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Topic Title: Cross bonding
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Created On: 08 January 2013 09:11 PM
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 08 January 2013 09:11 PM
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goldenboy1818

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In a domestic all with rcd and main bonding in place, there is no need for supplementary bonding. What about cross bonding ?? At boilers heating systems etc ???
 08 January 2013 09:33 PM
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DOUGIE1000

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Cross bonding not required but some still like to do it.

I haven't installed suplementry bonding in domestic bonding in years.......there I said it.

All new builds and any plumbers we work with install everything in plastic and copper tails on heating and all water.

D

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Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 08 January 2013 09:33 PM
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BrucieBonus

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Isn't 'cross bonding' the same as supplementary??

As long as main bonds in place, then I don't see any reason to add to it
 08 January 2013 10:12 PM
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goldenboy1818

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That's what I thought, just had a little random brain freeze today and suddenly thought hmmmm should it be in
 08 January 2013 10:19 PM
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spinlondon

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No supplementary would involve a conductor being run to the MET.
Cross bonding is not a recognized (by BS7671) term, for bonding adjacent pipework to each other.
 08 January 2013 10:27 PM
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Legh

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As I understand the term, its a generalization for running one green and yellow conductor to utility service pipes or /and structural steelwork, localized cross bonding is likely to refer specifically to supplementary bonding extraneous and exposed conductive parts in bathrooms, saunas and the like...

Legh

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 08 January 2013 10:31 PM
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spinlondon

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BS7671 requires that supplementary bonding connect not only extraneous-conductive-parts, but also the CPCs of any circuits of the location.
That the conductors be brought together at a point near to the location and terminated together along with a conductor connecting the conductors to the MET.

Whereas cross bonding as the termis generally used, is the connecting of the hot pipe to a sink, to the cold pipe of that sink.
Or the connection of all the pipework connected to a boiler.
 09 January 2013 12:11 AM
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geoffsd

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There is no requirement to connect supplementary bonding to the MET.

There is no requirement to 'cross bond' (as in the meaning in this thread).
 09 January 2013 07:24 AM
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tomgunn

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I thought that 'supplementary bonding' was required within, say the bathroom, from the lighting where you'd run a 4mm, ( 4mm for 'mechanical protection' ), to the pipework - and that there's no reason to run a separate earth to the MET as in the good olde days I would have run a continuous 6mm everywhere but some bright spark, ( sorry for the intended pun! ), came up with the formula of 'parallel bonding', whatever that means!? If you're using RCBO's then no supplementary bonding would be required.

Tom

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 09 January 2013 07:54 AM
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Fm

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Call it what you want, mi dont mind a few tenbys under the boiler, stops plumbers bad mouthing to customers etc.
Doesnt cost a lot and doesnt take too much time, not a fan on soley relying on rcds so i will continue to add them.
 09 January 2013 08:41 AM
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Parsley

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701.415.2

Local supplementary equipotential bonding according to Regulation 415.2 shall be established connecting together the terminals of the protective conductor of each circuit supplying Class I and Class II equipment to the accessible extraneous-conductive-parts, within a room containing a bath or shower, including the following:

(i) metallic pipes supplying services and metallic waste pipes (e.g. water, gas)
(ii) metallic central heating pipes and air conditioning systems
(iii) accessible metallic structural parts of the building (metallic door architraves, window frames and similar parts are not considered to be extraneous-conductive-parts unless they are connected to metallic structural parts of the building).

Supplementary equipotential bonding may be installed outside or inside rooms containing a bath or shower, preferably close to the point of entry of extraneous-conductive-parts into such rooms.
Where the location containing a bath or shower is in a building with a protective equipotential bonding system in accordance with Regulation 411.3.1.2, supplementary equipotential bonding may be omitted where all of the following conditions are met:
(iv) All final circuits of the location comply with the requirements for automatic disconnection according to Regulation 411.3.2
(v) All final circuits of the location have additional protection by means of an RCD in accordance with Regulation 701.411.3.3
(vi) All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding according to Regulation 411.3.1.2.
NOTE: The effectiveness of the connection of extraneous-conductive-parts in the location to the main earthing terminal may be assessed, where necessary, by the application of Regulation 415.2.2.

You may also want to consider not omitting supp bonding if you're modifying an older installation that still has circuits outside the bathroom that are not RCD protected, or if the original installation has circuits designed to have a disconnection times of 5 secs.

Regards
 09 January 2013 09:35 AM
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OMS

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Just go back to first principles

as an example - would you want to be touching a metal cased heater (say a Zip Hydroboil) and the CWS pipework when a fault occurs - answer no

If it does happen, would you be safer or not if :

The means of earthing is the circuit CPC and the bonding condutor is connected a long way from where you touch the pipe

If there was a bit of 4.0mm2 between the fused spur earth terminal or heater earth terminal and the CWS supply to the heater locally

hint - it's the difference between passive safe and active safe system design/installation

regards

OMS

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 09 January 2013 09:37 AM
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AJJewsbury

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It'd be nice to know definitively where the term "cross" bonding originally came from - I had it in my head that it referred to bonding across different services (electric-gas-water etc), but that's maybe just an unjustified assumption from years ago. Maybe it's just called cross because the subject annoys so many people....
- Andy.
 09 January 2013 09:48 AM
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daveparry1

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It's surprising how many manufacturers instruction leaflets still refer to zone 3!
 09 January 2013 10:16 AM
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OMS

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From "across" I guess Andy

Either "across" several components like all the pipework entering/leaving a boiler or across a less conductive component - say a meter or a pump with elastomeric anti vibration pipe inserts - a cable that connects the pipework electrically "across" the pump or meter.

It's slang essentially - it'll mean different things to different people in different circumstances - it's like "FCU's" - today I may use it in conversation with an electrical type and mean in refernce to a fused connection unit - tomorrow I may use it in reference to a fan coil unit with a mechanical type. It'll cause chaos in a conversation with a design team when someone says we need 140 FCU's on that floor of a building

Regards

OMS

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 09 January 2013 03:50 PM
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spinlondon

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I always thought it was just another slang term similar to 'safe' zones.
 10 January 2013 08:18 AM
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tomgunn

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well my cross bonding was if its a copper pipe, usually around the boiler, then bond each pipe in a nice pretty fashion so it looks nice... dunno whether it did anything actualy - but thinking about it - obviously it did but this was before the plastic pipework everywhere.

Tom

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Tom .... ( The TERMINATOR ).

handyTRADESMAN ... haha

Castle Builders

Why did Nick Clegg cross the road? Because he said he wouldn't!

I can resist anything..... except temptation! ( Karl Gunn ).
 10 January 2013 10:02 AM
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Jaymack

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I cringe when I see the unnecessary practice by plumbers (hopefully), of cross bonding at boilers and under sinks etc. It is probably a result of their training, and the absence of a christmas tree in the workshop!

Regards
 10 January 2013 10:31 PM
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MrOther

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With Fm on this.

Just done my Mum's bedroom up. Supp/Cross bonded both pipes on the room's only rad and bonded an old/possibly/probably discontinued pipe.

Reasoning same as Fm and OMS -- would you really want to rely on an RCD? Especially in a house where over a period of years the electrical system can have a huge turnover of interference, sometimes by idiots/DIYers/cowboys so the extra pathway to a nearby socket makes sense. Another consideration in a house is seperation from services -- it's non-existent.

Admittedly, I wouldn't of gone out of my way to bond in a bedroom, but as it's turned out to be a top-bottom strip out, new bed, new lights, new sockets, new switches, new skirting and so on, it made sense.

A final consideration: let's say a bathroom doesn't have supp bonding but needs itn or that your nieghbourhood friendly plumber has removed it -- under a fault conditions it may turnout that supp bonding else where may still offer decent low resistive path back to the MET.
 10 January 2013 10:33 PM
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MrOther

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Originally posted by: Jaymack

I cringe when I see the unnecessary practice by plumbers (hopefully), of cross bonding at boilers and under sinks etc. It is probably a result of their training, and the absence of a christmas tree in the workshop!



Regards


Rather see it then not. Bonding is so easily removed it all helps in the great scheme of things.

I just wish they hid it better. Nothing like seeing a bit of Green and Yellow on show.
IET » Wiring and the regulations » Cross bonding

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