POE port_fault

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Please advise if this is a software bug, but our x440-24p switch produced an error: POE port_fault and cause our access points to fail. To fix the issue the PoE had to be disable and re-enabled on the entire switch. However, the VoIP phones were no affected.
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Carol Oughton

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Posted 3 years ago

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Ronald Dvorak, Embassador

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(Edited)
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David Coglianese, Embassador

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Reset inline-power on the offending port did not resolve the issue? 90% of the POE faults I have seen have been drop related. The exception being pse uart errors which have also resulted in RMAs thus far. 
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Carol Oughton

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We did have a brown-out which may have caused the issue.
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Patrick Voss, Employee

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Do these brown outs happen often? Are the switches plugged into a UPS? I have seen the exact scenario in the past. Unfortunately this happens to prevent further issues with the switch.
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Carol Oughton

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Brown outs don't happen often, this was unusual & it knocked out power in a development, so something outside must have happened.  Yes, the switch is on a UPS, as all of our switches are.

Thanks again everyone for your assistance and pointing to great information.

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David Coglianese, Embassador

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FYI
We have found UPSs do not always prevent power issues, we have seen older UPSs or units with older batteries take too long to transfer to battery and as a result the switch can reboot or enter an odd state before the transfer takes place.
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Brandon Clay, Escalation Support Engineer

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To avoid what David is describing, you want a double-conversion UPS.

This type of UPS will constantly power the load (in this case the switch) from the battery, to prevent this delay between switching to the battery.
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Patrick Voss, Employee

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How many of the ports are being used for POE? All the POE classes have a range and if there is a spike in power needed this could cause some of the ports to go into a fault state. As David mentioned, have you tried to reset inline-power on the port that faulted? This should work.
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Carol Oughton

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On this 24 port switch, only 6 ports are enabled with PoE and only the 4 ports for access points went down.  Disabling and re-enabling inline-power did restore the ports.

Thanks everyone for your assistance.

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Brandon Clay, Escalation Support Engineer

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If this only occurred on the ports connected to APs, and it occurred following a brownout, it is possible that the brownout (or recovery from the brownout) on AC power cabling that runs near the data cables feeding the APs caused a current to be induced on the ethernet cabling leading to the APs, backfeeding the ports on the switch.

Was the fault condition 'UV/OV Fault'? If so, this would indicate that the switch put the port into the faulted state for either an under-voltage or over-voltage event.
(Edited)