Equipment substitutions: electrical load and mechanical clearance

Change the supplied quantity: kVA is not kW

Original comparison: a balanced three-phase load on a 208-V supply is stated as 78 kVA. Line current is 78,000/(√3 × 208) = 216.5 A. Power factor is not needed because apparent power is already supplied. If the load is instead 78 kW at power factor 0.80, apparent power is 78/0.80 = 97.5 kVA, and current becomes approximately 270.6 A.

Do not divide a stated kVA load by power factor a second time. Do not use a single-phase relationship for this balanced three-phase exercise. Both calculations assume line-to-line voltage and the supplied total input; actual feeder, conductor, protective-device, continuous-load and code checks are separate.

Original example: a replacement unit must fit two systems

A fictional equipment replacement adds 12 kVA to a 66-kVA balanced three-phase load on a 208-V panel. For this exercise, the existing and added values already include every required demand adjustment, and the project sets a 200-A panel limit. The replacement also needs 48 inches of manufacturer-specified service clearance where the plan provides 45 inches.

Total apparent load is 78 kVA. Current is 78,000 divided by the square root of three times 208, or approximately 216.5 A, above the stated project limit. The available clearance is also 3 inches short. Matching the mechanical duty point would not resolve either interface. Obtain coordinated electrical and spatial revisions before accepting the substitution; the example does not prescribe a conductor or protective-device size.

Keep the assumptions visible

• Use apparent power in VA with the three-phase current relationship; do not divide an already stated kVA input by power factor again.
• The 200-A limit is supplied for this exercise. This is not a complete electrical code sizing or protection problem.
• Maintenance clearance is a supplied manufacturer requirement. Matching the equipment footprint is a different check.
• Review controls, support, access and commissioning interfaces when the actual project requires them.

Two revisions must be checked independently

Alternative 1 reduces added input to 4 kVA while leaving clearance unchanged. Total 70 kVA gives approximately 194.3 A, within the stated 200-A limit, but the 45-inch space still fails the 48-inch service requirement. Alternative 2 provides 50 inches of clearance but leaves the original 78-kVA load; space passes, current remains approximately 216.5 A and fails the exercise limit. Neither partial revision alone satisfies both conditions.

A complete proposal must show evidence for each affected interface and be reviewed by the responsible disciplines. A favorable result in one domain cannot stand in for the coordinated decision.

Practice a new building-systems decision