Density – Electrical 102

How dense are you?

So some of you might be wondering why I’m running 20A 240V electrical circuits to power my mining operation.  The reason is pretty simple.  The basic electrical equation is Power=Voltage x Amperage.  Or stated another way, Amperage = Power / Voltage.  The amount of power a device consumes is pretty much fixed based on it’s design.  We can tinker with certain parameters to make our miners consume less power, but this isn’t what I’m talking about right now though this formula will apply there as well.  What I’m talking about right now is real simple.  Saving money by increasing density.

I’ll try to explain based on what I have done here at the Cointainer.  I had to make a 450′ run from my main power panel that has the service coming from the street to the Cointainer.  My primary meter socket is a 400A peak capacity, 360A load continuous base.  From that meter, I have power that runs to my home and then also makes a run to my Cointainer.  At my Cointainer, I installed another meter base so I could track my mining energy usage and then hooked up a 200A panel.  This panel could be configured in a variety of voltage and amperage combinations for the circuits.  Typically, most US households have 15a 120V circuits installed unless it’s to drive a larger appliance.  This is fine for your typical energy consuming devices but when you are going to pull a lot of constant power, it will create problems.

The Math

First, it is recommended that you never run a circuit continuously at more than 80% of it’s rated load.  That means that the typical 15a 120V circuit should only do 12a of constant energy flow.  If you have a device that is pulling 1000W at 120V, it’s consuming 8.33A.  That means you’ve used more than 66% of your capacity on just that one device.  That same device, if it operated at 240V, would only consume 4.166A of energy.  Now, don’t get fooled.  This does NOT mean you will save money in electricity.  Your wattage consumption is still the same which means what you pay your energy provider will remain the same.  What changes is you can DOUBLE your density and as an added BONUS, your devices will run cooler!

The Solution

Now many of you might be asking, but how can I implement this?  My computers all plug into 120V circuits!  Did you know that “most” computer equipment can be run at 120V AND 240V?  Some of the cheaper stuff can’t, but most can!  You used to have to throw a switch on the back but now a days most stuff is AUTO SENSING!  All you need to do is look at the sticker on your device.  It will say power input and usually has a range.  If it includes or rather, goes up to 240V, you are good!

So what is my trick with providing power to my boxes?  I run 20A 240V circuits from the panel to NEMA 20-6R receptacles.  From there I connect 16A PDUs.  What’s a PDU?  PDU stands for Power Distribution Unit and they are commonly used on server equipment in server farms for the exact reasons I’ve listed above.  You will have to spend some money on PDUs and the particular C13 to C14 cables they will need but you can find them cheap on Ebay.  Notice how I picked a 16A PDU?  Do you know why?  16A = 80% of 20A.  This keeps me within optimum power draw on the circuits!  I can tell you though that it takes about 21A to trip the 20A breaker.  Don’t ask me how I know.  😀

Bonus Trick

Another neat trick I do is that the 20A 240 circuits end up terminating not only with the NEMA 20-6R receptacle, but I also put 2 double outlets on them.  Each outlet is wired to a separate hot for load balancing.  This gives me the ultimate flexibility with power delivery options at the plug.  It’s great for testing a new rig because I can throw the killawatt on a 120V circuit and measure what the new box does before I put it into production on the 240V side.  It’s also great for the smaller devices like network switches, stereos etc that don’t pull any juice and don’t need to be on the PDU or can’t be on it due to being limited to 120V.




Note the power input and output.  Note how on these power supplies, they can actually deliver more power at higher voltage, hence the higher amp draw!

2 thoughts on “Density – Electrical 102”

  • Great article. I am in the process of implementing two of these circuits for my three HP DL580 G7, two Dell R815 and two Supermicro Servers.

    The only addition that should be added to the article is that the power cable to connect the PDU to the NEMA 20-6R receptacle is a Nema L6-20P to C-19 cable. I didn’t know that and had ordered (to be returned) two Nema L6-20P wire-able plugs.

  • Breakers have 2 types of triggers – one magnetic for almost instant trigger of short circuit (100-1000a) and thermal trigger for overload.
    Short circuit triggers for normal household breakers (type B in Europe) at 3x nominal current (so >60A for 20A breaker).
    Thermal trigger time depends on the current. It can take for example 1 hour to trigger the breakers with 1.1x nominal current. (Also the times depends on the temperature of the breaker itself.)

    See the diagram hereL

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