A 'rank amateur' should then just follow the guidance and not question his betters - that's what these FAQs are for. And if wants to understand the whys and wherefores can do some simple research.
A little knowledge is a dangerous thing - and aptly shown by those who query the need for equipotential bonding.
Yes, in any electrical installation.
To speak this language properly you just say "earthed" - not "bonded to earth." But yes, it will (or should, unless it's Class 2). So what? That earthing and equipotential bonding are distinct and separate concepts doesn't imply electrical separation.
[Towel rail example]I said that the o/c circuit protective (earth) conductor was a common fault. If the case becomes live through an insulation failure that is indeed a second fault. It's not an unknown situation though because the first fault can go undetected for years.
The casing of the appliance is _earthed_ via its circuit protective conductor (CPC) - typically the 'earth' wire in a twin-and-earth cable. In a bathroom, ignoring the 17th ed. for a moment, the casing should also be _bonded_ to the CPCs of circuits feeding any other equipment in the room, and to any other extraneous-conductive-parts (E-C-P). The latter term means anything that can import a potential into the room (usually, but not necessarily, earth and with the ability to sustain the flow of a dangerous current. So metal plumbing which might be earthed elsewhere counts as an E-C-P, but floating items don't. The bonding might or might not be earthed elsewhere.
Main bonding is the connection of incoming metal services such as gas and water to the main earth terminal, creating an equipotential zone. It's absolutely fundamental to the safety of PME supplies where it's possible for the suppliers combined neutral and earth conductor to come adrift, leaving all your earthing up at 230 V.
The supplementary bonding is connected to the earth terminal in the FCU. This achieves bonding to the case via the CPC in the flex. There are other situations where a green-and-yellow wire might be acting as both a CPC and a bonding conductor.
Earth-free bonding is one of the measures recognised in BS 7671 for special situations under an engineer's supervision. Green-and-yellow identifies protective conductors, whether earthed or not, and should have been used if this is something within the scope of BS 7671.
Well maybe the whole article should not be there then, if only pro electricians can read it.
The meaning of 'potential' was taught in first year physics when I were a lad. I'd have thought one such as you - who claims to have a science degree - to understand it too.
I didn't ay they did. I just object to being told bonding stuff to earth is wrong when in 99.999% of homes that is exactly what is done.
So you agree that I was correct in saying you bond it to earth.
And again.
I really don't see where you differ from what I said.
Use of the word "bonding" (which has specific meaning in BS7671) in this context only serves to confuse the issue. Class 1 appliances have an earth connection certainly - this is common practice. However it is only common practice to use equipotential bonding in areas of high shock risk rather than generally. Phrases like "bonded to earth" have no meaning within the wiring regulations - so if you use them, you can't expect people to know exactly what you are talking about.
There is a significant practical difference...
You might argue that if the installation has main equipotential bonding in place, and the towel rail has a protective earth connection, then by default, you also have a equipotential bond between them since there is an electrical path from the CPC of the towel rail to the water pipe (for example).
However this fortuitous EQ bond has not been designed to act as a equipotential bond, and in reality will quite probably fail to do what is required under fault conditions (i.e. reduce touch voltage between towel rail and pipework) to a safe level. Separate EQ bonding designed for the purpose is required to do that, and having it present also acts as a second line of defence should the CPC for the towel rail not be connected.
It is a wiki you know, feel free to add extra description if you think it would help.
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