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Topic Title: LPS Meets the Main Earth Bar
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Created On: 19 June 2017 10:42 AM
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 19 June 2017 10:42 AM
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sarandis10

Posts: 56
Joined: 21 November 2011

Gents

When do we need to bond the LPS to the MEB and when not?
what dictates the need of this bond?

Regards
 19 June 2017 10:58 AM
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John Peckham

Posts: 8793
Joined: 23 April 2005

When the LPS designer or contractor says it is OK to do so.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 19 June 2017 11:03 AM
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gkenyon

Posts: 4982
Joined: 06 May 2002

Originally posted by: sarandis10

Gents



When do we need to bond the LPS to the MEB and when not?

what dictates the need of this bond?



Regards
According to the Regs (wording as per BS 7671:2008+A3:2015) ... Always ... but in accordance with BS EN 62305. See Regulations 542.4.1 and 411.3.1.2. 411.3.1.2 includes the requirement "Connection of a lightning protection system to the protective equipotential bonding shall be made in accordance with BS EN 62305", and 542.4.1 tells you where to do it (the MET).

However, it's not always wise to connect the LPS to an electrical installation without integral SPDs (in both mains and telecom/data wiring).

If you are at all unsure, I'd recommend an LPS specialist look at it for you, rather than just connect it yourself.


IN ADDITION ... and quite importantly ... there is a potential issue with existing LPS installations.

Not all LPS on existing buildings comply with BS EN 62305. Older ones were designed in accordance with BS 6651, and connecting a BS 6651 LPS to the MET could well spell disaster for equipment in the installation !

If you are doing a re-wire of an installation in buildings with an older LPS, the issue you may have is that SPDs you may now be fitting to meet BS 7671 (or indeed BS 6701-related standards), may not be as effective unless the LPS is re-assessed in accordance with BS EN 62305, and appropriate modifications made.

Again, one for LPS specialists familiar with BS EN 62305.

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com

Edited: 19 June 2017 at 11:10 AM by gkenyon
 19 June 2017 11:04 AM
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gkenyon

Posts: 4982
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Originally posted by: John Peckham

When the LPS designer or contractor says it is OK to do so.
And John's more succinct answer is probably far easier to understand than mine

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 19 June 2017 11:16 AM
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John Peckham

Posts: 8793
Joined: 23 April 2005

Graham

I was paraphrasing what it says in BS7430.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 19 June 2017 11:59 AM
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sarandis10

Posts: 56
Joined: 21 November 2011

Graham

thanks for the reply. it is a new building. basically a crossrail building.
on the schematics we have a bong from the MEB to the LPS. we where thinking to challenge this bond. there is on the specs as well.
i will ask the LPS Specialists to establish this connection.

Regards
 19 June 2017 01:16 PM
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OMS

Posts: 22433
Joined: 23 March 2004

Originally posted by: sarandis10

Graham

thanks for the reply. it is a new building. basically a crossrail building.

on the schematics we have a bong from the MEB to the LPS. we where thinking to challenge this bond. there is on the specs as well.

i will ask the LPS Specialists to establish this connection.

Regards


It's almost certainly required - but as Graham notes the LPS is only part of the equation - to be effective you also need the SPD's (of the correct type) at relevant points in the electrical installation

Given the population type, I'd have thought there was a particularly significant risk criteria to meet anyway so most of the required SPD's will be in place

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 26 June 2017 09:54 AM
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sarandis10

Posts: 56
Joined: 21 November 2011

gents, still i dont understand why we need to bond them together!! what are we trying to achieve?
 26 June 2017 10:03 AM
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Fm

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Joined: 24 August 2011

Compliance with the appropriate British Standards
 26 June 2017 10:45 AM
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mapj1

Posts: 9698
Joined: 22 July 2004

Perhaps the deeper question is why do the BSI think its a good idea.
And that is to do with
a) What happens if there is a side-strike through the building, and the risks of some metal bits of the building not being at the same voltage as others during a lightning event, and if this voltage is large enough, you can have indoor flashover between for example building steels and installed wiring.
b) A desire not to inject a large common mode voltage pulse between the local true terra-firma ground and the CPC and wired services that leave the building. If this large CPC ground offset were permitted, there would be the risk of damage to equipment in adjacent buildings on the same circuits and to anyone unlucky enough to be holding on to it at the time.
This is summarising the lifetime works of several folk into a couple of paragraphs, it is a big area, and by no means clear cut in all cases,so it is worth doing some reading round.

-------------------------
regards Mike
 27 June 2017 09:39 AM
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gkenyon

Posts: 4982
Joined: 06 May 2002

Originally posted by: mapj1

Perhaps the deeper question is why do the BSI think its a good idea.

And that is to do with

a) What happens if there is a side-strike through the building, and the risks of some metal bits of the building not being at the same voltage as others during a lightning event, and if this voltage is large enough, you can have indoor flashover between for example building steels and installed wiring.
This is addressed by an appropriate application of [all parts of] BS EN 62305.

b) A desire not to inject a large common mode voltage pulse between the local true terra-firma ground and the CPC and wired services that leave the building. If this large CPC ground offset were permitted, there would be the risk of damage to equipment in adjacent buildings on the same circuits and to anyone unlucky enough to be holding on to it at the time.
This is addressed by correct application of BS EN 62305-4, BS 7671, and BS EN 50174-3 - although in some installations (especially those on railways), the bigger risk for Services is likely to be from impulses on the HV/LV supply from HV switching and similar disturbances.

This is summarising the lifetime works of several folk into a couple of paragraphs, it is a big area, and by no means clear cut in all cases,so it is worth doing some reading round.
Indeed. Noting that much of the experience is from other countries that have much higher ceraunic levels ... and has developed over time, along with the spread of technology.

So what was "good practice" 20-odd years ago, can actually be seen to be damaging for electronic installations today.

But also, what held well when we in the UK had metal piped services and hessian-covered lead sheathed HV cables, no longer holds true in the modern world of plastic sheathed HV cables and plastic piped-services.

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
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