Electronics > Beginners
How to wire up a 240VAC receptacle
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Spork Schivago:

--- Quote from: tpowell1830 on May 18, 2018, 08:12:52 pm ---
--- Quote from: Spork Schivago on May 18, 2018, 07:50:32 pm ---
--- Quote from: IanB on May 18, 2018, 05:30:26 am ---
--- Quote from: IanB on May 18, 2018, 04:51:11 am ---
--- Quote from: Monkeh on May 18, 2018, 03:52:21 am ---Change your PDUs for the type with double pole breakers and use your existing supply, or have an electrician (yes. really. please don't do it yourself.) install the transformer. Either will work.
--- End quote ---

It's not clear that there are any HPE PDUs with double pole breakers. The HPE literature divides the product range into two categories: NA/Japan which expects 200-208 V AC single phase, or INTL which expects 220-240 V AC single phase. In either case it is clear that this voltage is measured line to neutral, as is typically found in commercial premises.

--- End quote ---

OK, I stand corrected. The P9S13A does have a double pole breaker, as listed here: https://h20195.www2.hpe.com/v2/GetDocument.aspx?docname=a00002909enw

So it does appear that 240 V line to line or phase to phase should be acceptable for this particular PDU.



--- End quote ---

But then we're back to the power supplies being fed split-phase, aren't we?   It wasn't me who picked out the PDU or the PSUs.   And like I've stated, HPE could have been wrong during their power analysis, but after their power analysis there was one power supply that was available, and only one, the one we have.    And then when it came to a proper PDU, there was no PDUs available that would work with our PSUs and our split-phase, however, there were ones available that would work with 1-phase 240VAC or the 3-phase.   And eventually, we went for the 1-phase 240VAC out of the choices, because of the 3-phase being too much.

--- End quote ---

Back to the 3 phase system, I think that you are being told $50k to install is what I read? This seems very outrageous, having done this myself in my area. The 3 phase power lines were 1/4 mile away and the power company charged me a modest $300 to install the pole and transformer, however, I had to sign a 3 year contract with a minimal $25 charge for the service. Mind you, this was in 1980, so I could see a factor of 10 at least on that price, but still can't get to the $50k figure. You would still need to provide a distribution panel and do all of the wiring, which I did myself in 1980.

Hope this helps...

--- End quote ---

Yeah, 50k+ is what the electrician said it would cost us.   The actual electric company needed, I think around 2K, half up front, with a contract like you mentioned there.   And they needed the electrician to fill out some paperwork.   But that was just to get going.   After that, they'd send out some engineers and we'd be charged on stuff like the backhoe, and them running the wires, etc, etc.   A rough, overall estimate was over 50K, from the electrician, when all was said and done (which including the charges from the local power company).   We didn't get a second quote.   We just ruled it out all together.

But now, even if he lied because he didn't want to do it or something and someone came along and said we could get it for a couple grand, we'd have to change everything out.   All of our current rack mount equipment isn't designed for 3-phase.   I don't think we can do that though, we didn't make all purchases at once.   It took us years and years to buy things.   The rack was the start of the real business, but the other stuff I've been buying since 2005 and using it to make money.   It wasn't until we moved to the city that revenue started coming in real quick like and we had enough cash to purchase the rack, and then the switches, then the servers, the patch panel, the CAT6 shielded ethernet, the QFSP+ transceivers, etc.

My uncle passed away but was VP of the Science Division at one of the companies we're dealing with (the one that is insane about security).   My Aunt has a lot of money and my brothers and sisters have all asked her for some at one point in time.  She tried giving us some, but we refused because we believe we should earn our money, not accept it for free.   She wanted to help us though, and we told her about our new business and if she could spread the word, it would help generate some revenue.   Then shortly after, we had someone approach us at our house from that company where her now-deceased husband had worked.   He is a programmer and we were offered an opportunity to help with a project for income and we took it.   I think she had something to do with it.   The guy, we call him an employee, but he doesn't actually work for us.   He works for the other company.   He just helps us with stuff here and I'm what he calls the Team Leader.   I tell him what we need done, he'll work on it.   We use a VPN to connect to their network, but it's secure, where we have to use our cell phone and enter some code that changes every 30 seconds or we can't get in.   Two-Factor authentication.   But we also have these USB devices we plug into the PC to login and without the USB device, we cannot login at all.   We have to lock them up when we're not using them and we cannot keep them in any of the workstations.
Monkeh:
The supply you have is single-phase. The winding on the transformer is centre tapped to create what is referred to as a split-phase installation. The centre tap is grounded and forms the neutral.

If you disconnected the centre tap entirely and connected one side of the winding to ground, you would have a single-phase 240VAC supply with a neutral. If you forget about using the neutral entirely, and forget about needing any ground reference at all, you still have a single-phase 240VAC supply, with no neutral. 120VAC only arrives because you're using only half of the winding by using the centre tap. You could get that without grounding the centre tap, too, you just can't call it a neutral.

If you refer back to the transformer diagram, it has two secondary windings - X1 to X2, and X3 to X4. X1 and X4 are your hot legs. X2 and X3 are the centre tap. If you were to connect those together, and then connect that point to ground, you would arrive at the same split-phase setup coming into your house. And still have 240VAC between X1 and X4, which will still run your power supplies just fine.

If you use the entire winding, by using both hot conductors, you have a 240VAC single-phase supply. It simply doesn't have one leg connected to ground - and that does not matter at all for the load. It is only a concern for the installation, which is why the PDUs need to be suited to it. And they make PDUs which are designed for this.

Allow me to shamelessly steal these off the internet:

Spork Schivago:

--- Quote from: IanB on May 18, 2018, 08:20:07 pm ---
--- Quote from: Spork Schivago on May 18, 2018, 07:50:32 pm ---But then we're back to the power supplies being fed split-phase, aren't we?   It wasn't me who picked out the PDU or the PSUs.   And like I've stated, HPE could have been wrong during their power analysis, but after their power analysis there was one power supply that was available, and only one, the one we have.    And then when it came to a proper PDU, there was no PDUs available that would work with our PSUs and our split-phase, however, there were ones available that would work with 1-phase 240VAC or the 3-phase.   And eventually, we went for the 1-phase 240VAC out of the choices, because of the 3-phase being too much.

--- End quote ---

Except that split phase in this context is not relevant. All you need care about is that it is a 240 V single phase supply. The P9S13A is designed and manufactured for the North American market and comes already fitted with a NEMA L6-30P plug that your electrician would have no problems with. It has 2-pole breakers which is what are needed for North American standards, and it can work with 200-240 V, which is compatible with the 240 V in your house. It is all good. Buying something that is not marked NA/JP is what has got you into trouble here.

A possible lesson learned here is not to rely on the vendor or salespeople to give technical advice. They are mainly interested in making the sale and taking your money. The best way to get advice is to engage an independent consultant with appropriate industry knowledge and experience, someone who will know how everything works and who is not just reading off sales brochures.

--- End quote ---

Well, with the lesson part....I can do what you said, but I'll explain something.   We recently placed a small order for 1,000 foot of Beldin CAT6 SFTP ethernet, a shielded CAT6A 48-port patch panel, a crimper designed for shielded ends, and a pack of 100 RJ45 plugs.   We called our Account Executive and told him that we needed shielded ethernet, CAT6, a shielded patch panel, a crimper, and the plugs, plus the punch down tool.   He reaches out to C2G (I think that's their name) and we do a conference call, but they don't sell CAT6A in SFTP, so he goes to his technicians and asks what's the most common shielded stuff people buy, what's the better quality stuff, not necessarily the most expensive.   They tell him, we do another conference call, and we agree on prices and the company we (our Account Executive, me, and the other company) setup a purchase.   They know exactly what I need, what I want, etc.    Long story short, we receive everything and the ends are just regular CAT6 RJ45 plugs.   They're not shielded.    So we call our Account Executive back and tell him we believe we've gotten the wrong part, and how we should have studied the order sheet a bit more carefully, but he says no, this isn't on us because we went through him and he went through the company.

It's on the company.   They had to pay return shipping, and they had to accept the ends, and they had to send us the proper ends, for the difference in price, of course.   While we were talking, our Account Executive said we want to avoid ordering from the companies directly for multiple reasons.   1) We don't get the price that he gets but more importantly, 2) If they send us the wrong part or the part that we don't need, it's on them, not on us.   He made that very clear there.

So, I can send back that PDU and tell him it's the wrong PDU and then say exactly what PDU I need, however, if it turns out the PDU you say is the one I want does not power the equipment I have (the mainframe, the servers, etc), that's all on me, and I don't think I can send that back.

Keep in mind, I would need two of those P9S13A's, and then the equipment to daisy chain them together.   We'd have to make sure the additional accessories we purchased with the PDU are compatible, we might need to order another set of those accessories.   Wiring up a NEMA L6-30P and a NEMA L6-30R is something I definitely don't need an electrician for.   That's something I've done more than once and can easily keep that up to code and wire it safely.   No problems there.   It's just the concern of going against what they all state what I need.   I have the right to dispute it and send it back, but if I'm wrong and it doesn't power on the mainframe or the servers, then I might very well be out a lot of money because I might not be able to send them back, and I might have to end up buying the same PDU they said I needed again, but this time, probably not as cheap (they bid), and we're talking more time wasted because I'll be back here, asking again about the transformer, etc.

With that in mind, if you were me, would you take the chance and send the PDU back and order the other two, plus the additional equipment to get it running?   Or would you just purchase the transformer and new breaker panel?
Spork Schivago:

--- Quote from: Monkeh on May 18, 2018, 08:58:16 pm ---The supply you have is single-phase. The winding on the transformer is centre tapped to create what is referred to as a split-phase installation. The centre tap is grounded and forms the neutral.

If you disconnected the centre tap entirely and connected one side of the winding to ground, you would have a single-phase 240VAC supply with a neutral. If you forget about using the neutral entirely, and forget about needing any ground reference at all, you still have a single-phase 240VAC supply, with no neutral. 120VAC only arrives because you're using only half of the winding by using the centre tap. You could get that without grounding the centre tap, too, you just can't call it a neutral.

If you refer back to the transformer diagram, it has two secondary windings - X1 to X2, and X3 to X4. X1 and X4 are your hot legs. X2 and X3 are the centre tap. If you were to connect those together, and then connect that point to ground, you would arrive at the same split-phase setup coming into your house. And still have 240VAC between X1 and X4, which will still run your power supplies just fine.

If you use the entire winding, by using both hot conductors, you have a 240VAC single-phase supply. It simply doesn't have one leg connected to ground - and that does not matter at all for the load. It is only a concern for the installation, which is why the PDUs need to be suited to it. And they make PDUs which are designed for this.

Allow me to shamelessly steal these off the internet:



--- End quote ---
Wow!   I get it!   I actually understand how it works now!!!!!   I cannot thank you enough for explaining that!   You have no idea how long I've tried to wrap my head around the AC system coming into the house.   Just to make sure I'm following, in your second sentence, when you say the winding on the transformer is centre tapped....you're talking about the transformer on the pole, right?   I know that probably makes me sound like an idiot, but I just want to make sure I really do understand.   Those images helped a lot too.   But you explaining the x1 and x4 and x2 and x3, that's when it really hit.   So it's the number of winds on the transformers that determine the voltages then, isn't it?

Is it a magnetic field that transfers the energy from the primary to the secondary side of the transformers?   It'd have to be, I'd think, right?   Otherwise, it'd be like two windings in series and it'd affect the input voltage supply.   By that, I mean, instead of expecting 120VAC, it might expect 360VAC, if the windings where physically connected to each other.
Monkeh:

--- Quote from: Spork Schivago on May 18, 2018, 09:28:45 pm ---Wow!   I get it!   I actually understand how it works now!!!!!   I cannot thank you enough for explaining that!   You have no idea how long I've tried to wrap my head around the AC system coming into the house.   Just to make sure I'm following, in your second sentence, when you say the winding on the transformer is centre tapped....you're talking about the transformer on the pole, right?   I know that probably makes me sound like an idiot, but I just want to make sure I really do understand.   Those images helped a lot too.   But you explaining the x1 and x4 and x2 and x3, that's when it really hit.   So it's the number of winds on the transformers that determine the voltages then, isn't it?
--- End quote ---

Bingo. The transformer on the pole is indeed centre tapped (or two windings with the ends connected like the small one you're looking at - functionally equivalent for our purposes). Number of turns around the core determines the voltage. Centre tap it and you effectively cut the number of turns in half.


--- Quote ---Is it a magnetic field that transfers the energy from the primary to the secondary side of the transformers?   It'd have to be, I'd think, right?

--- End quote ---

Yes. Transformers transfer energy via magnetic field. In the case of a single-phase system, that is one single magnetic field rising and falling - that's why centre tapped systems are still single phase.

So with all that out the way.. you have 240VAC single phase. Neither conductor is directly connected to ground, which is a critical point to take care of with distribution. For loads, it's irrelevant.
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