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Discuss Volts drop too high... in the Business Related area at ElectrciansForums.co.uk.

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  1. Brutal
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    Brutal EF Member

    Location:
    Ipswich
    I have installed Ring Final Circuit in 2.5 LOR 120m protected by 32A breaker

    Volt drop calcs - 18mv/a/m x 32A x 120m / 1000 = 69.

    So the volts drop is 69 volts? which is way over the stated 3 or 5 %.

    Am I diong this corectly and if so what can I do about the volts drop?

    Cheers
     
  2. chrish_1977
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    chrish_1977 Electrician's Arms

    That does seem like a very big ring, you could try splitting it up into a smaller one(s)
     
  3. MDJ
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    MDJ Guest

    sure that is not 6.9?? I haven't got my brain on but that seems wrong
     
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  4. Brutal
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    Brutal EF Member

    Location:
    Ipswich
    volts drop of 6.9 you think? sounds better
     
  5. MDJ
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    MDJ Guest

    yep sounds better, 69 volts is a lot on 120 meters buddy.
     
  6. Brutal
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    Brutal EF Member

    Location:
    Ipswich
    It does seem a lot but the calcs give 69 volts.

    If my calcs are wrong.... Where am I going wrong?

    mv/a/m - 18

    Ib - 32a

    LOR 120

    18 x 32 x 120 = 69120

    divide by 1000 cos in milli volts gives me 69.1

    The 120 meters is the whole circuit (as in ring)

    surely I would just need to measure to the furthest point? say 60m

    Also If it is a ring circuit and the CSA is doubled as two 2.5mm cables.... The total CSA is 5mm - does this have an impact?

    I've been running my business for a while now so need to start getting this stuff right!
     
  7. Brutal
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    Brutal EF Member

    Location:
    Ipswich
    Splitting it would do no good... The rings are split into three with the longest being 120m. Its the distance travelled from the DB thats the problem
     
  8. MDJ
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    MDJ Guest

    You may be right, as I said I didn't have my head on, but that sounds a hell of a lot of volt drop for that circuit, however If your sure?? then fair enough
     
  9. Brutal
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    Brutal EF Member

    Location:
    Ipswich
    ok.... so what can I do about it? I have to provide calcs for the job, I can't show 69v volt drop
     
  10. MDJ
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    MDJ Guest

    One question fella, have you actually measured the results by instruments?
     
  11. Brutal
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    Brutal EF Member

    Location:
    Ipswich
    used a meter to measure the volts at the furthest point? I'm sure it was no less than 236 volts when I measured EFLI
     
  12. telectrix
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    telectrix Scouser and Proud of It Respected Member

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    it's more like (18 x 20 x 120)/4000 = 10.8V.

    20A because that's about the correct value of Ib. 4000 because it's a RFC. so you divide by 2 for the 2 cables, and 2 again because the cables are in parallel. same as R1+R2= ( r1+r20/4.
     
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  13. Brutal
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    Brutal EF Member

    Location:
    Ipswich
    so I need to put circuits on 20a breakers?
     
  14. telectrix
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    telectrix Scouser and Proud of It Respected Member

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    no. it's a 32A RFC. you assume 1/2 the current goes down each leg, but allow a bit more ,20A instead of 16A, as at most points on the ring, 1 leg will be shorter than the other and so carry more of the load current (less resistance). it's only at the mid point that each leg will carry the same current.
     
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  15. Brutal
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    Brutal EF Member

    Location:
    Ipswich
    ok, so if I put the calcs you quoted above I won't have any probs? the lighting circuits worked out fine anyway
     
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