Normal AC Source
| Normal and Bypass AC Input | |
| Number of conductors | Three phases |
| Rated voltage and tolerance | 480 V +/- 10% (adjustable to +/-15%) |
| Rated frequency and tolerance | 60 Hz +/- 10% |
The correct circuit breaker must be selected based on the following criteria.
- The breaking capacity for the circuit breaker.
- The expected short-circuit current at the installation site.
- The need to protect the static-switch semiconductors, that is, the maximum permissible current for the static-switch semiconductors must be considered.
- The selection must include the distinct needs for the UPS output fuses and protection devices on the load side of the UPS.
| Electrical Parameters for the Normal AC Source | ||||
| Rated UPS output in kVA | Normal AC source current | |||
| Rated current (In) for unit | For 25% overload (3) | For 50% overload (3) | ||
| With battery at start of charge cycle (1) | Without battery (2) | |||
| 150 | 245 | 236 | 295 | 354 |
| 180 | 295 | 283 | 354 | 425 |
| 225 | 332 | 320 | 400 | 480 |
| ( 3 ) | The normal AC source currents given for an overload of 25% or 50% are maximum values. The currents have been determined for a battery with a float charging voltage and a load power factor of 0.9. When choosing the circuit breaker rating, use the "rated current" column. Check that the circuit breaker tripping curves are compatible with the values in the overload columns. |
| ( 1 ) | The rated normal AC source currents (In) have been determined based on the following criteria. The rated phase-to-phase voltage is 480 V. The battery has a 10 minute backup time at the beginning of the charge. An example calculation is 412 x 1.2 = 494 V. The full rated load has a power factor of 0.9. |
| ( 2 ) | The rated normal AC source currents (In) have been determined. The currents take into account a float charging voltage and a full rated load with a power factor of 0.9. |
Bypass AC Source
Use the following information to determine the required rating of the protective circuit breaker on bypass AC input.
Note: If the installation includes a transformer on the bypass AC input, allow for the inrush current caused by magnetization of the transformer windings.
| Electrical Parameters for Bypass AC Source (480 V) | |||
| Rated UPS output in kVA | Current bypass AC source (4) | ||
| Rated current (In) for unit | Rate current for 25% overload | for 50% overload | |
| 150 | 180 | 236 | 270 |
| 180 | 217 | 283 | 325 |
| 225 | 271 | 320 | 407 |
| ( 4 ) | The bypass AC source currents have been determined for a rated phase-to-phase voltage of 480 V. The load power factor is 0.9. The bypass AC source currents have been determined for full rated load as well as overloads of 25% or 50%. When choosing the circuit breaker rating, use the "rated current" column. Check that the circuit breaker tripping curves are compatible with the data in the overload columns. |
| Maximum Permissible Current | |
| UPS output in kVA | Current/Time |
| 150 | 33 (In) for 20 ms |
| 180 | 27 (In) for 20 ms |
| 225 | 22 (In) for 20 ms |
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| Illustration 1 | g02383657 |
Fuse Usage Chart | |
Circuit Breaker for Line Side of UPS
The following information is provided for a single UPS unit.
Note: Ensure that short-circuit current and protection of the static switch semiconductors on the bypass AC input is considered.
| Recommended Ratings for Circuit Breakers for the Line Side of UPS | ||||
| Rated UPS output in kVA | CB on normal AC input | CB on bypass AC input | ||
| circuit breaker | control unit | circuit breaker | control unit | |
| 150 | 250A | 200A | 250A | 200A |
| 180 | 250A | 250A | 250A | 250A |
| 225 | 400A | 400A | 400A | 400A |
Circuit Breaker for Load Side of UPS
The load side breakers provide protection for each UPS output circuit.
Note: If the recommended breaker is not installed and a short-circuit occurs, a break longer than 20 minutes on the remaining output circuits may occur.
| Recommended Breaker Ratings for the Load Side of a Single UPS | ||
| Rated UPS output in kVA | Load side circuit breaker | |
| Circuit Breaker | Control Unit | |
| 100kVA to 225kVA | 100A | 63A curve C 100A curve B |
Parallel Connected UPS Units
For installations with redundant units, only the units required to supply the load power must be considered. An example is an installation that consists of three UPS units in parallel. One UPS unit is redundant and two UPS units are used to determine bypass AC source, load currents, and cable cross-sections.
Table 7 provides an example for rating of up to four UPS units in parallel.
| Parameters for Bypass AC Source and Load Cables for a UPS Units in Parallel | |||
| Rated unit output in kVA | Number of parallel connected | Total UPS rated output in kVA | Bypass AC source or load line current units in Amps |
| 150 | 2 3 4 |
300 450 600 |
360 540 720 |
| 180 | 2 3 4 |
360 540 720 |
434 651 868 |
| 225 | 2 3 4 |
450 675 900 |
542 813 1084 |