Kitchen Splashback Bonding (Earthing)

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Hyper

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#273217 10-Aug-2020 18:37

We are presently installing a new kitchen and part of this is a new splashback covering the wall above the full length of the bench.

We have chosen a Refections Splashback which is made up of a fire retardant core sandwiched between 2 sheets of aluminium and finished with a high gloss substance.

There is an electrical socket existing that I believe as a homeowner I can remove and replace In the same location once the Splashback is installed without getting a sparky involved (we live a considerable distance from any town so very expensive to get an electrician out here).

However I’m now wondering about the aluminium being conductive so may need bonding to earth once the outlet is fitted (although no mention of this in the installation instructions). I’m having visions of a lug and wire being visible.

Has anyone any idea of the regs and if bonding is necessary and the best way of achieving this.

SomeoneSomewhere

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#2538137 10-Aug-2020 18:50

You would not generally need to earth it as it is double insulated from all live electrical parts.

However, mounting a socket through it is likely to break that. There is only the basic (coloured) insulation between the live conductors and the aluminium.

I am not sure there would be a good way to earth it. It might be preferable to e.g. mount the socket on an insulating block and butt the splashback up to the edge of that.

neb

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#2538326 10-Aug-2020 22:43

Even without regs, I would earth it. I don't know what the sink bench is made of but if it's metal consider a kettle or coffee maker that develops a leak and connects 240V to the bench top and splashback...

SomeoneSomewhere

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#2538332 10-Aug-2020 23:35

This has been brought up before, but the advice is no longer to indiscriminately earth metallic objects like sink benches. Placing people in an earthed situation can result in a worse shock than leaving it floating.

neb

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#2539458 12-Aug-2020 15:03

SomeoneSomewhere:
This has been brought up before, but the advice is no longer to indiscriminately earth metallic objects like sink benches. Placing people in an earthed situation can result in a worse shock than leaving it floating.

Is there any data on what the better/worse option is? I wonder what the accident statistics show is more common, an accidentally live steel workbench or faulty equipment with a person bridging to an earthed workbench? Genuinely interested since we're about to put in a stainless steel surround in the laundry.

Daynger

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#2539460 12-Aug-2020 15:09

With most appliances being double insulated and the use of RCDs risk has come down considerably over the last couple of decades.

I have always thought along those lines SomeoneSomewhere, if an appliance has a fault to the external case and a person rests their hand on a bonded benchtop and grabs the appliance they will receive a much worse shock than if they were not touching a bonded surface.

But there are still many rules in place about what needs to be bonded and what doesnt, in fact there is a whole section of it in NZS3000.

mattwnz

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#2539480 12-Aug-2020 15:43

I looked into that, but decided against it. Did you look into a glass? We got a dark mirrored one, which has a special coating to reduce marks, and it looks and performs great, although the bench is deeper than most to avoid any cooking splashes. Also makes the space look bigger. We have a stainless benchtop, and I don't think that s earthed. Is it normal to earth them, or a requirement?

Hyper

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#2539735 12-Aug-2020 20:18

Spoke with an Electrical Inspector today and he suggests no bonding necessary, so long as the earthing is under 1 M ohm complies with all regs. Suggested installing new sockets though.

Looked at installing glass but nearly twice the price plus we are covering approx 6 sq m and numerous cutouts and corners would require specialist cutting and rehardning the glass, would have blown our budget. This material, although not quite as nice as glass, is still quite impressive and very diy.

Thanks for your inputs.

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gregmcc

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#2539744 12-Aug-2020 20:42

mattwnz:

I looked into that, but decided against it. Did you look into a glass? We got a dark mirrored one, which has a special coating to reduce marks, and it looks and performs great, although the bench is deeper than most to avoid any cooking splashes. Also makes the space look bigger. We have a stainless benchtop, and I don't think that s earthed. Is it normal to earth them, or a requirement?

In modern houses with a stainless steel bench top there is no conductive path via the PVC water pipes to earth so no need to bond the bench top, if there were metal water pipes then bonding would be required. This is because if there is a earth fault on anything in the house the benchtop would be at a higher voltage level (due to ground resistance/metal water pipe/benchtop) so you lean against your bench top and touch the metal earthed microwave or oven or fridge or electric jug and you would get a shock so bonding it keeps it all at the same potential or pretty close to it so you may not even get a shock or even just a slight tingle.

gregmcc

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#2539751 12-Aug-2020 21:04

Hyper: Spoke with an Electrical Inspector today and he suggests no bonding necessary, so long as the earthing is under 1 M ohm complies with all regs. Suggested installing new sockets though.

Looked at installing glass but nearly twice the price plus we are covering approx 6 sq m and numerous cutouts and corners would require specialist cutting and rehardning the glass, would have blown our budget. This material, although not quite as nice as glass, is still quite impressive and very diy.

Thanks for your inputs.

Hmm.... maybe you need to talk to your inspector again, maximum resistance for bonding is 0.5 ohm, not 1M ohm which is 1,000,000 ohms. Might be a bit of misunderstanding going on. This sounds like a minimum test result for insulation resistance to earth which is something totally different.

As far as bonding the splash back, there is nothing specific about bonding splash backs, but there is bonding for ".....Extraneous conductive and other parts as required" 5.3.1(F)

5.4.6 deals with Structural metalwork including conductive building materials, the splashback would fit this description (building materials), with a socket mounted it would fall under 5.4.6.1 (a) "the risk of contact with live parts of electrical equipment or insulated unsheathed cable exists.." So this means bonding the splashback as the wiring that connects to the socket is "insulated unsheathed cable" (when the white TPS is stripped back so the cores can be connected to the socket)

As far as making the bonding connection look good, there are some options, a bonding lug could be fitted on the edge of the cutout for the socket so it is hidden when the socket is screwed in to place, or swap out the double socket for a 4 way socket as the PDL 600 series and the HPM ones extend about 50mm beyond the flush box cut out, heaps of room to fit a bonding wire.

SomeoneSomewhere

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#2540512 13-Aug-2020 20:07

gregmcc:

mattwnz:

I looked into that, but decided against it. Did you look into a glass? We got a dark mirrored one, which has a special coating to reduce marks, and it looks and performs great, although the bench is deeper than most to avoid any cooking splashes. Also makes the space look bigger. We have a stainless benchtop, and I don't think that s earthed. Is it normal to earth them, or a requirement?

In modern houses with a stainless steel bench top there is no conductive path via the PVC water pipes to earth so no need to bond the bench top, if there were metal water pipes then bonding would be required. This is because if there is a earth fault on anything in the house the benchtop would be at a higher voltage level (due to ground resistance/metal water pipe/benchtop) so you lean against your bench top and touch the metal earthed microwave or oven or fridge or electric jug and you would get a shock so bonding it keeps it all at the same potential or pretty close to it so you may not even get a shock or even just a slight tingle.

My understanding is that this is handled by bonding the water pipe where it enters the building. Once that's bonded, no further bonds are needed.

Tracer

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#2540540 13-Aug-2020 20:58

neb: Even without regs, I would earth it. I don't know what the sink bench is made of but if it's metal consider a kettle or coffee maker that develops a leak and connects 240V to the bench top and splashback...

Those appliances are either double insulated or have earthed bodies, so you'd need a double fault.

gregmcc

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#2540633 14-Aug-2020 06:09

SomeoneSomewhere:

My understanding is that this is handled by bonding the water pipe where it enters the building. Once that's bonded, no further bonds are needed.

with the advent of PVC water pipes it makes it very difficult to attach a bonding wire to a plastic pipe, there really haven't been metal water pipes coming in to house in the past 35 years, there are exception for various reasons, but generally no.

SomeoneSomewhere

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#2541159 14-Aug-2020 17:07

I was referring to "if there were metal water pipes then bonding would be required". Where there are no conductive services entering the building, bonding is generally not required.

It is important to remember than bonding and earthing are not the same thing, though we do them in much the same way. Protecting against either a faulty appliance or the wiring behind a socket would be protective earthing, intended largely to trip an MCB/fuse. It's not required provided double insulation is maintained, but it's not forbidden.

Bonding is mostly protection against differing earth potentials, mostly due to voltage drop (or poor connections) in the main neutral to your or others' property, and properties on different transformers with separate earthing systems. It's not intended to carry fault current.