I am tying to educate myself on the options I have for Data Centre power connectivity in our racks, for both UK and USA Data Centres. I am UK based so have a better understanding of the UK options, and have minimal experience with US Data Centres. I am confused by the US Equivalents, as there seems to be many different options. I know their domestic power is typically 110V, but they also seem to use higher in some circumstances. All My DC's are in NY, so I am interested primarily from their perspective, if there are many state differences, but also good to understand the differences incase we have a presense elsewhere.

I usually use PDUs from APC. I am trying to choose from the Rack PDU Selector

In the UK, I have typically used 230/240v 16A or 32A single Phase delivered to my Rack PDU via a Blue IEC 60309 32A P+N+E or 2P+E. This is fairly simple. It seems there is a 60A version of this as well, but my DC's don't support it.

Q1. Is P+N+E The same as 2P+E? I am assuming P is Pin or Pole, not Phase. Or is the 2P+E doing something different?

My racks are starting to need more power than a single phase can deliver, and this is where my knowledge starts to reach it's limits. The kit in the racks is still all single Phase 230V on IEC C13/14 or C19/20 connectors. There is just more of it, and each socket is drawing more.

As I understand it in the UK, 3 phase power for racks is usually a Red 63A 3P+N+E. Which is Three Phases (L1,L2,L3), Neutral and Earth. The Voltage Between Phases is ~400V (Hence the red Plug) and the Voltage Between N and any single Phase is ~230V. The Rack PDU's present three banks of outlets one for each Phase, L1,L2&L3. This gives a total of ~25KW

Now that's all well and Good for the UK. How does it work in the US? I can see they often use the NEMA connectors, and the L6-30P seems to be roughly equivalent to the Blue 309 2P+E 230V.

Q2. Does the Data Centre kit in the US still run on 230v, or is it 110V?

Q3. What is the USA Equivalent or similar of the UK 3P+N+E 63A feed Connector, that would give me that would give me the similar total Power in the rack of around 25KW?

Q4. Why is it 63A and not 64A? 64 seems to be the logical progression from 16-32-64. I'm a data network engineer, I like numbers that are 2^n.

Q5. Is it ok if a device with dual PSU is plugged into different phases? Would bad things happen if someone accidentally plugged one side into L1 and the other into L2?

Q5. What are the most common power connectors in the USA for different levels of Power delivery?


1 Answer 1


In the US:

  • A 120V plug has Line, Neutral and optionally Earth.

  • A 240V Single-phase plug has Line L1, Line L2 plus Earth, or Neutral (3-wire systems), or both Earth and Neutral (4-wire system). I recommend the L14-30 (4-wire) type for the most flexibility, though L6-30 (3-wire, with Earth) is ok.

  • A popular option for data centers is 208 3-phase, delivered as 3 legs of 120V to neutral. Pairs of legs can be used for 208V.

Here’s a link below showing the lineup of NEMA types: https://www.lockingpowercords.com/topic/13-nema-locking-chart.aspx

And a discussion of using 208 3-phase power for the data center: https://www.raritan.com/blog/detail/3-phase-pdu-208v-60a-50a-power-strips-rack-pdus

As for 120 or 240v compatibility of specific US IT gear, you need to check with the vendor. Generally they do use universal AC power supplies, but there may be exceptions. The gear itself will usually have the ‘kettle cord’ IEC plug, and will use a specific cord to adapt to the wall plug in use.

  • \$\begingroup\$ Thanks @hacktastical. What typically is the maximum current 3phase feed you can get on 208v? When they say 3phase 20 amps, are they talking 20A per phase, or in total? \$\endgroup\$
    – SlyOne
    Feb 17, 2020 at 19:04
  • \$\begingroup\$ Per phase, but beware - the computation is more complex than that when using phase-to-phase. See the blog piece linked in my answer. \$\endgroup\$ Feb 18, 2020 at 0:06

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