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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#1
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Earth wire from consumer unit.
I'm having central heating installed, 75% done.
Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. mark |
#2
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Earth wire from consumer unit.
On Nov 5, 5:50 pm, "Mark" wrote:
I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. mark Is your plumber an electrician? Why is he even getting involved in this? |
#3
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Earth wire from consumer unit.
"stevelup" wrote in message ups.com... On Nov 5, 5:50 pm, "Mark" wrote: I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. mark Is your plumber an electrician? Why is he even getting involved in this? He isn't. He's not getting involved as he's put it on to me. I was going to route the cable then have an electrician do the connections but that's not my question. mark |
#4
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Earth wire from consumer unit.
In article ,
Mark wrote: I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. This cross bonding is concerned with the house pipework - not the supply. And the house gas pipework is likely copper? I'm pretty certain if the gas pipe is buried in concrete etc which makes it difficult to get to the meter end, bonding to where it first surfaces inside the house will be ok. However if it simply runs under floorboards where it's too much trouble to lift them this approach doesn't comply. -- *Xerox and Wurlitzer will merge to market reproductive organs. Dave Plowman London SW To e-mail, change noise into sound. |
#5
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Earth wire from consumer unit.
"Dave Plowman (News)" wrote in message ... In article , Mark wrote: I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. This cross bonding is concerned with the house pipework - not the supply. And the house gas pipework is likely copper? I'm pretty certain if the gas pipe is buried in concrete etc which makes it difficult to get to the meter end, bonding to where it first surfaces inside the house will be ok. However if it simply runs under floorboards where it's too much trouble to lift them this approach doesn't comply. Thanks for replying. The pipework is all copper. To get from the consumer unit to where the copper gas pipe enters the house is quite long route and lots of t&g floorboards to lift. Does it need to be as near the meter or house entry as possible? I guess what I'm trying to say is, can't it be connected to a copper pipe a bit more convenient. mark |
#6
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Earth wire from consumer unit.
On Nov 5, 6:36 pm, "Mark" wrote:
"stevelup" wrote in message ups.com... On Nov 5, 5:50 pm, "Mark" wrote: I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. mark Is your plumber an electrician? Why is he even getting involved in this? He isn't. He's not getting involved as he's put it on to me. I was going to route the cable then have an electrician do the connections but that's not my question. mark Sorry, you misunderstood me. What I mean is - why has the issue even arisen? How does the plumber - who is not an electrician - know there is something wrong with your earth bonding? Really all he needs to concern himself with is bonding all his pipework together at the boiler end. Has he explained why he thinks this extra work is necessary? You might not even have an electricity supply which requires supplementary bonding. How long has the current electrical installation been in place? Steve |
#7
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Earth wire from consumer unit.
stevelup wrote:
On Nov 5, 6:36 pm, "Mark" wrote: "stevelup" wrote in message ups.com... On Nov 5, 5:50 pm, "Mark" wrote: I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. mark Is your plumber an electrician? Why is he even getting involved in this? He isn't. He's not getting involved as he's put it on to me. I was going to route the cable then have an electrician do the connections but that's not my question. mark Sorry, you misunderstood me. What I mean is - why has the issue even arisen? How does the plumber - who is not an electrician - know there is something wrong with your earth bonding? If there's no bonding there, then there *is* a potential issue - simple as that. |
#8
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Earth wire from consumer unit.
On Nov 5, 9:54 pm, Lobster wrote:
stevelup wrote: On Nov 5, 6:36 pm, "Mark" wrote: "stevelup" wrote in message roups.com... On Nov 5, 5:50 pm, "Mark" wrote: I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. mark Is your plumber an electrician? Why is he even getting involved in this? He isn't. He's not getting involved as he's put it on to me. I was going to route the cable then have an electrician do the connections but that's not my question. mark Sorry, you misunderstood me. What I mean is - why has the issue even arisen? How does the plumber - who is not an electrician - know there is something wrong with your earth bonding? If there's no bonding there, then there *is* a potential issue - simple as that. Agreed but it is not forced to be the case - PME is not mandatory - it depends on the type of incoming supply. If there is no existing PME arrangement, then it is probable that it is not needed. Steve |
#9
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Earth wire from consumer unit.
.. What I mean is - why has the issue even arisen? How does the plumber - who is not an electrician - know there is something wrong with your earth bonding? Really all he needs to concern himself with is bonding all his pipework together at the boiler end. Has he explained why he thinks this extra work is necessary? You might not even have an electricity supply which requires supplementary bonding. How long has the current electrical installation been in place? Steve Rewiring is recent. Central heating is in progress. Seems like the electrician forgot to put an earth into the consumer unit. I just want it to end up safe and conforming. mark |
#10
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Earth wire from consumer unit.
"stevelup" wrote in message ups.com... On Nov 5, 5:50 pm, "Mark" wrote: I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. mark Is your plumber an electrician? Why is he even getting involved in this? Any CORGI plumber worth his salt would check for main equipotential bonding on the gas and advise the customer that it needs doing if it is not done. Adam |
#11
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Earth wire from consumer unit.
Any CORGI plumber worth his salt would check for main equipotential bonding on the gas and advise the customer that it needs doing if it is not done. He is. He has. Hence my original question. mark |
#12
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Earth wire from consumer unit.
Mark wrote:
"Dave Plowman (News)" wrote in message ... In article , Mark wrote: I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. This cross bonding is concerned with the house pipework - not the supply. And the house gas pipework is likely copper? I'm pretty certain if the gas pipe is buried in concrete etc which makes it difficult to get to the meter end, bonding to where it first surfaces inside the house will be ok. However if it simply runs under floorboards where it's too much trouble to lift them this approach doesn't comply. Thanks for replying. The pipework is all copper. To get from the consumer unit to where the copper gas pipe enters the house is quite long route and lots of t&g floorboards to lift. Does it need to be as near the meter or house entry as possible? I guess what I'm trying to say is, can't it be connected to a copper pipe a bit more convenient. mark I dont see how you expect folk to suggest how or where to route the wire when we dont know the construction or layout of the place. All that can be said is a few generalities, such as its often not necessary to lift floorboards to route wires, and that wire can be routed externally without it being too visible - but with no further info, who knows what details are involved. NT |
#13
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Earth wire from consumer unit.
stevelup wrote:
If there is no existing PME arrangement, then it is probable that it is not needed. This is nothing to do with PME. If the house has metallic gas pipeing then this must be included in the main equipotential bonding. This is irrespective of the type of earthing arrangement of the supply. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#14
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Earth wire from consumer unit.
Mark wrote:
I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. The requirement is that the house pipework is bonded on the consumers side of the meter as soon as is practical after it enters the house. Often this is actually implemented by effecting the bond in the external meter box if you have one, however this is not actually the letter of the requirement since it is not after entry as such. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#15
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Earth wire from consumer unit.
Mark wrote:
Thanks for replying. The pipework is all copper. To get from the consumer unit to where the copper gas pipe enters the house is quite long route and lots of t&g floorboards to lift. Does it need to be as near the meter or house entry as possible? I guess what I'm trying to say is, can't it be connected to a copper pipe a bit more convenient. In reality if all the pipe joints were soldered then that would achieve the desired result in practical terms. However it may not pass inspection since it is not to the letter of the regulation. There is nothing to stop you routing the main bond by a indirect route if it helps (i.e. outside and back in later, up into a first floor void etc). -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#16
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Earth wire from consumer unit.
"Mark" wrote in message ... Any CORGI plumber worth his salt would check for main equipotential bonding on the gas and advise the customer that it needs doing if it is not done. He is. He has. Hence my original question. mark If the copper pipework runs outside the house from the gas meter and then enters the house near the CU and has no branches from it before the point of entry to the house then bond the copper pipework at the point of entry to the building. Adam |
#17
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Earth wire from consumer unit.
"John Rumm" wrote in message ... Mark wrote: I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. The requirement is that the house pipework is bonded on the consumers side of the meter as soon as is practical after it enters the house. Often this is actually implemented by effecting the bond in the external meter box if you have one, however this is not actually the letter of the requirement since it is not after entry as such. Meter is in a semi-concealed box at side of house. A 28mm copper pipe runs up the wall and across the bedroom floor then into a landing cupboard where the boiler is housed. I can join the earth cable to this copper pipe in the bedroom without too much trouble. This will be my 'as soon as practical' solution. It was the thought of having to route it across the bedroom and down the wall which prompted my original question. I'm doing this to conform to regs. I don't really understand why. Thanks for all the responses. mark |
#18
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Earth wire from consumer unit.
In article ,
Mark wrote: Meter is in a semi-concealed box at side of house. A 28mm copper pipe runs up the wall and across the bedroom floor then into a landing cupboard where the boiler is housed. I can join the earth cable to this copper pipe in the bedroom without too much trouble. This will be my 'as soon as practical' solution. It was the thought of having to route it across the bedroom and down the wall which prompted my original question. It really needs to go where the pipe comes into the house. Unless you can prove it is a continuous length from there to where you propose fitting it. I'm doing this to conform to regs. I don't really understand why. Well, consider the fact that the pipe from the street is plastic. A metal one running through earth would provide an earth of sorts - but plastic won't. The copper within the house is connected to what? A boiler, gas fire, cooker etc all of may also be connected to electricity. If one of those developed a fault it's conceivable the electricity could get to the pipe. And make all the copper pipe 'live'. I know it's unlikely but protective measures have to allow for every possibility. Thanks for all the responses. -- *The average person falls asleep in seven minutes * Dave Plowman London SW To e-mail, change noise into sound. |
#19
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Earth wire from consumer unit.
"Mark" wrote I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. My understanding was that the point of connection to piping should be accessible so that the presence and security of a pipe clamp and cable could be checked in future. If this point would be under flooring at the point of entry into the house, shouldn't the connection deliberately be made in a cupboard or other downstream more accessible location anyway?? Phil |
#20
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Earth wire from consumer unit.
On 5 Nov, 22:36, "ARWadsworth" wrote:
"stevelup" wrote in message ups.com... On Nov 5, 5:50 pm, "Mark" wrote: I'm having central heating installed, 75% done. Plumber tells me I need an earth wire from the consumer unit to the outside gas meter. This is quite difficult to achieve without leaving lots of earth cable visible. Are there alternative options for me? Also, as the incoming gas supply is plastic I can't see the point. mark Is your plumber an electrician? Why is he even getting involved in this? Any CORGI plumber worth his salt would check for main equipotential bonding on the gas and advise the customer that it needs doing if it is not done. Adam Mine ran a new pipe back to the meter cupboard. No problem so far, except he removed the earth clamp attached to the old pipe, and left it dangling. Ben |
#21
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Earth wire from consumer unit.
On Nov 5, 11:51 pm, John Rumm wrote:
stevelup wrote: If there is no existing PME arrangement, then it is probable that it is not needed. This is nothing to do with PME. If the house has metallic gas pipeing then this must be included in the main equipotential bonding. This is irrespective of the type of earthing arrangement of the supply. I understand - sorry. Steve |
#22
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Earth wire from consumer unit.
Dave Plowman (News) wrote:
Well, consider the fact that the pipe from the street is plastic. A metal one running through earth would provide an earth of sorts - but plastic won't. Which means plastic is safer. If the gas pipe were metal, in contact with earth, then it would constitute an "extraneous-conductive-part" in the language of BS 7671 - i.e. it's capable of importing a potential (voltage) which might be different to that of the house electrical earthing. The extreme example of this is a house on a PME supply where the supplier's neutral connection has broken and all the electrical earths are live at 230 V relative to an unbonded service pipe which remains at the real local ground potential. Hence the requirement for *bonding* (not "earthing" or "earth bonding") all incoming services to equalise their potentials. *Bonding* reduces the risk of dangerous touch voltages appearing between different accessible bits of metal. Now, plastic service pipes don't constitute extraneous-conductive-parts, and nor does the metal installation pipework downstream, provided it doesn't come into contact with the ground. Hence, if you read BS 7671 literally, there's no requirement to bond metal gas or water pipework fed from plastic service pipes. However the IEE, in its practical advice (e.g. the OSG), continues to recommend that metal installation pipework is bonded, probably because of the risk of some ground contact occurring - contact with damp walls or grounded structural metalwork and that sort of thing. The upshot of this is that it will be very difficult to convince anyone doing formal inspection and testing that no bonding is necessary. The copper within the house is connected to what? A boiler, gas fire, cooker etc all of may also be connected to electricity. If one of those developed a fault it's conceivable the electricity could get to the pipe. And make all the copper pipe 'live'. I know it's unlikely but protective measures have to allow for every possibility. But the protective measure there is the *earthing* of the electrical equipment concerned [1] which ensures that the supply is quickly cut off (by fuse, MCB or RCD) when such a fault occurs. Note that earthing does *not* prevent the metalwork becoming live - during the fault a significant fraction of the mains voltage will be dropped across the relevant circuit protective conductor (CPC) - it just ensures that it won't stay live for very long. It really is quite important to understand that earthing and bonding are quite different things, even though the same piece of wire can sometimes carry out both jobs. Talking about "earth bonding" is strongly deprecated, even though the sort of bonding we're talking about here is earth/ed/. [1] Or the use of Class 2 equipment (sometimes incorrectly called double-insulated). -- Andy |
#23
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Earth wire from consumer unit.
In article ,
Andy Wade wrote: Well, consider the fact that the pipe from the street is plastic. A metal one running through earth would provide an earth of sorts - but plastic won't. Which means plastic is safer. Yes, have everything in the house made of plastic and the risk of electrocution diminishes. If the gas pipe were metal, in contact with earth, then it would constitute an "extraneous-conductive-part" in the language of BS 7671 - i.e. it's capable of importing a potential (voltage) which might be different to that of the house electrical earthing. Round here many are still iron barrel from house to street main - they simply pushed plastic through it when they changed. How it is sealed to the iron barrel I have no idea - but there is electrical continuity across the gas meter to the pipe which disappears to the street. The extreme example of this is a house on a PME supply where the supplier's neutral connection has broken and all the electrical earths are live at 230 V relative to an unbonded service pipe which remains at the real local ground potential. Hence the requirement for *bonding* (not "earthing" or "earth bonding") all incoming services to equalise their potentials. *Bonding* reduces the risk of dangerous touch voltages appearing between different accessible bits of metal. Think you're splitting hairs. Incoming services are bonded to the same 'earth'. Which may or may not be a true earth - whatever that is. Now, plastic service pipes don't constitute extraneous-conductive-parts, and nor does the metal installation pipework downstream, provided it doesn't come into contact with the ground. Hence, if you read BS 7671 literally, there's no requirement to bond metal gas or water pipework fed from plastic service pipes. However the IEE, in its practical advice (e.g. the OSG), continues to recommend that metal installation pipework is bonded, probably because of the risk of some ground contact occurring - contact with damp walls or grounded structural metalwork and that sort of thing. The upshot of this is that it will be very difficult to convince anyone doing formal inspection and testing that no bonding is necessary. The copper within the house is connected to what? A boiler, gas fire, cooker etc all of may also be connected to electricity. If one of those developed a fault it's conceivable the electricity could get to the pipe. And make all the copper pipe 'live'. I know it's unlikely but protective measures have to allow for every possibility. But the protective measure there is the *earthing* of the electrical equipment concerned [1] which ensures that the supply is quickly cut off (by fuse, MCB or RCD) when such a fault occurs. So you're happy to hypothesise about the neutral failing in a PME installation but not an appliance ground being faulty? I know which one I reckon is more common. Note that earthing does *not* prevent the metalwork becoming live - during the fault a significant fraction of the mains voltage will be dropped across the relevant circuit protective conductor (CPC) - it just ensures that it won't stay live for very long. Please define 'live'? It really is quite important to understand that earthing and bonding are quite different things, even though the same piece of wire can sometimes carry out both jobs. Talking about "earth bonding" is strongly deprecated, even though the sort of bonding we're talking about here is earth/ed/. What most set out to do is confuse. [1] Or the use of Class 2 equipment (sometimes incorrectly called double-insulated). More semantics. -- *I love cats...they taste just like chicken. Dave Plowman London SW To e-mail, change noise into sound. |
#24
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Earth wire from consumer unit.
In message , John Rumm
writes There is nothing to stop you routing the main bond by a indirect route if it helps (i.e. outside and back in later that's two suggestions to route it outside I've read - is it really a good idea to route a wire essential for safety via a place where it could be interfered with? -- So (must get this sig automated!) |
#25
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Earth wire from consumer unit.
dave wrote:
On Mon, 5 Nov 2007 19:56:49 -0000, "Mark" wrote: Thanks for replying. The pipework is all copper. To get from the consumer unit to where the copper gas pipe enters the house is quite long route and lots of t&g floorboards to lift. Does it need to be as near the meter or house entry as possible? I guess what I'm trying to say is, can't it be connected to a copper pipe a bit more convenient. OT but coincdentally, today I had a letter from the gas co. telling me that they want to come and change my gas meter for a newer one in a couple of weeks. Having read this thread I went and checked if the existing meter has an earth bond anywhere - and yipeee (sarcastic) it hasn't. Being pessimistic, does this mean the gas fitter could come along and refuse to install the new meter (after disconnecting the old one of course) because of this lack of an earth bond? The distance from gas meter to CU and earthbond is about 3 feet! Wouldn't this be one of those cases where there's no compulsion to upgrade an existing installation to meet modern regs? Surely cross-bonding of the incoming services to the main earth hasn't always been compulsory (at least, not judging by the number of times I've had to install it myself!) David |
#26
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Earth wire from consumer unit.
dave wrote:
OT but coincdentally, today I had a letter from the gas co. telling me that they want to come and change my gas meter for a newer one in a couple of weeks. Watch the guy like a hawk, and make sure they don't leave leaks. I don't know if the twit who changed my meter was a CORGI (looked more like a quickly trained temp), but we had to call out Transco when we started smelling something gassy soon after. Secondly, they have to reignite the boiler after completing the work. This is the point where he may shake his head (if qualified to do so), mutter something about poor servicing and ventilation - and plant an expensive for this time of year 'do not use' notice capping the pipe as well. Happened to me :-( Can't you put them off until the spring? -- Adrian C |
#27
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Earth wire from consumer unit.
Si wrote:
In message , John Rumm writes There is nothing to stop you routing the main bond by a indirect route if it helps (i.e. outside and back in later that's two suggestions to route it outside I've read - is it really a good idea to route a wire essential for safety via a place where it could be interfered with? Well its a judgement call. If its a short distance in your own garden, and especially if in conduit or trunking, then it seems pretty safe. If it was on the front of a building that was faced directly onto a public street, then the answer may well be different. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#28
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Earth wire from consumer unit.
Lobster wrote:
Wouldn't this be one of those cases where there's no compulsion to upgrade an existing installation to meet modern regs? There is no compulsion if you are not making changes. However, once you make a change anywhere then you ought to do it. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#29
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Earth wire from consumer unit.
Si wrote:
In message , John Rumm writes There is nothing to stop you routing the main bond by a indirect route if it helps (i.e. outside and back in later that's two suggestions to route it outside I've read - is it really a good idea to route a wire essential for safety via a place where it could be interfered with? Its not essential for safety, its a safety extra. NT |
#30
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Earth wire from consumer unit.
Dave Plowman (News) wrote:
In article , Andy Wade wrote: If the gas pipe were metal, in contact with earth, then it would constitute an "extraneous-conductive-part" in the language of BS 7671 - i.e. it's capable of importing a potential (voltage) which might be different to that of the house electrical earthing. Round here many are still iron barrel from house to street main - they simply pushed plastic through it when they changed. How it is sealed to the iron barrel I have no idea - but there is electrical continuity across the gas meter to the pipe which disappears to the street. Although Transco often use insulating inserts on the supply side of the meter, with the aim or preventing earth leakage and diverted neutral currents flowing in their metal pipes. (See 4.2(iii) and 4.3 in the OSG.) Think you're splitting hairs. No, I think that understanding the conceptual difference between earthing and bonding is key to understanding the subject. It's unhelpful when people muddy the water by referring to bonding as earthing or using woolly terms like "earth bonding." Think of earthing as being active protection, while bonding is passive. Incoming services are bonded to the same 'earth'. True, and ...? Which may or may not be a true earth - whatever that is. .... you've just demonstrated the need to define an equipotential zone by bonding, so that the local ground potential is made largely irrelevant. So you're happy to hypothesise about the neutral failing in a PME installation but not an appliance ground being faulty? I know which one I reckon is more common. That's unfair. The PME neutral failing brings immediate danger (mitigated by the bonding) but the o/c CPC situation requires a second fault (insulation failure) to develop before a dangerous situation arises. And that's why ... EaWR ... preventative maintenance ... etc. Note that earthing does *not* prevent the metalwork becoming live - during the fault a significant fraction of the mains voltage will be dropped across the relevant circuit protective conductor (CPC) - it just ensures that it won't stay live for very long. Please define 'live'? In this context just "at a hazardous voltage" (wrt surroundings) will do; above the ELV limit; 50 V AC. In a circuit where the phase and CPC are the same size (and simplifying by assuming that Ze Zs) then during an earth fault an exposed-conductive-part may rise to half mains voltage until the protective device operates. If the circuit's wired in T&E with a reduced size CPC then the voltage is higher, being Uo * m/(1+m), where m is the ratio of L&N size to CPC size. 4 mm^2 is the worst case with an m of 2.67, giving a fault voltage of around 170 V. More semantics. Isn't accurate use of language important in all technical disciplines? In the present field there's a well defined vocabulary and no excuse... -- Andy |
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Wire size for supply to small consumer unit in shed | UK diy | |||
Consumer unit Œ | UK diy | |||
Consumer unit change - earth bonding | UK diy | |||
new consumer unit-do i need an RCD? | UK diy | |||
Earth bonding at Consumer Unit. | UK diy |