ECN Forum Forums General Topics of the Trade General Discussion Area strange 45 klva 480/208 primary overcurrent occure

Yes to the question of changing out both disconnects to new ones. The existing 480v primary had a defective knife switch that meant the blades were only inserting half way in (lots of discoloration). new 600v 100amp disc9onnect with new 90 amp fuses took care of that problem. The secondary disconnect on the existing 45 kva wye transformer had formerly been a 100v 600v fused disconnect which kept blowing fuses as it was only fused at 90 amps 208v. I changed that existing secondary disconnect out to a new 200 amp 240v disconnect and replaced the secondary conductors (*which were previously too small 2 awg aluminum) with 1/0 copper and installed fuses for 150 smps. I am now changing out the rest of the feeder cable to 3/0 aluminum 5 wire to the existing 200amp 240vc panelboard.
in the whole history of this building, this 90 amp primary breaker had never triped and we could not replicate the problem. Everything today worked fine as well as yesterday after changing out the fuses (and extensive troubleshooting to be sure we did not overlook something).