Transformer Protection
Transformer Protection
(OP)
Hello all,
Situation: 75kVA 600V-240/120VAC 1P solidly grounded transformer with 200A fusible disconnect c/w TRS150R fuses on the primary, and a 400A 30CCt lighting panel on the secondary. Panel has main lugs only, 3x100A branch circuits, 1x60A branch circuit, 1x15A branch circuit. Items all located in the same lineup and the transformer is a dry type in a NEMA 4x non-ventilated enclosure. We are located in Ontario Canada.
Question: This seems to meet all codes (ESA inspector has confirmed). Does anyone see the need for a main on the secondary?
Thank-you in advance. TULUM.
Situation: 75kVA 600V-240/120VAC 1P solidly grounded transformer with 200A fusible disconnect c/w TRS150R fuses on the primary, and a 400A 30CCt lighting panel on the secondary. Panel has main lugs only, 3x100A branch circuits, 1x60A branch circuit, 1x15A branch circuit. Items all located in the same lineup and the transformer is a dry type in a NEMA 4x non-ventilated enclosure. We are located in Ontario Canada.
Question: This seems to meet all codes (ESA inspector has confirmed). Does anyone see the need for a main on the secondary?
Thank-you in advance. TULUM.






RE: Transformer Protection
RE: Transformer Protection
RE: Transformer Protection
RE: Transformer Protection
Bill
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"Why not the best?"
Jimmy Carter
RE: Transformer Protection
However, I have received the damage curve from the manufacturer and the fuses protect the transformer ok mechanically however, the thermal portion is really unprotected. I know this is typical in alot of applications, however in this case the manufacturer plotted the damage curve with points @100% rated current occurring at 10000s through 100000s. I thought transformers could handle 100% rated current for ever - not 10000s (2.76hrs) before damage begins? My fuse curves stop at 1000s so hard to verify what happens after that point....
I know minimum code says primary protection alone is ok as long as it is sized at 125%... but with 375A worth of load breakers, how can the transformer be protected with the above damage curve?
RE: Transformer Protection
If you put in a 125A fuse on the 600V side, that will mean you can pull around 312A on the downstream side before the fuse blows.
I suspect your panel is bigger than it needs to be and that your actual load is below 300A. You may want to turn everything on and put an amp clamp on the feeder to see what you're drawing.