bonding is required? |
#2
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Bathroom earth bonding
On Sat, 22 Apr 2017 10:50:44 +0100, Ivor Nastychestikov wrote:
Bathroom has hot and cold water pipes, electric towel rail and an electric shower, what bonding is required? Is everything RCD protected? Has the incoming water pipe (and gas/oil) got bonding in place? If so, then it is likely that there is no need for any Supplementary Bonding. If no RCD, or not all circuits in the bathroom are RCD protected, then you should have Supplementary Bonding between exposed conducitve metalwork, and the CPC of the circuit(s) in the bathroom. |
#3
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Bathroom earth bonding
On 22/04/2017 10:50, Ivor Nastychestikov wrote:
Firstly, no such thing as "earth bonding" - the phrase makes no sense. You can have earthing, and you can have equipotential bonding. Two different systems that work in different ways and are designed to provide shock protection by different mechanisms. (reduced shock duration for earthing, and reduced shock magnitude for EQ bonding). Bathroom has hot and cold water pipes, electric towel rail and an electric shower, what bonding is required? That depends... If the main equipotential bonding[1] is in place, and all the circuits that feed the bathroom are RCD protected (with 30mA trip devices), then since the 17th edition of the wiring regs, none is actually required. If the above requirements are not met (say the lighting circuit is not RCD protected), then you will need to equipotential bond the earth conductors of all the circuits that feed anything in the bathroom, along with any other metalwork that is capable of introducing a potential into the room (and that includes an earth potential). So typically that would include hot and cold water pipework, and possibly central heating pipework. You don't need to bond pipes that are plastic, or are just isolated bits of metal "show" pipework feed from plastic pipes. Nor do you need to bond radiators, baths or any other lump of metal that by itself is not able to introduce a potential into the room. You may need to bond waste pipes if they are metal and ultimately connected to earth. (if unsure measure the resistance between them a a known good earthing point) For more information see: [1] http://wiki.diyfaq.org.uk/index.php/...ng_and_Bonding -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#4
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Bathroom earth bonding
On 22-Apr-17 11:34 AM, Alan wrote:
On Sat, 22 Apr 2017 10:50:44 +0100, Ivor Nastychestikov wrote: Bathroom has hot and cold water pipes, electric towel rail and an electric shower, what bonding is required? Is everything RCD protected? Yes. Has the incoming water pipe (and gas/oil) got bonding in place? If so, then it is likely that there is no need for any Supplementary Bonding. The hot and cold water pipes are bonded to each other. The incoming water supply enters house by a pvc pipe. There is a 4mm earth cable back to the consumer unit, but that is not connected at the moment. There is no oil or gas. If no RCD, or not all circuits in the bathroom are RCD protected, then you should have Supplementary Bonding between exposed conducitve metalwork, and the CPC of the circuit(s) in the bathroom. |
#5
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Bathroom earth bonding
John Rumm wrote:
On 22/04/2017 10:50, Ivor Nastychestikov wrote: Firstly, no such thing as "earth bonding" - the phrase makes no sense. You can have earthing, and you can have equipotential bonding. Two different systems that work in different ways and are designed to provide shock protection by different mechanisms. (reduced shock duration for earthing, and reduced shock magnitude for EQ bonding). Bathroom has hot and cold water pipes, electric towel rail and an electric shower, what bonding is required? That depends... If the main equipotential bonding[1] is in place, and all the circuits that feed the bathroom are RCD protected (with 30mA trip devices), then since the 17th edition of the wiring regs, none is actually required. If the above requirements are not met (say the lighting circuit is not RCD protected), then you will need to equipotential bond the earth conductors of all the circuits that feed anything in the bathroom, along with any other metalwork that is capable of introducing a potential into the room (and that includes an earth potential). So typically that would include hot and cold water pipework, and possibly central heating pipework. You don't need to bond pipes that are plastic, or are just isolated bits of metal "show" pipework feed from plastic pipes. Nor do you need to bond radiators, baths or any other lump of metal that by itself is not able to introduce a potential into the room. You may need to bond waste pipes if they are metal and ultimately connected to earth. (if unsure measure the resistance between them a a known good earthing point) For more information see: [1] http://wiki.diyfaq.org.uk/index.php/...ng_and_Bonding I have a strange situation in my bathroom, all the copper water pipes are bonded to earth externally but I sometimes get a tingle to taps when standing in the shower, (About 5 volts measured from metal round drain to taps) I can only assume that when the house was built(on concrete slab) the reo steel in the concrete was not bonded to earth which is a requirement today |
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Bathroom earth bonding
On Sunday, 23 April 2017 09:21:57 UTC+1, F Murtz wrote:
I have a strange situation in my bathroom, all the copper water pipes are bonded to earth externally but I sometimes get a tingle to taps when standing in the shower, (About 5 volts measured from metal round drain to taps) I can only assume that when the house was built(on concrete slab) the reo steel in the concrete was not bonded to earth which is a requirement today You need to fix that. NT |
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Bathroom earth bonding
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Bathroom earth bonding
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Bathroom earth bonding
On Monday, 24 April 2017 08:20:05 UTC+1, Brian Reay wrote:
On 24/04/2017 06:53, F Murtz wrote: tabbypurr wrote: On Sunday, 23 April 2017 09:21:57 UTC+1, F Murtz wrote: I have a strange situation in my bathroom, all the copper water pipes are bonded to earth externally but I sometimes get a tingle to taps when standing in the shower, (About 5 volts measured from metal round drain to taps) I can only assume that when the house was built(on concrete slab) the reo steel in the concrete was not bonded to earth which is a requirement today You need to fix that. NT I can not be bothered at the moment am not the slightest bit worried that it is ever going to electrocute anyone, Some day I may jackhammer a bit of concrete to expose some reo and bond it, The 5V isn't but it is a sign of something more serious- it looks like you may have a PME earth and have 'imported' an external (real) earth. PME earths are fine but rely on your not 'mixing' a PME earth and a real earth in case there is a earth neutral fault- specifically a break in the combined Neutral and Earth conductor which supplies your property. It is indeed a hazard. A nearby strike would also put a massive voltage gradient across anyone in the shower. NT |
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Bathroom earth bonding
In article . com,
F Murtz wrote: I have a strange situation in my bathroom, all the copper water pipes are bonded to earth externally but I sometimes get a tingle to taps when standing in the shower, (About 5 volts measured from metal round drain to taps) I can only assume that when the house was built(on concrete slab) the reo steel in the concrete was not bonded to earth which is a requirement today Is it a wet room? I'd not expect the metal drain to be connected to anything other than a plastic waste pipe. I'd be inclined to check the potential between your copper pipes and true earth. I've be surprised if you could feel 5v. -- *Sherlock Holmes never said "Elementary, my dear Watson" * Dave Plowman London SW To e-mail, change noise into sound. |
#12
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Bathroom earth bonding
On 2017-04-22, John Rumm wrote:
On 22/04/2017 10:50, Ivor Nastychestikov wrote: Firstly, no such thing as "earth bonding" - the phrase makes no sense. You can have earthing, and you can have equipotential bonding. Two different systems that work in different ways and are designed to provide shock protection by different mechanisms. (reduced shock duration for earthing, and reduced shock magnitude for EQ bonding). But they're both done with green & yellow striped cable! |
#13
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Bathroom earth bonding
On 25/04/2017 12:16, Adam Funk wrote:
On 2017-04-22, John Rumm wrote: On 22/04/2017 10:50, Ivor Nastychestikov wrote: Firstly, no such thing as "earth bonding" - the phrase makes no sense. You can have earthing, and you can have equipotential bonding. Two different systems that work in different ways and are designed to provide shock protection by different mechanisms. (reduced shock duration for earthing, and reduced shock magnitude for EQ bonding). But they're both done with green & yellow striped cable! Hence why they call it a Circuit Protective Conductor (CPC) and not an "earth conductor" You have what are classed as "fortuitous effects"; in that equipotential bonding (by inclusion of multiple CPCs) may also lower the earth impedance at the point of a fault and hence improve disconnection times. Likewise earthing may add additional conductors that will also function as eq bonding, and hence lower the touch voltages. However these effects (while not unwelcome) may not be relied upon[1], and each system needs to function independently. [1] e.g. your main eq bond to the incoming water main may provide a good additional path to earth. However it would be unwise to rely on that as an earth since the water supplier may change it to plastic etc. So when testing your main earthing terminal, you disconnect any bonding connections to it for the duration of the test. Likewise eq bonding conductors in a bathroom, don't actually need any connection back to the main earth terminal to function correctly. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#14
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Bathroom earth bonding
On 2017-04-25, John Rumm wrote:
On 25/04/2017 12:16, Adam Funk wrote: On 2017-04-22, John Rumm wrote: On 22/04/2017 10:50, Ivor Nastychestikov wrote: Firstly, no such thing as "earth bonding" - the phrase makes no sense. You can have earthing, and you can have equipotential bonding. Two different systems that work in different ways and are designed to provide shock protection by different mechanisms. (reduced shock duration for earthing, and reduced shock magnitude for EQ bonding). But they're both done with green & yellow striped cable! Hence why they call it a Circuit Protective Conductor (CPC) and not an "earth conductor" I was just joking that using the same cable makes it easy for people to confuse the two. You have what are classed as "fortuitous effects"; in that equipotential bonding (by inclusion of multiple CPCs) may also lower the earth impedance at the point of a fault and hence improve disconnection times. Likewise earthing may add additional conductors that will also function as eq bonding, and hence lower the touch voltages. However these effects (while not unwelcome) may not be relied upon[1], and each system needs to function independently. [1] e.g. your main eq bond to the incoming water main may provide a good additional path to earth. However it would be unwise to rely on that as an earth since the water supplier may change it to plastic etc. So when testing your main earthing terminal, you disconnect any bonding connections to it for the duration of the test. Likewise eq bonding conductors in a bathroom, don't actually need any connection back to the main earth terminal to function correctly. |
#15
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Bathroom earth bonding
On 24/04/2017 06:53, F Murtz wrote:
wrote: On Sunday, 23 April 2017 09:21:57 UTC+1, F Murtz wrote: I have a strange situation in my bathroom, all the copper water pipes are bonded to earth externally but I sometimes get a tingle to taps when standing in the shower, (About 5 volts measured from metal round drain to taps) I can only assume that when the house was built(on concrete slab) the reo steel in the concrete was not bonded to earth which is a requirement today You need to fix that. NT I can not be bothered at the moment am not the slightest bit worried that it is ever going to electrocute anyone, Some day I may jackhammer a bit of concrete to expose some reo and bond it, I would not bother. If anything you bond the metal waste pipe (UK regs) -- Adam |
#16
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Bathroom earth bonding
On 25/04/2017 13:27, John Rumm wrote:
On 25/04/2017 12:16, Adam Funk wrote: On 2017-04-22, John Rumm wrote: On 22/04/2017 10:50, Ivor Nastychestikov wrote: Firstly, no such thing as "earth bonding" - the phrase makes no sense. You can have earthing, and you can have equipotential bonding. Two different systems that work in different ways and are designed to provide shock protection by different mechanisms. (reduced shock duration for earthing, and reduced shock magnitude for EQ bonding). But they're both done with green & yellow striped cable! Hence why they call it a Circuit Protective Conductor (CPC) and not an "earth conductor" You have what are classed as "fortuitous effects"; in that equipotential bonding (by inclusion of multiple CPCs) may also lower the earth impedance at the point of a fault and hence improve disconnection times. Likewise earthing may add additional conductors that will also function as eq bonding, and hence lower the touch voltages. However these effects (while not unwelcome) may not be relied upon[1], and each system needs to function independently. [1] e.g. your main eq bond to the incoming water main may provide a good additional path to earth. However it would be unwise to rely on that as an earth since the water supplier may change it to plastic etc. So when testing your main earthing terminal, you disconnect any bonding connections to it for the duration of the test. Likewise eq bonding conductors in a bathroom, don't actually need any connection back to the main earth terminal to function correctly. I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. -- Adam |
#17
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Bathroom earth bonding
On 25/04/2017 21:45, ARW wrote:
On 25/04/2017 13:27, John Rumm wrote: On 25/04/2017 12:16, Adam Funk wrote: On 2017-04-22, John Rumm wrote: On 22/04/2017 10:50, Ivor Nastychestikov wrote: Firstly, no such thing as "earth bonding" - the phrase makes no sense. You can have earthing, and you can have equipotential bonding. Two different systems that work in different ways and are designed to provide shock protection by different mechanisms. (reduced shock duration for earthing, and reduced shock magnitude for EQ bonding). But they're both done with green & yellow striped cable! Hence why they call it a Circuit Protective Conductor (CPC) and not an "earth conductor" You have what are classed as "fortuitous effects"; in that equipotential bonding (by inclusion of multiple CPCs) may also lower the earth impedance at the point of a fault and hence improve disconnection times. Likewise earthing may add additional conductors that will also function as eq bonding, and hence lower the touch voltages. However these effects (while not unwelcome) may not be relied upon[1], and each system needs to function independently. [1] e.g. your main eq bond to the incoming water main may provide a good additional path to earth. However it would be unwise to rely on that as an earth since the water supplier may change it to plastic etc. So when testing your main earthing terminal, you disconnect any bonding connections to it for the duration of the test. Likewise eq bonding conductors in a bathroom, don't actually need any connection back to the main earth terminal to function correctly. I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It has to be said that something that relies on a passive length of wire and some pipe clamps is likely to be more reliable than something that needs working electro mechanics. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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Bathroom earth bonding
On 2017-04-26, John Rumm wrote:
On 25/04/2017 21:45, ARW wrote: I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It has to be said that something that relies on a passive length of wire and some pipe clamps is likely to be more reliable than something that needs working electro mechanics. I'm struggling to imagine how it could do any harm to have more bonding than required, as long as it's sound (i.e., not connected to anything "bad"). |
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Bathroom earth bonding
On Wednesday, 26 April 2017 11:00:06 UTC+1, Adam Funk wrote:
On 2017-04-26, John Rumm wrote: On 25/04/2017 21:45, ARW wrote: I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It has to be said that something that relies on a passive length of wire and some pipe clamps is likely to be more reliable than something that needs working electro mechanics. I'm struggling to imagine how it could do any harm to have more bonding than required, as long as it's sound (i.e., not connected to anything "bad"). just a waste of money, some of which is used for useful purposes. NT |
#20
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Bathroom earth bonding
On 26/04/2017 10:58, Adam Funk wrote:
On 2017-04-26, John Rumm wrote: On 25/04/2017 21:45, ARW wrote: I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It has to be said that something that relies on a passive length of wire and some pipe clamps is likely to be more reliable than something that needs working electro mechanics. I'm struggling to imagine how it could do any harm to have more bonding than required, as long as it's sound (i.e., not connected to anything "bad"). Depends on your definition of more than required... if you mean including bonding in a bathroom which meets the 17th edition exception and hence could in theory do without, then yup no harm, and not expensive. However some places take it to the extreme and festoon every bit of pipework with bonding cables in places where there is not an elevated shock injury risk. In those cases, there are probably other things you could do with an installation to get a better return on the investment. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#21
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Bathroom earth bonding
On 26/04/2017 01:40, John Rumm wrote:
On 25/04/2017 21:45, ARW wrote: On 25/04/2017 13:27, John Rumm wrote: On 25/04/2017 12:16, Adam Funk wrote: On 2017-04-22, John Rumm wrote: On 22/04/2017 10:50, Ivor Nastychestikov wrote: Firstly, no such thing as "earth bonding" - the phrase makes no sense. You can have earthing, and you can have equipotential bonding. Two different systems that work in different ways and are designed to provide shock protection by different mechanisms. (reduced shock duration for earthing, and reduced shock magnitude for EQ bonding). But they're both done with green & yellow striped cable! Hence why they call it a Circuit Protective Conductor (CPC) and not an "earth conductor" You have what are classed as "fortuitous effects"; in that equipotential bonding (by inclusion of multiple CPCs) may also lower the earth impedance at the point of a fault and hence improve disconnection times. Likewise earthing may add additional conductors that will also function as eq bonding, and hence lower the touch voltages. However these effects (while not unwelcome) may not be relied upon[1], and each system needs to function independently. [1] e.g. your main eq bond to the incoming water main may provide a good additional path to earth. However it would be unwise to rely on that as an earth since the water supplier may change it to plastic etc. So when testing your main earthing terminal, you disconnect any bonding connections to it for the duration of the test. Likewise eq bonding conductors in a bathroom, don't actually need any connection back to the main earth terminal to function correctly. I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It has to be said that something that relies on a passive length of wire and some pipe clamps is likely to be more reliable than something that needs working electro mechanics. Give it 10 years before it happens:-) Or are we looking at the thin edge of the wedge where all 17th edition installations will have to be tested by law every ten years to check the RCDs work correctly? Possibly after someone has died due to a failed RCD? I do a swimming pool EICR every year and have done so for the last 5 years. Two RCBO's have gone down in that time (they were installed 10 years ago). -- Adam |
#22
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Bathroom earth bonding
John Rumm wrote:
On 26/04/2017 10:58, Adam Funk wrote: On 2017-04-26, John Rumm wrote: On 25/04/2017 21:45, ARW wrote: I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It has to be said that something that relies on a passive length of wire and some pipe clamps is likely to be more reliable than something that needs working electro mechanics. I'm struggling to imagine how it could do any harm to have more bonding than required, as long as it's sound (i.e., not connected to anything "bad"). Depends on your definition of more than required... if you mean including bonding in a bathroom which meets the 17th edition exception and hence could in theory do without, then yup no harm, and not expensive. However some places take it to the extreme and festoon every bit of pipework with bonding cables in places where there is not an elevated shock injury risk. In those cases, there are probably other things you could do with an installation to get a better return on the investment. My house was wired (presumably not by a professional) with 10mm^2 green/yellow wire parallelling all the T&E circuits from the CU branching repeatedly with connection to all the pipework in every room. Since it is all surface wiring (for structural reasons) in boxes and trunking of various kinds I tend to strip out great reams of it every time I redecorate or alter anything. As all circuits (except the economy 7 one) are fast 30mA RCD protected it is hard to see what the objective was, but it seems to imply a confusion between bonding and circuit protection. Most of the rooms have no locally unearthed metalwork in them apart from the central heating, which is all copper anyway. For reasons which seem arbitrary, even earthed electrical fittings (such as outside lights) seem often to have a parallel 10mm^2 earth connection back to the CU. -- Roger Hayter |
#23
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Bathroom earth bonding
On 26/04/17 10:58, Adam Funk wrote:
On 2017-04-26, John Rumm wrote: On 25/04/2017 21:45, ARW wrote: I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It has to be said that something that relies on a passive length of wire and some pipe clamps is likely to be more reliable than something that needs working electro mechanics. I'm struggling to imagine how it could do any harm to have more bonding than required, as long as it's sound (i.e., not connected to anything "bad"). I have another POV on this. I can't quote chapter and verse as I do not have my book to hand and my memory is ****e. However, the 17th requires, IIRC, that any extraneous conductive parts aka water pipes entering a bathroom/etc to be bonded to the main earth as one of the conditions of not having supplementary bonding? g So assuming the bonding is good and equally so across all such pipes entering the bathroom, even without an RCD, the situation is hardly worse than if supplementary bonding were present. As far as I can see, all supplementary bonding does is keep it all local, reducing the chance that it gets bypassed (eg plastic pipe sections) or a local fault exists in the CPC to say the shaver socket. So SB makes for perhaps a more robust solution and one that *may* be easier to verify[1] but 17th style if done correctly ought to be as good, even if the RCD fails. Thoughts? [1] In reality, SB wires disappear under the floor and are often clamped in inaccessible places like under the bath so how easy is it to verify these, as opposed to just doing a loop test on all extraneous conductive parts relative to the MET? |
#24
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Bathroom earth bonding
On 27/04/2017 22:19, Tim Watts wrote:
On 26/04/17 10:58, Adam Funk wrote: On 2017-04-26, John Rumm wrote: On 25/04/2017 21:45, ARW wrote: I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It has to be said that something that relies on a passive length of wire and some pipe clamps is likely to be more reliable than something that needs working electro mechanics. I'm struggling to imagine how it could do any harm to have more bonding than required, as long as it's sound (i.e., not connected to anything "bad"). I have another POV on this. I can't quote chapter and verse as I do not have my book to hand and my memory is ****e. However, the 17th requires, IIRC, that any extraneous conductive parts aka water pipes entering a bathroom/etc to be bonded to the main earth as one of the conditions of not having supplementary bonding? Yup the main bonding must be in place - so incoming services, and extraneous metalwork that can distribute a potential around the building (typically CH pipework) g So assuming the bonding is good and equally so across all such pipes entering the bathroom, even without an RCD, the situation is hardly worse than if supplementary bonding were present. As far as I can see, all supplementary bonding does is keep it all local, reducing the chance that it gets bypassed (eg plastic pipe sections) or a local fault exists in the CPC to say the shaver socket. It keeps it local, and also electrically short - so more tightly controlled voltage differentials. So SB makes for perhaps a more robust solution and one that *may* be easier to verify[1] but 17th style if done correctly ought to be as good, even if the RCD fails. Thoughts? [1] In reality, SB wires disappear under the floor and are often clamped in inaccessible places like under the bath so how easy is it to verify these, as opposed to just doing a loop test on all extraneous conductive parts relative to the MET? Although the loop test does not find the metal that does enter the EQ zone, and could be made live by a fault, but is not bonded at entry (say a partial metal pipe install where the incoming main and initial pipework is plastic, and hence not included in the main bonding) -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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Bathroom earth bonding
On 28/04/17 01:39, John Rumm wrote:
Although the loop test does not find the metal that does enter the EQ zone, and could be made live by a fault, but is not bonded at entry (say a partial metal pipe install where the incoming main and initial pipework is plastic, and hence not included in the main bonding) Hi John, I need to dig out the big red book (I know..) and find the exact wording. But from memory, doesn't the 17th say: plumbing that is extraneous must have continuity back to the main bond, or something along those lines. In other words, if you have pipes entering the bathroom which do not have continuity to the MET, then you cannot meet the conditions for not having SB. The one thing I am not sure of is what "continuity" means here, and I really do need to check. It could mean "sufficient to trip an RCD" or it could be "sufficient to disconnect a fuse/breaker in 0.4s". I have a 17th design, but I've got hot, cold and eventually all CH main feeds cross bonded to each other in the hall cupboard as good measure - mostly to ensure hot and cold pipes and radiator (when fitted) have good continuity. |
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Bathroom earth bonding
On 28/04/2017 08:21, Tim Watts wrote:
On 28/04/17 01:39, John Rumm wrote: Although the loop test does not find the metal that does enter the EQ zone, and could be made live by a fault, but is not bonded at entry (say a partial metal pipe install where the incoming main and initial pipework is plastic, and hence not included in the main bonding) Hi John, I need to dig out the big red book (I know..) and find the exact wording. But from memory, doesn't the 17th say: plumbing that is extraneous must have continuity back to the main bond, or something along those lines. In other words, if you have pipes entering the bathroom which do not have continuity to the MET, then you cannot meet the conditions for not having SB. The one thing I am not sure of is what "continuity" means here, and I really do need to check. It could mean "sufficient to trip an RCD" or it could be "sufficient to disconnect a fuse/breaker in 0.4s". Sufficient to trip a 30mA RCD. Which of course may might when then the electrician did the work but may fail when some pipework is altered (and that pipework need not be in the bathroom). Local supplementary bonding removes that risk. -- Adam |
#27
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Bathroom earth bonding
On 27/04/2017 20:35, Roger Hayter wrote:
John Rumm wrote: On 26/04/2017 10:58, Adam Funk wrote: On 2017-04-26, John Rumm wrote: On 25/04/2017 21:45, ARW wrote: I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It has to be said that something that relies on a passive length of wire and some pipe clamps is likely to be more reliable than something that needs working electro mechanics. I'm struggling to imagine how it could do any harm to have more bonding than required, as long as it's sound (i.e., not connected to anything "bad"). Depends on your definition of more than required... if you mean including bonding in a bathroom which meets the 17th edition exception and hence could in theory do without, then yup no harm, and not expensive. However some places take it to the extreme and festoon every bit of pipework with bonding cables in places where there is not an elevated shock injury risk. In those cases, there are probably other things you could do with an installation to get a better return on the investment. My house was wired (presumably not by a professional) with 10mm^2 green/yellow wire parallelling all the T&E circuits from the CU branching repeatedly with connection to all the pipework in every room. Since it is all surface wiring (for structural reasons) in boxes and trunking of various kinds I tend to strip out great reams of it every time I redecorate or alter anything. As all circuits (except the economy 7 one) are fast 30mA RCD protected it is hard to see what the objective was, but it seems to imply a confusion between bonding and circuit protection. Most of the rooms have no locally unearthed metalwork in them apart from the central heating, which is all copper anyway. For reasons which seem arbitrary, even earthed electrical fittings (such as outside lights) seem often to have a parallel 10mm^2 earth connection back to the CU. Perhaps someone read this and got confused. http://electrical.theiet.org/wiring-...g.cfm?type=pdf -- Adam |
#28
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Bathroom earth bonding
On 28/04/17 18:22, ARW wrote:
Sufficient to trip a 30mA RCD. Thanks Adam. Which of course may might when then the electrician did the work but may fail when some pipework is altered (and that pipework need not be in the bathroom). Local supplementary bonding removes that risk. I agree that it's more foolproof in general (with the caveats that it's not always easy to inspect once things are panelled in). I'm happy with my house being sans SB as it was designed with that in mind from the get go, but I do have cross bonding straps in the cupboard where the pipes disappear off to the bathroom - mostly to ensure continuity remains between hot, cold and heating pipes (when they exist) and are not reliant on the boiler manifold (when it exists) to achieve this. I also test loop impedance is sufficient to trip the relevant MCBs in 0.4sec - I am surprised that was not written into the regs as it would have reduced the reliance on the RCD element. That's more identifying a likely scenario where things might get buggered up (eg boiler removed or replaced) and dealing with that rather than any book standard approach. I was keen to avoid SB as I have all my pipes on show - but if that weren't a consideration, I'd have put it in conventionally. In fact I will possibly build SB into the shower room as the pipes are mostly bunched in the underbasin cupboard. |
#29
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Bathroom earth bonding
ARW wrote:
On 27/04/2017 20:35, Roger Hayter wrote: snip My house was wired (presumably not by a professional) with 10mm^2 green/yellow wire parallelling all the T&E circuits from the CU branching repeatedly with connection to all the pipework in every room. Since it is all surface wiring (for structural reasons) in boxes and trunking of various kinds I tend to strip out great reams of it every time I redecorate or alter anything. As all circuits (except the economy 7 one) are fast 30mA RCD protected it is hard to see what the objective was, but it seems to imply a confusion between bonding and circuit protection. Most of the rooms have no locally unearthed metalwork in them apart from the central heating, which is all copper anyway. For reasons which seem arbitrary, even earthed electrical fittings (such as outside lights) seem often to have a parallel 10mm^2 earth connection back to the CU. Perhaps someone read this and got confused. http://electrical.theiet.org/wiring-...g.cfm?type=pdf That's a thought, but seeing it was an ordinary house and done about thirty years ago I suspect it was just a misunderstanding of supplementary bonding. It is a PME installation. -- Roger Hayter |
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Bathroom earth bonding
On 25/04/17 21:45, ARW wrote:
I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It's worth noting (from the Red Book, I've mislaid my green): 701.415.2 " .... Supplementary equipotential bonding may be installed outside or inside a room containing a bath or a shower, preferably close to the point of entry of extraneous conductive parts into such rooms." (I'd be grateful to know if that wording remains in the latest 17th?) ....So you don't have to make a mess of a tiled room and have clamps on show everywhere to meet SB. I've been thinking about your argument Adam, and it is persuasive. And I would not be surprised either if they revise it - maybe in 10 years when a couple of people who never test their RCDs have got a belt. I am going to build SB into my shower room (we're laying the floor screed for that in 2 weeks) - that's really trivial as the shaver socket and pipes all pass through to or back onto the lobby cupboard so the clamps can go there. I am tempted, at some point to add SB back to the main bathroom at some point. The 17th exemption seemed like a good idea at the time, but... Only problem there is the SB runs are tortuous. Pipes exit under the stairs 1m from bathroom - that's OK, convenient and fairly obvious clamping point. But to get to shaver socket and bit of pipe to high level loo cistern (if that's in the zones, have to check) require going up through the ceiling and some 5-7 metres around. It would work and I can see nothing in the regs that precludes this - it just won't be terribly obvious what's going on to anyone else. What's your opinion on that (long SB wire routing)? Cheers, Tim |
#31
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Bathroom earth bonding
On 30/04/2017 16:33, Tim Watts wrote:
On 25/04/17 21:45, ARW wrote: I have said it before, and I'll say it again. Bathroom electrics will one day need supplementary bonding fitting again. RCDs are not good enough. It's worth noting (from the Red Book, I've mislaid my green): 701.415.2 " ... Supplementary equipotential bonding may be installed outside or inside a room containing a bath or a shower, preferably close to the point of entry of extraneous conductive parts into such rooms." (I'd be grateful to know if that wording remains in the latest 17th?) ...So you don't have to make a mess of a tiled room and have clamps on show everywhere to meet SB. I've been thinking about your argument Adam, and it is persuasive. And I would not be surprised either if they revise it - maybe in 10 years when a couple of people who never test their RCDs have got a belt. I am going to build SB into my shower room (we're laying the floor screed for that in 2 weeks) - that's really trivial as the shaver socket and pipes all pass through to or back onto the lobby cupboard so the clamps can go there. I am tempted, at some point to add SB back to the main bathroom at some point. The 17th exemption seemed like a good idea at the time, but... Only problem there is the SB runs are tortuous. Pipes exit under the stairs 1m from bathroom - that's OK, convenient and fairly obvious clamping point. But to get to shaver socket and bit of pipe to high level loo cistern (if that's in the zones, have to check) require going up through the ceiling and some 5-7 metres around. It would work and I can see nothing in the regs that precludes this - it just won't be terribly obvious what's going on to anyone else. What's your opinion on that (long SB wire routing)? It's possible to work out a maximum touch voltage between two metallic objects (one at 230V and one at 0V) bonded by a 4 mm earth cable. However I have been in the pub for 6 hours (mt apologies to Wakefield) and I'll pass on trying that calculation today. -- Adam |
#32
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Bathroom earth bonding
On 30/04/17 18:03, ARW wrote:
On 30/04/2017 16:33, Tim Watts wrote: What's your opinion on that (long SB wire routing)? It's possible to work out a maximum touch voltage between two metallic objects (one at 230V and one at 0V) bonded by a 4 mm earth cable. However I have been in the pub for 6 hours (mt apologies to Wakefield) and I'll pass on trying that calculation today. Thanks Adam. If that's all it comes down to, fair enough. However, the potential difference would also depend on what's connecting the Ov and 230V sides. 4mm2 is not much compared to the area of copper in a 15mm water pipe which is about 32mm2 for 0.7mm walled pipe. OTOH 4mm2 is vastly larger than the 1 - 1.5mm2 CPC in the lighting circuit which also has a long run to origin. Less true with a shower though that might have a 4mm2 CPC and larger live conductors. So how is the theory of supplementary bonding handled? Presumably some allowance must be made for ADS being operational? |
#33
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Bathroom earth bonding
On 30/04/2017 18:56, Tim Watts wrote:
On 30/04/17 18:03, ARW wrote: On 30/04/2017 16:33, Tim Watts wrote: What's your opinion on that (long SB wire routing)? It's possible to work out a maximum touch voltage between two metallic objects (one at 230V and one at 0V) bonded by a 4 mm earth cable. However I have been in the pub for 6 hours (mt apologies to Wakefield) and I'll pass on trying that calculation today. Thanks Adam. If that's all it comes down to, fair enough. However, the potential difference would also depend on what's connecting the Ov and 230V sides. 4mm2 is not much compared to the area of copper in a 15mm water pipe which is about 32mm2 for 0.7mm walled pipe. OTOH 4mm2 is vastly larger than the 1 - 1.5mm2 CPC in the lighting circuit which also has a long run to origin. Less true with a shower though that might have a 4mm2 CPC and larger live conductors. So how is the theory of supplementary bonding handled? Presumably some allowance must be made for ADS being operational? You keep the touch voltages between two objects to less than 50V. If the ADS is still working in 10 years time (ie the RCDs) then fine. The maximum potential difference with EEBADs is down to the resistance of the 4mm cable between the two points connected by that cable. And yes I would expect an MCB or fuse to trip before this sort of thing happened. No matter what you design for some pillock will still manage to mess it up. -- Adam |
#34
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Bathroom earth bonding
On Monday, 1 May 2017 17:01:01 UTC+1, ARW wrote:
On 30/04/2017 18:56, Tim Watts wrote: On 30/04/17 18:03, ARW wrote: On 30/04/2017 16:33, Tim Watts wrote: What's your opinion on that (long SB wire routing)? It's possible to work out a maximum touch voltage between two metallic objects (one at 230V and one at 0V) bonded by a 4 mm earth cable. However I have been in the pub for 6 hours (mt apologies to Wakefield) and I'll pass on trying that calculation today. Thanks Adam. If that's all it comes down to, fair enough. However, the potential difference would also depend on what's connecting the Ov and 230V sides. 4mm2 is not much compared to the area of copper in a 15mm water pipe which is about 32mm2 for 0.7mm walled pipe. OTOH 4mm2 is vastly larger than the 1 - 1.5mm2 CPC in the lighting circuit which also has a long run to origin. Less true with a shower though that might have a 4mm2 CPC and larger live conductors. So how is the theory of supplementary bonding handled? Presumably some allowance must be made for ADS being operational? You keep the touch voltages between two objects to less than 50V. If the ADS is still working in 10 years time (ie the RCDs) then fine. The maximum potential difference with EEBADs is down to the resistance of the 4mm cable between the two points connected by that cable. And yes I would expect an MCB or fuse to trip before this sort of thing happened. No matter what you design for some pillock will still manage to mess it up. PSCC of domstic wiring is anything upto 6kA. 4mm2 voltage drop is 5.5mV/A/m or 5.5v/kA/m You can calculate from that, adding in the R of the supplying lighting circuit. NT |
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