Slugbabydotcom said:
This thread is such an abuse and misuse of bs7671 not the least the worcester education literature. they should stick to making boilers.
Main equpotential bonding conductor size depends on type of earthing system and size of meter tails. This often means you are using 10mm csa but not always.
The need to bond pipes (if any ) beneath a boiler is open to interpretation.
The only part of a house where suplementary equipotential bonding is required is aspecial location such as a room with a bath or shower or a sauna or swimming pool, but excluding the kitchen. End of.
If the boiler is proximal to one of these rooms you may perform any necessary suplementary bonding at the boiler. The csa of the protective conductor again is dependent, but in most situations ends up being 4mm. To take it back to the main earth terminal (met) would be admirable but all that is required is to take it to the circuit protective conductor of one of the appliances inside the zones of the special location, and if there are none it is customary to use the light fitting, but if the bonding takes place at the boiler then naturally you would cage (faraday) it to the boiler cpc. This could take place at the boiler casework or at the fused spur.
In one place only bs7671 mensions that metal frames and central heating are part of the main equipotential bonding (which remember takes place within 600mm of entry to the building of external influences, is unbroken and goes right back to the met.).
This has to be interpreted with understanding. We must first decide the purpose of main equipotential bonding. the purpose is to provide a sone of safety. we call the safety system used to preserve life in household wiring EEBADS (earthed equipotential bonding and automatic disconnection of supply). In this system of protecting you we create a safe zone where all outside influences are bonded together as soon as they enter it. This is the equipotential zone. The rules for disconnection of supply are different inside this zone because of it's inherant safety to outside. (disconnection of supply is performed by fuses or breakers sometimes supplemented with rcd's combined with circuit protective conductors). We (those trained in household elctrical instalation inspecting and testing) are taught that an electrical fault outside this zone is invariably fatal, hence the requirement for rcd protection for equipment used outside the equipotential zone (garden and garage).
To create the equipotential zone we must therefore electrically bond together any metal part which starts life outside the zone. That is clearly metal gas metal oil and metal water services. These are made explicit in the regs. But metal heating systems which do not come from outside the zones are not any more introducing a potential from outside as is a metal water pipe internally joined to an alcathene supply pipe (which no should not be bonded).
It is also well within the scope of a suitably qualified person to decide that the bonding conductor may be of a different material to copper of 10mm csa. For instance the metal trunking is sometimes relied upon. It is not outside the realms of possibility that should a 22mm gas pipe be suitably joined with solder after testing,an electrician could decide that to bond it more conveniently than 600mm from the point of entry is satisfactory.
the beauty of the eleltrical rules is that they allow for interpretation by a person of suitable qualification, equipment to test continuity, and sufficient understanding of the purpose and requirements of the statements within bs7671, some of which to the ignorant apear to contradict..
It is my interpretation that heating pipes which do not enter the zone from outside are not part of the main equipotential bonding. As long as all incoming (metal) services are bonded, and all special locations are bonded, and the boiler is not in a special location, no bonding needs take place.
The problem we have now found ourselves with is that a few idiot leaders like that worcester one have gone baah, and all gas fitters like sheep are going baah baah. Now up and down the land there are little ewes's under boilers.
If my corgi inspector questions my rationale I will show him my qualifications and say show me more qualifications or leave it to me. If my Napit inspector questions it I will thrash it out with him, but would stand my ground.
It might be of interest to you that when I searched by enquiry the issue of heating bonding at Napit I had the examiner spinning in circles until he eventually conceded that it must be a "corgi requirement". in other words the elctrical bodies haven't a problem with my practice, as long as corgi haven't. My view on that is show me more qualifications and understanding and I'll go baah like the rest otherwise stay out of a field you clearly don't understand.
