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Cisco 12000 Series Routers

Field Notice: FN - 12830 - Cisco 12000 Power Supply Isolation Diode Shorted (Safety Hazard) - RMA Required

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Revised April 4, 2006

July 28, 2000

NOTICE:

THIS FIELD NOTICE IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTY OF MERCHANTABILITY. YOUR USE OF THE INFORMATION ON THE FIELD NOTICE OR MATERIALS LINKED FROM THE FIELD NOTICE IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS FIELD NOTICE AT ANY TIME.

Products Affected 
Product Top Assembly Printed Circuit Assembly Comments HW Rev.
Part Number Rev. Part Number Rev.
PWR-GSR12-DC/2   34-0795-01   -C0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -C0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -C0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -D0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -D0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -D0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -D0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -E0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -E0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -E0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -E0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -F0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -F0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -F0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -F0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -G0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -G0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -G0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -G0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -G1   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -G1   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -G1   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -G1   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -C0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR8-DC   34-0821-01   -C0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -C0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -D0   73-2146-06   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -D0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -D0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -D0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -D0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -D1   73-2146-06   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -D1   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -D1   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -D1   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -D1   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -A0   73-2146-06   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -A0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -A0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -A0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -A0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -B0   73-2146-06   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -B0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -B0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -B0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -B0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -C0   73-2146-06   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -C0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -C0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -C0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -C0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -D0   73-2146-06   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -D0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -D0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -D0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -D0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -D1   73-2146-06   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -D1   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -D1   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -D1   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC/2   34-0821-01   -D1   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR16-DC   34-0935-01   -A0       PWRSPLY,DC,PEM,2400W   N/A  
PWR-GSR16-DC=   34-0935-01   -A0       PWRSPLY,DC,PEM,2400W   N/A  
PWR-GSR12-DC   34-0795-01   -A0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -A0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -B0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -B0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -C0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -C0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -D0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -D0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -E0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -E0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -F0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -F0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -G0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -G0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -G1   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC   34-0795-01   -G1   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -A0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -A0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -A0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR8-DC   34-0821-01   -C0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR12-DC/2   34-0795-01   -A0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -B0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -B0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -B0   73-2146-07   -A0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR12-DC/2   34-0795-01   -B0   73-2146-07   -B0   PWRSPLY,3400W DC POWER MODULE   N/A  
PWR-GSR8-DC   34-0821-01   -A0   73-2146-06   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -A0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -A0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -A0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -A0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -B0   73-2146-06   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -B0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -B0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -B0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -B0   73-2146-07   -B0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -C0   73-2146-06   -A0   PWRSPLY,1700W,DC,MFR   N/A  
PWR-GSR8-DC   34-0821-01   -C0   73-2146-07   -A0   PWRSPLY,1700W,DC,MFR   N/A  

Problem Description 

A component failure (an isolation diode) may have occurred in some Cisco 12000 DC power entry modules (PEMs) during a manufacturing test, which was not subsequently detected and fixed prior to shipment. In a Cisco 12000 chassis using redundant DC PEMs, one of which has a bad isolation diode, it is possible for a safety hazard to exist under certain conditions. The safety hazard can exist in areas of the building that are not in close physical proximity to the Cisco 12000 chassis. The component failure is not traffic affecting, even for systems with non-redundant DC PEMs. The component failure does not affect redundancy or normal chassis operation.

The type of safety hazard that can exist is an energy hazard, which is defined as a situation in which more than 240 VA (volt-amperes) are available between two components that can be short-circuited.

Cisco estimates that less than 10 percent of PEMs are affected by this problem.

WARNING: Failure to follow the instructions presented here can lead to a burn hazard and personal injury.

Background

The diagram below (Figure 1) shows how a Cisco 12000 chassis is typically connected to the -48VDC battery feed of a data center or central office. Both A and B battery feeds are shown. The A and B battery feed circuit breakers isolate all equipment from each battery feed. The branch circuit breakers typically disconnect individual equipment or clusters of equipment.

Battery Feed

Figure 1: Typical Connection of Cisco 12000 Series Router to -48VDC Battery

The diagram below (Figure 2) shows how the PEMs on the Cisco 12000 feed power into the chassis itself. The PEM circuit breaker disconnects incoming battery feed power from the chassis. The auxiliary power supply provides power to the MBUS controller which, in turn, controls the power supply LED indicators (the 12016 does not have an MBUS controller). The isolation diode prevents reverse current flow and allows for redundant PEM operation.

Figure 2: Cisco 12000 Series PEM to Backplane Power Bus Interconnection

The diagram below depicts a scenario in which, for maintenance reasons, one of the PEMs has been disconnected from the battery feed while the other PEM remains connected to its battery feed. The connected PEM provides power to the chassis backplane power bus. In the event of an external short circuit across the disconnected PEM terminal lugs (indicated here with a wrench), power does not flow through this external circuit due to the blocking action of the isolation diode.

Figure 3: Function of the Isolation Diode on a Cisco 12000 Series PEM

Problem Symptoms

The diagram below (Figure 4) depicts a scenario in which a component failure (shorted isolation diode) permits current flow externally to a PEM that has been disconnected from its battery feed (through either a cable disconnection or a circuit breaker being switched off), but which is shorted by a conductive device (such as a wrench). Current to this external circuit comes from the backplane through the disconnected PEM. The backplane is receiving power from the PEM that is still connected to its battery feed. Note that in order for current to flow externally to the PEM, that PEM circuit breaker must be in the ON position. This situation may occur if maintenance personnel have switched the battery A or B feed main disconnect circuit breaker to OFF, have turned the battery feed branch circuit breaker to OFF, or have disconnected battery plant cabling without turning the PEM circuit breaker off. Note that such a short circuit could occur anywhere on that particular battery feed branch circuit, even if the equipment being worked on is not in close physical proximity to the Cisco 12000 chassis.

Figure 4: Failure of an Isolation Diode on a Cisco 12000 Series PEM

Workaround/Solution 

The following diagram (Figure 5) shows what happens if the circuit breaker on a PEM with a shorted isolation diode is switched to OFF while still installed in the Cisco 12000 chassis. Current is able to flow through the PEM auxiliary power supply from the backplane power bus, which causes the "Input OK" or "Power OK" LED to be ON on the disconnected PEM. On a PEM in which the isolation diode has not been shorted, the "Input OK" or "Power OK" LED would be OFF in this situation. Therefore, turning the PEM circuit breaker OFF can be used as a test to detect if the PEM has a shorted isolation diode.

Figure 5: Failure of an Isolation Diode on a Cisco 12000 Series PEM with PEM Circuit Breaker Switched to "OFF" Position

Cisco recommends the following procedure to test for a DC PEM with a shorted isolation diode. To use this procedure, you should be familiar with Cisco or equivalent router hardware and cabling, electronic circuitry and wiring practices, and preferably have experience as an electronic or electromechanical technician.

  1. Insure that the safety covers are in place (covering the input terminals) prior to starting this procedure.

  2. This procedure applies only to Cisco 12000 chassis equipped with redundant DC power entry modules (PEMs). Cisco 12000 chassis equipped with either AC power supplies or a single DC PEM are not affected by this Field Notice. (Note, however, that whenever a Cisco 12000 chassis is upgraded from a single DC PEM to a redundant DC PEM configuration, this procedure should be performed immediately to detect the presence of a shorted isolation diode in either the original or newly installed PEM.)

  3. In order to perform this procedure, both DC PEMs must be connected to external, energized DC power and both PEM circuit breakers must be ON. The external DC power can come from either redundant (for example, "A" and "B") battery feeds or from a single feed. Since this procedure involves switching OFF each of the PEMs individually, the technician must be satisfied that DC power is being supplied to both DC PEMs from an external source prior to performing the procedure.

  4. Before performing this procedure, check that the "Input OK" or "Power OK" LEDs on both PEMs are ON and that all other LEDs on both PEMs are OFF. If the LEDs on the PEMs show any other combination, this procedure should not be performed.

  5. Once the above conditions are met, turn the circuit breaker on one PEM OFF and observe the LED indications on that PEM. Note that on 12008 and 12012 chassis it may take 1-2 seconds for the LED to turn OFF, and on the 12016 chassis it may take up to 5 seconds to turn OFF. If the "Input OK" or "Power OK" LED is OFF, it indicates that the isolation diode is not shorted and is working properly. If the "Input OK" or "Power OK" LED stays ON, it indicates that that PEM has a shorted isolation diode, and that the PEM should be replaced. Once this determination has been made, the circuit breaker on that PEM should be turned ON, the "Input OK" or "Power OK" LED should come ON, and the procedure repeated on the other PEM..

If one or both PEMs have shorted isolation diodes, Cisco recommends a fix-on-fail strategy for this problem.

As of approximately March 1, 2002, new products that were manufactured under Engineering Change Order (ECO) E006073 are guaranteed to be free of this problem. Refer to How to Identify Hardware Levels below for instructions on how to view the version of in-service product. Service Logistics has known-good inventory at this time. The standard RMA process and delivery times are in effect.

Once replacement hardware is available on-site:

  1. Turn the battery feed branch circuit breaker OFF (or otherwise de-energize the cables providing DC power to the affected PEM).

  2. Turn the circuit breaker on the affected PEM OFF.

  3. Check that no voltage is present on the PEM terminal lugs with a voltmeter as shown below (Figure 6). Any voltage reading below 2 VDC is acceptable.

    4. Figure 6: Checking Input Voltage on a Cisco 12000 Series PEM with PEM Circuit Breaker and Battery Feed Branch Circuit Breaker Both Switched to "OFF" Position

  4. If no voltage is present on the terminal lugs, remove the safety covers, disconnect the DC power cables by disconnecting -48 first, +48 second, and GND last. Replace the PEM. Re-attach the power cables connecting GND first, +48 second and -48 last. Replace the safety covers, turn the battery feed branch circuit breaker ON (or otherwise energize the cables providing DC power to the affected PEM), and turn the PEM circuit breaker ON.

Note: The Cisco 12016 chassis can have up to four DC PEMs. The four PEMs are divided between two "zones", each zone connecting to "A" and "B" battery plants via two PEMs as shown in the following diagram (Figure 7):

Figure 7: Schematic Representation of Battery Plant Connections for Cisco 12016 Chassis with Four (4) DC PEMs

When performing the above procedure on a Cisco 12016 chassis, treat the "A" and "B" PEM pair in each zone separately. Test the "A" PEM in zone 1 first, then test the "B" PEM in zone 1, then test the "A" PEM in zone 2, then test the "B" PEM in zone 2.

Please note that silkscreen label for the power source input LED can either be "Input OK" or "Power OK" depending on the particular model of PEM. The following table describes what silkscreen label is present for the PEMs affected by this issue:

Product ID (PID) Top Level Assembly Number (TAN) Silkscreen Present
PWR-GSR8-DC
34-0795-01
"Input OK"
PWR-GSR8-DC
34-0821-01
"Input OK"
PWR-GSR12-DC
34-0935-01
"Power OK"
PWR-GSR12-DC
34-0795-01
"Input OK"
PWR-GSR12-DC/2
34-0795-01
"Input OK"
PWR-GSR16-DC
34-0935-01
"Power OK"

How To Identify Hardware Levels

 None of the Cisco 12000 power supplies shipped after March 1, 2002 from Manufacturing or RMA Spare Depots have this problem. Cisco has purged the effected power supplies from our RMA stock.

Other Considerations 

This section explains some of the different ways in which an safety energy hazard can manifest itself. The diagram below (Figure 8) shows a facility with two Cisco 12000 routers (GSR A and GSR B), along with three other pieces of equipment (C, D and E). Also shown in the diagram are independent battery feeds (A and B), along with main feed and branch circuit breakers. Also shown within the GSR equipment symbols are the PEM circuit breakers. In this discussion we assume that both GSR routers have shorted isolation diodes on the "A" PEM.

Figure 8: Schematic Representation of Example Battery Plant Connections for Two (2) Cisco 12000 Series Chassis with Three (3) Other Pieces of Equipment

The next diagram (Figure 9) shows what happens when a technician shuts off the main circuit breaker for the A battery plant. The technician may make the assumption that the A power circuits downstream from the main A breaker are de-energized, when in fact they are energized from the B battery plant via the two Cisco 12000 routers. Power circuits that remain energized, but which a technician may believe are de-energized, are shown in red. Note that a technician may be performing power system maintenance on equipment D and that equipment D may not be in close physical proximity to either of the Cisco 12000 routers. Note also that equipment E is not even connected to the B battery plant, yet it remains energized in this scenario.

Figure 9: Schematic Representation of Example Battery Plant Connections for Two (2) Cisco 12000 Series Chassis with Three (3) Other Pieces of Equipment After Disconnect of Battery "A" Main Feed - Energized Sections of the Circuit are Shown in RED

In the diagram above (Figure 9), note that the Cisco 12012 and 12016 routers with shorted isolation diodes allow up to 60A of current to flow from the B battery side into the A side of the circuit shown in red. This is because the Cisco 12012 and 12016 router circuit breakers are rated at 60A. Cisco 12008 routers allow up to 40A. In the diagram above, if the GSRs are 12016s, the total available current in the circuit shown in red would be 120A. Total available power would be 5760VA. The more Cisco 12000 routers connected into the circuit with shorted isolation diodes, the greater the available current in the presumed de-energized circuit.

Turning off branch distribution circuit breakers can also lead to a technician believing a power circuit is de-energized when it is not. This is shown in the following diagram (Figure 10). In this case, a technician may believe the power circuits downstream from the branch circuit breakers are de-energized when in fact they remain energized as shown in red.

Figure 10: Schematic Representation of Example Battery Plant Connections for Two (2) Cisco 12000 Series Chassis with Three (3) Other Pieces of Equipment After Switching Branch Circuit Disconnects to "OFF" Position - Energized Sections of the Circuit are Shown in RED

Whenever maintenance is being performed on a power distribution system that has one or more Cisco 12000 routers attached, Cisco recommends explicitly checking the power circuit with a voltmeter prior to performing any maintenance until such time as all of the Cisco 12000 PEMs on the circuit have been tested and repaired. The voltage reading should be below 2VDC before maintenance is performed on the circuit.

WARNING: Failure to follow the instructions presented here can lead to a burn hazard and personal injury.

For More Information

 If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) at (800) 553-24HR, (408) 526-7209, or send e-mail to tac@cisco.com.