earthing gas supply

[2face]

you cant bond externally,

17th ask for 10mm as above,

you can bond on entry to the building but add a note on the circuit design or minor works cert that you issue to the were abouts of the clamp for testing etc.

 

[Spark123]

Where does the 17th ask for 10mm?

 

[2face]

http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=22449

Subcategory - 1. BS7671



On a domestic job TN-C-S or TN-S, Is It with in the regs to bond gas and water pipes, using one 10mm earth for both, If the cable is not cut at the first bond connection, ie just the insulation removed and then terminated onto the gas bonding clip and then connected at the water pipe bonding clip

most people use separate 10mm to each point.

check onsite guide for diagram page 27 sec 4 (16th edition book my 17th is in van )

 

[Spark123]

Can't see subcategory??

What if it is TT?
Thought except for pme it depended on the size of the earthing conductor as to what size main protective bonding is required? Where PME applies - the size of the neutral conductor is taken into account but the DNO may require the MPB to be larger.

Yes you may use a single conductor providing it remains unbroken and of course, providing the resistance of it is low enough.

 

[2face]

TT can be different as you say but 10mm usually is ok.

i am talking about the usual 3 bed semi domestic property were things rarely change from the norm.

25mm tails,
16mm main earth conductor,
10 mm mains.

anything else confuses people. and yes they can alter depending on the circuit design and location etc.

 

[Spark123]

What I am saying is you cannot definitevely say that a 100A TN-CS with a 25mm neutral conductor & 16mm main earth requires 10mm Main Protective Bonding.
There is more to consider than a wiring by numbers approach. The DNO can require this to be larger, the length of the conductor can require it be larger too.

 

[2face]

spark you obviously know your stuff and i am really not looking for the usual forum row and general slagging off.

i have never gone bigger than 10mm on a domestic property, on testing my work never even been close to looking for larger main bonds.

this is a typical earthing arrangement for a typical domestic property in the UK.

we can both start quoting regs and try and catch each other out.

i dont want to and i am sure you have better things to do at midnight on a weekend.

can we agree to disagree .

 

[Spark123]

Not looking to start a row - just pointing out that the regs can require you to go a size bigger, even on domestics.
I usually try to rise above slagging off, have the occasional discussion though

 

[2face]

i agree . it is good to stretch the old grey stuff now and again .

and with over 8000 posts obviously a knowledgeable lad to .

respect m8.

 

[ericmark]

Where does the 17th ask for 10mm?

2, main protective bonding conductors for extraneous-conductive-part and main metallic water pipe (extraneous-conductive-part) min 6mm² see 544.1.1 (Not PME) For PME 10 min² see Table 54.8
Since the supply authority may up-grade TT systems to PME most people will use 10 min² min at all times.
Also point of entry rules is only when meter is outside see 544.1.2 Where there is a meter, the connection shall be made to the consumer's hard metal pipework and before any branch pipework. Which is what the gas fitter said his regulations said there is no difference.

 

[Spark123]

So you can get away with 6mm for a TT and possibly for a TN-S depending on its size
There is a note at the top of table 54.8 about the network operator may require larger sizes for PME so it is always advisable to contact them first.

 

[ericmark]

I do agree with you just you asked where.
There are some silly bits about earths its been an eye opener when my son got a boat seems to have turned everything upside down with "Diodes" in earth wires goes completely against the grain. And loop impedance on isolation transformers with "No" earth connected to boat. Seems I am learning all over again!
Happy new year Eric

 

[Spark123]

Yep - I did ask in direct response to the post above mine. The required size depends on supply type amongst other things.
Don't know about diodes in the earth path - anything like that I'd be afraid that it would fail. Loop impedance on an isolation transformer can only be live to live as it doesn't have an earth unless you deliberately connect one side of it to earth, in the case of a boat the earth would have to be to the boats metal body.

 

[ericmark]

3 months ago I would have agreed with you diodes in earth would fail. But seems this is recognised method to give the 2.4 volt differential required to stop electrolysis and resultant damage to boat. Yet another hat I had to eat!
As to transformer yes one leg is earthed but it is the impedance of transformer which causes the problem. Big transformers are not so much a problem but small 4KVA transformers may only have 3 ohm impedance so how will a B16 MCB ever trip on the magnetic trip when they need a 2.875 ohm impedance to trip? Yes they will trip in the end on thermal trip but the magnetic bit will never work.
But of course they don't come under 17th Edition so does not really matter. With 110V RLV you are allowed 5 seconds instead of 0.4 although that depends on where you look in 17th Table 41.1 gives 0.4 but 411.8.3 gives 5 seconds and then people wonder why we can't seem to agree with each other!
All best for New Year Eric