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Sizing Neutrals from TX to LV Panel

Adrian B
A bit of help/ advice needed if anyone has a moment to spare please.


I have carried out numerous cable calculations using Amtech (Trimble) over the years, but, have for the first time come accross an example where I cannot use the software.


Basically, I am looking at a project requiring 2 new TX's from UKPN, serving 2 new LV Switch Panels (Clients).  UKPN have kindly given me all the necessary info on the ACB's etc. and also tell me that I can have 3 No. Al singles per phase up to 630mm CSA, but, I can only have 2 No. Al singles for the Neutral.


Now my helpful friend from Amtech support has just advised that you cannot select 3 cables per phase and only have 2 cables for neutral using the software, leaving me in a position where I have to (dare I say it) manually calc. the nuetral size.


What I do know is that my Amtech calc tells me that I need 3x 600mm CSA Al cables per phase, and it currently tells me I need 3x 600mm CSA neutrals (which I can not have).


I also know that the max permitted neutral size is 630mm CSA, which now leaves me in a postion of concern that being only permitted 2 neutrals, they may calculate out to be too large for the UKPN TX's.


Any help would be hugely appreciated by someone who should know better than to rely on Amtech all the time.


Thanks in advance


Adrian
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  • 0
    If the guy designing the transfomer has done his job correctly then, on the insides of the transformer, the neutral connection may only have the same capacity as 2 x 630mmsq anyway. It would be odd to have reduced terminal capacity if the insides were at full size. I'd believe the UKPN transfomer designs.
  • 0
    My apologies fore the sidetrack Adrian but just out of interest, has the electrical design sought to facilitate EV charging?
  • 0
    Hi Parsley

    Yes, UKPN are entirely responsible for the TX's

    Regards
  • 0
    Morning Harry


    I believe that the issue comes from the ACB that UKPN are intending to use.  This is my understanding to date, although they may tell me differently in the forth coming days.


    Regards
  • 0
    Morning Lyledunn

    No problem, but simple answer is no, EV charging not included within electrical design, nor stipulated as a requirement.  Basement level is generally going to be for disabled vehicles and bicycles.  Apparently, nobody needs cars any more when living in apartment blocks.

    Regards

    Adrian
  • 0
    Hi John


    Did leave you a message on your profile, not sure if you have seen it yet.  Would be helpful to see some info, thanks.


    Regards


    Adrian
  • 0
    Adrian Burgess:

    No problem, but simple answer is no, EV charging not included within electrical design, nor stipulated as a requirement.  Basement level is generally going to be for disabled vehicles and bicycles.


    At risk of drifting off topic, there are a number of EVs within the Motability scheme for vehicles for disabled people. (As opposed to vehicles which have been rendered unserviceable. ? )


  • 0
    The ACB that UKPN are intending to provide should be fit for purpose so they must know the cable size to use as they have provided the terminals to connect it to.

    You should hand over the responsibility for cable sizing to UKPN and, if they agree to 2 x 630 then fine, if they say 3 x 630 then they need to provide a different ACB.
  • 0
    Afternoon Harry


    You are correct, UKPN do know the cable size for the neutrals, and this is "up to 2 No. 630mm sq. AWA" cables.


    Unfortunately, UKPN (and a few other companies) are amongst the last companies to still only offering half sized neutrals.  Also, although I am able to request full sized neutrals, UKPN (within their rights) are saying no.


    So, albeit they may be oversized, I can include 2 No. 630mm sq. AWA cables for the 50% neutral.  But, my concern was more the fact that firstly my software (Amtech) cannot be utilised to include for this within my design (as I have 3 single AWA's per phase and it will not let me select 2 AWA's for neutrals), and secondly, I was concerned about only being offered a half sized neutral.


    Finally, I am not sure about you, but I have never had much luck in asking UKPN to carry out calculations on my behalf, when it is they who have specified that somebody else has to carry out the calculations in the first place.


    Regards


    Adrian
  • Former Community Member
    0 Former Community Member
    Hi Adrian 


    Did you have a look at the Dropbox file i put in above? If you want to provide more data i can help you complete the calculation checks

    https://www.dropbox.com/s/48hx9j2cnt5o7fu/Report Export IET forum.pdf?dl=0
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