Dell PowerEdge Server Power Requirements

Question: I have several Dell PE2950 Servers and several 20A Powerstrips, my facility provides 120VAC.  How many PE2950′s can I plug into the 20A Powerstrip without tripping the breaker?

Answer: The Dell PE2950 has a manufacturer’s rating of 750W, however this rating can vary by +/- 20% depending upon the operating efficiency of the primary power supply.  The operating efficiency is mainly affected by temperature but there are a host of other things that can affect the operation as well.

Start by calculating an operational range for a single server:

750W + 20% = 900W
750W – 20% = 600W

The next step is to determine the Amperage: W/VAC=A

900W/120VAC = 7.5A (max)
750W/120VAC = 6.25A (spec)
600W/120VAC = 5A (min)

The operating load of the Powerstrips must be determined.  This is where the 20% variation in operating efficiency is important.  If you load the Powerstrips over 80% you can run the risk of overloading the breaker under a maximum load.

20A * 80% = 16A
20A * 85% = 17A
20A * 90% = 18A

Using these guidelines you can easily determine how many PE2950′s you can plug into your 20A Powerstrips:

7.5A * 2 = 15A (max load)
6.25A * 2 = 12.5A (spec)
5A * 3 = 15A (min load)

Written by will

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4 Responses to “Dell PowerEdge Server Power Requirements”

  1. Mark Says:

    While this is an older article, it presents a dangerous view of power scaling for anyone to actually follow.

    First, all power strip input circuits must be derated to 80% by UL/NEC standards, limiting a 20A / 120V circuit to delivering 16A of available power. Your load percentage should be taken from this 16A, not the full line amperage. The 80% load per power strip would be 12.8A not 16A.

    Second, power supply nameplate ratings are a peak max draw in wattage. If a 750W power supply were suddenly to draw 900W the power supply would likely be shorted and about to catch fire. Power supplies are also inefficient in transforming AC to DC power and this power loss is known as the power factor. The actual max output wattage of a power supply is the name plate (here 750W) x the power factor, often .9 (or 90%) for modern power supplies. A 750W name plate power supply can really supply 625W at peak load. True usage of the server of the power supply is usually somewhere on the order of 75% at peak usage and as low as 15% at idle. An average configuration for a PE2950 would draw somewhere on the order of 425W at max load, or 3.5A @ 120V.

  2. will Says:

    I don’t agree with you on derating devices like that. If you could provide some additional information on this I would be very interested in reading it.

    True power consumption by a server can really only be calculated with metered powerstrips or other similar equipment. These metrics should be recorded over a given period of time to determine what the exact load is. Any fluctuation in the ambient room temperature will also effect these metrics and should be recorded and taken into account as well. Without knowing this definative data, we’re just making a good estimate of power consumption.

    Note: Metered powerstrips are much more expensive than a basic powerstrip.

  3. Matt Says:

    I also disagree with Mark’s comment. NEC guidelines do derate the amperage of a circuit to 80% for devices that have continuous power draw (like computers). There is no reason to derate a second time (to 12.8A on a 16A derated 20A circuit in Mark’s example). You’ll be able to continuously pull 16A on a 20A circuit.

    Nearly all modern servers, routers, and switching gear (including the Dell PowerEdge’s) have Power Factor Corrected power supplies that have PF’s of 1.0. (Normal PCs with capacitor-input type supplies have PF’s of ~0.7 or so.) As for the power draw of the PowerEdge 2950 servers, I agree wholeheartedly with Will. A lot depends on the specs and components in the server (CPU(s), disk drives, cards, etc.). We’ve found that our moderate to heavy configured PE2950 servers draw b/w 2.5 and 3.0 amps at 120V, or b/w 300Watts and 360Watts…well under the rated 700Watt power supply(ies). Realistically I’d say you could easily place 5 or 6 servers on that 20A (16A) circuit. Make sure you do not have the servers auto-power up after a power failure (in BIOS), otherwise the inrush amperage would likely trip the circuit breaker.

    Metered powerstrips, while more expensive, are often worth the cost to take the guesswork out of the power configurations.

  4. John Culbreath Says:

    If the Dell PowerEdge servers have a power requirement of 750w and they are uitilizing both of there power supplies, then when calculating heat disapation and computing the BTU cooling requirement, do I calculate only the required 750w or must I consider that both power supplies are exhausting the 750w each?

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