BONDING METAL WORKTOPS

[mainline]

Metal is just that, it doesn't make it an exposed conductive part, it only becomes an exposed conductive part if there is a possibility of a live conductor (due to a fault of some type) making it live.

So a random metal worktop would not require any bonding or earthing.

However if the worktop arrangement or use makes it possible; then it needs supplementary bonding.

It is not clear cut.

In general if you have fixed metal worktops, and electrical equipment on them in a commercial kitchen environment, I would consider it needs bonding.

What would happen if trailing leads for kitchen tools got damaged and came in contact with the metal worktop? In general the way most commercial kitchens end up, I would bond.

But there is no absolute requirement.

Maybe a better idea would be to try to ensure that the cables etc are protected.

 

[Jonny72]

I always run the balance between options.

Option 1 - supplementary bonding in accordance with 415.2.1

If there is a fault of poor cabling etc contacting the worktop and the person with wet hands, there is a big bang, no current goes through the person to speak of , no one dies, you don't go to court.

Option 2 - it's not mandatory to bond so no bond.

If there is a fault of poor cabling etc contacting the worktop and the person with wet hands, the current goes through the person, even though the rcbo trips (or perhaps fails to) the shock is still sufficient to cause serious injury or death, you go to court, but can prove you did comply with the minimum requirements, so would likely be able to fend off any charges etc.

That's my reasoning! I would prefer the former rather than the latter.

As for the Connections, take a look at 415.2.1, it makes it fairly clear what is suitable.

I would bond between pipes, tables and the earth/cpc points of the socket outlets all locally.

Julie thanks. Used to 'spark' Airframes lol - bonding on aircraft more for lightening strike potential. Can understand bonding between pipes and cables but CPCs of outlets sockets. Never seen this!!! This a matter of just tapping and earth from the socket??? All the sockets??? Can understand Mainlines point too. It would be fairly easy to run a 10mm cable from the DB put may be 20m length in 10mm conduit from the outside but obviously the sockets will only provide 1mm as lightly on 2.5mm ring. Really appreciate all u guys help as although I have plenty of Quals, installation is fairly new to me. I will have read of 415.2.1 but find IET Genuinely thanks so far. I am learning.

 

[GBDamo]

Maybe a better idea would be to try to ensure that the cables etc are protected.

Isn't this why we have additional protection it the form of RCDs?

What is bonding going to achieve?

It's going to introduce an alternative, low resistance, earth path.

Take, for example, a hand held blender. You're stood holding it and a metal mixing bowl on our metal worktop. There is a fault to the casing of the blender.

With RCD only protection you'd have a <30ms trip and a very minor electric shock.

With RCD and Bonding would the low resistance earth path allow for a larger shock whilst still tripping in <30ms?

With no RCD relying on Bonding only, your getting a right belt, but hopefully our circuits are well designed and OPCDs correctly selected and we get a <0.4 second frying.

With no RCD and no Bonding our face slowly melts, like the ---- (Wow, we can't refer to the goose stepping, dapper krauts) in Indiana Jones and the Raiders of the Lost Ark, as nobody bats an eyelid as the smell of burning meat eminantes from the kitchen.


So, are the bonding fetishists suggesting we bond to mitigate a failure of the RCD.

Where does that stop? Two I dependant bondings in case one fails?

Belt, braces, elasticated wasteband and a little person with a modesty curtain.

 

[Jonny72]

Isn't this why we have additional protection it the form of RCDs?

What is bonding going to achieve?

It's going to introduce an alternative, low resistance, earth path.

Take, for example, a hand held blender. You're stood holding it and a metal mixing bowl on our metal worktop. There is a fault to the casing of the blender.

With RCD only protection you'd have a <30ms trip and a very minor electric shock.

With RCD and Bonding would the low resistance earth path allow for a larger shock whilst still tripping in <30ms?

With no RCD relying on Bonding only, your getting a right belt, but hopefully our circuits are well designed and OPCDs correctly selected and we get a <0.4 second frying.

With no RCD and no Bonding our face slowly melts, like the ---- in Indiana Jones and the Raiders of the Lost Ark, as nobody bats an eyelid as the smell of burning meat eminantes from the kitchen.


So, are the bonding fetishists suggesting we bond to mitigate a failure of the RCD.

Where does that stop? Two I dependant bondings in case one fails?

Belt, braces, elasticated wasteband and a little person with a modesty curtain.

There are RCBOs in the DB. Yea I may be one of those ppl with a earthing fetish sorry. I suppose only fear is the RCBO may not trip and earth connection is 'good old faithful'. I saw a kitchen recently similar which had earth connections every metal surface but may have been done 15 years ago when earthing and bonding was a bit mental. Would RCD sockets in the areas of risk be sensible or is this just going to bring an issue and be nonsensical with RCBOs in DB 20m away? Maybe local RCB Think protecting the cables may be an idea too. Seriously what I found in there during a PAT would curl your hair . That's what brought about my concern. Be nice - I am learning

 

[littlespark]

We don’t bond every lump of metal in a domestic kitchen…. Dishwashers, ovens etc… we rely on the earth wire it came with…. And this is where a fault in itself could happen…. Not from another appliance.

If it was all to be bonded, there would be a section for commercial kitchens under “special locations” like there is with swimming pools.

The RCD protection does away with bonding in most other cases, on the assumption they are tested regularly and replaced if faulty.

 

[mainline]

There are RCBOs in the DB. Yea I may be one of those ppl with a earthing fetish sorry. I suppose only fear is the RCBO may not trip and earth connection is 'good old faithful'. I saw a kitchen recently similar which had earth connections every metal surface but may have been done 15 years ago when earthing and bonding was a bit mental. Would RCD sockets in the areas of risk be sensible or is this just going to bring an issue and be nonsensical with RCBOs in DB 20m away? Maybe local RCB Think protecting the cables may be an idea too. Seriously what I found in there during a PAT would curl your hair . That's what brought about my concern. Be nice - I am learning

What are the chances that a live conductor is going to come in contact with the metal table ? I would say very unlikely.

If this unlikely event did happen, the person touching the now live table would have to be standing on a very earthy floor with wet hands in bare feet to receive anything substantial also if the floor is that earthy the table would also be.

Is the supply PME ? As something that maybe worth considering is a PEN fault that could cause all your now earthy metal to go live and your rcbo isn't going to help at all.

 

[newfutile]

You have to determine if it’s and extraneous conductive part. This can be as acheived by an IR test from the metalwork to the MET , I always 10 ma current therefore 23 KiloOhms or less makes it an en extraneous conductive part

 

[mainline]

You have to determine if it’s and extraneous conductive part. This can be as acheived by an IR test from the metalwork to the MET , I always 10 ma current therefore 23 KiloOhms or less makes it an en extraneous conductive part

He said that he has tested and there is no earth to any of it.

 

[Jonny72]

You have to determine if it’s and extraneous conductive part. This can be as acheived by an IR test from the metalwork to the MET , I always 10 ma current therefore 23 KiloOhms or less makes it an en extraneous conductive part

Yes I did that. I tested between earth on a socket and all benches. Was open circuit and I used Dilog MFT.

 

[Julie.]

There is no way I would suggest that we bond all random bits of metal, in fact this never was a requirement, and the old interpretation many followed of doing something like that was as incorrect then as it is now (even though it ended up in guidelines and other supportingdocuments).

However there are circumstances where it is beneficial to bond metallic material where a particular risk may exist.

The regs actually assign a name to this (supplementary bonding), and detail how it needs to be done.

Indeed if we just take the minimum requirement from the regs as all that should be done, then the whole definition and detail of supplementary bonding needs to be removed from the regs.

The reason it is there is for circumstances such as this (in my opinion), but in doing so it doesn't follow that "by the same thought everything needs to be bonded" or similar arguments.

 

[7029 dave]

A lot of electricians get confused between equipotential bonding and supplementary bonding.

 

[mainline]

There is no way I would suggest that we bond all random bits of metal, in fact this never was a requirement, and the old interpretation many followed of doing something like that was as incorrect then as it is now (even though it ended up in guidelines and other supportingdocuments).

However there are circumstances where it is beneficial to bond metallic material where a particular risk may exist.

The regs actually assign a name to this (supplementary bonding), and detail how it needs to be done.

Indeed if we just take the minimum requirement from the regs as all that should be done, then the whole definition and detail of supplementary bonding needs to be removed from the regs.

The reason it is there is for circumstances such as this (in my opinion), but in doing so it doesn't follow that "by the same thought everything needs to be bonded" or similar arguments.

It is a common misconception that bonding such items won’t cause any harm so a “better to be safe than sorry” attitude is taken. However, it is important to remember that by connecting to the main earthing terminal, in some circumstances, fault currents can be exported throughout the installation which would not be there if protective bonding had not been applied. This can cause an electric shock risk for persons outside of the installation in contact with the general mass of Earth and earthed equipment such as pipework, for example an outside tap or metal (class 1) electrical equipment.

 

[cliffed]

These would most certainly NOT be extraneous conductive parts.

Unless the kitchen surfaces themselves extend externally and to the ground itself.

However I would consider them an extension of exposed conductive parts, and require supplementary bonding.

But it very much depends on circumstances, movable tables no, but if it is a complete kitchen fitted worktop with appliances resting on or adjacent to it I would add supplementary

Yea definitely a thing in days gone by we bonded everything, & agree with your last statement regarding fixed metal worktops with electrical appliances