# Thread: Two Phase Installation system???

1. ## Two Phase Installation system???

I was just reading through SANS 10142, and under annex P, Authority for issuing a test report and a Certificate of Compliance.
Which is installation is Two-phase, is it two phases from three phase system?

Any one to assist

2. Yes, a two-phase system consists of 2 live phases, one neutral and an earth, as you say it's basically a 3-phase system that's missing one phase. It's not very often you see a 2-phase installation nowadays, I've come across only one in the last 15 years or so. Maybe they're more common in certain areas, I'm not sure TBH.

3. Thank you very much AndyD,

Am a bit confused here regarding Voltage drop calculation,

E.1.4 Circuit DB/C
Selected cable voltage drop to be repeated for each load point from the
From table 6.4(b) (voltage drop), for a 16 mm2 two-core cable single-phase a.c., the voltage drop is 2,8 mV/A/m

DB to C1 voltage drop = (2,8 x 10-3) x (5 x 15) x 10 = 2,10 V Amdt 5
C1 to C2 voltage drop = (2,8 x 10-3) x (4 x 15) x 8 = 1,34 V Amdt 5
C2 to C3 voltage drop = (2,8 x 10-3) x (3 x 15) x 8 = 1,01 V Amdt 5
C3 to C4 voltage drop = (2,8 x 10-3) x (2 x 15) x 6 = 0,50 V Amdt 5
C4 to C5 voltage drop = (2,8 x 10-3) x (1 x 15) x 9 = 0,38 V Amdt 5
Total voltage drop DB to C5 (red phase) = 5,33 V [1] Amdt 5

My question is: why should they multiple the current by 5 at C1, by 4 at C2, by 3 at C3, by 2 at C4 and by 1 and C5.

is this really right?

My total voltage drop is 1.722V

4. Originally Posted by Smut
My question is: why should they multiple the current by 5 at C1, by 4 at C2, by 3 at C3, by 2 at C4 and by 1 and C5.
Point C1 is carrying 5 x 15A draw points, 1 at C1 and another 4 further down the line.
Similarly C2 is carrying 4 x 15A draw points.

From a "follow the logic" point of view, it might have been better if they started the point numbering from the furtherest point and worked back towards the supply point for these sorts of schematics. Of course from a signage point of view (if you were actually physically labelling each point) it makes more sense to number from point of supply...

5. ## Thanks given for this post:

Smut (14-Mar-13)

6. Thanks Dave,

I really washed my brain.

7. Can the neutral be regarded as a live phase?

8. it is regarded as a live conductor according to 10142. its not a live phase,otherwise 2 phases and neutral would be 3 phase.