Installation manual

Appendix: External Bypass Switches

If your UPS does not have output receptacles, you may have an external UPS Bypass Switch with an

AC Line Disconnect Switch. Figure 3 on page 5 shows a Best Power bypass switch.

The UPS Bypass Switch has three positions: Line, Off, and UPS (see Table 13).

Table 13: External Bypass Switch Positions

NOTE:In all three UPS Bypass Switch positions, AC input power may still be connected to the input

terminals inside the UPS. To disconnect AC input power to the UPS, you must use the AC

Line Disconnect Switch.

An external bypass switch may be “Make-Before-Break” (MBB) or “Break-Before-Make” (BBM).

• A Make-Before-Break (MBB) switchmakes a new connection before it breaks the present con-

nection. If you turn the switch from “UPS” to “Line,” the bypass switch connects the load equip-

ment to AC input power before disconnecting the equipment from UPS output power. In other

words, there is no break in power to the load equipment during the switch from UPS output

power to AC input power.

• A Break-Before-Make (BBM) switchbreaks the present connection before it makes the new

one. When you turn the switch from “UPS” to “Line,” the switch moves through the “Off” posi-

tion. The bypass switch disconnects the load equipment from UPS output power before connect-

ing it to AC input power.

For external bypass switch models and ratings, see Section 101.

For external bypass switch dimensions, see Section 102.

UPS Bypass Switch Position Explanation

LINE Connects AC input power (line) directly to the load equipment.

OFF

Disconnects the load equipment from both UPS output power and AC

input power (line).

UPS Connects the UPS output to the load equipment.

CAUTION!

Before switching an external make-before-break (MBB) bypass switch, the BYPASS light on the

UPS front panel must be lit. If you operate an external MBB bypass switch while the UPS is

operating on line power or on battery power, equipment damage may result. Refer to Best Power

publication TIP 410 for proper bypass switch operating instructions.