Exactly ... they are typically for redundancy/failover, not for extra power.  Larger servers with 3-4 power supplies do use 2-3 of them for total power load, with a failover.  Some servers with dual power supplies will actually do load balancing, but not to exceed the wattage of a single power supply - simply to reduce the load on any one unit.

Doesn't dual power supply equipment only require the power of one supply, so that if one fails, it will keep working normally?

Now if it's triple power supply, that could be the power of 2 of them, with the ability to only lose one.

But they both are 'live' by simple fact that are powered no? Doesn't that imply they are using some power?Maybe adding 20% of 1 power supply and 100% of the other is fair usage?

Again, I am no electrical engineer but rather an admin and this is slightly out of my scope...or learning process at least to say.

Do you think that the formula in the article is good approach to calculating AC power?

I also read at this article that power consumption might go up depending on # of disks and memory. Is this true?

...that disk drives require about 10 watts and each GB of memory requires about 12 watts...

Thanks guys!

With varied equipment you have, the easiest method to get the total wattage use would be to use a clamp on ammeter (preferrably with a peak hold) on each circuit feeding the room, adding all the amperage draws of all the circuits, multiple this by the voltage, giving the total wattage of the room, not an Engineer, but I would add approx 25% to that for expansion/ambient building temperature changes/peak usage times.

Thanks,

I am running it all through an APC SmartUPS 3000XL with 2 additional battery packs....would it be an accurate measurement if I just inserted the ammeter between the UPS and wall plug? ...sort of just clamped it on the 1 power cored powering the UPS.

Thanks a bunch!

I strongly suggest you leave any current measuring to qualified electricians/electrical engineers. Do not open any service panels since there is exposed wiring capable of providing lethal currents and voltages.

The safest way is to determine what configuration of your dual power supplies are running in is to find the manual online or contact the service representative. Dual supplies typically are configured to run with only one providing the power or both providing half the power each but never double.  The amount of power the "off' supply is probably less than 10%.

Get one of the meters from Megger.  It uses hall effect sensors to allow it to give you a reading while clamping all of the wires in the cable.

Agree with engr00 the power at a breaker panel can be dangerous, so get either an electrician or the building engineer to get your readings if your a candidate for the Darwin Awards. Using the info from the manuals will not give you the peak wattage used nor will it give you an accurate average usage of the server room , as a meter which can do both peak and average will. The room may or may not have more then one circuit for all plugs, lighting will also be on a separate circuit form the plugs.

Dell has an online tool for capacity planning,

This can work out power and cooling requirements for your estate.

p

Definitely a lot of free tools.  ESSA AND DCCP.

Optimizing Data Center Power Requirements

The Dell Energy Smart Solution Advisor and Data Center Capacity Planner help IT professionals plan and tune their compute and infrastructure equipment for maximum efficiency. Offering a wide range of configuration flexibility and environmental inputs, both tools can help right-size your IT environment. Energy Smart Solution Advisor (ESSA) Supported Products: Blade Servers: M1000e, C5000, M915, M910, M710, M710HD, M610X, M610, C5220 Rack Servers: R910, R815, R810, R715, R710, R610, R515, R510, R415, R410, R310, R210 II, C6145, C6145 1MB, C6105 4MB, C6105, C6100 4MB, C6100, C2100, C1100 Tower Servers: T710, T610, T410, T310, T110, T110 II Storage: MD3220i, MD3220, MD3200i, MD3200, MD1220, MD1200 Rack Enclosures: PE4820, PE4220, PE2420 Start ESSA Dell Data Center Capacity Planner (DCCP)1 For all other Dell Servers, Networking, and Storage DCCP Tutorial Start the DCCP 3.04 web version

I am going to be receiving a pe2900 and wanted to find out what ampage it produces I have a 20 amp supply will it be ok to run on this supply? 

I'd love this to be possible but I am not aware of any physics that might allow it.   The magnetic fields of the live and neutral conductors mostly cancel, it does not matter whether you use AC coupled coil or a Hall sensor, you are still measuring, at best, a mostly canceled field depending on how close the conductors are.  You might get some reading depending on the rotational position against the alignment of the 2 conductor centres axis but it will be 80-100% wrong.

Hall sensors are to allow the measurement of DC current using the magnetic field.

Correct! If you have two SM power supplies, one acts as a redundant power source in case any one of them fails. which means the apparent power is shared between the two SMPSs .