Just to start an argument.

[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?