boiler earth bonding

[Scoobydoo]

Insulation tests do not tell you how good the earth is just that one wire is insulted from the other and how good that insulation is. An Earth loop test tells you how much current your earth path will take. It would be point less earthing with fine wire it would burn out if you got a 230 volt 13 amp fault discharging to earth and leave your pipework still live and able to deliver a big shock for anybody touching it.

The RCD is intended to sense the current is the same voltage in both the Neutral and Positive wire in the cable. If its equal it stays open, if its more in one wire than it is in the other it shuts down because in an AC system it means the current is running to earth somewhere. But its relying on a mechanical RCD to always be working and not seized up over many years. That is why they have test buttons on them that should be tested every month or so. But who does?

It is right though, you do not have to supplementary bond providing the pipework is connected somewhere along its length to the main Earthing point and protected by an RCD. But how would you know it was connected without testing the earth and how good was the connection?

Anyway as Tamz says its not our job, but its interesting.

Bernie, please listen to sambotc, as what you are saying is not correct. You obviously have some knowledge, but "a little knowledge" and all that...

 

[chris watkins]

Hi, can I just throw a few bits into this long running thread.

1. Another one of the common misconception to do with water (implanted by school teachers) water itself does not conduct electricity, its the bits in it that do, so pumps using probe set controls (low voltage) can not be used with pure water say from condensation sources, they won't work. What's the point of this, well you can't rely on the water inside a pipe as an earth path & yes you must apply bonding across any breaks in metallic pipework created by inserting a plastic fitting. (next they will be tell the kids that hot water / air rises !!)

2. Gas supplier (Transco) came around my house short while ago as I had a leak on the incoming supply. They take the risk of electrocution of their staff (& risk of ignition) so seriously now, that all are issued with a electrical clamp meter which they have to use to test for current flowing through the metallic gas supply. There are 3 level, the second requires temporary earth bonding is applied, the third they will not work on it until the leak / source is found & rectified by you. The damager of cause would only become apparent when they cut through the pipe to carry out repair / replacement. There have been many cases of electrocution or fire from arcing resulting in injuries but can not confirm fatality's. Please use your temporary earth bonds when cutting into water & gas pipes it does happen.

3. Referring to my earlier post in this thread "Did you know that a plumbing apprentice now has to complete 100 + hours of electrical training as part of their level 3, more than cold water or heating !!!!!"
Clearly a knowledge of electrics & electrical systems is now required to be a plumber / heating engineer in the modern wold. To what level this knowledge should extend is the question C&G seem to hold the view that they need to mini elections before they have even mastered plumbing !!! trying to teach an 18-19 year old the vagaries of electrical testing to Part P standards is fun with a capital F.

 

[Nostrum]

Until the day we have distilled or RO water coming out of our taps, I will assume tap water is conductive! After all if it wasn't then why the need for stricter regulation for electrical work in special locations. Otherwise you'll get people thinking that you can only get electrocuted once you've added the orange squash!

I'm pretty sure I have had a little shock off a gas meter before, just doing a soundness test although it was a long time ago. Cutting into a pipe is a different story as you are very likely to bridge the gap to earth at some point!

Thats why RCDS are so useful and safe and should be fitted wherever possible in my opinion

 

[chris watkins]

OK Sam you win, but my juice (don't have squash we'r posh) is smooth so can't tell how conductive it is ??
Make you right about the RCD's (or RCBO's). Last thought, why do rad's or boilers in all plastic systems require no bonding ??

 

[Nostrum]

As i'm so sad, but it is also interesting, if i get time later I will do a test with a piece of 15mm. I'll test the resistance off a straight piece of copper, then I will cut a hep fitting into it, then i will fill it with water as see what the results are.

re: plastic piepwork, they may do, if when you test them they have a resistance of less than 22k to earth as they would still be classed as an extraneous-conductive part? It's basically ensuring that the potential between an object that you may be touching and the radiator is not high enough to create a hazard. (equipotential zone)

What I don't understand is how you can get a shock stood on a carpet which is on wooden floorboard, in a pair of shoes with rubber soles by just touching the live conductor. Where did it track back to earth and what would the resistance be? Yet if you are floating in mid air and touched the same live you probably wouldn't get a shock. (not tried)

Don't get me wrong, electricity still mystify's me, but it would seem that it does to a lot of electricians as well in that respect. Not being able to understand where the path to earth is. I've got a metrel multifunction tester and the test button has a metallic button that when touched, won't let you carry out the test if it senses a touch voltage of, i think, 5 volts. It took me ages to figure out what it was doing as the instructions were pants, but it's surprising how often it locks you out, particularly when stood on aluminium steps! (need some new fibreglass ones i think)

 

[Bernie2]

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.

 

[Bernie2]

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, but that does not include an earth loop test with an earth loop meter.

 

[Nostrum]

Hi Bernie2,

We are talking about supplementary bonding in this thread which has nothing to do with the connection to earth (not bonding) within the fused spur or similar :stooge_curly:

You are right you should test there is a path to earth before connecting, but unless you understand disconnection times with regards to the circuit protective device, you will not be able to make an informed decision on whether or not the earth loop impedance test is satisfactory or not anyway. You are mearly testing for continuity between the fused spur and the main earth terminal.

As most boilers rely on flame rectification devices to ensure the burner is lit, most boilers wouldn't fire without some kind of path to earth anyway, although I am not saying there is no need to test.

What tester are you using to carry out the earth loop impedance test bernie2 and what result are you getting from it out of curiosity?

 

[Scoobydoo]

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.

As a fully qualified, apprenticeship served, part P registered electrician with over 20 years experience, I don't think that I need telling about "Earth loop testing", as you call it. sambotc gave a good explanation and clearly understands the difference between earthing and bonding, along with which tests are required. The cable "bonding" sizes are laid down in the IET 17th edition regulations, you do not need to work them out. I apologise if I have offended you, but I am very worried that you are getting confused over this subject. I will give up now and wish you all the best.

Btw, for those interested, water itself is a very poor conductor. A bathroom and shower room is a special location due to the fact that after immersion in water, your body resistance will drop considerably and you are at a much higher risk of receiving a shock (along with the fact that you will be barefoot).
A kitchen is a special location in building regs only, not the electrical regs, due to the fact that you will be using hand-held equipment in a room where water is used.

 

[Nostrum]

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?

 

[Scoobydoo]

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?

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

 

[Bernie2]

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.

 

[Scoobydoo]

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.

With the greatest respect Bernie, we never use an earth fault loop impedance tester for bonding... We use it for testing Ze and Zs on the earthing system, not bonding, which is a completely different kettle of fish.
As sambotc has already written, our EFLI test is to make sure that the "loop" resistance is below a certain amount to allow our circuit protective device to operate within a certain time, such as 1.16 ohms for a 32 amp type B MCB. This is "earthing" and not "bonding".
To make sure that our 10mm main bonding is continuous and correct, we must EITHER -
1) Inspect it along its entire length, or
2) Using the long-lead method, check that it has a nominal resistance from one end to the other.

This is in the regs.

Regarding our supplementary bonding, again we would test between pipework for a nominal resistance if we had ascertained that bonding was indeed required, using the correct sized cable.

If you personally use an EFLI tester to check your bonding, then please tell me how you do it. I would love to know

 

[Bernie2]

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.

 

[mountainman]

So much expert knowledge and responsibilty for little more wage and respect than Sergei Meerkat receives!

 

[Scoobydoo]

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.

 

[AWheating]

tap water is generally very clean making it a very poor conductor. Possibly water in a heating system may conduct slightly better due to contaminates. To what effect a badly sludged system full of magnetite would have on its waters conductivity would be interesting to know i guess but i dont think its going to make an amazing difference.

 

[AWheating]

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?

 

[Scoobydoo]

is the megger 1730 a 2 wire loop tester? if so do you find it an advantage?

It is. However, the 1700 series is only really accurate using 2-wire with a high-current test (no RCD in circuit) such as for Ze readings. For accurate no-trip, 3-wire is essential. The 1730 is selectable between 2/3 wire for high and no-trip so you have the choice. DO NOT try carrying out Ze with no-trip...totally wrong reading.

 

[AWheating]

I have one of the older megger mft's and did wonder how better or worse a 2wire tester was. when i did my 2391 the college used megger 2 wire testers but the tutors did state they prefered 3wire over 2 but was easier to teach with the 2.

 

[Bernie2]

Scoobydoo, I had no intention of advising people to do it themselves, as you say a meter with figures enables you to workout the Ze and the Zs which is the kind of meter I use. I have not fortunately given out any info to enable somebody to conduct an Earth Loop test only that they need a meter to do it.

I never gave any information out other than to use an Earth Loop Tester.

The testing you were talking about is one often used to test whether an item is an extraneous conductive part or not. It did not explain the quality of Earth required. A physical inspection to ensure all is correctly connected is possible if you know what your looking at but would a plumber without electrical knowledge know? And as you know an insulation test involves high Mega Ohms a Loop Test low Ohms. They are two different meters used for two different kinds of test. I was trying to get the point over to none electrical people that Earth path quality is important if the system is to be safe.

The point of using a plug top Earth Loop test is because probably many of the people on this forum are not electricians, so instead of them doing no Earth Loop test, surely a simple one is better than none?

I have no objection to giving advice but you have to give enough to enable the person to recognise the dangers, my object is safety. They probably would not have asked the question in the first place if they were not interested or did not want some form of advice about it or thought it was simple and where going to have a go anyway. I feel it is better they know as much as possible about what is involved and how dangerous it can be, than perhaps let them try it out for themselves and perhaps kill themselves. I find that withholding information can be as dangerous as giving to much. I try not to assume the average person is stupid and is likely to go and do something if they know the risks involved whereas if they do not know the risks they may very well try.

 

[AWheating]

i agree bernie that those plug top testers can be helpful. They are neither aimed or needed by qualified electricians who need to test and certify there work but non electrical trades who want to do a basic check of a socket before pluging anything could find them helpful.

 

[Scoobydoo]

Bernie, could you please tell me exactly how you use an earth loop impedance tester when testing bonding. Where do you make your connections and do you use 2 or 3 wire, high or low current?

 

[Nostrum]

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

Probably didn't explain myself very well in the above post. Just to clarify my point.

If plastic fittings were used to connect a bathroom radiator, they are likely to increase the resistance to earth. Therefore, when carrying out a test to confirm whether or not said radiator was an extraneous-conductive part, it is more likely to not require bonding if plastic fittings/pipe were used due to the fact that the plastic would increase the resistance to possible above 22k ohms.

If plastic fittings were used on the incoming cold water main service pipework, after the MEB connection were made, then surely there is a possible increased risk due to the fact that the pipework before, and pipework after would have a different potential. If, somehow you managed to bridge this by contact, and under fault conditions, you may receive a shock. This is assuming that the fault was to occur on the pipework after the plastic fitting/pipe.

If carrying out a PIR would you be happy to confirm MEB at the service, at point of entry and assume that the rest of the pipework connected to that supply had an equally low resistance to earth, or would you physically perform the test at multiple parts of the installation to confirm continuity etc?

I am doing 2391 in July so glad to receive any advise on whether or not I may be misunderstanding the situation.

 

[Scoobydoo]

sambotc, the radiator itself would not be an ECP, as it is only services entering the property which can be classed as this. The problems occur when there are plastic fittings amongst a copper system, as there may be some continuity due to connections via boilers etc, but no "direct" contact, this being the problem with P.D and hence facilitating the need for supplementary bonding.
If you are really interested in this subject then I would strongly recommend searching on the electricians forum as we have had some quite in-depth discussions on there.