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Discuss Ring finals and fused spurs in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Evening all. The OSG says "As a rule of thumb for rings, unfused spur lengths should not exceed 1/8 the cable length from the spur to the furthest point of the ring.".

Okay, so what is the maximum length for a fused spur then? I don't seem to be able to find the answer in the OSG or BBB. I assume the limiting factor is voltage drop, but how is this determined?
 
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That must be total length of cable then. But for sure the OSG also states an A1 RFC is maximum 100sqm floor space.
 
  • Thread Starter Thread Starter
  • #11
I think we're driving down the wrong road here Charlie. The OSG states that 1/8th rule is for unfused spurs, I want to know the max length of fused spurs. I assume there is a difference, otherwise why would the OSG say 'unfused spurs' rather than just 'spurs'?
 

Charlie_

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Arms
Ahh sorry didn’t realise you mentioned fused spurs..
Yes as you say it would be down to volt drop for the length of the cable and current
 
  • Thread Starter Thread Starter
  • #13
That's the problem, determining the volt drop for a spur from a ring. How do you do it? Calculating the voltage drop for the spur bit I can do, but not sure about the ring part.
 

H

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Arms
You can also do it using Zs tables and R1+R2 values..
By this method do you mean
L = R x 1000 / millohmpermeter

And then Vd calculation?

Which I presume would suitably work if conductors were the same csa?
 
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