I doubled the length of the conductors, but now I'm confused:
Table 4D1B in Appendix 4 states that 10mm sq cable in conduit drops 4.4mV/A/m at 70 °C
The title at the top states: 'Single-core ... cables', so I'd assume the values are for one conductor only.
The table in the question paper is different. 'Figure 1 below shows information on the resistance of conductors in mΩ/A/m.'
The bottom row says nothing more than: 1m of a 10mm² conductor has a resistance of 1.83mΩ at 20°C.
At 1amp, this gives a voltage drop of 1.83mV.
The scenario also mentions single cables in trunking and conduit.
Sadly, when I compare the figures with BS7671, logic and common-sense cease to apply.
The values on the exam paper should be the same as the values listed in BS7671, table 4D1B, but reduced a certain amount because they're at 20°C instead of 70.
BS7671 says a 1m length of 10mm ² cable drops 4.4V per amp,
C&G say that the same cable drops 1.83mV.
Temperature correction is 4% increase in resistance per 10°Cincrease in temperature, i.e. 20% for a 50°C difference.
The difference in these two figures is 58%.
What's going on?
