Sun 15 Mar, 2015 05:11 pm
When a number of Single phase loads are powered/fed through a TPN DB. How do we get/calculate the Three Phase Total Loading of the DB, especially to aid sizing of the DB's 3-Phase Main Breaker and Feed Cable selection?
Sounds like the apprenticeship classes are in full swing again. The quick answer is the total power on a 3Ph -4W 120/208-Y panel can be found by dividing by 360. On a 3ph-4w 277/480-Y panel you can divide the total power by 831. When load include single-phase loads, do a panel schedule and balance the loads the best you can and be sure to cover the load on the highest phase, with room for growth. You need to allow for 100% of the non-continuous loads plus 125% of the continuous loads. There are various considerations given to loads (duty cycle etc) but in general thats the short answer.