Maintenance Bypass is used to switch off the incoming utility power of the UPS and directly to the load so that maintenance can be performed on the UPS system.
Note: The load is not protected while in Maintenance Bypass Mode and will be affected by a disruption in the incoming power.
Cabinet Description
The Maintenance Bypass Cabinet is a 53.34 cm (21.0 inch) wide cabinet. The Maintenance Bypass Cabinet is located to the left of the Input/Output Cabinet.
The Maintenance Bypass Cabinet is only found in UPS/SMS systems. The Maintenance Bypass Cabinet is included in the paralleled MMU systems.
Three-phase utility power comes in through the top of the Maintenance Bypass Cabinet. The cables for the three-phase utility power connect to each of three cable landing bus bars and one ground bus bar.
In installations where utility power comes into the UPS via a bottom entry cabinet, the cable landing bus bars in the Maintenance Bypass Cabinet are accessed through the sides of the Maintenance Bypass Cabinet and the bottom entry cabinet.
The Maintenance Bypass Cabinet includes left and right internal component panels. A two-piece steel baffle shields the internal components of the cabinet. Only the front panel of the Maintenance Bypass Circuit Breaker and the two illuminated green Bypass Push Buttons are accessible when the door to the cabinet is open and the baffles have not been removed.
Near the middle of the cabinet the panel contains the two illuminated push-button switches. These switches provide the following functions:
- Transfer TO maintenance bypass.
- Transfer FROM maintenance bypass.
These switches are connected to an electronic circuit that controls the circuit breaker in this cabinet, as well as the UPS Output Disconnect Switch (K5), in order to provide for controlled make-before-break transfers to bypass and from bypass.
Note: The UPS Output Disconnect Switch (K5) is located in the Input/Output Cabinet.
The left panel of the cabinet contains the two boards. Refer to Illustration 3. The top board is the Maintenance Bypass Control Board, and the bottom board is the Maintenance Bypass Power Supply Board. The Time Delay Relay is also located on this panel.
The right panel contains three transformers that provide stepped down power to the Boards on the left panel. Refer to Illustration 4. The fuse block that is located below the transformers contain the fuses for these transformers.
Located at the bottom of the cabinet is the Maintenance Bypass Circuit Breaker.
Above the Maintenance Bypass Circuit Breaker are the cable landings for the utility input into the Maintenance Bypass Cabinet. There are three landings that are connected to the Maintenance Bypass Circuit Breaker inputs for Phase A, Phase B, and Phase C. There is also a ground landing that is connected to the right side of the cabinet for utility ground connection.
Below and behind the Maintenance Bypass Circuit Breaker are horizontal output bus bars that lead to the right, into the System Input/Output Cabinet.
In the case of a 4-wire installation there are also vertical bus bars that run up and left into the 4-wire Input cabinet.
Switching to or from Maintenance Bypass Mode is effected by pressing one of two switches located on the shield behind the Maintenance Bypass Cabinet door. These push buttons automatically open or close all the proper switches and circuit breakers in the UPS system, in the proper order, so that the UPS is taken off line cleanly, providing no interruption of electrical power to the main load.
Note: The load is not protected while in Maintenance Bypass Mode and will be affected by a disruption in the incoming power.
Note: The transfer to and from maintenance bypass can only be performed when the UPS is in the Bypass mode.
Cabinet Diagrams
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| Illustration 1 | g01272800 |
Maintenance Bypass Cabinet - Left View (1) MBP Left Panel (2) Circuit Breaker (MBP) (3) Output Bus Bar (Phase C) (4) Output Bus Bar (Phase B) (5) Output Bus Bar (Phase A) (6) Input Cable Landing (Phase C) (7) Input Cable Landing (Phase B) (8) Input Cable Landing (Phase A) (9) Cable Landing (Ground) | |
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| Illustration 2 | g01272801 |
Maintenance Bypass Cabinet - Right View (2) Circuit Breaker (MBP) (10) MBP Right Panel | |
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| Illustration 3 | g01272803 |
MBP Left Panel Components (11) MBP Controller Board (MBC) (12) MBP Power Supply Board (MPS) (13) Time Delay Relay | |
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| Illustration 4 | g01272805 |
MBP Right Panel Components (14) Transformer T9 (15) Transformer T10 (16) Transformer T11 (17) Fuse Block F52-F54, F57, F67, F68 | |