wirenut1980
Senior Member
- Location
- Plainfield, IN
Hi all, I am doing a design for an electrical branch circuit upgrade (commercial application) fed from an MCC which is fed from the transformer and wanted some opinions on my design. I am told by the electric shop that the MCC and conductors feeding the MCC, and the transformer do not need to be replaced.
Background: Project to upgrade wiring and OCP for Hydraulic Component Test Stand. Customer is swapping out similar equipment for a bigger one and needs to upgrade electrical back to MCC. The new equipment will be adding approximately 200 Amps load. The equipment has some kind of variable speed drive, and various motor loads all contained inside with only one disconnect for the whole machine required.
Full Load Current = 525 Amps per manufacturer specs
Existing 4? EMT available for use in facility.
Equipment is a continuous load, so size conductors and OCP for 525 Amps*1.25 = 656.25 Amps.
Required Equipment Voltage = 480 V
I plan to have parallel conductors pulled in accordance with article 310.4. From this I see no reason why I cannot pull both parallel circuits in one conduit. Any objections?
I will have 6 current carrying conductors. De-rate 80% per table 310.15(B)(2)(a). Requires ampacity of at least 820.3125 Amps.
Choose dual circuits with 600 MCM THHN Cu conductors from table 310.16, 75 deg C column, 420 Amps each circuit for a total of 840 Amps capacity.
Looking in Annex C, Table C1(A), it appears I can fit (6) 600 MCM THHN Cu conductors and (1) 1/0 AWG Cu EGC conductor in a 4? EMT conduit.
Round down OCP from 820 Amps to 800 Amps per 240.4(C).
Planning on replacing existing 400 Amp breaker on MCC feeding this circuit with 800 Amp Breaker. I am not sure how the best way would be to choose what type or size would be best for this breaker? Should I be looking at a 600 Amp breaker instead? I am not sure exactly how much inrush current to expect, so I am thinking 6-8 times FLC.
Planning on replacing existing 400 Amp fusible disconnect with 800 Amp fusible disconnect placed in accordance with article 430. Required by manufacturer to be fused. Again, I am not sure how the best way would be to choose what type or size would be best for this fuse? Should it be 600 Amps fused disconnect?
EGC sized per 250.122 will be 1/0 AWG Cu.
Run is approximately 350 feet from MCC to equipment. Calculating voltage drop as follows:
Voltage drop for 480 V 3 phase branch circuit in Volts = 2*K*L*I*0.866/CM
Vdrop= (2*12.9*350*525*0.866)/(2*600,000) = 3.42 Volts = 0.713% drop
Misc. ? Need to install splice box near fusible disconnect to account for too many 90 deg bends along the way from MCC to equipment.
This seems like an awful lot of conductor for what I need. Am I way off here?
Thanks!
Background: Project to upgrade wiring and OCP for Hydraulic Component Test Stand. Customer is swapping out similar equipment for a bigger one and needs to upgrade electrical back to MCC. The new equipment will be adding approximately 200 Amps load. The equipment has some kind of variable speed drive, and various motor loads all contained inside with only one disconnect for the whole machine required.
Full Load Current = 525 Amps per manufacturer specs
Existing 4? EMT available for use in facility.
Equipment is a continuous load, so size conductors and OCP for 525 Amps*1.25 = 656.25 Amps.
Required Equipment Voltage = 480 V
I plan to have parallel conductors pulled in accordance with article 310.4. From this I see no reason why I cannot pull both parallel circuits in one conduit. Any objections?
I will have 6 current carrying conductors. De-rate 80% per table 310.15(B)(2)(a). Requires ampacity of at least 820.3125 Amps.
Choose dual circuits with 600 MCM THHN Cu conductors from table 310.16, 75 deg C column, 420 Amps each circuit for a total of 840 Amps capacity.
Looking in Annex C, Table C1(A), it appears I can fit (6) 600 MCM THHN Cu conductors and (1) 1/0 AWG Cu EGC conductor in a 4? EMT conduit.
Round down OCP from 820 Amps to 800 Amps per 240.4(C).
Planning on replacing existing 400 Amp breaker on MCC feeding this circuit with 800 Amp Breaker. I am not sure how the best way would be to choose what type or size would be best for this breaker? Should I be looking at a 600 Amp breaker instead? I am not sure exactly how much inrush current to expect, so I am thinking 6-8 times FLC.
Planning on replacing existing 400 Amp fusible disconnect with 800 Amp fusible disconnect placed in accordance with article 430. Required by manufacturer to be fused. Again, I am not sure how the best way would be to choose what type or size would be best for this fuse? Should it be 600 Amps fused disconnect?
EGC sized per 250.122 will be 1/0 AWG Cu.
Run is approximately 350 feet from MCC to equipment. Calculating voltage drop as follows:
Voltage drop for 480 V 3 phase branch circuit in Volts = 2*K*L*I*0.866/CM
Vdrop= (2*12.9*350*525*0.866)/(2*600,000) = 3.42 Volts = 0.713% drop
Misc. ? Need to install splice box near fusible disconnect to account for too many 90 deg bends along the way from MCC to equipment.
This seems like an awful lot of conductor for what I need. Am I way off here?
Thanks!