Extraneous conductive parts in outbuildings

[soulman]

Hi, i am after a bit of advice. I went to a property which had 3 outbuilding, all were separate from the main building, one garage, one shed, & a workshop. Circuits all supplied from main building. Earthing system is TT. In all of the 3 outbuilding there is a separate water supply with metallic pipes. There is one socket outlet & one light in each building.

My question is, should these pipes be supplementary bonded? or would they need m.p.b to the MET.

cheers

 

[Badged01]

Not wanting to steal anyones thunder, I'll pass on this question and await appropriate responses .......

 

[D Skelton]

Are the metallic water supplies extraneous? They might seem metallic but they're often fed in plastic. If they are extraneous, are they continuos from the main building to the outbuildings? If they are, are they bonded at the main building?

A few different scenarios and solutions here:

1. The water pipes are not extraneous - They need no bonding.

2. The water pipes are extraneous and are not already bonded (for example a completely seperate water supply or there is plastic between the main building and the outbuilding but enough copper in the ground to make them extraneous) - They need bonding back to the MET at the main building if you are extending the equipotential zone or bondng back to the outhouse MET is you are creating a TT system.

3. The water pipes are extraneous but they are effectively connected to earth already via the MET at the main building - They need no additional bonding, however supplementary bonding may be prudent.

 

[trev]

The only way to know is to test them to see if they are actually ECPs.

 

[soulman]

Yes they are definately ECP. They are connected to the main building & the main building has mpb.
The circuits are protected by 30ma rcd.

 

[D Skelton]

You need to do two things.

First, disconnect the main earthing conductor from the MET at the main building and test between the incoming water pipe and the main earthing conductor. This will determine whether it is extraneous, anything less than 45,000 ohms and it is.

Second, with the main earth still disconnected, long lead test between the water pipe at the outbuilding and the incoming water at the main building (remember to null the lead!), anything around 0.05 ohms or less and it is effectively connected to earth throughout its entire length.

If the incoming water pipe at the outbuilding is effectively connected to earth, no further bonding is required, however I would personally still add supplementary bonding at the outbuilding.

 

[mechelec]

Not wanting to steal anyones thunder, I'll pass on this question and await appropriate responses .......

??????????????????? If you know the answer say so. Don't be shy.

 

[spark 68]

There should be still MPB installed at each building locally, to an EMET (411.3.1.2) applies (taken from GN8), providing it is an ECP of course.

 

[Richard Burns]

You need to do two things.

First, disconnect the main earthing conductor from the MET at the main building and test between the incoming water pipe and the main earthing conductor. This will determine whether it is extraneous, anything less than 45,000 ohms and it is.

With the 45KΩ you are aiming for a 5mA safe current, what is the basis of this level of current?
Perception is lower and let go is higher, is this just a very safe level?

 

[spark 68]

Here you go Soulman, that is the basic gist of it

 

[jamie-spark]

That's the way I like it

 

[jamie-spark]

If it comes in building A say in metallic and goes out in metallic there are two points to bond in building A alone. Then there is the other buildings that will require further bondage

 

[Hawkmoon]

If it comes in building A say in metallic and goes out in metallic there are two points to bond in building A alone. Then there is the other buildings that will require further bondage

Why bond it twice?

 

[Engineer54]

If the incoming water pipe at the outbuilding is effectively connected to earth, no further bonding is required, however I would personally still add supplementary bonding at the outbuilding.

You'd be a bloody fool not to bond any metallic extraneous earth entering a stand alone building, whether it had been bonded at say the main house or another building or not!!. Call it whatever you like supplementary bonding, main bonding or whatever!!

Same goes for blocks of flats, every flat should be classed as a separate entity, as far as main bonding of extraneous metal pipework etc is concerned....

 

[Richard Burns]

If an earth potential is introduce to the building because a metallic service enters then it should be bonded.
If the metallic service later passes into the ground again as it leaves the building it is also introducing an earth potential at that point and so should be bonded there.
However if it is continuous I would not bother, but if someone replaces some of the internal pipework with plastic then there could be problems.

Perhaps

 

[jamie-spark]

Why bond it twice?

When mr wet head comes in and does alternations in plastic. Two extraneous parts.

What do the regs say ? Point of entry to the building,which end is the entry ?

 

[jamie-spark]

I know what u are thinking multiple steels in ground ( large industrial buildings ) effectively connected together, and only one bonding conductor.

 

[Hawkmoon]

When mr wet head comes in and does alternations in plastic. Two extraneous parts.

What do the regs say ? Point of entry to building which end is the entry ?

Yeah, take your point - with future plumbers intent on 'spoiling' things lol, that would probably be wise.

 

[soulman]

Hi, I have managed to find my GN8. The separate buildings ECP do require main protective bonding back to the MET in the main building. I thought supplementary bonding would suffice, but the book says not.

Thanks for your help.

P.s Cheers to spark 68

 

[D Skelton]

You'd be a bloody fool not to bond any metallic extraneous earth entering a stand alone building, whether it had been bonded at say the main house or another building or not!!. Call it whatever you like supplementary bonding, main bonding or whatever!!

Same goes for blocks of flats, every flat should be classed as a separate entity, as far as main bonding of extraneous metal pipework etc is concerned....

Well that was kind of my point lol.

It would be supplementary if already bonded and yes, you would be a fool not to IMHO