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Topic Title: Earthing Arrangement of transportable generating sets
Topic Summary: TN-S or TT
Created On: 06 March 2013 01:31 PM
Status: Post and Reply
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 06 March 2013 01:31 PM
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carllangwood

Posts: 8
Joined: 08 February 2012

With respect to temporary power supplies when a generator is utilised, is it regarded as a TN-S or TT system?

Is it regulation to drive an earth electrode for the generator?
 06 March 2013 02:00 PM
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AJJewsbury

Posts: 11493
Joined: 13 August 2003

There's not much point in having two separate electrodes in a local setup (one for the generator and another separate one for the "installation") - so it's unlikely to be TT.

TN-S is the norm for larger, especially 3-phase generators, but for small systems a unearthed separated system is common.

If it's on a vehicle, using the chassis as "earth" is an option.

So it all depends...

- Andy.
 06 March 2013 02:51 PM
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carllangwood

Posts: 8
Joined: 08 February 2012

Thank you for your response, the reason why I ask is with relation to the NICEIC test certification, the company I work for does mainly site set ups in remote locations. I have always been led to believe that it was a TN-S configuration, however I have been told to put it in as a TT?

Is there any formal documentation stating that generating sets (transportable types) are of a TN-S configuration. I would like to present this to our Electrical Engineering Manager.

The range of generators we use is anything from 10kVA single phase up to 1250kVA three phase, depending purely on size of application.
 06 March 2013 03:31 PM
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AJJewsbury

Posts: 11493
Joined: 13 August 2003

The range of generators we use is anything from 10kVA single phase up to 1250kVA three phase, depending purely on size of application.

I'd expect those to be TN-S - although it's not impossible that they're another arrangement. The 10kVA for instance is on the upper end of what might be acceptable for might be unearthed/separated.

Is there any formal documentation stating that generating sets (transportable types) are of a TN-S configuration. I would like to present this to our Electrical Engineering Manager.

As I said there are a number of possibilities - so you won't find any 3rd party documentation saying what you've got. There's plenty describing good practice etc (e.g.http://www.hse.gov.uk/foi/inte...cs/400-499/oc482_2.htm ), but you presumably need to certify what's actually there, rather than what someone in an ivory tower says should be.

I have been told to put it in as a TT?

By someone who knows what they're talking about?

It's not impossible, but if there aren't two separate electrodes for the source and load, then it ain't TT - just point them to the diagrams in BS 7671 (e.g. 3.10 on page 45) and ask where the 2nd electrode is.

- Andy.
 06 March 2013 03:59 PM
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jcm256

Posts: 1878
Joined: 01 April 2006

Have a look at 7.2.8 in BS 7430:2011This British Standard supersedes BS 7430:1998, which is withdrawn.

Copyright protected. Information should be in there for your question but, as Mr Jewsbury and 2011 39 Summer Wiring Matters pointed out is not TT.


Compliance with a British Standard cannot confer immunity from legal obligations.


BRITISH STANDARD BS 7430:2011
©

http://www.ussu.co.uk/ClubsSoc...EF%20BS7430%202011.pdf
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