[c-nsp] 7200 AC & DC

[Jon Lewis]

cisco.com has this to say about mixing AC and DC power supplies in the 
7206:

  Caution Do not mix power supplies in the Cisco 7206. In dual power supply
  router configurations, both power supplies must be of the same type (two
  AC-input power supplies or two DC-input power supplies).

I've seen posts from people saying that they have mixed AC & DC in 7206's 
with both types powered up at the same time...and nothing bad happening. 
Can anyone say why cisco cautions against doing this?  Is it just a 
grounding issue (possibly very different grounds provided by the AC power 
and rack's ground (used when using DC power)?

If it's just that, I would think that if the measured voltage between AC 
ground and rack ground is close to 0v, then this might be safe to do, 
especially as a short term situation while migrating from one type of 
power to the other.

----------------------------------------------------------------------
  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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