With reference to 433.1.204 and cable as installed has min capacity of 20A if protected by a 30A or 32A. If the protective device is reduced to 20A how is the new minimum as installed capacity calculated or arrived at ? I've been looking in the Electrical Installation Design Guide, but the answer is avoiding my eyes.
Hi Mike, in your example the leg carrying 27A would be running hot, perhaps 70 deg C, therefore would have higher resistivity than the cooler longer leg. I can't do the maths but would this make a huge difference?
i found this calculator Temperature Coefficient of Resistance (gsu.edu) and plugging in a few numbers gives a rise in resistance of 20% for copper, initial temp 20, final temp 70. So in Mike's example above the worst case first leg of the ring of length 1M would have an equivalent length running at 70 deg C of 1.2 Metres, so hardly any difference at all to the load sharing calculations.
Hi Mike, in your example the leg carrying 27A would be running hot, perhaps 70 deg C, therefore would have higher resistivity than the cooler longer leg. I can't do the maths but would this make a huge difference?
i found this calculator Temperature Coefficient of Resistance (gsu.edu) and plugging in a few numbers gives a rise in resistance of 20% for copper, initial temp 20, final temp 70. So in Mike's example above the worst case first leg of the ring of length 1M would have an equivalent length running at 70 deg C of 1.2 Metres, so hardly any difference at all to the load sharing calculations.
