If the current flows back to the panel in the neutral for a 120v circuit, how does it get back in a 240v circuit? Would you measure current in the ground?
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If the current flows back to the panel in the neutral for a 120v circuit, how does it get back in a 240v circuit? Would you measure current in the ground?
Member
In Germany (and probably most other locations too) it is just a standard 3-phase wye distribution system, but residential service is just given one phase off the wye. It works just like the U.S. 120/208 3-Phase system with a grounded neutral, except theirs is 240/415 3-Phase wye.Originally Posted by Mike Henderson
Saying that "current flows back to the panel on the neutral" isn't totally correct, but most importantly leads to a misunderstanding of the system. It's an AC system, so current flows back and forth 60 times a second. For 1/120th of a second, current flows out on L1 and returns on Neutral, but for the next 1/120th of a second, current flows out on the neutral and returns on L1. That's why it is not really correct to say that the neutral is a return.
Both L1 and neutral are the same and both are current carrying conductors. The only difference is that we "anchor" the neutral to Earth potential as a safety measure. The word "Neutral" doesn't come from the fact that the wire is grounded. The term Neutral means it is the center-tap of a transformer. It is the Neutral-point (middle point) between the two main terminals of the transformer.
A 240 volt circuit is no different than a 120 volt circuit. The current flows back and forth between L1 and L2, just like it flows back and forth between L1 and N.
Member
Thanks Rick,
I'm a mechanical guy and found your stair analogy helpful too.
Contributor
I'm not understanding. The service to the neighborhood I assume is at some high voltage in a 3 phase wye configuration. Then, they probably take one phase, put it through a transformer to bring it down to 220V and take that into the residence. On the secondary of that transformer, is there a ground?
Mike
Go into the world and do well. But more importantly, go into the world and do good.
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With the higher population density, I have a feeling they leave it as 3-phase after the transformer and split off a phase to each customer. The shared neutral would make the distribution more efficient than feeding everyone from a single phase.
Member
Now the OP knows everything he needs to know about which voltage machine he needs to buy.
Last edited by Julie Moriarty; 05-10-2015 at 12:20 PM.
Contributor
As you know, when you transform 3-phase in voltage, you actually use three transformers, one for each phase. So as I understand what you're saying, they wire the secondaries in a wye and ground the center. That would mean that one side of the 220V in the residence is at ground potential and the other is at 220V.
Can anyone living in Europe confirm that. I've always wondered how the single phase residential power is wired in Europe. It seems that they would want a ground in the system.
Mike
[Oops, looks like Julie answered the question while I was typing. Julie, from your diagram it looks like they bring three phase into the residence. Is that correct? And is 220V from line to center of the wye? That would indicate one side of the 220V power in the home is grounded.]
Last edited by Mike Henderson; 05-10-2015 at 12:22 PM.
Go into the world and do well. But more importantly, go into the world and do good.
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I don't know Mike. I grabbed that from here: http://electrical-engineering-portal...bution-systems
Contributor
From what I remember when I worked in Germany, everyone gets 3 phase. I think some appliances were even wired to use 3 phase.
Member
Sorry, I had assumed that you knew this part or I would have explained that better. The one-sided neutral and ground is the result of having the wye on the secondary side, versus if they had used single-phase transformers off the primary 3-phase (like we do).
However, that doesn't mean that some areas with non-industrial needs may not use single-phase transformers where it suits the need. But they'd still have to treat it (for grounding) as though it was the same just for consistency.
Member
I don't think so. The 3-phase is available at the street, but they only bring single phase to the residence. Otherwise they would have 415 volts in a residence, and that would be pretty dicey.
Member
What's kind of interesting is that European construction regulations require workers to use 120 volt power for construction activity. That means most workers have to carry a transformer with them and buy 120 volt power tools.
Contributor
The residential supply is 3 phase, not single phase like the UK or New Zealand. 230V for most items & 400V for the range.
Contributor
That is just in the UK, a site transformer has a 240 volt primary, 110V secondary with each leg being 55 volts, no neutral.
Contributor
Thanks for the information everyone. That's very interesting - I've always wondered how 220V (or 230V) was brought into the home (in places other than North America). From what everyone is saying, it looks like the center of the wye is grounded and the standard residential voltage is taken from one of the lines to the center of the wye (neutral). I imply this because of the voltages specified in Juile's diagram and the comments made by others. In a wye configuration, the voltage from line to neutral is the line-to-line voltage divided by the square root of three (about 1.732). So as in Rollie's example, 230V for small appliances and 400V for the range (230 is 400/1.732).
This would also imply that one side of the circuit for standard distribution around the house is connected to ground. Again, using Rollie's example, one side of the 230V would be connected to ground, while both sides of the 400V circuit are at 230V to ground.
If anyone has any corrections to this, please post. Thank you all again for your input.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
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