Just to start an argument.

[Knobhead]

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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!

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[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?