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Test certification & changes to supply characteristics

TaZ10101

Looking for some guidance please, I am working on a construction site with a large temporary accommodation block due to be occupied asap. Due to design issues the HV/ LV supply has been delayed, to work around this a generator will be utilised as a short term solution. 
This means testing & inspection will be completed via the genset and certs issued, when the new substation is completed the generator will be disconnected and sub-mains will be connected to the permanent LV supply. 
This raises a question regarding re-test, in my experience usually best practice would be a full re-test, but some on the project are suggesting only the sub-mains will require re-testing. 
To me this would probably come down to the designer signing the test cert and what they are prepared to accept, if only re-testing the sub-mains  I would think the final circuits Zs/ Pfc would have to be calculated as the previous test results/certs from the generator would be invalid due to the change of supply characteristics right?

So can anyone offer advice as to the options and is there anything in BS7671 regs that would be relevant to this situation, it’s also worth considering that if a EIC is issued for the generator can there be another issued for the LV supply? Is it possible to issue more than 1 EIC or  update the original or would be a condition report? 
I’ve come across this situation before and it always seems to be a contentious subject with lots of different opinions, sorry for the long winded post, but would really appreciate some professional opinions on this, thanks Pray 

  • 0

    Is it TNS now and TT after connection to the grid? Thinking different disconnection times, and possibly bonding sizes if TNCS after.

  • 0 in reply to OlympusMons

    The existing network is TNS, the generator I believe is also TNS I think, I’m not sure if it has a protective earth + neutral link but it definitely wasn’t obvious at the output terminals, so I think it’s TNS 

  • 0

    Essentially that is not the problem, but the point with a local substation is making sure the switchgear is rated for the much higher PSCC. If the test cert for use with the generator, I see no reason to retest everything, but the upfront switchgear must be suitable for the mains supply. As the original EIC is presumably satisfactory and BS 7671 only applies after metering, there is no reason for any documentation change, provided my point is met. BS7671 does not cover the supply source as such, although generator supplies have a few points and maybe you should check section 704 for construction sites.

  • 0

    The recommended EICR re inspection period is twelve weeks for construction sites, so on that basis the installation will be due another inspection and test anyway.

  • 0 in reply to Sparkingchip

    On site yes, but I think accommodation can stretch to 12 months 

  • 0

    The sub-mains, are these distribution circuits actually flexible cables from the generators to the accommodation blocks?

  • 0 in reply to Sparkingchip

    Armoured cables to the MDU’s I think, this part of the installation is also not complete yet. The accommodation is pre-wired modular, the question is will the results from the generator supply for the final circuits in the accommodation still be valid after the generator is gone and the MDU’s are connected to the network. I don’t see how the initial certificate can be valid, the reactance of the genset will be different from the network characteristics and there are 2 separate designs for each 

  • 0

    It sounds like there may be little point in repeating the dead testing in the accommodation within a year or so, but the live testing should be repeated along with the full testing of distribution circuits when the supply is changed over. 

  • 0 in reply to TaZ10101

    The modular units will have there own certificates showing dead tests. Once connected to whatever supply, ADS needs to be addressed whether TT or TNS.

    I would expect a report showing live tests following connection to whatever the source supply is. Probably an EICR would be fine to show the ADS compliance coupled with the dead test certificates.

  • 0

    I agree there shouldn't be a problem. Ideally the design should accommodate both the generator and grid options - the initial I&T should basically confirm that the installation meets the design (R1+R2 etc values as expected and breaking capacity of devices meets what the design called for). After the switch-over only that part of the installation actually altered for the switch-over will need a further I&T.

    If the design was initially for grid-only and was then adapted for generator (say by adding an extra RCD or three) then a bit more care is needed. but basically the same position.

       - Andy.

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