mike k
Member
- Location
- Pennsylvania
Recently our service department responded to a service call after an electrical outage.
The customer lost 1-phase of a 120/208 Y system. The piece of equipment in question that would not work after the lost phase was restored by the power company was a printing press. After our service tech. inspected the wiring we found several problems.
The equipment was feed from a 120/208 volt 200- amp fused disconnect with 150-amp fuses. It then went to a 45 kva 120/208Y (Secondary) to 480 delta (primary) transformer connected in reverse to get 480-Volts. From this transformer it feed another multiple tap transformer that took the 480-volt primary and adjusted it to the machinery factory voltage of 380-volts. The disconnect had 150-amps feeding it from a MDP via EMT conduit, the 1st violation was that the neutral and the grounding conductors were connected together and bonded to the disconnect can. From the disconnect (Secondary side) to the 1st transformer was feed with (3) # 1 wires and (1) #4 wire for the ground, the ground was connected to the can in the disconnect (where the neutral & the ground were bonded) and connected to the transformers XO connection which was also bonded to the can this being the second violation. From this point the 480-voltage and the ground connected to the transformer can (where the XO was bonded) was taken to the 2nd transformer and connected to the can and the (3) phase went to the primary side. The secondary side of the 2nd transformer was connected to the printing press using the same equipment ground that came from the 1st transformer Via the 200-amp disconnect. The ground wire was #4 connected to both transformer cases and bonded to the 1st transformers XO neutral connection. This wire is the problem from the disconnect to the 1st transformer the insulation was completely melted and the conductor was starting to melt. And as for the conduit it also had signs of carrying a load it was black at the connectors and had appeared the it to was starting to melt the heat was very excessive and the plastic bushings were melted to the pipe. Eventually it blew (1) of the 150-amp fuses in the disconnect. The customer had told us this exact same situation occurred before when they lost a phase during a storm. (A couple of years ago)
1) Should the neutral be connected to the 1st transformer for this application?
2) Should it be bonded to the transformer can?
3) If so the conductor that was installed was too small (#4) and should be changed to a #1?
4) What caused this wire to breakdown after loosing 1?phase?
5) After reviewing the code I believe that each of the (2) transformers on the secondary side should be bonded to the building steel form the can?
The customer lost 1-phase of a 120/208 Y system. The piece of equipment in question that would not work after the lost phase was restored by the power company was a printing press. After our service tech. inspected the wiring we found several problems.
The equipment was feed from a 120/208 volt 200- amp fused disconnect with 150-amp fuses. It then went to a 45 kva 120/208Y (Secondary) to 480 delta (primary) transformer connected in reverse to get 480-Volts. From this transformer it feed another multiple tap transformer that took the 480-volt primary and adjusted it to the machinery factory voltage of 380-volts. The disconnect had 150-amps feeding it from a MDP via EMT conduit, the 1st violation was that the neutral and the grounding conductors were connected together and bonded to the disconnect can. From the disconnect (Secondary side) to the 1st transformer was feed with (3) # 1 wires and (1) #4 wire for the ground, the ground was connected to the can in the disconnect (where the neutral & the ground were bonded) and connected to the transformers XO connection which was also bonded to the can this being the second violation. From this point the 480-voltage and the ground connected to the transformer can (where the XO was bonded) was taken to the 2nd transformer and connected to the can and the (3) phase went to the primary side. The secondary side of the 2nd transformer was connected to the printing press using the same equipment ground that came from the 1st transformer Via the 200-amp disconnect. The ground wire was #4 connected to both transformer cases and bonded to the 1st transformers XO neutral connection. This wire is the problem from the disconnect to the 1st transformer the insulation was completely melted and the conductor was starting to melt. And as for the conduit it also had signs of carrying a load it was black at the connectors and had appeared the it to was starting to melt the heat was very excessive and the plastic bushings were melted to the pipe. Eventually it blew (1) of the 150-amp fuses in the disconnect. The customer had told us this exact same situation occurred before when they lost a phase during a storm. (A couple of years ago)
1) Should the neutral be connected to the 1st transformer for this application?
2) Should it be bonded to the transformer can?
3) If so the conductor that was installed was too small (#4) and should be changed to a #1?
4) What caused this wire to breakdown after loosing 1?phase?
5) After reviewing the code I believe that each of the (2) transformers on the secondary side should be bonded to the building steel form the can?
