Discuss boiler earth bonding in the Plumbing Jobs | The Job-board area at PlumbersForums.net
I am sorry you seem to be having trouble understanding me scoobydoo in my explanation of electricity and how it and earth bonding is supposed to work. I am not saying I am right and sambotc is wrong, we are talking about two different tests.
Please go careful scoobydoo and look up Earth loop testing as well as electrical safety testing and why they are done for both your own safety and your customers.
Don't get me wrong I am not advocating plumbers conduct these tests except the basic boiler safety electrical test which they are advised to do after a boiler repair and for which an insulation tester may be very handy. The question was about earth bonding not insulation testing.
I was alluding to the quality of earth and the amount of earth fault charge it can take. Sambotc was referring to the quality of the insulation isolating the wires from each other. They are two different things.
Most MI's will tell you a basic electrical safety test is required on a boiler after any electrical repairs.
Can't argue with that, glad to hear that I have the right end of the stick as it is often discussed in much detail in electrical forums by qualified electricians with some confusion.
Can you confirm whether or not there are any regulations regarding bridging plastic fittings within BS7671 as I can't find it! Surely it depends what the fitting is on and whether or not it forms part of the main equipotential bonding or supplementary bonding? If the later then I would imagine a plastic fitting would actually help as it will increase resistance and lower the potential?
I was tying to inform the original writer not cause a problem. I am not getting confused at all. Ask yourself what purpose supplementary bonding serves if it is not connected to a low resistance earth path? The 17th edition requires main equipotential bonding to be in place as well as RCD's, if it is not, you may have to bond as per the 16th.
To me it sounds silly not to check the quality of earth as well as its continuity. An earth loop test does both.
You may for instance find yourself in a house with the bonding done in the bathroom so you figure its okay. However the pipework may not have a path to the main house earthing terminal. So a fault current cannot freely flow to earth and cause the disconnect. Until that is you get hold of the pipe yourself and I have been in that situation. The electricity finds it easier to go through you than down the metal pipework.
However as a plumber, you are not usually required to do anything about it, just be aware of the problems. A simple Neutral to Earth and Phase to Earth test using a voltage test lamp should show up any problems. But go careful doing the test for as an earth Loop test it may make anything connected to the earth system live. Phase to Earth should light the test lamp, Neutral to Earth should not.
Yes as you say scoobydoo Earth Loop testing is for measuring Ze and Zs internal and external impedance. I am not saying people should test for Earth Loop impedance it can be quite complicated and dangerous in some cases when live testing. But it is thought important enough for Fluke to incorporate an Earth Loop tester into one of its plug top meters. It gives a simple straight forward safe or unsafe reading using minimum set safety values for the earth loop.
I must also say I used a more complicated one than that one that actually gives you a reading so you can work out the potential fault current carrying capacity of the circuit.
Which would be ideal for the likes of a Plumber or gas fitter to test any sockets or otherwise they were considering plugging a boiler into.
My object was to point out to newbies that whilst supplementary bonding may not be required there is quite a lot more to it than just a couple of earth clips and some earth wire. We have obviously been talking at cross purposes. Its good to be friends again.
Always good to be friends Bernie. My primary concern is that people work safely and within their limits
The plugtop EFLI tester that you speak of is intended for socket testing to ensure that the resistance of the path is within the limits imposed for safe operation of the OCPD.
Personally, I would never use one of these devices, and I'm sure that you can understand how they are of limited use to an electrician, who needs actual figures as opposed to a "safe/unsafe" indication. I would hope that most plumbers would connect a boiler to a 3 amp SFCU, which isn't "testable" without using leads and an MFT such as the Megger 1730 which I use.
Always be careful of the advice you give. It can be taken out of context.
is the megger 1730 a 2 wire loop tester? if so do you find it an advantage?
The whole point of main bonding is to stop a potential difference occurring when extraneous conductive parts (metalwork brought into the building and in contact with the general mass of earth) enter a property
If the electrician bonds back to the MET in 10mm any metalwork entering the property (gas/oil/water), then technically that risk has been dealt with, as any further metalwork on the other side of a plastic join will not be connected to that particular pipe or structure. In the event of a fault, the incoming pipe will be connected to the main earthing terminal and therefore cannot create a potential difference (voltage) due to the earth reference being different to anything else entering the property. As you have said, if a service entering the building has a resistance of 23k ohms or above when tested against the MET, then it is considered to not be an ECP and will not require main bonding..... That said, many electricians will main bond a service entering a property, regardless of all this if so that they are covered if that service were to become an ECP at some point in the future. We do NOT bond plastic pipe...ever, but we do bond to copper pipe above the stopcock if it changes to copper. Many designers specify a short length of copper pipe after the stopcock even if the plumbing then reverts back to plastic, for this very reason.
To cut to the chase, if the system requires supplementary bonding (as it does not fulfil the requirements you mentioned in an earlier thread, mainly RCD protection on all circuits in a special location), then plastic connectors will need to be bridged with correctly connected, labelled and sized straps. There is a bit more to it than this unfortunately, and that is why, as others have said, get an electrician to carry out any tests and make the decision on what needs bonding. For all and any tests concerning bonding, a continuity/insulation tester will be the only item of equipment used.
Incidentally, there is NO instance when a plastic fitting helps any situation
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