Bonding/Earthing

[b33k34]

Doing a refurb at the moment. I'm doing the first fix electrics with an electrician doing the final fix and signing off.

A new fuse box meeting 17th edition is going in so all circuits will be protected by RCDs.

I working on the basis that -
Main bonding - at the Consumer Unit the gas and water supply need to be connected. This should now be done with 16mm cable. The boiler, gas meter and CU are all in the same cupboard so I'm assuming connecting them together there is fine.

However, I'm a bit confused about the requirements for cross bonding/earthing elsewhere. At present there is 6mm cable looping between the hot and cold supplies in the bathroom, on to the kitchen and then back to the CU. My reading of the 17th edition is that cross bonding is no longer required provided the main bonding is in place and RCDs cover all circuits. I'd have thought that there is no harm in tidying this up/leaving it in place but the electrician is talking about replacing all of this with 16mm cable.

This is going to be expensive and time consuming so I don't want to do it if it's not required. Any views here?

 

[sparkiemike]

To start with main equipotential bonding is required for all extraneous-conductive-parts, including the following:
(i) Water installation pipes
(ii) Gas installation pipes
(iii) Other installation pipework and ducting
(iv) Central heating and air conditioning systems
(v) Exposed metallic structural parts of the building.

Reg 411.3.1.2 refers

sizing will be determined by the size of your neutral conductor and earthing arrangements, 16mm seems a bit big for domestic.

The requirements to omit supplementary bonding in bathrooms is not as straight forward as you make out. Ask the electrician who will be signing off as furter tests are required and (unlbelievingly) he will also be taking responsibility for your work.

 

[b33k34]

Ok - so we're only talking water/heating/gas and they'll all be bonded in the cupboard at the meter.

Cross bonding within the bathroom and kitchen is no problem but does that need to be run back to the CU as well? That's the difficult/expensive bit (in terms of cabling)

 

[ricicle]

Why don't you leave the technical stuff to the guy who has to sign the work off ?

 

[PrenticeBoyofDerry]

It can depend on the your earthing arrangements and calculation to the sizing of Earthing Conductor and main bonding conductor.

Generally when upgrading go for 16mm for the Earthing Conductor(from incoming supply to MET/earth busbar in CU) and 10mm Main bonding from MET/earth busbar) to gas, water, oil, steel work etc..
You will be looking for a reading of less than 0.05 ohms between Earth busbar and water, gas, oil pipes etc...

 

[JohnW2]

Generally when upgrading go for 16mm for the Earthing Conductor(from incoming supply to MET/earth busbar in CU) and 10mm Main bonding from MET/earth busbar) to gas, water, oil, steel work etc..

The OP seems to be saying that all that will be done in 16mm² - a bit OTT for the MPB, but neverthess fine. The main problem seems to be that the electrician has advised him not only that he needs to retain supplementary bonding in kitchen/bathroom (which he may well not need), but that it should be upgraded to 16mm², which is way OTT. I cannot help but wonder whether there might not be misunderstanding between OP and electrician.

Kind Regards, John.

 

[PrenticeBoyofDerry]

I think there has been some confusions/misunderstanding between OP and electrician
Or is this purely a misunderstanding between OP and BS7671:2008

Supplementary bonding in kitchen can now be omitted.
In Bathrooms it is a little different.
16mm way too big, 4mm is normally good enough! If you have 6mm in place belt/braces leave it.
//www.diynot.com/wiki/electrics:speclcn:supbond17th