Supplementary Bonding - part copper/part PVC

[SW1970]

Hi Folks, gas service engineer reported incorrect bonding to gas so customer calls me in to fix. Fixed that no worries. Explain earthing & bonding to customer; they say they've got sinks in every bedroom and ask me to have a look.

Scenario is CU is mechanically poor and needs replacing (strangely it's a metal MK sentry but front cover is flexing and can get finger in around the side). Looks like done to a good standard at 16th. No RCD protection on lighting circuits. I'm going to propose a CU upgrade but for the purposes of my proposal I want to build on wider bonding issue as follows but a few questions arise:

1. In one bedroom, there's no pendant lamp, only wall lighting, and a sink with copper all the way to the taps. If the light switch and the wall lighting are located such that there's no way a user could touch the taps and an exposed conductive part at the same time then I think that these items are not "simultaneously accessible" per reg 415.2.1 (Not worried about items plugged into sockets because they are RCD protected). Does that sound about right?

2. In another bedroom, inside the bottom of the sink unit and usually covered in toiletries etc, about 10cm of copper water pipe is visible and then PVC up to taps. Should these copper pipes have supplementary bonding or is the simultaneously accessible rule as per Q1 considered before anything else?

3. In another bedroom, it's copper water pipe all the way up to the taps and the (non SELV) light fitting is directly above the sink. Using wander lead I measured R2 at the copper pipe where it meets the tap and recorded 0.03ohm back to the MET. This copper may already have supplementary bonding but I can't locate it. Is there a threshold below which an extraneous conductive part is considered to adequately bonded? Maybe 0.05ohm? If yes, but the bonding cannot actually been seen (perhaps under a floorboard), is that considered satisfactory or must it be inspectable?

Thanks loads! SW

 

[Chr!s]

First of all i would ensure all extraneous conductive parts have main protective bonding in place. If that's ok then we can then look to locations of increased risk (special locations) Part 6 16th, part 7 17th.

1. In one bedroom, there's no pendant lamp, only wall lighting, and a sink with copper all the way to the taps. If the light switch and the wall lighting are located such that there's no way a user could touch the taps and an exposed conductive part at the same time then I think that these items are not "simultaneously accessible" per reg 415.2.1 (Not worried about items plugged into sockets because they are RCD protected). Does that sound about right?

Is this a location of increased risk of shock? And if the items are not simultaneously accessible then i see no issue.

2. In another bedroom, inside the bottom of the sink unit and usually covered in toiletries etc, about 10cm of copper water pipe is visible and then PVC up to taps. Should these copper pipes have supplementary bonding or is the simultaneously accessible rule as per Q1 considered before anything else?

If the copper pipes are extraneous then they should have Main protective bonding at the point of entry, where plastic pipe is connected further down there is no need to maintain continuity in that respect. Again is this a location of increased risk of shock? Its not defined in part 6 16th, nor the part 7 17th, though the sections are not exhaustive.

If you decide this is a location of increased risk of electric shock then to the 16th edition supplementary bonding would be required if exposed and extraneous parts are simultaneously accessible. the 17th allows us to omit supplementary bonding providing we meet certain conditions.

3. In another bedroom, it's copper water pipe all the way up to the taps and the (non SELV) light fitting is directly above the sink. Using wander lead I measured R2 at the copper pipe where it meets the tap and recorded 0.03ohm back to the MET. This copper may already have supplementary bonding but I can't locate it. Is there a threshold below which an extraneous conductive part is considered to adequately bonded? Maybe 0.05ohm? If yes, but the bonding cannot actually been seen (perhaps under a floorboard), is that considered satisfactory or must it be inspectable?

Well i would suggest you use 415.2, if you test between the light fitting and the tap you may find that without supplementary bonding that you meet the equation in 415.2, added to the fact that in my opinion this is not a location of increased electric shock then i see nothing to worry about.

Regards chris

 

[Chr!s]

Oh and before ox pulls me up again, im assuming disconnection times are met.:biggrin:

Regards Chris

 

[SW1970]

Many thanks Chris. To confirm, do you read that a bedroom sink with copper pipes to the taps, a non SELV light above the sink is not a location with increased risk of electric shock?

For the effectiveness of the bonding, 415.2.2 - 6A type B MCB, so that's 30A with a 5s auto disconnection time (from Appendix 3, fig 3.4) therefore R needs to be <= 50/30, ie. <=1.67ohms. Have I got that right?

Cheers loads, SW

 

[telectrix]

no from 415.2.2. R<= 50V / Ia . you forgot V.

 

[IQ Electrical]

Many thanks Chris. To confirm, do you read that a bedroom sink with copper pipes to the taps, a non SELV light above the sink is not a location with increased risk of electric shock?

For the effectiveness of the bonding, 415.2.2 - 6A type B MCB, so that's 30A with a 5s auto disconnection time (from Appendix 3, fig 3.4) therefore R needs to be <= 50/30, ie. <=1.67ohms. Have I got that right?

Cheers loads, SW

Hi SW, just to confirm, if you check Part 7 of BS7671:2008 (page 164) you'll see the list of special locations which have been deemed to have additional requirements over and above the general requirements.

As long as the light is suitable for its location with regard to splashing and other external influences then there is no need to employ other methods of protection.

 

[SW1970]

no from 415.2.2. R<= 50V / Ia . you forgot V.

Blonde moment. That's what happens when you rush. It's 383ohms. Thanks tele

 

[SW1970]

Hi SW, just to confirm, if you check Part 7 of BS7671:2008 (page 164) you'll see the list of special locations which have been deemed to have additional requirements over and above the general requirements.

As long as the light is suitable for its location with regard to splashing and other external influences then there is no need to employ other methods of protection.

Thanks IQ, a sink in a bedroom (or any other room) isn't covered by Part 7. The light is suitable for external influences (512.2). So provided the external parts of the light fitting are not metallic (they're not), then the requirements of 544.2 (exposed-to-extraneous bonding) don't apply either. I guess that sinks aren't really rated very highly in the risk table despite the presence of water and potential for wet floor around the sink. Do you have any concerns in the scenario where client is changing a bulb in this lamp above the sink with power on and has one hand on tap for support? Cheers, SW

 

[IQ Electrical]

Thanks IQ, a sink in a bedroom (or any other room) isn't covered by Part 7. The light is suitable for external influences (512.2). So provided the external parts of the light fitting are not metallic (they're not), then the requirements of 544.2 (exposed-to-extraneous bonding) don't apply either. I guess that sinks aren't really rated very highly in the risk table despite the presence of water and potential for wet floor around the sink. Do you have any concerns in the scenario where client is changing a bulb in this lamp above the sink with power on and has one hand on tap for support? Cheers, SW

No, where do you stop? Hopefully he/she will turn off the fitting at the switch at least...

We can only go so far to reduce danger, there'll always be an idiot that circumvents any measure that we might put in place but just stick with the good book and you are doing all that is asked of you.