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I live in a three story building. Last night, the top floor lost power for about 30 minutes while the rest of the building was not affected.

When I asked a local electrician, he said this was due to the three-phase power coming from the local power company.

I am a software engineer, not well-versed in electrical topics, so I would appreciate insight into what's going on.

Is this type of configuration of wiring by the power company something that is good, or should I ask them to change it?

Where I live, the mains voltage is 220 v.

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closed as off-topic by Brian Carlton, Enric Blanco, Voltage Spike, Dmitry Grigoryev, winny Jun 26 '17 at 14:44

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Brian Carlton, Enric Blanco, Voltage Spike, winny
If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ 30 minutes is not a lot of time. Isn't it possible that a large circuit breaker that handles that floor's power was tripped, and the 30 minutes was the response time for maintenance workers at the building to find and re-set it? that would make more sense to me than some comment about three-phase power... \$\endgroup\$ – schizoid04 Jun 24 '17 at 19:49
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    \$\begingroup\$ @Sabuncu I thought you were a software engineer? \$\endgroup\$ – schizoid04 Jun 24 '17 at 19:50
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    \$\begingroup\$ @schizoid04 That and a lot of other hats! \$\endgroup\$ – Sabuncu Jun 24 '17 at 19:51
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    \$\begingroup\$ USA has split phase, i.e. single phase, center tap. There's no multiphase on the pole. it's very inefficient, at 200A a US house gets 48kw on 3 wires, Euro homes get 138kw on 4 wires. 2-phase is something else. \$\endgroup\$ – Harper Jun 25 '17 at 4:01
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    \$\begingroup\$ Wait, you had a 30 minutes blackout and now you want the electric company to rewire the whole building? \$\endgroup\$ – Dmitry Grigoryev Jun 26 '17 at 10:51
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What you have is 380V three-phase "wye".

Think of the three phases as a triangle. "Wye" means there is a "neutral" wire in the center of the triangle. Any phase to neutral is 220V as you are accustomed. (Distance is voltage).

That is how power is wired on five continents and New York City. Three-phase power is brought to the pole in back of your house, or inside your apartment building.

Some houses get only 1 phase (that's all they need for household loads), some get two phases (doubles available power, only 1 more wire), and some get all three either because they need a lot of power, or to run fairly large loads (A/C system, heat pump emergency heat, etc.) Three-phase power is ideal for motors.

Three-phase power is best loaded evenly. So for any group of houses or apartments, they will put 1/3 of them on each phase, with the idea that they will tend to average out. If you have more than one phase in your house, they will spread your loads around as equal as they can.

What happened is one of the "hot" phases came loose or had a breaker trip. This shut off one phase, and killed 220V power on the 1/3 of your outlets that used that phase. Heaters would be 2/3 out. Motors would not run.

If you were skilled with electrical, you could have opened up your service panel/consumer unit and moved the blacked out loads onto one of the phases that was still working.

The bigger worry is losing a neutral. Remember the triangle I mentioned? If your neutral wire had failed instead, neutral is no longer held in the center. It will float around anywhere inside that triangle, depending on the load on each phase. That means any phase to neutral voltage could be as low as 0 and as high as 380. If the problem was inside your house, check your neutral wire also.

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  • \$\begingroup\$ I appreciate your detailed explanation. Some of it is over my head, but gives me a foundation for further research on my own. \$\endgroup\$ – Sabuncu Jun 26 '17 at 14:50
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Three phase is used to supply large loads and large buildings have their loads equally divided between the phases to even out the load for the generator. This happens with houses the first house on one phase the second house on phase 2 etc. So, for your building first floor one phase, second floor second phase etc. The third phase may have gone down due to someone else causing a problem.

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Is this type of configuration of wiring by the power company something that is good, or should I ask them to change it?

Three-phase wiring is common, if not standard, for AC-current.


From Wikipedia:

"Three-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power."

So, to answer your question, no, you shouldn't need to ask them to change the wiring.

I'm not an expert in this field though, so it's possible I've missed an important detail.

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As already stated it is normal to spread distribution over three phases to multiple domestic users. if all the apartments were on the same phase, as well as the load on that phase being much heavier requiring larger cables, all the user would have lost power instead of just your floor. next time a phase goes down for a short time it may well be the phase you are asking about having your supply changed to. In short, stay as you are, it's normal. John

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