Just to start an argument.

[Knobhead]

View attachment 8788

OK what started this was reading a post where someone was asking why there house should be ripped apart for an earth wire.

The first rewire I did was my own house and this has been puzzling me ever since. I did all the plumping myself including the gas. Everything was bonded and as was as then required cross-bonded. I had one hell of a struggle getting a 16mm to the gas meter, water wasn’t too bad. Cross-bonding was in 6mm. All the pipe was copper, soldered throughout except for about 18” of lead which I couldn’t get rid of and that I plumbed.

Now the bit that puzzled me, where is the best place to make main earthing connections?

Given that the specific gravity of copper is 8930Kg/m³

Wire
A 1m length of 6mm² =0.0358Kg
A 1m length of 10mm² =0.089Kg
A 1m length of 16mm² = 0.142Kg

Pipe (from tables)
A 1m length of 15mm = 0.391Kg
A 1m length of 22mm = 0.587Kg

Cross sectional area and therefore resistance is directly proportional to weight and length.

So if we compare the linear resistance of the smallest (normally) copper pipe against the largest (normally) used CPC the pipe is 2.736 times better.

I know this is against all that is in the Bible (red with green stripes) but I give you this argument:
A central point would be electrically the best point.
Right where’s my tin hat! Incoming FLACK!

View attachment 8787

 

[alarm man]

as close as you can,isnt that what it says..

 

[GaryM]

When you say main earthing, do you mean protective equipotential bonding?
If so then I would disagree with a central connection and agree that BS7671 has it right with as close to the entry into the equipotential zone as possible and before any branches for obvious reasons.

 

[telectrix]

so then, the fact that i have bonded my gas pipe where it runs past the CU, instead of struggling to get a 10mm cable 20ft to the gas meter in the garage is not, after all, bone idleness, but has a good sound basis in mechanical and chemical engineering, not to mention the lower resistivity of 22mm copper pipe against some cable made in china. a good argument there , tony, can't fault it.

 

[Paul.M]

Tony I agree with your argument/question but I believe the answer for the regs for having an earth clamp within the first 600mm of the incoming gas/water/oil is that it is easy to locate for testing/maintaining and that it is easier to find than a 50% length of cooper pipe in a house etc. Also which would be the least restrictive path under fault condictions if the fault occurred at 25% and 75% of the length? You do the math?

I think it boils down to ease of locating a clamp although 2 or 3 clamps along any length of conducting pipe would be a safer option.

Take your tin hat off now mate .

 

[Knobhead]

I knew the moment I started to write it I would get the Bible (red with green stripes) quoted at me but you have to look at:
Logistics / practicality
Basic physics
By running to a remote point you aren’t making the situation better.
Ohms law won’t change for the IEE!

 

[telectrix]

another way of looking at it , apart from comparing weights is:

15mm copper pipe has a circumference of 15 x pi = 47mm . times by 1mm thick gives it a csa of 47sq.mm which is just under 3 x the csa of 16mm cable. compares favourably with your figure of 2.76.

figures approximate and roughly correct at the time of printing. no responsiblity accepted for injuries caused by trying to split gas pipes open to check my findings.

 

[Paul.M]

You also have to take into account the connections of the pipe whereas earth wire is solid throughout its length. Takes away the uncertainty of bad joints or poly pipe push fittings so only the water would conduct the fault current and we all know that water doesn't conduct electricity all that well unless it has a high mineral count.

 

[SirKit Breaker]

kin el, i am off to bed.:dizzy2:

 

[telectrix]

You also have to take into account the connections of the pipe whereas earth wire is solid throughout its length. Takes away the uncertainty of bad joints or poly pipe push fittings so only the water would conduct the fault current and we all know that water doesn't conduct electricity all that well unless it has a high mineral count.

but , then again, plumbers do't usually disconnect water and gas pipes. they do disconnect bonding cables.

 

[Engineer54]

I think you'll find the main reason for connection of the bonding conductors within 600mm is it will be before any branching of the water and gas systems. If bonded after the branching off you could well end up with problems...

All too often, sections of pipe are cut out and replaced with plastic these days. so you could end up with bonding pipework that now doesn't need bonding and having pipework that needs bonding, that is no longer bonded....

 

[ExArmy]

do gas pipes not have to be in copper throughout?
also are they not required to be 22mm now, i've just had my combi moved and the gas supply is done in 22mm

 

[Paul.M]

Supply to combi boilers min is 22mm, anything less is against gas regs on psi drops once boiler and other gas appliences are in use (i think).

 

[telectrix]

it's 22mm so you use more gas.

 

[Knobhead]

I think you'll find the main reason for connection of the bonding conductors within 600mm is it will be before any branching of the water and gas systems. If bonded after the branching off you could well end up with problems...

All too often, sections of pipe are cut out and replaced with plastic these days. so you could end up with bonding pipework that now doesn't need bonding and having pipework that needs bonding, that is no longer bonded....

As you say sections of plastic or other things could be added at any point to break continuity, be it in a domestic or industrial situation.

I’ve fallen foul of it several times. One classic was I was called to a coal plant because the CO readings in the pulverised coal ducting “must be wrong, we keep getting POPs in the duct”. So did all the calibration tests and couldn’t find anything wrong. Walking back to the control room I kicked a piece of copper strap on the floor. The fitters had replaced a section of duct. The duct is steel lined with basalt cement, the joints being pure basalt. The Muppets had replaced the section and just chucked the bonding on the floor. Static and pulverised coal just doesn’t go together! (By POPs I mean almighty explosions, but the plant was designed to withstand them).

No matter what we do at some point someone will come along and, at times in all innocence completely f**k up the safety systems we put in place.

Now where can I buy a Faraday suit?

 

[supasparxs]

The whole purpose of bonding the Gas and any other services coming into a premises is to stop fault currents coming in from outside.

You guy must know about cows, or even what happened last year race horses getting electrocuted from a fault in another installation. A fault elsewhere can travel though the ground and cause a shock or even worse.

The 10mm Earth to the Gas, Water etc is to protect your installation from a fault outside your installation.
If a fault occurs the 10mm Main Earth will cause the fault to go down to the earth on the service head.

This is why the 17th edition regs state that if the circuits in a bathroom are RCD protected there is no need for the equipotential bonding

 

[supasparxs]

Wire
A 1m length of 6mm² =0.0358Kg
A 1m length of 10mm² =0.089Kg
A 1m length of 16mm² = 0.142Kg

Pipe (from tables)
A 1m length of 15mm = 0.391Kg
A 1m length of 22mm = 0.587Kg

Tony your forgetting the copper content of cable compared to the content of 15 or 22mm pipe

 

[Deleted member 9648]

The whole purpose of bonding the Gas and any other services coming into a premises is to stop fault currents coming in from outside.

You guy must know about cows, or even what happened last year race horses getting electrocuted from a fault in another installation. A fault elsewhere can travel though the ground and cause a shock or even worse.

The 10mm Earth to the Gas, Water etc is to protect your installation from a fault outside your installation.
If a fault occurs the 10mm Main Earth will cause the fault to go down to the earth on the service head.

This is why the 17th edition regs state that if the circuits in a bathroom are RCD protected there is no need for the equipotential bonding

Have I been hibernating?...is it April 1st already?

 

[needasparks]

Do we have to take the bonds off during the winter so the meter reader can warm his hands up on the gas meter. ?

 

[Knobhead]

Tony your forgetting the copper content of cable compared to the content of 15 or 22mm pipe

Well unless someone has started making copper pipe out of something other than copper, the weight per meter is the copper content be it pipe or wire.

Based on a wall thickness of 1mm:
15mm pipe = 44mm CSA
22mm pipe = 66mm CSA

All pipe figures from Copper Plumbing Tubes & Copper Water Supply Tubes - Metal Agencies Ltd

 

[Knobhead]

I’m not saying go against the regulations but I’m trying to point out using physics that the regulations aren’t always right.

If there is an exported or imported fault it will travel through the gas meter whatever method you use, unless you fit a jumper across the meter (electrical, not a bit of fancy bit of plumbing to bypass the meter).

This drawing is based on a typical installation based on the GAS pipe only.

View attachment 8835

Give a nominal resistance value of 10Ώ for drawing A. The “correct way according to the regulations”.
Where as B has a resistance of 3.21Ώ.
(10 / 66 x 8 = 1.21 for the pipe + 2 for the bonding.)

QED the regulations aren’t always right.

View attachment 8836

Every installation is different. Service positions can be any where. I based this on Tel’s post #4

 

[sambotc]

Surely the regulation is there to standardise the requirement for each installation to ensure that it is fitted in a position where it will provide adequate protection in all installations? That's not to say that there may be an alternative which could preform better in a fault current situation, but without a specific requirement, the onus would be on the installer to assess the resistance and pipework routing to ensure there are no tee's before the connection etc. Whilst most people on here seem to know what they are doing, I certainly wouldn't like to assume that everybody with the relevent tickets are?

Sam

 

[telectrix]

it's always good to query the status quo. just because it's a regulation doesn't mean it's right. just look at the smoking ban in pubs for one.

 

[telectrix]

that ban has been in force now for 4 years?. have we seen a fall in the cases of lung cancer?... NO. have we seen an increase in the number of bankrupt publicans with their pubs demolished and old folks homes built on the sites ... YES.

 

[alarm man]

that ban has been in force now for 4 years?. have we seen a fall in the cases of lung cancer?... NO. have we seen an increase in the number of bankrupt publicans with their pubs demolished and old folks homes built on the sites ... YES.

your right tel..biggest causes of cancer are not smoking/drinking which are all natural substances i add but the preservatives/pesticides modified foods we eat,add mobile phones etc,people have smoked and drank for thousands of years,but the food chain remained untouched and fresh.

 

[PC Electrics]

another way of looking at it , apart from comparing weights is:

15mm copper pipe has a circumference of 15 x pi = 47mm . times by 1mm thick gives it a csa of 47sq.mm which is just under 3 x the csa of 16mm cable. compares favourably with your figure of 2.76.

figures approximate and roughly correct at the time of printing. no responsiblity accepted for injuries caused by trying to split gas pipes open to check my findings.

Just for info, 15 and 22mm copper tubing to the relevant BS has a wall thickness of 0.8mm.
Also bear in mind that the copper used in tubing is less pure than that reequired for cable, so the specific resistance will be greater (but not by much, about 10-15% I would guess).

 

[Knobhead]

Thanks I’d looked for UK standards but couldn’t see the wood for the trees with Google. (And before anyone says anything, I did find wooden pipes).

With .8 wall thickness then it should be

π x (Do/2)² - π x (Di/2)² = CSA mm²
Where:
Do = outside diameter
Di = inside diameter

Therefore:
15mm pipe = 35.69mm²
22mm pipe = 53.28mm²

Still better than a bit of 10mm singles and less prone to damage or disconnection.

The revised figures for drawing B
Pipe 10/53.28 x 8 = 1.5 + Bonding 2 = 3.5Ώ

 

[Richard Burns]

Absolutely right Tony, I have thought this before, the only disadvantage (which I consider lower than disconnecting bonding cables) is the pipework discontinuity. Having the bonding after a branch makes no difference because electricity will flow either way in a conductor so all pipework will maintain the same voltage across the system wherever you bond.
Oh yes but the regs do not allow this; ah! but is this a better method and therefore safer than BS7671 so OK:hurray:.

 

[cornburn]

your right tel..biggest causes of cancer are not smoking/drinking which are all natural substances i add but the preservatives/pesticides modified foods we eat,add mobile phones etc,people have smoked and drank for thousands of years,but the food chain remained untouched and fresh.

Oh dear. Yes life expectancy 1000 years ago was much higher than today, due to the fact we didn't have pesticides or mobile phones. In fact everyone protected themselves by smoking and drinking natural substances like opium, tobacco and cocaine and as a race we'd never been healthier :S

Re the bond, surely it's where there's entry to the building so that when you spur a tap off the pipe using a pushfit T piece you don't break the bond?

 

[Engineer54]

Errrr!! I don't think so, life expectancey 1000 years ago was in fact considerably lower than it is today!! Average life span back then was around 35 to 45 years or lower.... That's if you managed to live beyound 3yrs from birth. Infant mortallity rate was very high back then....

 

[ExArmy]

gas has to be done in copper, so my argument is why can you not connect a gas bond to most conveinient place possible as theres no way sections could be done in plastic.
I suppose theres a possibility that that particular branch of gas pipe could be removed which would mean the gas bond could become disconnected, but all this work should be done by a competent person and they would know that and bond the gas from the next most conveinient place.

 

[jaresquire]

I think cornburn (!) was being sarcastic

 

[sambotc]

What about if your gas pipe goes from copper off the meter to mild steel then back to copper again, not uncommon in local authority housing where pipework was concealed in floor screeds or behind plaster? What does the lead in every fitting do to the resistance, or the brass fitting if compression?

Too many variables to make an across the board decision in my opinion.

 

[johnboy6083]

It is permitted to use any extraneous metalwork as a bonding conductor anyway, so in theory you could bond at the closest point to the CU. this is an academic point though due to the points already raised regarding joints, plastic sections ect.

 

[Knobhead]

I thought this was dead and buried.

But let the argument continue. Anything to prove the regulations wrong.

 

[telectrix]

tony, i like your thinking. as douglas bader once said, " rules are made for breaking"

 

[B16 Tom]

Ahhhh That must of been cus thay drank to much and smoked to much.

 

[SparkyJoe]

its so we can find it ;p

 

[johnboy6083]

I thought this was dead and buried.

But let the argument continue. Anything to prove the regulations wrong.

It was, until you linked to it from another post. also i like playing devils advocate, and promoting technical discussion.

anyway about rules. The main ones i hate are specifications drawn up by some clients, often they are a one spec covers all situations. Im a spark, and sometimes i know when im right, and they are wrong! I suppose its their money.

Cant you tell i work for a company and not myself!!

 

[Knobhead]

Like you John, I’ve always worked for companies.

I’ve worked most of my life under M&Q reg’s. Woe betide you if you stepped out side those rules. They make the 17[SUP]th[/SUP] look like Alice in Wonderland. We had a new plant installed to the then 15[SUP]th [/SUP] edition it was condemned out of hand, it didn’t meet our standards for isolation and earthing.

The bible says in big letters “requirements for electrical installations”. They are not rules or legislation, they should be regarded as guidelines. But unfortunately if you step out side those lines the men in suits will jump on your wallet or soul.

Where this thread started was the stupidity of running a 10mm from the MET along side a copper gas pipe that is a better conductor than the 10mm! It’s one of the most glaring points of ineptitude in the 17[SUP]th [/SUP]and it’s precursors.

I loved my work, but now I’m glad I’m out of it. Common sense has gone out of the window!
Physics and chemistry are what started our trade, where have the basics gone?