Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, concerning where the maximum demand load should be calculated when carrying out additions or alterations to large installations, is answered by SELECT:
I recently installed a radial circuit from a single-phase distribution board for a curtain heater in the reception of a very large commercial property. If the maximum demand is to be taken at the point of isolation, at origin, this would be a main panel switch 60947/2 with a current rating of 2000A. I assume that having to calculate the whole demand for the building because of one additional radial circuit is not expected?
So, I ask, where in the long line of main switches and switch fuses from my distribution board, should it be calculated - the MCB, distribution board main switch, distribution board 100A switch fuse, the rising busbar 300A switch fuse, main panel 600A main switch, or the point of origin as mentioned?
Answer: I would suggest that it would be unlikely that you can accurately calculate the true maximum demand of this installation. Your check should be restricted to measuring the additional load of your alteration, or addition, and for you to ensure that this does not overload the system.
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