Bonding Gas Supply in an Outbuilding

[Piratepete]

Hi Guys
Doing an EICR of a property.
The client has an outbuilding with gas and water supplies. It has it's own CU fed from the main CU in the house.
The water is bonded but the gas is not.
The water supply is underground from the house in plastic and then changes to copper which is bonded.

The gas supply comes from the house in an underground copper pipe linked to the gas pipes in the house. So, electrically, it would be subject to the bonding in the house.
But does this negate the need to bond it in the outbuilding?

Looking forward to wise words!

Cheers
Pete

 

[Piratepete]

Thanks for your entertaining and informative (some) replies. Rather gobsmacked to see this continue for 5 pages!:angel_smile:

Pete

 

[Piratepete]

NO, it doesn't negate main bonding to the outbuildings CU (EMT) especially if the supply is PME, in which case the sub-main earth should be a minimum of 10mm....

Why should the sub-main earth be a minimum of 10mm? Doesn't table 54.7 apply for a PME supply? Also Table 4.4 (clearer) in the On Site Guide. 6mm supply 6mm earth. Or have I missed something?
Cheers
Pete

 

[Leesparkykent]

Why should the sub-main earth be a minimum of 10mm? Doesn't table 54.7 apply for a PME supply? Also Table 4.4 (clearer) in the On Site Guide. 6mm supply 6mm earth. Or have I missed something?
Cheers
Pete

Have a look at Regulation 543.1.1 and 544.1.1

 

[Des 56]

Thanks for your entertaining and informative (some) replies. Rather gobsmacked to see this continue for 5 pages!:angel_smile:

Pete

Sorry Pete but it seems that even after those 5 pages Leespakykent is still providing info you don't seem to twig

 

[davesparks]

Why should the sub-main earth be a minimum of 10mm? Doesn't table 54.7 apply for a PME supply? Also Table 4.4 (clearer) in the On Site Guide. 6mm supply 6mm earth. Or have I missed something?
Cheers
Pete

Minimum size of a main bond on a PME supply is 10mm. Main bonds must be sized according to the incoming service not for the size of any submains.

 

[Piratepete]

Minimum size of a main bond on a PME supply is 10mm. Main bonds must be sized according to the incoming service not for the size of any submains.

Read my text. I'm querying the sub-main earth size, not main bonding.

 

[Piratepete]

Have a look at Regulation 543.1.1 and 544.1.1

I've looked. where does it say min 10mm? As this section of the regs is a nightmare of cross references, please read the whole of section 4.4 in the On Site Guide and table 4.4(i) in particular.
There is a minumum size, 10mm, for main protective bonding but for the Earthing conductor it is 6mm where 'buried and protected against corrosion and mechanical damage'.

 

[spark 68]

Read my text. I'm querying the sub-main earth size, not main bonding.

The point being made is that if bonding is required at the remote end of the sub-main, then that sub-main's CPC will be required to be sized to act as both a CPC and a main bonding conductor, which means the sub-mains CPC will need to be 10mm minimum to satisfy the PME regs.

 

[Leesparkykent]

But the whole purpose of this thread is about bonding the gas supply in an out building.
If you connect your 10mm bond to the EMT in the outbuilding then the CPC in the cable feeding the sub board in the outbuilding will have to be adequate to comply with the minimum CSA of the bond to the gas. For example it's no good having a 6mm 3core SWA feeding the sub board in the outbuilding when you are required to bond the gas in the out building in 10mm (if it's TNC-S), The CPC in the sub main cable would have to Adequately sized for the bond as well.

 

[Leesparkykent]

The point being made is that if bonding is required at the remote end of the sub-main, then that sub-main's CPC will be required to be sized to act as both a CPC and a main bonding conductor, which means the sub-mains CPC will need to be 10mm minimum to satisfy the PME regs.

I was trying to write the same thing but it took me nearly 10mins lol so didn't see your post.

 

[Piratepete]

But the whole purpose of this thread is about bonding the gas supply in an out building.
If you connect your 10mm bond to the EMT in the outbuilding then the CPC in the cable feeding the sub board in the outbuilding will have to be adequate to comply with the minimum CSA of the bond to the gas. For example it's no good having a 6mm 3core SWA feeding the sub board in the outbuilding when you are required to bond the gas in the out building in 10mm (if it's TNC-S), The CPC in the sub main cable would have to Adequately sized for the bond as well.

Ok. I can see where you're coming from, but can you please explain the application of the first 2 columns in table 4.4 On Site Guide?

 

[Leesparkykent]

Ok. I can see where you're coming from, but can you please explain the application of the first 2 columns in table 4.4 On Site Guide?

Sorry mate haven't got the OSG near me, would have to look later unless someone else can point you in the right direction.

 

[spark 68]

Ok. I can see where you're coming from, but can you please explain the application of the first 2 columns in table 4.4 On Site Guide?

What is there to explain ?

As you go down those first two columns in 4.4 (i) it gives the minimum sizes according to function of said conductor, obviously if it is only an EC then the minimum size is given, likewise for a MPB, where it is used as both functions again the minimum size is given, so a combined EC and MPB then the minimum size for the MPB is used (or whichever is the larger minimum size to satisfy that particular requirement/s), the last row in that table refers specifically to PME/TNC-S, as that table covers both TNS an TNC-S systems, table 4.4 (ii) being for TT

 

[telectrix]

Ok. I can see where you're coming from, but can you please explain the application of the first 2 columns in table 4.4 On Site Guide?

you will not see 4mm, 6mm, or even 10mm for supply live conductors in the normal course of your travels.

 

[Piratepete]

What is there to explain ?

As you go down those first two columns in 4.4 (i) it gives the minimum sizes according to function of said conductor, obviously if it is only an EC then the minimum size is given, likewise for a MPB, where it is used as both functions again the minimum size is given, so a combined EC and MPB then the minimum size for the MPB is used (or whichever is the larger minimum size to satisfy that particular requirement/s), the last row in that table refers specifically to PME/TNC-S, as that table covers both TNS an TNC-S systems, table 4.4 (ii) being for TT

Yes, it's obvious. Mea culpa! I assume there is a statement somewhere about a combined EC and MPB, but then if I'd used my brain.... I was thinking technically.

The CU in this outbuilding is from a 32Amp 6kA MCB in the house CU via a 6mm 3core SWA cable. Main Bonding (min 10mm) is required to the gas and water installations in the outbuilding. Technically, a 6mm earth will easily carry the maximum fault current of the installation. The regs would require the main earth to be 10mm, just because the minimum bonding size you are allowed is 10mm. So on an EICR would this count as a C3 or would you not even bother mentioning it? IMHO i don't see this as a C1 or C2. (Shoot me down again!)