Replacing an M320 Fuse
 | Warning: You must power off the router before removing or installing a fuse. |
To replace a fuse, you remove the power supply in slot PEM0—while the router is powered on—to determine which fuse has blown. Before you remove the fuse, you must power off the router, then remove the power supply in slot PEM1 to access the fuse.
To replace a fuse (see Figure 1):
- Attach an electrostatic discharge (ESD) grounding strap to your bare wrist, and connect the strap to one of the ESD points on the chassis. For more information about ESD, see Preventing Electrostatic Discharge Damage to an M Series, MX Series, or T Series Router.
- Power off and remove the power supply in slot PEM0. For complete instructions, see Replacing an M320 AC Power Supply or Replacing an M320 DC Power Supply.
Caution: Consider the following before you remove a power supply:
- An AC-powered router can continue to provide power for all router hardware configurations with three operating power supplies. If removing the power supply from slot PEM0 leaves only two power supplies in the router, you must first ensure that the router does not consume more than 2500 W. If the router does not consume more than 2500 W, you can safely operate the router with a total of two AC power supplies. To calculate the power consumption for various hardware configurations, see M320 Power Requirements.
- If you remove a DC power supply from slot PEM0, slot PEM2 must contain an operating DC power supply in
order to keep the router operating.
For more information about power supply redundancy, see M320 AC Power Supply and M320 DC Power Supply.
- Determine which fuse has blown. The yellow LED under the fuse lights and the indicator bulb becomes visible through the clear cover on the fuse.
- Power off the router as described in Powering Off the M320 Router.
- Remove the power supply in slot PEM1. For complete instructions, see Replacing an M320 AC Power Supply or Replacing an M320 DC Power Supply.
- Grasp the blown fuse by the edges and rock it up
and down in its slot until it disconnects. If the cover slips off
the fuse, snap the cover back into place and begin again.
Note: We recommend that you use an insulated fuse removal tool to remove fuses.
- Remove the appropriate fuse from the selection of spare fuses labeled SPARE in Figure 1. (The labels shown in the figure do not appear on the actual fuses—the clear cover on every fuse reads BUSS GMT-X—and might not match the labels on the midplane. Ignore the labels on the midplane.) Verify that the spare has the same rating and color coding as the fuse it is replacing, as specified in M320 Fuse Specifications. To see the indicator bulb and printed rating, look at the fuse from the side.
- Orient the replacement fuse over the slot so that the text on the fuse cover (BUSS GMT-X) reads from bottom to top.
- Press the new fuse into the slot.
- Reinstall the power supply into slot PEM1. For complete instructions, see Installing an M320 AC Power Supply or Installing an M320 DC Power Supply.
- Power on the router as described in Powering On the M320 Router.
- Verify that the yellow LED under the replacement fuse is no longer lit.
- Reinstall the power supply into slot PEM0 and power it on. For complete instructions, see Installing an M320 AC Power Supply or Installing an M320 DC Power Supply.
- Order new fuses from an electrical supply house to replace the spare fuses. The Cooper Bussman product number for each fuse is GMT-X, where X is the amperage rating. For example, product number GMT-15 is a 15-A fuse, required for an FPC.
Figure 1: Fuses in the Midplane
