An electrical puzzle.

[EmgeeParticipant @emgee]

In the article linked to by Michael one paragraph sums up 1 reason why the insulating insert is fitted:

It is a common misconception that bonding such items won’t cause any harm even if it is not required by BS 7671:2018 so a “better to be safe than sorry” attitude is taken. However, it is important to remember that by connecting to the main earthing terminal, in some circumstances, fault currents can be exported throughout the installation which would not be there if protective bonding had not been applied. This can cause an electric shock risk for persons outside of the installation in contact with the general mass of Earth and earthed equipment such as pipework, for example an outside tap or metal (class 1) electrical equipment.

The older electricians will remember the fault voltages from ELCB (Earth leakage circuit breaker) devices passing via the ground to the neighbours ELCB and tripping that also, not easy to get good separation distance for the earth stake in a row of small cottages.

Perhaps someone here has the latest BS7671 for reference to the reg.

Emgee

[Robin GrahamParticipant @robingraham42208]

This is quite fascinating. Much more complicated than I thought. Would I be right in thinking that if it could all be designed from scratch it would be possible to simplify? My house is maybe 200 years old and has seen many changes – the plumbing is crazy, lead water pipes in some places, dead legs all over the place and still after 7 years in here coming across lead gas lighting pipes. The electrics, though obviously more more recent, have clearly 'evolved'. Some black and red, some blue and brown. I suspect that it's a bit of a mess, though when I had the cellars wired up to make workshops the sparks tested the whole house and gave me a piece of paper saying it was OK.

In the picture below is the bulging out bit before the meter a conventional (ie it melts) 100A fuse? The leccy comes in through the connection labelled L1. Strangely the bulgy bit isn't secured with a seal – I can wiggle it and suspect I could pull it out.

Robin.

 

 

Edited By Robin Graham on 12/04/2023 00:11:16

Edited By Robin Graham on 12/04/2023 00:12:23

Edited By Robin Graham on 12/04/2023 00:16:12

Edited By Robin Graham on 12/04/2023 00:31:53

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Robin, yes that is a fuse, and they do normally have a seal.

Regards Nick.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Robin Graham on 12/04/2023 00:09:37:

This is quite fascinating. Much more complicated than I thought. Would I be right in thinking that if it could all be designed from scratch it would be possible to simplify? My house is maybe 200 years old …

Robin.

I don't think so: the systems used are designed to meet requirements, which vary with circumstances. For example, the PME system common in modern homes is unsuitable for a long list of industrial needs. The house being 200 years old is a bit of a red-herring: although it may be wired as a patchwork, it's probably compliant with one of the legal alternatives.

In the UK, there are (I believe), 4 basic single-phase variants, each with pros and cons:

These days PME is preferred in UK homes, option 3 above, because it saves the cost of separate earth wires running back to the transformer and avoids the problems caused by dodgy consumer provided earths. Home earths suffer a multitude of practical difficulties – corrosion, difficult to fit in terraced houses with no gardens, water-pipes later converted to plastic, unsuitable geology, and DIY bodges galore. But there are circumstances where a consumer provided earth is essential, like a chemical plant manufacturing TNT. These earths have to be properly engineered, not just a spike banged into the ground.

The last option, with no earth, isn't general purpose. An electrical engineer would recommend it for needs not met by more conventional solutions.

I'm dimly aware what goes on abroad electrically may be different. For example, although rings are beloved in the UK (reduced cable costs), the rest of the world prefer spurs. Differences occur because the engineers who consider risks and requirements before setting standards respond to local needs. In the UK we were happy to risk 250V in the home (reduced cable costs again), whilst the US wimped out and went for 110V. The rest of the world decided we were both wrong and standardised on 220V. Similar local considerations led 50Hz vs 60Hz.

The engineering logic isn't obvious, not least because standards rarely explain the background thinking or history. In truth most practical earthing systems are a compromise between safety, cost, and convenience. There isn't a single simple right answer that meets all requirements.

Dave

[KWILParticipant @kwil]

If I had to be on an all radial system I would need a room just to house the dis boards, having 6 ring mains to cover all the outlets. I do not believe in long trailing leads and adaptors so all rooms have ample double sockets within easy reach of where they are needed.

On the subject of the US (and Canada) their practise of using screwits, small cup shaped internally taper threaded to hold twisted wire joints is seriously old fashoined.

[Chris Pearson 1Participant @chrispearson1]

Posted by Robin Graham on 12/04/2023 00:09:37:

Strangely the bulgy bit isn't secured with a seal – I can wiggle it and suspect I could pull it out.

The seal fairy must have stopped off and removed it.

The seals are the property of the DNO and must not be removed by unauthorised persons. Some DNOs will permit registered electricians to remove them subject to certain conditions.

Whatever you do, do not be tempted to remove the fuse. First, if you do it under load, you may suffer an injury from an arc. Second, you would feel pretty foolish if removal of the fuse carrier pulled the service head off the wall, or even worse, displaced one of the cables.

[Chris Pearson 1Participant @chrispearson1]

Posted by Emgee on 11/04/2023 22:32:11:

Perhaps someone here has the latest BS7671 for reference to the reg.

Where do you look for a regulation which does not exist?

Perhaps confusion has arisen in the light of 542.2.6, which prohibits the use of a metallic pipe of a water utility supply as an earth electrode.

[Chris Pearson 1Participant @chrispearson1]

In response to SillyOldDuffer, the nominal voltage in UK has been 230 V for some time.

The type of supplier's earth depends largely upon the type of cable. PME (TN-C-S) is standard but a factory, for example, with its own transformer may well prefer TN-S.

It is safest to assume that all domestic supplier's earths are PME.

In the countryside, there may be no alternative to TT because of the distance from the transformer.

[duncan webster 1Participant @duncanwebster1]

So can anyone tell me which of SOD's options I have? House built 1930, rewired since. Used to have 3 phase but take out when meter moved. I've measured the earth neutral potential at a socket near the consumer unit at 160mV with hardly anything switched on.

Neither the gas nor water pipes are earthed, water is in plastic pipe up to my stop tap. It's complicated by the unit on the right, which monitors my consumption for some research project (and pays me a small sum each year). The fat green/yellow wire is my system earth, connected to a brass block on the side of the fuse carrier. Next question will be should they be earthed, I'm confused by what's gone before on this thread

[duncan webster 1Participant @duncanwebster1]

Forgot to mention, I have RCD and MBCs in the consumer unit

[Chris Pearson 1Participant @chrispearson1]

Posted by duncan webster on 12/04/2023 17:12:38:

So can anyone tell me which of SOD's options I have?

PME/TN-C-S. You can tell because the earthing conductor comes off the side of the service head.

Does it matter?

[SillyOldDufferModerator @sillyoldduffer]

Posted by Chris Pearson 1 on 12/04/2023 16:09:22:

In response to SillyOldDuffer, the nominal voltage in UK has been 230 V for some time.

…

Yes, I should have been clear I was taking a historical perspective. Power systems did not start in the well organised form they are today, it happened in steps starting about 1880. Back then, there were a multitude of supply options, where pretty much every local authority and insurance company had their own ideas, mostly incompatible. In 1900, an electrician had to make sure the switchboard was made of an acceptable material, usually either Marble or Slate. Only problem was, Slate was unacceptable to Marble loving authorities, and Marble unacceptable in the next town. More disagreements about paper, rubber, asbestos, and other types of insulation, and some insisted on Lead sheathed cables whilst others banned it outright. DC was initially universal, with domestic systems available in odd steps between 30V and 500V, maybe more. When AC arrived, early systems also delivered individualistic voltages, and alternated from as low as 15Hz to as high as 120Hz, not necessarily accurately. For several years 30Hz was the most common system in the UK.

It was a mess, typical of new technology, where Tom, Dick and Harry competed laissez faire for work, and it wasn't clear which system was best. Lots of electrocutions and fires, and enormous fun with tram systems before earthing was introduced. Very dangerous by today's standards! In the end, government intervened, set up the National Grid, standardised on 50Hz, and either absorbed compliant generators or shut them down. 60Hz was thought to be too racy for British generators at that time and 50Hz puts less strain on the mechanicals. Others realised technology was improving and reliable 60Hz was achievable and more efficient.

UK Domestic supply started as a nominal 250V, then dropped to a nominal 240V, I think to save energy during WW2, then was made a nominal 230V on paper for compliance with Europe, though the system didn't change. Actual UK voltage seems to vary by time and location – anything between 216V and 253V is within tolerance, and it's not unknown for local bits of the network to run outside those limits. I've never seen 230Vac in the real world, usually higher where I live, 237V as I type this.

Frequency varies too: the grid originally maintained a strictly accurate 50Hz, but at some point it was realised peak loads can be managed by altering frequency slightly. Now if the system starts to overload, cuts can often be avoided by dropping frequency a little so less energy per second is delivered to consumers. TVs carry on as normal, but kettles take longer to boil.

So the mains probably isn't 230V at 50Hz, and 13 Amp fuses don't blow at 13A. But it all works reasonably well.

Dave

[FulmenParticipant @fulmen]

i believe all European countries use "time correction" these days, meaning the average frequency will be constant. This keeps watches with synchronous motors correct with no manual correction needed.

[duncan webster 1Participant @duncanwebster1]

Posted by Chris Pearson 1 on 12/04/2023 19:02:34:

Posted by duncan webster on 12/04/2023 17:12:38:

So can anyone tell me which of SOD's options I have?

PME/TN-C-S. You can tell because the earthing conductor comes off the side of the service head.

Does it matter?

Do should I earthe my water/gas pipes?

[Maurice TaylorParticipant @mauricetaylor82093]

Hi Duncan

After reading this thread .

There is only one answer to your question ,get the advice of a qualified electrician.

Maurice

[Chris Pearson 1Participant @chrispearson1]

Posted by SillyOldDuffer on 12/04/2023 20:26:11:

13 Amp fuses don't blow at 13A.

Indeed not – they will go more or less for ever at 15 A, but will go pretty promptly at 20 A.

[Chris Pearson 1Participant @chrispearson1]

Posted by Maurice Taylor on 12/04/2023 21:27:28:

Hi Duncan

After reading this thread .

There is only one answer to your question ,get the advice of a qualified electrician.

We have been told that the water pipe is plastic to the stop cock, so there is nothing to bond.

However, we haven't been told about the gas supply. If it is yellow plastic, there is also nothing to bond; but if it is metal (cast iron) then it should be bonded.

If the installation is reasonably modern and has been certified, then it should be all right. If not, get an EICR -,an electrical installation condition report.

[EmgeeParticipant @emgee]

Posted by Chris Pearson 1 on 12/04/2023 21:35:20:

Posted by Maurice Taylor on 12/04/2023 21:27:28:

Hi Duncan

After reading this thread .

There is only one answer to your question ,get the advice of a qualified electrician.

We have been told that the water pipe is plastic to the stop cock, so there is nothing to bond.

However, we haven't been told about the gas supply. If it is yellow plastic, there is also nothing to bond; but if it is metal (cast iron) then it should be bonded.

If required any bonding is on the consumer side of the gas meter, not to the supply pipe.
Same applies to the water supply, bonding is on the installation sfter the stopcock if needed.

Emgee

[Chris Pearson 1Participant @chrispearson1]

Posted by Emgee on 12/04/2023 22:32:13:

Posted by Chris Pearson 1 on 12/04/2023 21:35:20:

Posted by Maurice Taylor on 12/04/2023 21:27:28:

Hi Duncan

After reading this thread .

There is only one answer to your question ,get the advice of a qualified electrician.

We have been told that the water pipe is plastic to the stop cock, so there is nothing to bond.

However, we haven't been told about the gas supply. If it is yellow plastic, there is also nothing to bond; but if it is metal (cast iron) then it should be bonded.

If required any bonding is on the consumer side of the gas meter, not to the supply pipe.
Same applies to the water supply, bonding is on the installation sfter the stopcock if needed.

Where the bonding is attached was not the point. After all, if the supply is plastic, it would be pretty pointless to put a cable clamp around such a pipe. However, Emgee is correct per 544.1.2.

[Robert Atkinson 2Participant @robertatkinson2]

Dave (SOD) said:
" Frequency varies too: the grid originally maintained a strictly accurate 50Hz, but at some point it was realised peak loads can be managed by altering frequency slightly. Now if the system starts to overload, cuts can often be avoided by dropping frequency a little so less energy per second is delivered to consumers. TVs carry on as normal, but kettles take longer to boil. "

Not quire correct. The average frequency is held accuratly to 50Hz. Changing frequency does not change the power consumed by resistive loads like kettles or electronic equipment. Induction motors will change power with frequency but only if the change in speed alters the power consumed mechanically.

That said, the power stations DO vary the frequency of their indiividual generators slightly to control power. This is to control the power supplied to the grid by that particular generator. It may be easier to think about the resulting phase shift controlling the power.

Robert.

[SillyOldDufferModerator @sillyoldduffer]

Many thanks to those who clarified my earlier misunderstandings. Very educational, this forum.

In my home, the rising water-main is plastic, connected through a brass stop-cock to the usual copper pipes inside the building. When the house was heated electrically with hot-air, the water pipe wasn't earthed. However, when I switched to gas central heating, the whole system was. Now a thick copper wire runs from just above the stop-cock back to the consumer unit. Also, in the bathroom, the radiator is wired back to earth. The gas-piping is earthed on the consumer side of the meter. The gas supply pipe is plastic.

Reading the regulations the bonding is optional, but I think it's been done to address two different risks, They arise because copper pipes are poorly insulated:

• To prevent electrocution inside the house should Live accidentally connect to a pipe anywhere in the building. This is particularly important in the bathroom.
• Wherever the uninsulated copper pipes touch the wall and floor they are partially earthed. Thus there's a risk of a fault starting a fire. Badly earthed pipes become a hazard if there's anything in the electrical installation that could connect to them. They allow current to flow without blowing the fuse.

In my home, both risks were geographically impossible when I had hot-air heating, but both became possible as a result of fitting copper connected central-heating radiators in every room. Both risk are avoided by bonding.

A third risk doesn't apply. In my home, the supply pipes are both plastic, so there isn't any risk of a large fault current damaging the gas or water system by earthing through them.

Dave

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, as the frequency of the mains is concerned, measuring mine it fluctuates quite randomly between about 49.9 to 50.9, but it is mostly just either side of 50, this is over a period of about 15 minuets.

Regards Nick.

[Chris Pearson 1Participant @chrispearson1]

Posted by SillyOldDuffer on 13/04/2023 10:19:41:In my home, the rising water-main is plastic, connected through a brass stop-cock to the usual copper pipes inside the building. When the house was heated electrically with hot-air, the water pipe wasn't earthed. However, when I switched to gas central heating, the whole system was. Now a thick copper wire runs from just above the stop-cock back to the consumer unit. Also, in the bathroom, the radiator is wired back to earth. The gas-piping is earthed on the consumer side of the meter. The gas supply pipe is plastic.

There is no need at all for that main equipotential bonding – the plastic pipes cannot introduce a potential into the building and its electrical installation.

My house was wired to 15th Edition and has a van's worth of supplementary equipotential bonding. Both pairs of hot and cold water pipes are joined under the double stainless steel sink and even the sink is bonded to them. This is all despite electrical continuity of the copper pipes, brass taps, and steel sink. It is mad!

Bonding is not the same as earthing even though green and yellow cables are used for both. If there is a fault within a boiler or fan-assisted radiator (where else could one occur?), the fact that the appliances are earthed will ensure ADS: the fault circuit is along the circuit protective conductor and not the pipes and bonding.

Seeking to rely upon bonding for ADS would not be safe – the copper pipes could be replaced by plastic ones or insulating joints could be installed.

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