Two electrical questions


Although I have spent almost forty years in the electronics/control engineering industry I am not an electrician and, therefore, don't claim any sort of expertise with domestic electrics. With that in mind, I would be grateful (as I have been a number of times before) for the advice of those here with more knowledge and experience than myself in these matters.
My first question relates to a problem with our cooker - a bog-standard, inexpensive Creda 'Expression'. For some little while two of the hotplates have had the annoying tendency to cause the RCD in the CU to trip about once in every 5 or 6 times they were switched on from cold (never if still warm from having been used a short time previously).
I remember, that when doing some PAT testing a few years back, an incidence of some portable cookers, with similar hotplates, continually failing insulation tests when cold - if switched on for a while before testing they would pass ok. Upon detailed investigation, it was decided that there wasn't really a fault and we just made sure that they were run for a short while before testing.
With this in mind, I decided that my cooker probably wasn't faulty but that for some reason when cold there was just sufficient earth-leakage current to cause the RCD to trip. I therefore decided - particularly as we intend to replace the cooker fairly soon - to connect it to the non-RCD side of the CU. I did this about two weeks ago and there have been no problems.
My question is: was this an acceptable thing to do?
My second question is about earth bonding in a toilet/shower room that I have built at the rear of my garage. The room contains a shower cubicle, with 8.5kW electric shower, a toilet and washbasin , and a small electrical hand-wash unit. There is no hot water supply to the room, just a single 15mm cold water supply.
Can anyone tell me what type of earth bonding is required?
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Yes provided that there is not a cooker switch with a socket built in and this socket could reasonably be expected to supply outside portable equipment.

Read this. Everything about supplementary (not earth) bonding is there.
Adam
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"ARWadsworth" wrote:

Should there be a link?
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Yes
http://www.niceic.org.uk/downloads/NL139supp.pdf
Sorry
Adam
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I have just read through the link above with regards to earth bonding in my bathroom, but found it a little confusing. Perhaps you could give your interpretation on my bathroom requirements.
I have installed a central heating radiator which is fed with plastic water pipes. All the water pipes have been changed from copper to plastic. The vanity sink is plastic with 2 taps and these are fed with plastic water pipes. The bath is made of steel. There is a Triton shower fitted on the wall above the bath.
The plastic pipes were all installed after the new combi boiler were installed
If I have read the link properly, I think that my bath is the only item that requires a earth bond.
Thanks in advance
--
the_constructor



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It is not an earth bond in the sense that you are earthing anything. You are equipotential bonding things. The idea is that all metal work that may go live under fault conditions is at the same voltage. This voltage is usually tied back to the earth at the CU but only because the lights, electric shower, electric towel heaters etc are already connected to this earth bar. There is no requirement to take the supplementary bonding back to the CU. A good example is say, a hot tap is live at 230V due to a fault that has not caused a trip on an MCB or RCD and the cold tap is at earth due to the copper on the cold supply going back to the main incoming stop tap which acts an earth rod. If you touch both taps at the same time you get 230V across you. Equipotential bonding would have brought the cold tap up to 230V (probably tripping something in the CU) or even if it did not both taps would be at 230V and you would not receive a shock. Personally I would not try this out to prove it works and the chances of it happening are low, it was just an example.
In answer to your question.
Do not bond the bath. Firstly, if you have nothing to bond it to (you must have high ceilings as the lights are usually part of the bonding) then how can it be bonded and secondly a metal bath that is fed by plastic pipe and is not attatched to the metallic building structure should not be bonded. See table A in the link.
<http://www.iee.org/Publish/WireRegs/WiringMatters/Documents/PreIssue14/1999_6_autumn_plastic_pipes_to_bond_or_not_to_bond.pdf
HTH
Adam
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<http://www.iee.org/Publish/WireRegs/WiringMatters/Documents/PreIssue14/1999_6_autumn_plastic_pipes_to_bond_or_not_to_bond.pdf
My thanks Adam.
--
the_constructor



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ARWadsworth wrote:

Thanks, Adam. The cooker switch does have a socket built in , but we rarely use this - and have never used it for outside equipment, although it would be perfectly possible to do so from where it is positioned. Whenever I use one of the household sockets to supply outside portable equipment I always do so using an extension lead protected with its own plug-in RCD.

I will read through it (I have the link from your next post), and then do the bonding accordingly. Many thanks.
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Giles, just to follow up on the roofing problem, what's the latest.
Regards Keith (Nottm)
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keith_765 wrote:

I haven't spoken to my friend for a few days, Keith, but I will during the next day or so and will let you know of any developments. As I said previously, he has had some extra ridge ventilation fitted, so it may take a little while to see if this has been effective - particularly as the weather is very mild presently.
Thanks for asking, I am very grateful for your interest.
All the best.
Giles.
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