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Where can I find information on the AMS (Alternate Maintenance Settings) switch, including the purpose, installation, testing, and troubleshooting?

What is the function of the AMS switch, and how should it be installed and tested, and how can you troubleshoot it if it doesn't work properly

Product Line:
Masterpact and Powerpact circuit breakers with advanced Micrologic trip units

The AMS switch temporarily eliminates the short-time delay setting of the circuit breaker and provides a circuit protection system with two modes: a normal mode and a maintenance mode (in which potential arc flash energy is reduced).
In normal mode, the upstream circuit breaker acts in accordance with the settings provided in the electronic trip unit that provides selective coordination of the electrical distribution system.
In maintenance mode, the upstream circuit breaker disregards the preset time-delay and operates to clear the fault condition with no intentional short-time delay. In this mode, the upstream circuit breaker responds as a ZSI circuit breaker that fails to receive a restraint signal, as described previously. By responding quickly to an arcing fault, incident energy is reduced. However, selective coordination is not preserved when the AMS is in maintenance mode.

The AMS switch is designed to be factory installed in Switchboard and Switchgear. It can be installed in the field but it requires a breaker with an A, P, or H trip unit and purchase of the following:
  • Restraint Interface Module (RIM), catalog number S48890 (120 Vac/24 Vdc) or S48895 (240 Vac/24 Vdc).
  • Kit 84957 (label and components for required switches; includes the following
    -Instruction Bulletin NHA40218
    -AMS nameplate (80298-173-01)
    -AMS dange label (NHA41456)
    -C&KJ AMS push button (KM3301RR05Q) (button used for testing)
  • Order the following parts separately:
    -RIM (S48890)
    -Switch with blue indicator light (9001K11J38LLL)
    -Switch contact block (9001KA3)
    -Padlock attachment (9001K7)
    -Remote Pilot Light (the bulletin shows 9001KP1L9 or 9001KP35L9 but they use whatever they want)
See attachment for installation instructions. 

See attached bulletin for testing instructions.

Ensure wiring is correct and all components are functioning properly.

Related documentation:
• Reducing Fault Stress with Zone-Selective Interlocking (Document No. 0600DB0001)
• Guide to Power System Selective Coordination 600 V and Below  (Document No. 0100DB0603)
• Alternate Maintenance Setting (AMS) Switch Handout (Document No. 8998HO1001)
• Arc Flash Reduction Systems—Are They Always a Good Idea? (Document No. 0600DB0901)
You can download these documents from our website at, or by searching for the document in a search engine such as Google.
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