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How to wire up a 240VAC receptacle
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Gregg:

--- Quote from: C on May 17, 2018, 06:23:59 pm ---Actually Split-phase can be safer.

First you have GFCI or RCD to think about.
To reduce EMI or RFI X-cap's or Y-cap's are used. With two wire power and one side Neutral you are connecting 1/2 AC voltage to somethiing, the Neutral lead or safety ground. To work around this the GFCI or RCD has to be made less sensitive. With the center Neutral you have 0 volt AC EMI/RFI connected to Neutral so a more sensitive GFCI/RCD is possible..

There is no perfect wire so there is always a voltage drop on the Neutral lead making it NOT ground. A short from Neutral to something is connecting the voltage drop to something and not detected with fuse or circuit breaker in the hot lead. With split-phase this is detected. Shorts like this do happen and can have many watts of power turned in to heat.

Then you have 1/2 voltage difference to actual ground, again safer

The big cost is often just the one added wire and dual breakers.

Equipment designed for split-phase can be designed three ways.

1. You have Equipment that needs some 110-120 for internal use in addition to 220-240. Here three wire or safer 4 wire connection.

2. like above but with no 110-120 internal use so that the Neutral lead supplies no power.

3. A variation of #2 is Two hots and where Neutral lead is just used for a safety ground.

Three phase is just a shift to three hots vs two hots.

C

--- End quote ---

Three phase is far from just a shift to three hot leads.  There are several methods of connection used in the US, but all of the large data centers I have worked with use 480 volt 3ph UPSs connected to 208/120V transformers and then breaker panels.  Several customers had large cabinets that had 40 amp 208V 3ph power supplied.  3ph when rectified has far less ripple than single phase and the 3ph SMPS are more efficient.   

Neutral conductors should never be used as ground connectors.  True, there are a few cases where the NEC allows a ground conductor to carry a small neutral current; but I would never wire my house in such a manner, even if it is officially OK. 

Back to the subject at hand; Richard Crowley is absolutely correct and it is sad that Spork purchased the wrong PDU.  It isn’t our fault he didn’t ask first and now there isn’t any way to easily fix the situation short of taking it apart and seeing if it can be modified to install 2 pole breakers and to ensure the switching mechanism switches both hot legs of the 240V. 

If I were in Spork’s shoes, I would try to return the PDU on the grounds that they didn’t properly describe it in their literature and instead purchase two of the P9S13A units if he needs the capability to switch each branch circuit remotely. 

Let’s consider the possible unsafe modes of failure using the P9S16A PDU:

Suppose there is an internal ground fault in one of the server power supplies that is from the hot without the single pole breaker.  The single pole breaker doesn’t respond and the fault remains until the 40 amp two pole breaker trips after things catch fire.  Or the fault gets to the point where it blows up the power supply and possibly ruining the whole server.  If the 40 amp breaker trips, and nothing much else happens your whole system still goes down until you figure out the problem.  Assuming your server racks/cabinets are properly grounded; if they are not, you could be in for the shock of your life.

Suppose you figure out there is something wonky with one of the server power supplies and you turn it off remotely because you are not at home; but the PDU switch only turns off one hot leg.  Failure modes are the same as above.

I’m sure others on the forum could add to this list.
james_s:

--- Quote from: Bratster on May 17, 2018, 01:17:39 am ---

Same thing with 110 115 and 120, all of them acceptable.

In the US the nominal is 120 and 240, but it's quite common for people to say 110 and 220 Etc.

I'm not familiar with the UK at all, but I think their nominal voltage is 230 volts? But the specification allows anywhere from 220 to 240 or something like that.

*Except in some special cases, mainly on large equipment that has its own transformer built-in, then there are multiple Taps to get the voltage just right.

--- End quote ---


The nominal voltage in the US has gradually crept up over the years, I suspect to squeeze a bit more capacity out of the existing grid but I don't really know. In the early days it was 110/220, then it was 115/230, then it rose to 117/234, and finally to what it has been throughout most/all of my own life, the 120/240 that we have today. Quite a few people still refer to it by the old ratings though.
Spork Schivago:

--- Quote from: Richard Crowley on May 17, 2018, 12:54:15 am ---Note that "120VAC - 0 - 120VAC" is the same thing as "split-phase".

None of the HPE PDU are designed to handle split-phase.  They are all designed for schemes where Neutral = Ground.

If you connect any of those HPE PDU things to domestic split-phase where Neutral = 120VAC, you are setting up a situation that is dangerous for both equipment and people.

That is why a transformer is need to convert 120-0-120 ("split-phase")  into 240-0 ("single-phase")

--- End quote ---

I agree the transformer is needed.   That's why I posted that in my second post I think.   I just wasn't sure what transformer.   But then people started suggesting that I should rewire the PDU, etc.

I called HPE again and verified that we do need the 1400 watt PSUs that only come in 240VAC single-phase.   I had asked you if 120-0-120 was split-phase and you said NO!!!!   So that confused me a bit, but I think I worded it weirdly.

Sending back the PDU and replacing it with a PDU that handles split phase isn't an option because the PSUs cannot run off split-phase.   They won't power up, they won't provide power to the servers.   So, we need the transformer, even if people think it's a hack job or dangerous or stupid or whatever.   That appears to be our only option at this point.
Monkeh:

--- Quote from: Spork Schivago on May 18, 2018, 01:18:04 am ---the PSUs cannot run off split-phase.   They won't power up, they won't provide power to the servers. 

--- End quote ---

And you know this how?
Spork Schivago:

--- Quote from: Bratster on May 17, 2018, 01:17:39 am ---
--- Quote from: Spork Schivago on May 17, 2018, 12:19:48 am ---
--- Quote from: C on May 16, 2018, 09:41:40 pm ---
Looks like you like to ignore simple facts.

In the USA the standard electrical outlet is 110-120 volts 60hz.

All 220-240 volt stuff uses different connectors. Because of the difference people take more care.

Think of how many people in the USA have used computer power cords. For the USA the end that connects to a computer is 115volts. For a lot of the world that is 220volts but not in USA.

So now you have people seeing the computer end thinking 115volts and connecting an extension cord to your PDU, but that is not 115 volts. A part of safe is knowing what to expect.
So what is a safe European standard is not as safe in the USA due to common thought.

The added transformer is creating a safe NON-USA standard in addition to wasting power. That transformer will get hot, and that is a waste of power. 

One thing you might like to know is that 220 volt 60hz is more dangerous then 220 volt 50hz. The 60hz has a greater chance of messing up your heart beat then 50hz.

If you want real safe 220 volts using a USA split phase( 220 Volts with a neutral center tap) you use a four wire connection. The forth connection the safety ground.
Unlike the rest of the world USA 220 volt equipment often has some 115 volt loads.

C

--- End quote ---

We need 240VAC, again, for the server, not 220VAC, although it would run on 220VAC.   Most of our equipment is NOT from the USA.   The cords to power these devices are NOT what you find with a NORMAL USA bought PC, so I highly doubt anyone who is allowed to be around the rack will try plugging anything into the PDU.    I mean, simple fact, strangers aren't going to be down here, and if they are, they're breaking the law.   Eventually, we have to worry about my daughter, but that's a long ways away, and even then, she cannot physically get into the rack to plug anything into the PDU.   Ohm's law shows us if we double the volts, we cut the current draw in half.   200v * 2 amp = 400 watts.   20 amp * 20v = 400 watts.    I think I'd rather get shocked, if I had to get shocked, at the 200v, 2 amp, rather than the 20 amp.

I have no idea how anyone is going to plug any cords into the PDU, I don't know what you think the inputs look like, but you physically cannot take a normal PC cord and plug it into the PDU.   You need special cords....most of our energy hungry equipment is designed to run off 240VAC, but most of it can go down to 100VAC.   I mean, we have some American made workstations, but they're not going into the rack at all, and aren't being powered by this PDU.   A lot of stuff came from Germany.   There's usually no switch on these pieces of equipment to flip.   They say 100VAC - 240VAC.

I mentioned in a previous post that security was our responsibility and we get audited, where some people from some companies come in and check to make sure everything is up to their standard.   We get a report on what needs to change, if anything, and it's our responsibility to change what they list.   Once we wire up the 15kVA transformer (or higher someone to wire it up for us), we'll have to have yet another one of those pesky audits.

There's security in place.  Maybe you can take comfort in knowing that currently, no one who is specifically supposed allowed in the datacenter can get into the datacenter without doing a lot of illegal work?   This isn't a playroom.   The idea is though, we do our own thing once these contracts are up, and hopefully, later on in life, our daughter takes interest.   If not, that's okay, we'll love and accept her no matter what.   That's years down the road before we burn that bridge though.

Heck, do you know how hard it was to say no to the three phase installation?   We were talking over 50,000$ and almost went for it, because then we can purchase stuff that's a bit more suited to our task at hand.   I feel better having a PDU hooked up with a backup sitting on the shelf in case one shits the bed, rather than daisy chaining a whole bunch to try and get my systems running.

--- End quote ---
220 230 and 240 volts are all the same.
Voltage wise all of those are acceptable. *

Same thing with 110 115 and 120, all of them acceptable.

In the US the nominal is 120 and 240, but it's quite common for people to say 110 and 220 Etc.

I'm not familiar with the UK at all, but I think their nominal voltage is 230 volts? But the specification allows anywhere from 220 to 240 or something like that.

*Except in some special cases, mainly on large equipment that has its own transformer built-in, then there are multiple Taps to get the voltage just right.



Sent from my Moto x4 using Tapatalk

--- End quote ---

Yes, and our power supplies can take anything from 220VAC - 240VAC, but run optimally with 240VAC.   Thankfully, here, we actually have 120VAC when I measure the receptacles and not 115VAC.   The transformer will be an Edison, but they're literally the exact same thing as Acme Electronics.   Same catalog number, everything.   Hopefully, the transformer will put out 240VAC and not something lower, like 220VAC or 230VAC.
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