US 2-phase conversion to EU one phase

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12
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I recently bought a machine from china. The power requirements are 220v single phase with 4 motors that draw about 16A collectively. The factory told me 5.5KVA as a minimum power source. If I use a step up transformer from 120v this means 45A max current draw.

US 220v(240v) is really 2-phase power because the two hot lines in your plug are 120v potential from ground, 180deg out of phase. Measuring across the two hot line yields 240v because of the phase difference. This can be configured as 3 wire or 4 wires depending on the appliance needs of a return.

3 wire - 2 hot, 1 ground
4 wire - 2 hot, 1 return, 1 gound

where 4 wire is used for appliances that have need of 120v power for onboard electronics they can internally tap one hot line and use the return to safely power the 120v electronics while the main load uses the 240v across the two hot lines.

My piece of equipment is configured for 1 hot wire 220v, 1 return, and 1 ground.

My question with this configuration, is their a way to convert from US 220v(240v) into EU configuration of 220v. I dont have space in my panel for a 50A breaker single phase, so how can I convert 2 phase US power into single phase 220v.

EU configuration requires 230v on a single line.

As I understand the source of the power at the power company transformer:

US 2 hot lines from either end of a 240v transformer with a return line center tap.
EU 1 hot line and a center tapped return from a 480v transformer.
 
667
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is their a way to convert from US 220v(240v) into EU configuration of 220v.
There isn't anything to convert between. 1

In the US, we'd hook the machine up across L1 and L2 for 220V.
For 120V, the connection would be between L1 and Neutral or L2 and Neutral.

220v single phase with 4 motors that draw about 16A collectively. The factory told me 5.5KVA as a minimum power source. If I use a step up transformer from 120v this means 45A max current draw.
  1. If you have 220V motors, and 220V available, why would you need to step up from 120V? Is this what the control circuit operates at?
  2. 220V at 16A (3520 volt amps) is 32A at 120V.
  3. I'm thinking the 5.5 KVA minimum power source rating is to allow overhead for motor inrush current in at startup.

1. What will make a difference is whether the motors are 60 HZ versus 50 Hz.
 
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So my question is what is the difference?

In the US if you hook the machine across L1 and L2 your sending two 120v sign waves into the machine that creates a potential of 240v. Which will run the motors, but the onboard electronics no longer have a return.

The plug on the machine has three prongs. 1 hot, 1 return, 1 neutral.

1. Is their an difference electrically between wiring L1 to the plugs hot, L2 to the plugs neutral, and ground to ground? Seems to me that electronics will burn up with 120v on the neutral line.

2. Do you wire a motor differently with the US vs the EU configuration?

3. The motors and controllers are supposed to run on 60hz, although I suspect they just assume the motors will run 20% faster. Chinese engineering...
 

berkeman

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My piece of equipment is configured for 1 hot wire 220v, 1 return, and 1 ground.
How is the ground configured? How is the device grounded? That seems like the key question in this...
 
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In the US if you hook the machine across L1 and L2 your sending two 120v sign waves into the machine that creates a potential of 240v
Not quite so. Typical US residential wiring is technically called "split single phase". It is single phase 240V (L1 to L2) with a center tap (called Neutral). Voltage is 120V between L1 and N, and between L2 and N.

https://en.wikipedia.org/wiki/Split-phase_electric_power

The plug on the machine has three prongs. 1 hot, 1 return, 1 neutral.
Does it look like this NEMA 6-30P? If so, it has two ungrounded line conductors (blades), and a safety ground (pin).

NEMA 6-30P Plug.jpg

Can you post an electrical schematic of your machine (at least, the 'elementary' drawing showing power connections) so we can see what you have?
 
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EU 1 hot line and a center tapped return from a 480v transformer.
EU domestic secondary sides are wye/star, with 400V between phases and 230 from each phase to the star point (neutral).


The motors need 16A at 220V, which is pretty modest, equivalent to about 3.5 kVA, easily carried by bog standard 2.5mm2 cable (Romex?) but you would be wise to install more robust 4mm2. The extra headroom quoted by the company might be accommodated by a suitably rated breaker (C-type trip rather than B-type in the UK).


If your panel won’t take that, it will need to be upgraded professionally.
 
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@berkeman The machine is grounded to the frame. The hot and the neural wires are connected to the power bus accordingly. Per the factory, one plug is expecting to be hot, 1 is neutral(return), 1 is ground.

@Asymptotic while typical 240v US wiring is technically called single phase, in reality its 2 phase. If you were to hook a o-scope up to the two wires and display them on the same screen, you would see two sign waves that are 180deg out of phase. If you probe 3 phase power you will see three sign waves that are each 120deg out of phase. I am not sure logically how else you could create a 2 phase system other than 180deg out of phase.

The people that determine the naming conventions in this country for electricians to use are also the reason that I have a machine that runs on 220v. In the USA we say 110 and 220 but its actually 120 and 240...syntax be what it may.

See attachment for the plug configuration. I believe this is a Chinese standard?
 

Attachments

Averagesupernova

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@berkeman The machine is grounded to the frame. The hot and the neural wires are connected to the power bus accordingly. Per the factory, one plug is expecting to be hot, 1 is neutral(return), 1 is ground.

@Asymptotic while typical 240v US wiring is technically called single phase, in reality its 2 phase. If you were to hook a o-scope up to the two wires and display them on the same screen, you would see two sign waves that are 180deg out of phase. If you probe 3 phase power you will see three sign waves that are each 120deg out of phase. I am not sure logically how else you could create a 2 phase system other than 180deg out of phase.
It IS in fact single-phase, or if you wish, split-phase. This has been discussed to death here on PF and I would recommend you do a search and read up. There exists, or has existed, a true 2 phase system that has the phase conductors 90 degrees out of phase. To get actual poly-phase it take more than two conductors from the utility on the primary side of the transformer.
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Concerning the question at hand, the only reason I can see that the machine would not be suitable here in the good old USA is the conductor you call return is not 120 volts away from ground in China where it would be here in the USA. This may cause a safety issue but I doubt it.
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Why do you think the onboard electronics would not have a return?
 

berkeman

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@berkeman The machine is grounded to the frame. The hot and the neural wires are connected to the power bus accordingly. Per the factory, one plug is expecting to be hot, 1 is neutral(return), 1 is ground.
Does the machine assume any relationship between Neutral and Earth/Safety Ground? The reason I'm wondering about that is because the US 240VAC split phase has a hard connection to Earth Ground (at the center tap, effectively), and the Chinese version may not be expecting that. Is this machine rated as "Double Insulated"? That may make it okay. Otherwise, you may need a pretty high power isolation transformer...
 
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240v US wiring is technically called single phase, in reality its 2 phase
No, it is single phase. 2 phase is an entirely different beast.
https://en.wikipedia.org/wiki/Two-phase_electric_power

but I see @Averagesupernova has already addressed this.

The plug you have is an ungrounded "crowsfoot", and by it's size is probably the smaller amp rated one (NEMA 10-20R is 125/250V, 20 amp, while the larger one, NEMA 10-50R, is 125/250V, 50A). These are depreciated connector types, and while legit in grandfathered applications, have been against NEC code since 1999 to use in new installations since they don't have a separate safety ground pin.

On these, the X and Y terminals (angled blades) are connected to L1 and L2, and W terminal (straight blade) is connected to neutral and equipment frame ground. This is problematic from a safety perspective, and why it has fallen out of favor.

In the USA we say 110 and 220
Not for a long time. 110/220V mains goes back to the time of Edison. Over the years, nominal mains voltage was upped to 115/230, post WWII it became 117/234, and has been 120/240V since the late 1960s.

In Post #1 it seemed you want to connect this machine wired for US service to a European power supply, but didn't specify where in Europe. It appears there are a host of different plug standards and mains distributions in use, and are outside of my experience.

One way to approach this is to:
  • find out which connector type must be used in that locale and change the machine's power connector to suit.
  • If the supply is 230V without a neutral, add a smallish 240/120 V control transformer (500 to 750 VA ballpark estimate; can't say without seeing the schematic) to derive the required 120V control voltage.
 

Averagesupernova

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No, it is single phase. 2 phase is an entirely different beast.
https://en.wikipedia.org/wiki/Two-phase_electric_power

but I see @Averagesupernova has already addressed this.

The plug you have is an ungrounded "crowsfoot", and by it's size is probably the smaller amp rated one (NEMA 10-20R is 125/250V, 20 amp, while the larger one, NEMA 10-50R, is 125/250V, 50A). These are depreciated connector types, and while legit in grandfathered applications, have been against NEC code since 1999 to use in new installations since they don't have a separate safety ground pin.

On these, the X and Y terminals (angled blades) are connected to L1 and L2, and W terminal (straight blade) is connected to neutral and equipment frame ground. This is problematic from a safety perspective, and why it has fallen out of favor.
There is nothing wrong with using the plug you describe above if the device has no need for a neutral. In other words, the straight blade is only meant to carry fault current. Many 240 devices do not have a need for a true neutral that is expected to carry some kind of load current and these 3 blade plugs are commonly still used.
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Admittedly, in the past the code has allowed the straight blade to carry neutral current, but not for a long time. I would say before 1999, and NEVER in a mobile home.
 
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There is nothing wrong with using the plug you describe above if the device has no need for a neutral. In other words, the straight blade is only meant to carry fault current. Many 240 devices do not have a need for a true neutral that is expected to carry some kind of load current and these 3 blade plugs are commonly still used.
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Admittedly, in the past the code has allowed the straight blade to carry neutral current, but not for a long time. I would say before 1999, and NEVER in a mobile home.
The reason I say the onboard electronics will have no return, is if I follow the prescribed method of connecting to US 240v. From the breaker you have L1 and L2 as hot and then a ground. From the machines perspective, you need 1 hot, 1 neutral, and 1 ground. Where the ground wire is tied directly to the frame. The electronics are not tied to the ground wire of the frame. The electronics are connected between the hot and the return. As you suspected the machine is not expecting a potential of 120v between the return line and ground.

The plug itself is not the question here. I doubt I can even find and outlet retail in USA that it would fit in. I can easily add a new plug to the machine. But my concern is L1 connects to hot, L2 connected to return(null as the factory calls it) and ground connected to ground.

My memory of AC from circuits 10 yrs ago is very vague, but the voice in my head keeps throwing up an objection to cramming 120v into a line that is supposed to be return. And then not providing a dedicated return line.

As for the step up transformer, the minimum spec from the factory is 5.5KVA. I was hoping to find a way to get the US 240v to work because my panel is full. The only open spot is the two pole breaker that is dedicated to this machine.

Thanks for all the explanations.
 
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machines perspective, you need 1 hot, 1 neutral, and 1 ground.
This terminology is causing my confusion.

"Hot" is the ungrounded black wire in a 120V residential circuit, and is connected to one side of the source (either L1 or L2) on the center-tapped pole transformer.

In 240V-only circuits, both L1 and L2 ungrounded "hot" wires are connected across the load, and white "neutral" wire isn't used.​

"Neutral" is the white wire in a 120V residential circuit, connected to ground at the service entrance (circuit breaker box), and is the intended path through which line current flows back to the source (the pole transformer center tap, 0V).
"Ground" is the green wire safety ground that is bonded to the equipment frame, is connected to ground at the service entrance (circuit breaker box), and is the intended path for fault current only.

If the machine doesn't require a 120V supply then neutral doesn't come into the picture. Both L1 and L2 are ungrounded conductors and considered "hot" in reference to ground. The plug will be wired to L1 and L2 (240V, between X and Y poles) with the equipment frame connected to the ground pole (W, in legacy connectors, or G, in modern connectors).

Legacy connectors
X and Y poles are ungrounded "hot" wires. W pole is equipment ground.

No separate neutral pole is provided. Modern NEC code no longer allows the ground conductor (W pole) to serve as a neutral return.

125-250(ungrounded).jpg


Preferred, modern connectors
X and Y are ungrounded "hot" wires. W pole is neutral return. G pole is equipment ground.

125-250(grounded).jpg


Images courtesy of waterheatertimer.org

I recently bought a machine from china. The power requirements are 220v single phase with 4 motors that draw about 16A collectively. The factory told me 5.5KVA as a minimum power source. If I use a step up transformer from 120v this means 45A max current draw.
This is another point of confusion. If both the supply and motors are 230V, what is the purpose of a 120/240V step up transformer?

my head keeps throwing up an objection to cramming 120v into a line that is supposed to be return
And this simply puzzles me. A voltage can exist between two conductors. No cramming involved.

Much of this ambiguity and confusion could be cleared up if you would excerpt and post the power circuit schematic, or provide a link (if available) to the manufacturer's manual.

There is nothing wrong with using the plug you describe above if the device has no need for a neutral. In other words, the straight blade is only meant to carry fault current. Many 240 devices do not have a need for a true neutral that is expected to carry some kind of load current and these 3 blade plugs are commonly still used.
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Admittedly, in the past the code has allowed the straight blade to carry neutral current, but not for a long time. I would say before 1999, and NEVER in a mobile home.
I was checking earlier, and using ground as a neutral return in 3P/3W connectors was still permissible (although discouraged) in the 1996 code book. The only appliance I can recall using it as such was an old electric range my grandparents owned that had a built-in 120V fluorescent lamp, and a 120V/15A courtesy outlet that could be controlled by the clock/oven timer.
 
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The machine is ‘expecting’ 220V ac rms across the lower blades of the plug. It does not care if one is bonded to earth at the transformer (neutral) or not.

Your 220V system is equivalent to running the machine through an isolation transformer in its country of origin - no neutral. It will run perfectly happily.

The only difference is the ground, which will be 120V away from either conductor rather than either 0V or 220V. 120V should give plenty of fault current to pop the breaker in the event of a phase-ground fault.
 
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My memory of AC from circuits 10 yrs ago is very vague, but the voice in my head keeps throwing up an objection to cramming 120v into a line that is supposed to be return. And then not providing a dedicated return line.
‘Return’ is not a helpful term. AC alternates; it doesn’t feed and return on respective conductors. The neutral safety system commonly used is there to provide a consistent ‘polarity’, so that switches and fuses can be placed on the line conductors where critical, and so that a line-ground fault isn’t silent, amongst other reasons.

Whether the 220V live conductors alternate with respect to each other, or whether the line alternates above and below the neutral and ground is irrelevant to the machine.


If the machine doesn't require a 120V supply then neutral doesn't come into the picture. Both L1 and L2 are ungrounded conductors and considered "hot" in reference to ground. The plug will be wired to L1 and L2 (240V, between X and Y poles) with the equipment frame connected to the ground pole (W, in legacy connectors, or G, in modern connectors).
Nail on head.
 

Baluncore

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So much confusion.
220V 230V or 240V is not really important, they all meet the European 230V ±10%. These days the world standard has become 230V single phase, 400V 3PH. It takes time before the taps on distribution transformers need any attention.

The Chinese three pin plug is the same as the Australian. Equipment is designed to remain safe even when the active and neutral are swapped. Either way, RCDs will detect the active-neutral imbalance that results due to any ground leakage.

Chinese 230V ±10% equipment will work on the US split single phase 240V system. Just make sure you connect the Earth if it is present.
 
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If I had a schematic I would gladly post it. China custom built's do not come with this luxury. The instruction manual is computer print outs.
 
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3 Things.

1) Per the manufacture, the machine is wired to have a 220v hot, a null(in my above statements, this is synonymous with neutral/return), and a ground. It requires a neutral and a ground. Within the machine, the Neutral leads of the onboard electronics are not tied to ground(the frame), they are tied to the neutral connector. If I connect the neutral lead of the machine to L1 or L2 of the transformer, this would be "cramming" 120v up the neutral "return".

2) The machine is custom made. It is not designed to operate with the US power configuration.

3) Their is not schematic. Their is no manufacture website. This is not a GE product. What I have to go on is what I get from talking to the manufacture. "DO NOT CONNECT 120v potential to the Neutral. The machine requires a dedicated neutral". Is the manufacture wrong? I badgered the english speaking sales staff for days until they promised me they talked to the design engineer(only speaks chinese) to confirm this statement.

This machine was not built to a particular countries power spec. It was built as requested by the electrician that I brought with me to china when the machine design was being hashed out. The wiring configuration of US power 220v was never conveyed to the manufacture. The need to have single phase 220v was. So the manufacture built a machine around the expectation that 220v would be present on one lead, the next lead would be neutral, and the 3rd lead would be ground. The power bus has two lead from the plug with one as neutral, one and hot(240v) and the ground is tied to the machine frame.

My question is not about NEC code. Its about how to power this machine without blowing it up. If I hook up the machine with L1 and L2 across the hot and neutral line of its internal power bus this would be in direct conflict of what the manufacture is telling me to do. I understand that this is code and that every single machine that is built and sold retail in the USA meets this requirement. But unfortunately this is not the domain I am operating in. To follow the US wiring standard would be in direct conflict with the manufactures specifications.

If I purchased a step up transformer, to convert from 120/240v. What would the power configuration look like on the machine side of the transformer? Would it be possible to have 240v on one lead and neutral on the other and 3rd ground? 3 lines, Hot, Neutral, ground. Where the potential from hot to ground is 240v. The potential from neutral to ground is 0v. And the potential from hot to neutral is 240v. This is how I understand the factory requirements. This is the puzzle I am trying to solve.
 
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This is the puzzle I am trying to solve.
You’ve got three or four posters up there who have given the same answer. You seem to be stuck on the idea that neutral is somehow ‘passive’ in the power circuit, which it is not. It sinks and sources current just as much as the phase.

If you insist on a set-up from 120V, you’d need to ensure the output was fully floating, then bond an earth wire to one output, take this to an earth stake, then carry that forward as the earth. The bonded output would then become neutral. The other output, phase/hot. Any safety breakers and RCDs/GFCIs would need to be on the output side of the transformer. You would be, in effect, making your own mini domestic supply. Totally unnecessary and not recommended.

In the Chinese/EU set-up, the neutral has 240V ‘crammed’ up it relative to the phase every half-cycle.
 

Baluncore

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What I have to go on is what I get from talking to the manufacture. "DO NOT CONNECT 120v potential to the Neutral. The machine requires a dedicated neutral". Is the manufacture wrong?
It costs the manufacturer absolutely nothing to issue that statement. As a bonus it frees them from all liability. It costs you real dollars to provide a modified supply. That is now your problem.

Maybe, if it makes you happier, you could use a VFD between the mains supply and the device.

It would worry me that a line fault that often occurs could damage the equipment. I would follow the wires into the power supply and identify why Neutral must be at Earth potential. I would be surprised if the active and neutral had different insulation.
 
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So sticking an ohm meter onto the neutral line is infinite. Their is no connection, so I am starting to think that the chinese sales man is lying about talking to the engineers.

@Baluncore liability was never on the table. Foreign business in chinese court system?
 
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So sticking an ohm meter onto the neutral line is infinite. Their is no connection, so I am starting to think that the chinese sales man is lying about talking to the engineers.

@Baluncore liability was never on the table. Foreign business in chinese court system?
There should be no continuity between neutral and earth/ground, since such a connection would provide a parallel path and trip an RCD/GFCI.
 
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When I stick an ohm meter into the 120v socket I get continuity between ground and the neutral/return line. So what is the difference?
 

Baluncore

Science Advisor
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When I stick an ohm meter into the 120v socket I get continuity between ground and the neutral/return line. So what is the difference?
You are brave. The neutral and active may have been reversed. I hope you checked first.
The supply Neutral bar should be connected to the Earth bar in the building at one point only, usually in the meter box before the fuses. You should expect to measure a short circuit.
You need to test the device insulation breakdown voltage between Earth and Neutral with a 500V megger, not just a low voltage ohm meter.
 
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The Neutral and the ground are only connected at one place in the building. Inside the breaker box. But they are copper wires. If they are connected anywhere in the building even 1000 miles away(assuming 1000 miles of the wires resistance is low enough), then an ohm meter is going to find the path between the two. I am not sure I follow what you are saying.

Fuses? Neutral and ground wires do not go anywhere near the breakers. What do you mean?

120v circuit.
1 - hot
2 - neutral
3 - ground

Voltage
1-2 - 120v
1-3 - 120v
2-3 - 0v

Resistance in Ohms
1-2 - infinite
1-3 - infinite
2-3 - 0

240v circuit 3 wire
1- L1
2 - L2
3 - ground

Voltage
1-2 - 240v
1-3 - 120v
2-3 - 120v
 

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