This article describes the root cause behind the ACX box alarm PEM 0 Not OK and the steps to follow before concluding that this is a hardware issue.

The ACX1100, ACX2100, ACX2200 and ACX5448 platforms generate a "PEM 0 Not OK" chassis alarm and log the following messages:

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user@ACX> show chassis alarms 
1 alarms currently active
Alarm time               Class  Description
2015-07-24 09:46:13 UTC  Major  PEM 0 Not OK


Jul 24 09:46:13  send: red alarm set, device PEM 0, reason PEM 0 Not OK
Jul 24 09:49:10 CHASSISD_SNMP_TRAP6: SNMP trap generated: Power Supply failed (jnxContentsContainerIndex 2, jnxContentsL1Index 1, jnxContentsL2Index 0, jnxContentsL3Index 0, jnxContentsDescr PEM 0, jnxOperatingState/Temp 6)
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The "PEM 0 Not OK" alarm on the ACX1100, ACX2100, ACX2200, and ACX5448 platforms is triggered when the router detects a loss of power redundancy or an unstable power feed. These platforms are designed with two power inputs (Input 1 and Input 2).

The alarm is generated under the following conditions:
• One of the power inputs is not connected to a valid power source.
• Both inputs are connected, but one input is not receiving power due to an upstream issue.
• A connected power feed is unstable, intermittent, or not providing a steady voltage.

This behavior is intentional and alerts you that the router is operating on a single power source, which eliminates power redundancy.

Recommended Actions when the PEM 0 Not OK alarm appears:

1. Verify both power inputs are connected to active and stable power sources.
2. Inspect power cables for signs of wear, looseness, or physical damage.
3. Ensure that power feeds are firmly seated in their respective inputs.
4. Confirm that upstream power circuits (PSU, PDU, breakers) are supplying clean, steady power.

If all inputs and power sources appear normal but the alarm persists, open a case with JTAC. 
JTAC will assist in determining whether the issue is caused by an internal power module fault and whether an RMA is required.

Added support for ACX5448