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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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Earth Bonding Water Heater
I need to cross bond two sinks fed by an instant electric water heater in a
cloakroom (no bath or shower.) I intend to bond the water inlet and outlet pipes at the water heater with 6mm earth cable - all pipework and connections from here to the taps are metal. Do I need to run the earth bonding cable into the water heater earth terminal as well? The heater is fed by a 10mm cable with a 45 amp double pole switch just below the ceiling. I suspect that it will be very tight to get another cable into the terminal block! Thanks. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.624 / Virus Database: 401 - Release Date: 15/03/2004 |
#2
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Earth Bonding Water Heater
I need to cross bond two sinks fed by an instant electric water heater in
a cloakroom (no bath or shower.) No you don't. Supplementary bonding is not required. Christian. |
#3
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Earth Bonding Water Heater
"Christian McArdle" wrote in message et... I need to cross bond two sinks fed by an instant electric water heater in a cloakroom (no bath or shower.) No you don't. Supplementary bonding is not required. Christian. Thanks. Interesting. I have a failure certificate from an NICEIC member electrician stating that this needs to be done before we get a pass! Would it make a difference that this installation is in a public building and not a domestic property? --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.624 / Virus Database: 401 - Release Date: 15/03/2004 |
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Earth Bonding Water Heater
On Thu, 18 Mar 2004 17:34:26 -0000, in uk.d-i-y "Doctor D."
strung together this: "Christian McArdle" wrote in message . net... I need to cross bond two sinks fed by an instant electric water heater in a cloakroom (no bath or shower.) No you don't. Supplementary bonding is not required. Christian. Thanks. Interesting. I have a failure certificate from an NICEIC member electrician stating that this needs to be done before we get a pass! I know of an NICEIC member who is obsessed with bonding anything remotely metallic, regardless of whether it inherantly reduces safety or not! It doesn't neccesarily mean they know what they're doing because they're in the NICEIC or similar. Would it make a difference that this installation is in a public building and not a domestic property? Regs is regs. Although it does depend on what type of public building, and whereabouts within it the pipework is. Also some authorities specify 'extra regulations' over and above BS7671 so it may need doing. Doubtful though. -- SJW A.C.S. Ltd. |
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Earth Bonding Water Heater
In message j3l6c.284$W11.194@newsfe1-win,
"Doctor D." wrote: "Christian McArdle" wrote in message et... I need to cross bond two sinks fed by an instant electric water heater in a cloakroom (no bath or shower.) No you don't. Supplementary bonding is not required. Christian. Thanks. Interesting. I have a failure certificate from an NICEIC member electrician stating that this needs to be done before we get a pass! Would it make a difference that this installation is in a public building and not a domestic property? Quite the opposite. BS7671 specifically isn't statutory (yet) for domestic properties, but through the Electricity at Work Act etc. is for just about everywhere else. I've always found this aspect of supplementary bonding puzzling, and I now think I've found the reason. John Whitfield's excellent "The Electrician's Guide to the 16th Edition of the IEE Wiring Regulations BS7671" quite emphatically states that all extraneous conductive parts should be bonded anywhere where there is a chance of a person simultaneously touching an earthed electrical device and the aforementioned extraneous conductive part (section 5.4.3). This book is in many ways the jobbing electrician's Bible, and I'm sure that this is why you see bonding in kitchens, loos and laundry rooms. But the purpose of this bonding is to ensure that a person doing so doesn't experience dangerous level of exposure. John Whitfield does some needlessly complicated multiplication and division, based on some rules of thumb about safe levels of current and the average resistance of the human body and comes to the conclusion that unless your extraneous conductive part has 25kR or more of resistance to the system earth it *must* be bonded. If this is really the case then why the heck don't we bond radiators next to sockets in living rooms and bedrooms? The safety requirement is enshrined in BS7671:2001 413-02-04 where as far as I can tell it actually states that the requirement for TN systems is a 0.4s disconnection time (413-02-08) and for TT systems that (basically) there should never be more than 50V between an exposed conductive part (e.g. the metal case of an electrical item) and an extraneous conductive part (your water pipes) (413-02-20). There's something in there about 5s disconnection too, but the 50V is the important bit for this discussion. So, apart from "locations containing a bath or shower" which have their own over-riding supplementary bonding rules (section 601) and certain other applications (part 6), this means that if you can prove that a phase-earth short will trip your MCB in 0.4 seconds (TN systems) or not give rise to more than 50V (TT systems) you are ok. The complication is that the 50V requirement is almost impossible to meet for a TT system as the impedance of the earth rod is usually too high. In this case an RCD is fitted which of course will trip with a much lower current and hence makes meeting the 50V test easy. So is supplementary bonding in locations outside a bathroom ever neccessary? Let's go back to 413-02-04: "Where the conditions for automatic disconnection [discussed above]... cannot be fulfilled by using overcurrent protective devices, then either: (i) local supplementary equipotential bonding shall be applied... but the use of such bonding does not obviate the need to disconnect the supply for reasons other than protection against electric shock, such as thermal effects, or (ii) protection shall be provided by means of a residual current device." To summarise, the way I see it is this: Supplementary bonding is *always* required in a bathroom. If your circuits meet the 0.4s / 50V tests then it is *not* required in kitchens, downstairs loos, places with sinks or laundry rooms etc. Point the electrician who failed you in the direction of 413-02. The reason you see such a lot of bonding in places like this, even on new installations is not that the circuits don't meet the tests but rather that the electricians in question have read John Whitfield's book :-) fx: sits back and waits to be shot down in flames HTH Hwyl! M. -- Martin Angove: http://www.tridwr.demon.co.uk/ Two free issues: http://www.livtech.co.uk/ Living With Technology .... Dessert? I'll take a piece of cherry ã. |
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Earth Bonding Water Heater
Martin,
Some comprehensive research there! Diolch Yn Fawr. David. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.624 / Virus Database: 401 - Release Date: 15/03/2004 |
#7
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Earth Bonding Water Heater
In message ,
"Doctor D." wrote: Martin, Some comprehensive research there! Diolch Yn Fawr. Pleser. What worries me is that no-one has argued with it yet... almost 24 hours... Hwyl! M. -- Martin Angove: http://www.tridwr.demon.co.uk/ Two free issues: http://www.livtech.co.uk/ Living With Technology .... A trampoline is for cunning stunts, a truncheon for apprehending criminals |
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Earth Bonding Water Heater
In message , Martin Angove
writes What worries me is that no-one has argued with it yet... almost 24 hours... Hwyl! M. That's because you're probably right in your analysis. John Whitfield's book is probably being followed unthinkingly by electricians up and down the country. -- Steve |
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