We had a 1750 HP, DC, hoist motor connection that failed in the motor junction box and caused a fire in the wire trough. The resulting fire was put out with a dry type fire extinguisher and the dust from it was pulled into the Siemens SCR drive by the cooling fans. The result was 3 changed motors, 12 leg modules (SCR assemblies), power interface board, gate board, motor leads, and 2 days production. The motor was checked with infrared the day before the failure because of a hot insulation smell that was thought to be coming from a winding but nothing was indicated. The motor connections were a combination of Al lugs, Cu bus, and carbon steel bolts – recipe for disaster. A window into the J box will allow future inspections. Does anyone have a detailed instruction on how the connections should be made? Several 500 MCM cables are connected to a Cu bus and duct sealed to allow taping.

Was there any No-Alox (or similiar) compound used on the connections?

Dave

You have written AL Lugs and copper Bus. so are you using any bimetal strips for termination?

No, No-Alox or bimetal strips were used. That is the reason for the need for a detailed instruction for connections. There are concerns of oxidation, cleaning, joint compounds, type connections, torque, temperature measurements, etc. We have many motors and lots of opportunities for failure.