[c-nsp] Power Supply 2 ouput has dropped

[Justin M. Streiner]

On Sat, 5 Jan 2013, Farooq Razzaque wrote:

> As you can see from the errors that it is showing 'AC low' (sh 
> environment switch 1 status power-supply 2) when the power is dropped to 
> 26721.20W and after sometime the power is adjusting back to desired 
> Watts (5771.64W) and showing 'AC High'.
>
> I m getting these errors very frequently with the time differene of seconds.
>
> As per your below comments, you mean to say that one input of power 
> supply 2 is being affected when the below error (Power supply 2 input 
> has changed. Power capacity adjusted to 2671.20W) is generated and when 
> this input gets the desired power then the system shows the messages 
> (Power supply 2 input has changed. Power capacity adjusted to 
> 5771.64W)..... Am i write..

There are three possibilities that I see:

1. A software bug could cause the error condition you mentioned.  I 
haven't looked through Cisco's bug search tool to find a matching bug, 
but it is possible.

2. The power supply is malfunctioning and needs to be replaced.

3. There is an electrical problem that is affecting one of the circuits 
that is feeding power to your switch.

If you have a spare power supply, try replacing the power supply that is 
reporting the errors, since that would be the least impact to your users. 
If the errors go away, you know you have a bad power supply.  If you have 
a support contract with Cisco that allows for hardware replacement, you 
can open a case with the TAC and have them send you a replacement power 
supply.

If Cisco doesn't feel the power supply itself is bad, then a software bug 
could be the culprit.  The TAC could recommend a new IOS version if there 
is a bug, and the bug has been fixed.

> "If so, it's also possible, but probably less likely that you lost one 
> of the two  hot legs on the affected input"
>
> Can you please re-explain the below as i could not understand .

A "leg" is a conductor (wire, etc) that carries electrical current.  In 
the United States and Canada, a 3-wire circuit capable of carrying the 208 
or 240 volts needed to energize a 6,000 watt AC power supply would have 
two legs, and a ground connection.

I made the statement above assuming that you are located in the the United 
States or Canada.  If you are in another country, their power delivery 
could operate differently (different frequency, voltages for 'end user' 
equipment, maximum allowed current draw, how and where systems are 
grounded (or earthed) etc), and my original statement might not apply.
In any event, you would be best advised to refer any electrical testing to 
a qualified electrician, for safety reasons.

> What does hot legs means. Is it the power cords that plugs into the two 
> input connections of power supply.  Do we need  to turn off the power 
> supply 2 and take out the two power cords from the power supply for the 
> below testing.

See above for my definition of a 'leg'.  You would need to unplug the 
power cords to do this testing.  The purpose of the testing would be to 
verify that both of the circuits that feeding the inputs on the power 
supply are providing the correct voltage on each leg.  If they are not, 
your power supply will not be able to operate at its maximum capacity.

> "If you have a voltage tester (or an electrician who has one) you can 
> test if you're getting ~120V from each of the hot legs to ground, and 
> ~208/240V from leg to leg.  If you are, and you're testing from the 
> inlet at the end of the cord that plugs into the  power supply, then the 
> circuit and cord are good, and you'll likely need  to replace the power 
> supply."
>
> Also please can you let me know what does (It turned out that one input 
> on the power  supply had gone bad) means ...

In the case I mentioned in my original post (see below), I had a 6000 watt 
power supply with a configuration similar to yours.  I tested both of the 
circuits that provided power to the unit, and they were operating 
correctly.  I then replaced the power supply with another one that I had 
on hand, and the problem went away, so in my case, the power supply was 
bad.

> I've seen this before, with a 6000 watt  AC power supply in a 6509.  It 
> turned out that one input on the power  supply had gone bad.
>
> Can we check with the command that which input out of the 2 input of 
>power supply is having issue ..

I don't think any of the CLI commands will tell you which input is having 
the problem, but the lights on the front of the power supply will.  If 
an INPUT light is brightly lit, it should be receiving power at the right 
voltage.  If the light is dimly lit, it is receiving less power than is 
needed.

jms