I am installing a 208Y/120, 125A, 3 Phase panel, 4 wire panel in a newly constructed press box at a sports field. The nearest power source is in a storage building which contains a 45 KVA, 480v, 3 phase - 208Y/120 3 phase transformer. This transformer feeds a 208Y/120v, 125A, 3 Phase panel in this same storage building. My question is. Can I add a second set of cables to the secondary taps of the transformer? I would then connect these cables to a fused disconnect before the cables leave the storage building.
Adding new panel to transformer
- Thread starter dime
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Yes, you can add a second set of secondary connections, provided you install the overcurrent protection in the manner you described. However, you are talking about having two panels, each rated 125 amps, connected to a transformer with a rating of 125 amps. What steps are you taking to ensure the transformer does not get overloaded?
The transformer total load was my second problem. I will present all the options to the customer and let them decide. I first wanted to see if I could tap the transformer. I feal I have a couple of options to limit the load on the transformer. First,the existing storage shed load consists of lighting and GFI outlets and the load for the press box is the same. The panel in the shed is a 125A main breaker. I could replace the main breaker in this panel with a smaller one say 75A. I haven't check the panel to see how low I can go. If I do that, then I would use 50A fuses in the disconnect (if I tap the transformer) and downsize the press box mainlug panel. Second, I could put a 50A 3 pole breaker in the storage shed panel to feed the press box. Third, if I have to stick with the load of two 125A panels then the 45 kva transformer will have to be changed.
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- Massachusetts
Note 2 to Table 450.3(B) is worth a look. It backs up Charlie's comments. :smile:
As Charlie mentioned the load can not exceed 125 amps, but the combined total of the over current protection could be 175 amps. (see Note 1 to Table 450.3(B) and 240.6)
As Charlie mentioned the load can not exceed 125 amps, but the combined total of the over current protection could be 175 amps. (see Note 1 to Table 450.3(B) and 240.6)
Time to go to Art. 220 and do some load calculations to see if you are overloaded or not.:smile: Just because the secondary panel has a 125a main doesn't mean much to "what is the true load", you may find that the true load is far different then what the panel is breakered at.
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