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Topic Title: Two supplies entering one building and main protective bonding.
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Created On: 04 October 2012 08:14 PM
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 04 October 2012 08:14 PM
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hertzal123

Posts: 303
Joined: 26 August 2007

Two buildings with separate supplies have been made into one,the distance between meters being about 25/30M.The gas service enters near one meter,is bonded & then runs thro the basement to emerge in the
other part of the building,which has no bonding,and will be on the seperate
supply.Is it necessary to to link the 2 service heads with a main bonding
conductor,or can the gas pipe be bonded where it emerges from the basement.Thanx for any advice,
hz.
 04 October 2012 10:02 PM
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jcm256

Posts: 1866
Joined: 01 April 2006

You can only go with what one big EGGon says : (If applicable to your suitation)


Only one point of LV supply will be provided to each customer within a building or site.
Where two or more customers occupy the same building refer to Section 1.3.1.3 Multi occupancy
buildings.
Note that if two or more services were to be provided there is a danger that neutral current from the
electrically remote one service(s) may return to the substation via the service cable electrically nearest
the substation. This is due to the interconnection of the service neutrals by the PME equipotential
bonding and other conductive routes such as metallic pipe-work. The passage of neutral current may
cause high electro magnetic fields (emf) which may cause electronic equipment to malfunction. More
importantly, the PME bonding and metallic pipes etc. are not designed to be load carrying and may
represent a fire risk.
 04 October 2012 10:45 PM
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hertzal123

Posts: 303
Joined: 26 August 2007

Jcm,
Thanx for the reply..
Are you stating that the building owner will not be allowed 2 supplies,even if main bonding conductors are not interconnected?I have noticed that one supply is tncs & the other is tnc.
Regards,hz.
 04 October 2012 11:02 PM
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Parsley

Posts: 1006
Joined: 04 November 2004

I have an old London Electricity earthing guide that I will have a look at in the morning. I'm sure it states that when you have more than one supply into a building they should all be the same earthing type and be interlinked with a suitable earthing/bonding conductor. The DNO required us to do this on a large residential development with 4 switchrooms served from one TX a few years ago.

I do agree with JCM's comments though about diverted neutrals, I thought that it was more about steel framed sheds, that were split into separate units with incoming supplies in each unit and the need to TT the 2, 3, 4 unit etc to avoid the diverted neutrals returning to the incoming supply in the1st unit via the common steelwork etc.

Regards
 05 October 2012 12:20 AM
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alancapon

Posts: 5768
Joined: 27 December 2005

Assuming that the DNO allow two supplies into the one property (some don't) and assuming that the customer is happy to pay two standing charges, then two TNS or two TT would be ok. With one supply TNC-S, then the additional supply should be connected as TT.


Regards,

Alan.
 05 October 2012 09:12 AM
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Parsley

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Originally posted by: Parsley

I have an old London Electricity earthing guide that I will have a look at in the morning. I'm sure it states that when you have more than one supply into a building they should all be the same earthing type and be interlinked with a suitable earthing/bonding conductor. The DNO required us to do this on a large residential development with 4 switchrooms served from one TX a few years ago.



I do agree with JCM's comments though about diverted neutrals, I thought that it was more about steel framed sheds, that were split into separate units with incoming supplies in each unit and the need to TT the 2, 3, 4 unit etc to avoid the diverted neutrals returning to the incoming supply in the1st unit via the common steelwork etc.



Regards


The text below comes from an old London Electricity PME booklet that I was given by one of their enginners a few years ago.

9.12 Buildings with more than one supply

In exceptional circumstances it is sometimes necessary for London Electricity to install two (or more) services into a single premises.
These services may be physically separated and also fed from differing originating sources of supply.

In order to prevent voltages occurring, under normal conditions, between simultaneously accessible conductive parts connected to the two services, the two services shall provide the same means of earthing.

Either

i) both services shall be TT, - the customer shall provide his own means of earth and fault protection.

Or

ii) both services shall be either TN-C-S or TN-S and appropriate cross bonding shall be installed between the two services.

In either case a label inscribed:

'THIS BUILDING IS CONNECTERD TO MORE THAN ONE SOURCE OF SUPPLY'
SHALL BE FITTED IN A PROMINENT POSITION ADJACENT TO BOTH SERVICE CUT OUTS.

EON's E6 manual section 3.2.21 Multiple services to steel framed buildings states that where two or more services are installed into a single steel framed building:
Only one services shall make us of the PME terminal.
The additonal service should use an alternative method such as TT earthing. These cut-outs should be labelled PME not available
The service nearest the substation most be at least 95mm CNE.

Where a TT is unacceptable to the applicant he must be advised that multiple PME services in the building could cause problems as outlined in the explantory note.
Several PME services may be provided subject to the applicant agreeing to be responsible for resolving any problems caused by stray neutral currents.

I haven't got time to type the note, it's the same as what JCM posted last night.

Regards
 05 October 2012 11:27 PM
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hertzal123

Posts: 303
Joined: 26 August 2007

Thank you for all the replies,I,ve decided to use one tns supply & run swa
to feed db near other disused supply.
Regards,hz.
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