lakee911
Senior Member
- Location
- Columbus, OH
I had a shop drawing come in that was as follows:
480VAC single phase power feed (from 2P 20A CB, wiresize #12) to a panel. In that panel, the main CB is 7A. From that they are feeding only a 480VAC x 120VAC 2KVA transformer. There is no secondary protection and they wire to power distribution blocks and feed various loads with their own seperate CBs.
According to the NEC (if you make the assumption that industrial control panels are covered by the NEC), the incoming CB can be sized to a maximum of 167% of the tranny rated current. There is no round-up rule here. 2000VA/480V*167% = 6.958A. Is this close enough or is 7A too big?
Given that 2000VA/120V = 16.667A, what size wire should be used after the transformer? I would think that #12 is too small because 16.667 is greater than 80% of 20A. Would 10A be correct because 16.667A * 167% * 125% = 34.792A?
Thanks,
Jason
480VAC single phase power feed (from 2P 20A CB, wiresize #12) to a panel. In that panel, the main CB is 7A. From that they are feeding only a 480VAC x 120VAC 2KVA transformer. There is no secondary protection and they wire to power distribution blocks and feed various loads with their own seperate CBs.
According to the NEC (if you make the assumption that industrial control panels are covered by the NEC), the incoming CB can be sized to a maximum of 167% of the tranny rated current. There is no round-up rule here. 2000VA/480V*167% = 6.958A. Is this close enough or is 7A too big?
Given that 2000VA/120V = 16.667A, what size wire should be used after the transformer? I would think that #12 is too small because 16.667 is greater than 80% of 20A. Would 10A be correct because 16.667A * 167% * 125% = 34.792A?
Thanks,
Jason