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Powering a mainframe

The last few days have been eventful. I was contacted by the datacenter that the mainframe's cage is now ready for moving in, and the power has been made available. Very exciting! I grabbed my home-made power cables (more on that later) and my best screwdrivers and set off to the datacenter.

The view next to the datacenter
The datacenter staff, not needing a forklift in their day-to-day, had managed to solicit the services of a forklift, the associated operator, and some very handy folks to help navigate the mainframe from the storage space to its final location.

After some intense period of fighting the inclination of the road between the storage facility and the cage (and a door that was a bit too small) it was finally in place. Incidentally we were forced to trust the wheels on this pretty rough floor. I did not expect it to roll that well on raw concrete, I was pleasantly surprised. This thing is a tank!

Finally in place!
Now, everybody wanted to see if it was working. My machine did not come with a power cable so I had to source one myself. The various guides did hint towards how the phases are connected to various Bulk Power Regulators (BPR) but nothing was very definite. I tried to do my best to construct a power cable, choosing to attach a classical CEE 230V16A connector at the end.

The pretty important power cable
The connector is a GT06PCM32-ARS-30(29R) with the following pin/phase mapping:
  • A = Phase 1
  • B = Phase 2
  • C = Phase 3
  • G = GND
Now, I assumed that given there is no neutral it has to be a delta system where one BPR is powered by the voltage between e.g. A-B, the next one B-C, and the final one C-A. That would make the "balanced power" configuration that comes with all BPRs make sense from a three phase perspective. One thing to note about the phase-delta connection is that in a normal three-phase system in Europe you have 400V between the phases and 230V between phase and neutral. Sadly this was a neutral-less system and we do not have 400V, so what to do?

Turns out that in the US the phase-neutral voltage is 120V as commonly known, which by luck is 240V phase-phase. My hypothesis was that we should be able to attach our 230V neutral to Phase X and phase to Phase X+1. The resulting delta would look like a two phase delta from the US.

Looking at the power receptacle and physical planning guides confirmed that the voltage is at least sane 

Voltage rating on the power receptacle
At least I was pretty certain that if something did not hold, the mainframe should probably not turn into a cloud of magic smoke.

I confirmed the wiring scheme with some friends I have that do the power installations at Dreamhack, and even had them do the wiring as they have all the qualifications needed to do so safely and legally.

Did it work? Yes! It absolutely did! The uncertainty was which phase-pair powered the lowest BPR? I guessed A-B and, thankfully, that appears to have been correct!

The mainframe is alive!
That was a big relief. A lot of things could had happened making it so that the mainframe would not power on. Thankfully it seems the stars aligned in this case. Given that the seller of this particular mainframe was not equipped to power it on this had been a big concern of mine. Very happy to have that behind me.

There was one final thing to do, to anchor the mainframe to ensure it does not escape or fall over somebody. It does weigh a steady 700 kg after all. We found a wrench that was a bit oversized but did the job well :-).

Sam with a way too big wrench
What's next? The datacenter still needs to install some shelves for my router and all storage gear, that will likely happen in August. Until then I would love to play a bit with the Support Element and HMC, luckily the SEs are laptops and can be removed.

A Support Element from the mainframe joining me at home
As I'm writing this a computer next to me is taking a backup of the harddrive in one of the SEs, and I will use that image to do some experimentation and playing with it to see how it works.

As always, thanks for reading - until next time!


  1. I would recommend a NEMA 6-30 or 14-30 in the US.

    1. Hi! Thanks for reading, you're probably correct - I barely know anything about US power :-)

  2. Have you thought of renting VMs or LPARs to the lesser mainframe fans and learners?
    That would be an awesome service, assuming the license allows that.

    1. Yep, that's something I'm considering. I should at least be able to rent out LPARs I'm thinking. It would be a bit higher cost I guess as I understand the resource allocations are a bit more rigid, but we will see.

  3. That is one helluva big wrench.

  4. What OS are you planning to run on it? z/OS, z/VM?

    1. Hi! Linux in the beginning when I start to learn the hardware.


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