Quote:
Originally Posted by Wgoodrich
Martyn
You are confusing the relationship of a grounding connection for the electrical system and a bonding grid system. A bonding grid system bonds any metal 4" square or larger within 5' of the hot tub or pool. This bonding grid is not designed to be part of any electrical premisis grounding system other than incidental connections through equipment. What you are discribing if I understand you right is to connect the metal parts of the hot tub to the equipment grounding using the electrical system grounding electrode to make an intentional connection to earth. This is not the intent of a bonding grid found in 680 of the NEC. A bonding grid is designed as an expotential plain so electricity can not flow from metal to metal through the water or other equipment of the hot tub or pool.
Copied section of NEC 2008 handbook commentary;
680.26 NEC commentary - As described in 680.26(A), the function of equipotential bonding differs from the primary function of bonding to meet the requirements of Article 250 in that providing a path for ground-fault current is not the function of the equipotential bonding grid and associated bonding conductors.
electrical system equipment grounding and a bonding grid aka expotential plane are two different systems used for different principles to enhance safety.
Roger, SueMarkup and I were discussing a fine point of the design of the bonding grid requirements not having the equipment grounding system of the structural electrical involved in the discussion at this time.
Wg
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I stand corrected
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I know that main bonding and supplementary bonding differ somewhat. Its just I thought that north American main bonding and supplementary grounding requirements were carried out to the same standard as UK earthing arrangements EEBAD (equipotential earth bonding and automatic disconnection).
With this in mind I was referring to the recent UK 17th editon wiring regs 2008, which states that all circuits supplying equipment in a location containing a bath or shower are required to have gfci's (RCDs) installed. There is no requirement to bond extraneous metal work if this requirement has been met. but then it reads in another chapter.
Supplementary bonding of locations containing a bath or shower is required unless the following requirements have been met. the same location is required unless the following requirements are met. 701.415.2
a/ All circuits of the location meet the required disconnection times, 411.3.2.2
b/ All circuits of the location are additionally protected by 30 ma rcds, (gfci's)701.411.3.3
c/ All extraneous conductive parts within the location are effectively connected via the main protective equipotential bonding to the main earthing terminal, 411.3.1.2(main ground connection)
This is misleading because it suggests that you can supplementary bond and not bother with the gfci's.
With regards to c, an extraneous conductive part can mean a metal waste pipe connected to a bath or sink then to an internal or external metal stack or a plastic waste pipe connected to the exposed 4" square of metal waste within the location, thus introducing a ground potential therefore requiring bonding to the main earthing terminal/grounding connection as well as the gfci protection.
In the UK we also run a main equipotential bond to the water mains pipe, oil and gas pipes and gas meter, ducting, exsposed metallic structural parts of the building and lightening conductors etc. If the pipes are plastic there is also no need to bond. With regards to water, gas and oil pipes, where it feeds into the building it has to connect to the pipe within 2' of the stop **** (fawcette isolation valve) on the consumers side. With the execption that not all installations are connected to ground via a spiked electrode or buried taped grids, these are only found in remote areas where the supplies are fed overhead via poles and tranny's and the main service incomer has to be in turn protected by a 100 ma gfci as a main isolator with a time delay, then with further 30 ma rcbo's (combined gfci/mcbs) protecting further circuits.
Most incoming services have a main earth (ground) supplied by the power companies in the form of a sealed connection to the service neutral within the cutout fuse unit. And sometimes on the older supplies the lead sheaths/ wire armourings that are on the service feeder cables are used to supply main earths via an earth clamp. Both systems then in turn are fed from a sub and have one or more earth spikes connecting the substation star/wye mesh to ground.
Supplementary bonding and the main bonding arrangement has become a grey area once again with its wording, so many sparkies in the UK are still supplementary bonding whether or not its required as well as installing gfci's. That way the job will comply if they ever change it back, as some requirements from older regs have been brought back.
Also another problem that I have experienced with plastic pipe installations, is when the mains water feeding a pottable plastic water tank via a plastic pipe to feed all the house. Any continuity to ground potential is lost when the tank has stopped filling as there is no main bond to the pipe and assuming that the water is at ground potential when it is filling. The only ground connection it may have is from a water heater circuit heating a copper tank with a bad/corroded ground connection on the flex to the heater.
Case scenario.
A cast iron bath is fed from this copper tank via plastic pipes and overflows or has a leaking waste and saturates the floorboards and joists and water runs along under the floor and comes into contact with any hot connections within plastic (class 2 insulated) junction boxes. Or outlets under the floor that may feed circuits on the lower floor that in turn have non gfci;d circuits contained within them, the water if still running, the bath and the floor can potentially become live and cause the person in the bath to get a shock if they were to touch the damp wall or any surrounding surface full of condensation. As this could introduce a ground potential leakage through the fabric of the building.
If the bath had been grounded along with an insert within the plastic pipes, this could have been avoided. This actually happened to a customer of mine who had bought a house that had the wiring tested and passed. Luckily she wasn't injured when I got there, but I did measure a voltage of 130-175 volts between the saturated floor and damp walls and other surfaces. As in the UK our domestic household voltage is 230v/240v single phase.
To remedy this I supplementary bonded the bath repaired and bonded the leaking waste as it was a plastic one connected to a metal stack, and inserted copper nipples to the hot and cold pipes and bonded them also and in turn connected the bonding cable to the water heater ground which I had also repaired. The house was of masonary construction and the bathroom walls were also tiled but still, a ground potential was introduced by the general fabric of the building.
This is why I always recommend a metal nipple insert is put in the incoming feed and bathroom pipework to maintain a ground potential in the water, and main bond and supplementary bond where applicable when I do any design even if its required or not.
In addition to your discussion to grounding I am trying to find out where to purchase the NEC and the CEC to see how many harmonizations exist regarding the safety issues especially with grounding between north America and the UK. As this seems to something that keeps changing.
Regards
Martyn
