Hey guys,
Ran in to one this last week that I wanted to run by everybody and get some ideas. I was given the job of wiring (2) 30 hp bin fan motors on some grain bins. The service is a 3-phase high-leg 230 volt system. The service conductors run about 250 feet from the pole mounted transformer and stop in a terminal box like a CT can. The service conductors from the pole to the CT cab are (2) parallel sets of 250 USE quad-plex AL direct burial cable (I DID NOT INSTALL THIS!). I tapped from the CT cabinet and installed a 200 amp QO 3-phase loadcenter to supply these two motors only. The motors bump tested fine a couple of months ago when we installed the new equipment and got everything wired. The owner called me last week after they needed them for the first time and said that they will only start intermittently. Before I even stopped out there I called to order (2) 125 amp breakers to replace the recommended size of 100 amp figuring it was a start-up current issue, only to find out that in the 3-phase line they do not manufacture a QO breaker bigger then 100 amp.
I showed up to do some checking and found out that when the motors were tripping the breakers it was only on start-up. Each motor has its own start-stop. One time they would both start fine, the next one would start while the other wouldn't, and then first one would trip and the second would start and run fine. When they would trip the motor wouldn't even start to budge, it was more like a dead short style trip. Then they will start three or four times in a row and run just fine. Each motor has its own conduit, own conductors, and is about 125 feet away from the panel. I am stumped. The voltage was bit little low, but was within means. The coil voltage is correct on the motor starters. Wire size is correct. Motors are wired correctly. Anybody have any ideas? Thanks in advance.
Ran in to one this last week that I wanted to run by everybody and get some ideas. I was given the job of wiring (2) 30 hp bin fan motors on some grain bins. The service is a 3-phase high-leg 230 volt system. The service conductors run about 250 feet from the pole mounted transformer and stop in a terminal box like a CT can. The service conductors from the pole to the CT cab are (2) parallel sets of 250 USE quad-plex AL direct burial cable (I DID NOT INSTALL THIS!). I tapped from the CT cabinet and installed a 200 amp QO 3-phase loadcenter to supply these two motors only. The motors bump tested fine a couple of months ago when we installed the new equipment and got everything wired. The owner called me last week after they needed them for the first time and said that they will only start intermittently. Before I even stopped out there I called to order (2) 125 amp breakers to replace the recommended size of 100 amp figuring it was a start-up current issue, only to find out that in the 3-phase line they do not manufacture a QO breaker bigger then 100 amp.
I showed up to do some checking and found out that when the motors were tripping the breakers it was only on start-up. Each motor has its own start-stop. One time they would both start fine, the next one would start while the other wouldn't, and then first one would trip and the second would start and run fine. When they would trip the motor wouldn't even start to budge, it was more like a dead short style trip. Then they will start three or four times in a row and run just fine. Each motor has its own conduit, own conductors, and is about 125 feet away from the panel. I am stumped. The voltage was bit little low, but was within means. The coil voltage is correct on the motor starters. Wire size is correct. Motors are wired correctly. Anybody have any ideas? Thanks in advance.
