Volt drop on three phase sub main

[Keith the beef]

Can anyone tell me is the allowable volt drop for a three phase supply to a sub main 3%?????

Cable length 120m
100A supply
Correction factor .81 per ampere per meter

100Ax120mx.81
1000 = 9.72v


400x3%=12v

so this is good ya?


Keith

 

[crabapple]

BRB app 12

5%
length=110
current loading of cable???
what size cable??? 50mm??

 

[Keith the beef]

length is 120m
CSA is 50mm 4 core
100A bs 88

 

[crabapple]

BRB pp 287

50mm 4c

resistive 0.86

120*100*0.86/1000 = 10320/1000 = 10.32v

any good ??

400* 5% = 20v

 

[Keith the beef]

.86 is that table 4d1b?

 

[crabapple]

that the one im looking at

 

[Keith the beef]

ok, i got my .81 off table 4D4B
As table 4D4A opposite shows CCC for ref method D buried in ground.

Am i correct in this????

Thanks Keith

 

[scotsparky]

remmeber the maximum volt drop permitied is from origin of installation. What its best to do is to keep the volt drop of the sub mains to a maximum of 1% so the rest can go on the final circuits.
3% lighting
5% power
Also dont use the protective device size use the design current it gives a tru volt drop.
hope this helps.

 

[Keith the beef]

i have this bloody armoured that is in situ and am trying to work out what fuse ratings it should be backed up with, i've found out from the manufacturer it's a 50mm 4 core, they have used the swa as earth the csa of the steel braiding is 85mm. i believe this translate to approx a 10mm cpc copper conductor, am struggling with adiabatic equation trying to work what fuses can safely be put in front of this cable, currently has 100A bs 88's

Can anyone guide me on this for a 3 phase supply?

 

[john.irvine]

Minimum Size of Earth = K1 x S
K2…2

K1 = 115 K2 = 51 S = 50

115/51 = 2.255
50/2 = 25
2.255 x 25 = 56mm well under your 86mm

What rating is the sub main as that would be the Ib the fuses are for

Don’t for get the K value in the adiabatic will be 51