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17th Edition and Bonding Info Required

Discussion in 'Electrics UK' started by CliveDiy, 29 Jan 2009.

  1. CliveDiy

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    Hi

    Can anyone help please.

    First of all can I say I am fully aware of part P of the Building Regs and it’s constraints.

    My house does have a main 10mm bonding conductor from the consumer unit onto the gas service pipe and then looped across onto the rising main water pipe with no break in the cable.

    Bonding in bathrooms, I’ve seen bonding in bathrooms where the hot and cold water pipes below the wash basin have been bonded to each other and then onto the waste pipe if it's metal.

    Hot and cold pipes to the bath which again have been bonded onto the waste pipe and also onto the leg of the bath if they are metal, but I have not seen an earth wire connecting the two areas of bonding together like I’ve seen in some books.
    As the same copper water pipes run throughout the house is it necessary to daisy chain every section of bonding together within the bathroom? I do understand that every part needs to be at the same potential, under fault conditions.

    With the 17 Edition Regs stating that RCDs will be needed in most domestic wiring situations.
    Can anyone advise if it is still necessary to bond pipes together and then onto the sink top in kitchen areas, assuming they are metal?

    Long, long ago well before RCDs were around socket outlet faceplates used to have a flyer earth connected back onto the metal box which was sunk into the wall, is this still required with the arrival of RCDs and the fact the fixing screws make contact with faceplate and the fixing lugs of the boxes?

    RCBOs, can anyone confirm if the fly lead should be connected to earth, because the rcbo has a solid neutral (ie not switched)?

    Many thanks to anyone who can advise.
     
  2. sparkyspike

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    No, you don't need to link the cross-bonding areas together. Yes, you still need to cross-bond even with an RCD on the circuit. No, you don't have to fly-earth back boxes with a fixed lug, but most sparkies do, I think. Although the NICEIC don't specify it, my inspector prefers it to be done - a bit of a contradiction really. Metal sinks don't need bonding afaik. The white fly-lead on an RCBO needs to be marked with g/y sleeving and earthed.
     
  3. Spark123

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    Bonding in bathrooms can be ommitted under certain circumstances in the 17th edn regs, under the 16th edn regs the pipework with reliable joints could be used as part of the bonding conductors.
    If a drain is a metal extraneous conductive part it will need to be main protective equipotentially bonded too.

    I don't think it has been a requirement since the 15th edn to bond kitchen sinks.

    I tend to connect the fly lead on sockets etc, I believe that if there is one fixed lug then this link can be ommitted however I consider it good practice.

    If there is a fly lead on an RCBO or RCCB then it MUST be connected. Cream is the colour for a functional earth, doesn't really matter about sleeving the cream wire with gn/yel.
     
  4. CliveDiy

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    Thanks for your advice guys, I must admit I have not put flyer earths from the faceplates to the metal boxes, buts it’s no sweat I can always bung them in, unusually I use 2.5mm2 for this purpose on 2.5mm2 ring mains., though I’m not sure what size I should use when bonding back onto the box which is for a cooker control.

    What size flyer cable do you guys use on 1.5mm2 twin and earth lighting circuits and do you use multistrand or single strand?

    Spark123 you said if a drain is a metal extraneous conductive part it will need to be main protective equipotentially bonded too.
    Does this mean it would need to be earthed back to the consumer unit in 10mm2 assuming the supply is TN-C-S?
     
  5. ricicle

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    The fly lead does need fitting from box to socket though if the system is wired in steel conduit without a CPC core or MI cable where the earth continuity is via glands/bushes/locknuts etc.
    But this situation will possibly require a wiring inspection/upgrade anyway.
     
  6. Spark123

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    For a ring final circuit fed from a 32A MCB a 1.5mm link to the back box is fine, this is the normal size for the CPC in twin and earth.
    If you stick with the CPC size from the cable you won't go wrong. Can't answer the one for the cooker control as this might be fed from any size supply.
    Bit of 1mm single strand will be fine - same as in the cable.
    Yep, as with all extraneous conductive parts. If it can introduce a potential different to that of the MET including earth potential then it needs to be main protectively bonded. In the above case the metal drain will more than likely need to be in contact with the general mass of earth.for it to be extraneous.
     
  7. widdler

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    The earth cable coming with an RCBO is a functional earth, which must remain cream and not be identified otherwise.
    Be carefull to not over bond parts of the installation. It is sometimes more dangerous as you are introducing a 0V potential in places where no risk was present.
    With the kitchen sink, check to see if any of the pipework is plastic, if so then the possibility is that no potential exists.
    If the circuits are RCD protected then you can use the 415.2.2 rule, which assuming the RCD is 30mA suggests that if you taken a continuity (R2) measurement from the suggested extraneous conductive part (the sink drainer), to a local exposed conductive part, if your reading is less or equal to 1667ohms then bonding is not required.
    If no RCD is present then you will have to use Tab 41.3, which then should be used with ohms law to find the Ia for the 415.2.2 formula.
     
  8. Spark123

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    Reg 415 it talking about supplementary bonding - there is no requirement to carry out supplementary bonding in a kitchen.
    There is however a requirement to main protective bond all extraneous conductive parts back to the MET.
    A metal drain may be an extraneous conductive part if it is in contact with the general mass of earth and therefore if it is it should be bonded to the MET where it enters the building.
     
  9. CliveDiy

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    Thanks for your comments guys, I think in view of what as been said, I’ll bond the ring circuits to the boxes with 1.5mm, the lighting with 1mm and just put a small section of green/yellow sleeving on the cream RCBO leads, so the cream is still also visible.

    Sparky123 thanks for your comment about the metal waste pipe, I’ve just had a look in the On Site Guide 4.2 (V) exposed metallic structural parts of building and you are right it needs to go all the way back to the MET. plus what you said about using the same size earth wire as the earth which is running with the circuit wires, to bond back onto the boxes makes sense.

    I assume central heating radiators within the bathroom area still need to have one of the small clamps attached to it and supplementary bonded onto a nearby water pipe?
     
  10. Spark123

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    Metallic central heating pipes need included in the supplementary bonding for a bathroom if you have not met all the criteria for the ommision of supplementary bonding in section 701 of the IEE regs.
    If your heating is done in placcy pipes then no need to bond the radiator at all. There is an article (based on 16th edn regs) on placcy pipes here: http://www.theiet.org/publishing/wi...004/pre14-earthing-plastic-pipes.cfm?type=pdf
     
  11. CliveDiy

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    Hi 123

    One way to tell if something is extraneous is to conduct a measurement between the said item and the MET. If the resistance is below 22KΩ then it can be considered to be extraneous hence needs to be bonded.
    If it is above 22KΩ then it doesn't need bonding.

    Hope you don't mind me asking you, where have you got the figure of 22KΩ from, it's only so I can have a read of it for myself.

    You seem to know your stuff, so if it's ok I'd like to ask you something about down lighting and also wiring for an oven.

    The oven first. It's maximum wattage is 5200w, the cable run is only 9 metres, I've run the cable in 6mm and was going to put it on a 32 amp RCBO, do you think this will be ok?

    The downlights, I'm installing some in a kitchen and others in a bathroom.
    They are all mains voltage, the ones in the bathroom I thought of using IP65 rating because some are over the bath and there is one in the shower cubicle.
    The ones in the kitchen will be just the run of the mill downlights.
    Question: Do they all need to be firecheck, with regs stating I could be helping the spread of fire by cutting holes through the plasterboard ceilings?
     
  12. CliveDiy

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    123

    About MET, the existing earthing in my house is a bit like the pic. in the on site guide for TN-C-S except the 16mm earth does not go onto an earth block and with 10mm earths going onto the various services.

    Instead the 16mm incoming earth goes straight onto the earth connecting strip within the consumer unit, the 10mm earths are then run from the consumer unit to the various services.

    I take it that the above method of connection is also ok?

    If it is when you talk of testing resistance of extraneous parts back to the MET, am I right in assuming this would be back to suppliers earth and not the earth connecting strip within the consumer unit?
     
  13. Spark123

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    The figure comes from guidance note 5 or guidance note 7, can't remember. It is taking into consideration the average resistance of the human body across a section of the pupulation being iirc 1KΩ. Under a fault condition should a person touch the said part the total resistance being 23KΩ, the part being live at 230v the current passing through said body will be less than I=V/R = 230/23000= 0.01A or 10mA. This current passing through a human body is considered to be non-fatal.

    5200w/230v= 22.6A, the next normal protective device size up is 32A. 6mm should be OK providing you haven't installed it in a thermally insulating environment.
    Work is notifiable to your LABC under part p (England + Wales)
    I take it you are using RCD protection for the lighting too? Personally in a shower cubicle I'd like to use a SELV type light IPX4 minimum.
    Depends if they are going into a fire barrier, only normally a concern if you live in a flat or it is going into a garage. Worth checking with your building inspector though as this is notifiable work too.
     
  14. Spark123

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    Yes, it is fine. The earth rail inside the CU is being used as the Main Earthing Terminal.

    Technically if your MET is the one in the CU you should use that as that is your reference point for all potentials within the property - doubt there would be much difference to be honest as they are linked with a piece of 16mm and you are looking at K ohms.
     
  15. CliveDiy

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    The cooker cable isn’t running through any insulation, I guess I could have got away with a smaller one, but put the larger one in just in case a slightly higher wattage cooker is installed at some time.

    The ground floor and upstairs lights will be on two separate RCDs, with the bathroom lights being on their own RCBO, so three lighting circuits in effect.

    Yes I have notified the LABC and had the first fix checked, may I add not by them, I had to find a registered company myself and pay them to check it.
    I still had to pay the council mind you just to handle the paper work, obviously it will all be tested when I’ve finished.

    I note your comment about the down lights going into a fire barrier, I live in a detached house, but when I saw something about fire barriers and down lights, I wondered if it also meant such things as kitchen ceilings with perhaps a bedroom or bathroom above but in a single dwelling not flats.
    Some of the building regulations certainly take some interpreting, I think one needs to be a barrister to understand some of it :LOL:

    I may try a new thread about the downlights and fire barriers.

    Thanks for all your help once again
     

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