boiler earth bonding

[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.

 

[Nostrum]

Hi scooby,

I am a member on there and have been for some time. I am a little confused when you say '

the radiator itself would not be an ECP, as it is only services entering the property which can be classed as this'

As the way I read the regulations is that anything can be ECP especially metallic objects, including structural steel, stainless steel wall coverings in commercial kitchens etc?




​

 

[Scoobydoo]

Hi sambo,

Strictly speaking, you are correct. The definition of an ECP, as you know, is "A conductive part liable to introduce a potential, generally Earth potential, and not forming part of the electrical installation".
However, there is some debate over where and when "extraneous" becomes "exposed". The pipework itself, if isolated from all electrical items, would definitely be considered extraneous, whereas the pipework/radiator fed from a boiler with an earthed chassis which is isolated in some way from the incoming mains or anything else which enters the property such as structural steelwork or pipework could be considered "exposed".
Hope this makes some kind of sense 🙂

 

[Nostrum]

As much as anything else in any BS document does! Really then it comes down to testing and common sense to identify/verify. So in actual fact using the example above, the radiator fitted in a bathroom with plastic pipe/fittings could be classed as extraneous (if tested and 22k or less) as you have effectively decoupled it from the boiler/gas/cold water main and MEB? but in reality, if that was the case then it would probably also have a poor path to earth anyway.. :dizzy2:

Thanks

 

[Scoobydoo]

If a rad is connected via plastic only then it will undoubtedly over 23k, under that and there will be a tenuous earth connection somewhere and hence need bonding. That is, unless it is below 1667 ohms and all circuits are RCD protected etc. Gotta love it 🙂

 

[zzzjim]

A case for earth bonding , could it reduce likely hood of corrosion , by preventing DC potentials forming ( If there are un-earthed metal parts present in a plastic install )

 

[Howsie]

OMG! I'm off to the pub 🙂

 

[mutley racers]

way over my head. So do most of you chaps tell the custard to get an electrician in to check bonding and so on then?