4mm Supplementary Bonding for new kitchen install??

[chrisgc]

On a TT system (protected by RCD's), 4mm earthing cable has been run to the cu.

I know regs indicate that supplementary bonding is not required for kitchens but did read somewhere that some kitchen fitters may want bonding available as they may simply follow manufacturers instruction (ie. for installation of sink).

The property is natural stone so cant chase and is all due to be plastered and floor laid so the earth cable has been left in place just in case as cant be put in afterwards.

Is the 4mm sufficient as there was 6mm originally there (a reel of 4mm not long bought in by owner)??

 

[Richard Burns]

As far as I understand it, if this is supplementary bonding it should not be run back to the CU, however 4mm should be OK as a supplementary bonding conductor for normal domestic circuits. If this is a main equipotential bonding conductor going from the MET to the water supply then it must be at least 6mm.
Kitchen fitters would just want to supplementary bond the kitchen metal together (with 4mm).

 

[malcolmsanford]

On a TT system (protected by RCD's), 4mm earthing cable has been run to the cu. Is that the main earthing conductor from the electrode?

I know regs indicate that supplementary bonding is not required for kitchens but did read somewhere that some kitchen fitters may want bonding available as they may simply follow manufacturers instruction (ie. for installation of sink). I would not tell my doctor if I had a cold that I need an operation, and I would not rely on kitchen fitters to tell me if I have or don't have an extraneous conductive parts that need bonding. If your services are bonded at the entry into the house then you should not need to bond in the kitchen.

The property is natural stone so cant chase and is all due to be plastered and floor laid so the earth cable has been left in place just in case as cant be put in afterwards. Earth or bonding cable ?

Is the 4mm sufficient as there was 6mm originally there (a reel of 4mm not long bought in by owner)?? For the main earth or for this "bonding"

...............................

 

[Deleted member 9648]

I've come across "THIS SINK MUST BE EARTHED" instructions with new stainless sinks before,which is interesting as it clearly means manufacturers do not understand the regulations,or the difference between earthing and supplementary bonding.
It's up to you whether you argue the case or simply do it to avoid the arguments if a bonding conductor is not installed,I would always point out the regulations and tell the client they would be paying for pointless work.....That said it's not always easy when they have seen the EARTHING statement on the box,and manufacturers still fit an EARTHING tag to the sinks!......Another phenonema you are up against is that clients always believe the kitchen fitter rather than the electrician when this is being discussed...their arguments usually involving "Well what if you dont and the sink comes live?"........sometimes it's easier just to do it and keep 'em happy.

 

[malcolmsanford]

Agree since coming on this forum there are many "sparks" that don't understand bonding let alone sink makers.

I have no problem with stringing G/Y cables across pipes, as long as if they are not extraneous conductive parts they are therefore not connected to an earth.

Problem is because of the lack of understanding regarding bonding, some "sparks" still have this mentality if it's metal bond it, better safe than sorry, and as we know WP that is not true.

 

[oxocube]

What about a SS sink fed by plastic H&C waterpipes and connected to a copper/lead waste and cast iron/copper down pipe.

 

[malcolmsanford]

It boils down to section 415 and regulation 415.2.2 in general. If you prove that the waste pipe is an extraneous conductive part then there may be a need to bond it in a kitchen if you can not achieve the disconnection times of the protective device.

As this installation is covered by an RCD and it trips within the specified times, then I doubt very much any metal work in a kitchen will need supplementary bonding.

 

[oxocube]

But there are a lot of sparks that think kitchen sinks never have to be bonded.

And you address one of the issues, but the other one is of whole house equipotential bonding. If the sink I described is not connected to the main bonding but the radiator beside the sink is, an external neutral fault could create a lethal potential between the two.

 

[malcolmsanford]

Yes OC if I saw a sink connected to the waste by a metal cast/copper drain then I would be doing a lot of testing in that kitchen to see if you did need to bond the sink, but these are rarities in modern plumbing.

There are always exceptions to a rule, and your scenario may be one, but to blanket bond metal because of the adage it is better to be safe than sorry is just as dangerous as not bonding an extraneous conductive part.

 

[oxocube]

Metallic drain pipes are standard in a lot of commercial property and are still in use in many old buildings, inc housing. Construction techniques are also a factor, the last house I rewired looked like a standard brick built house. When I tried doing the Grd floor power I got a surprise, chiselling down behind the skirting I hit solid steel. Got the floorboards up and I discovered the whole house was built on a framework of very heavy RSJ's, or extraneous metal work, as we say.

So, which blanket statement is the most dangerous!

"Kitchen sinks never need bonding" or "kitchen sinks should always be bonded"

 

[Deleted member 26818]

Would it not be that the extraneous-conductive "copper/lead waste and cast iron/copper down pipe" requires bonding, rather than the sink, and wouldn't that bonding be required to be 6mm²?

 

[Deleted member 9648]

Would it not be that the extraneous-conductive "copper/lead waste and cast iron/copper down pipe" requires bonding, rather than the sink, and wouldn't that bonding be required to be 6mm²?

Exactly^^^....a metallic drain entering the building and in contact with the ground is likely to require main bonding.....and once that has been dealt with the sink matters not.

 

[oxocube]

Would'nt you want to ensure that the sink had a low resistance connection to the drain? Or are you 'a kitchen sinks never need bonding' type of guy

 

[Deleted member 26818]

Would'nt you want to ensure that the sink had a low resistance connection to the drain? Or are you 'a kitchen sinks never need bonding' type of guy

Why would it matter?

 

[oxocube]

There are only two conditions for metallic parts in any building. Are they guaranteed permanently isolated from other earths as proved by inspection? If they are then no need to earth. If not they should be permanently earthed via tested and visible connections to ensure same potential difference and disconnection times of devices.

Thats why it matters.