Voltage drop

[hogan]

How do we calculate voltage drop on a ring final sockets only, Given the length of the circuit is 40 meters the cable is 2.5mm so therefore the amp per meter is 18, the mcb is 32 so is it 40 x 18 x 32 / 1000 = 23.04 but thats more than 5% = 11.5. Do we not use the mcb for socket outlets as we could not get a run bigger than 20 meters in 2.5mm.

 

[DYCHE4230]

table 7,1 page 40 osg gives you maximum lengths of cable for various circuits to account for maximum allowed volt drop....
saves time on calculations

 

[kung]

table 7,1 page 40 osg gives you maximum lengths of cable for various circuits to account for maximum allowed volt drop....
saves time on calculations

Good table 7.1 on page 44.

 

[Guest123]

Hi

In a ring circuit in effect two cables are run so your mv/A/m value is halved whereas the length of the cable to the farthest point is half the length of the cable in the ring giving you a multiplier of 4.

23.04/4 = 5.76V.

Dont forget the max circuit length for a 32A 2.5mm ring is 100mSq and they use the max volt drop to calculate this.

The current in a ring circuit isn't the same all the way round so technically you dont use the 32A rating of the breaker as the max would be 26A.

Hope this helps.