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ARMS/Maintenance Mode on 520MC and 1150+ trip units

The Maintenance Mode function of the Digitrip 520MC and Digitrip 1150+ can reduce arc flash incident energy that is generated on a fault condition, as required by the NEC on breakers 1200A and above. Maintenance Mode can be enabled at the trip unit, via communications, or using a remote switch wired through the breaker secondary contacts. If Maintenance Mode is enabled remotely, it must be disabled using the same method.

On the 520MC trip unit, Maintenance Mode is locally enabled locally using the switch on the top left of the trip unit next to the display. On the 1150+ trip unit, Maintenance Mode is locally enabled using the "SYSTEM" submenu of the programmable setting menu ("PGM SET").

For Magnum breakers, a switch can be wired across pins A12 and B7 to remotely enable Maintenance Mode (see below image). For NRX breakers, the pins are W33 and W34 (note that ARMS is optional on the NRX 520M). The switch must have logic level contacts. The maximum length of this wiring to the remote Arcflash Reduction Maintenance System switch (or alternate relay contact) is 9.78 feet (3m). Use #20 AWG wire or larger. You can wire a light for indication when Maintenance Mode is enabled. The 520MC has a dedicated contact (pins A9-A10). For the 1150+ trip unit, you must program relay A: PGM SET -> AUXRLY -> RELAY A -> set MM InUse to ENABLED (don't forget to press the save button twice).

An option for a 30mm padlockable switch with a blue knob uses these components:

  • E34VFBK6 – maintained two position knob, blue
  • 10250T53E – logic level contact block, 1NO
  • 10250TA38 – padlock hasp
    • This allows you to use a padlock to prevent other people from operating the switch
  • E34SP42 – OFF/ON legend plate

Nominal trip current of Maintenance Mode settings:

  • 2.5 x Rating Plug Amperes (520MC setting R5)
  • 4.0 x Rating Plug Amperes (520MC setting R4)
  • 6.0 x Rating Plug Amperes (520MC setting R3)
  • 8.0 x Rating Plug Amperes (520MC setting R2)
  • 10.0 x Rating Plug Amperes (520MC setting R1)

Time/Current Curves are available on the Magnum website.

If you want to upgrade a 520 series trip unit or an older 1150 trip unit to have ARMS capabilities, contact for guidance in selecting the appropriate kit.

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