I work for a mining company and we have been provided ( by an equipment manufacturer) a movable skid with a 1500 kva, 12,470 - 480/277 volt transformer and a building with a motor control center ( mcc) installed. The provider had wired the installation as follows. The transformer is 32" from the building and four 4" RGC conduits run from the transformer secondary cabinet into the building and into the mcc main lug section. There was no "main disconnect" between the transformer secondary and the mcc main lugs. The mcc has 1600 amp bus and 5 motor starters and a disconnect for a 120/240 volt transformer. { the local utility is supplying power to a step down transformer ( owned by my company) to step down from their distribution voltage to 12,470 volt. The 12,470 volt line is run overhead into an open pit mine to the location of the movable skid. Therefore, the "service" point is at the first step down transformer.}
The supplier of the skid ran phase A conductors from the secondary cabinet of the transformer through the first of the 4" conduits to the main lugs of the mcc. Also, phase B conductors were run through conduit 2. Phase C conductors were run in conduit 3. They then ran motor leads (600 volt insulation) for (2) 350 hp, 480 volt motors from the mcc into the transformer secondary cabinet, one set of motor leads were in conduit 3 with the phase C leads and the other set of motor leads were in conduit 4. The motor leads were then spliced into rubber cord by means of open power block connectors. The rubber cord then ran into , through and out of the high voltage (12,470 volt) cabinet of the transformer to plugs mounted on the front of the skid.
The supplier has agreed that the phase conductors being run in seperate conduits violates the NEC and that the 600 volt rubber cord going through the transformer high voltage cabinet also violates the NEC. These problems have been corrected.
We believe that there must be a "main" disconnect between the transformer secondary and the mcc main lugs, NEC 430.94. Is this required in the NEC?
We also believe that the secondary cabinet of the transformer can not be used as a wire way and splice point of the motor leads. However since this is not the service location ,I can not locate a section of the NEC that prohibits this type of installation. Is this or is it not allowed by the NEC?
The supplier of the equipment says that the NEC allowes the secondary conductors of the transformer to be protected by the transformer primary protection and therefore no disconnect is needed between the transformer and the mcc main lugs. They also say that the motor leads are allowed to be run through and to have open splices in the transformer secondary cabinet. Can you please help clarify there questions.
For your information we have rerouted the motor leads away from the transformer and have installed a disconnect between the transformer and the mcc main lugs
[ December 07, 2005, 01:32 PM: Message edited by: adamsz ]
The supplier of the skid ran phase A conductors from the secondary cabinet of the transformer through the first of the 4" conduits to the main lugs of the mcc. Also, phase B conductors were run through conduit 2. Phase C conductors were run in conduit 3. They then ran motor leads (600 volt insulation) for (2) 350 hp, 480 volt motors from the mcc into the transformer secondary cabinet, one set of motor leads were in conduit 3 with the phase C leads and the other set of motor leads were in conduit 4. The motor leads were then spliced into rubber cord by means of open power block connectors. The rubber cord then ran into , through and out of the high voltage (12,470 volt) cabinet of the transformer to plugs mounted on the front of the skid.
The supplier has agreed that the phase conductors being run in seperate conduits violates the NEC and that the 600 volt rubber cord going through the transformer high voltage cabinet also violates the NEC. These problems have been corrected.
We believe that there must be a "main" disconnect between the transformer secondary and the mcc main lugs, NEC 430.94. Is this required in the NEC?
We also believe that the secondary cabinet of the transformer can not be used as a wire way and splice point of the motor leads. However since this is not the service location ,I can not locate a section of the NEC that prohibits this type of installation. Is this or is it not allowed by the NEC?
The supplier of the equipment says that the NEC allowes the secondary conductors of the transformer to be protected by the transformer primary protection and therefore no disconnect is needed between the transformer and the mcc main lugs. They also say that the motor leads are allowed to be run through and to have open splices in the transformer secondary cabinet. Can you please help clarify there questions.
For your information we have rerouted the motor leads away from the transformer and have installed a disconnect between the transformer and the mcc main lugs
[ December 07, 2005, 01:32 PM: Message edited by: adamsz ]
