I'm trying to be brief as best as I can, There are only two phases working (Red & Yellow), so the electrician shared Yellow phase between two terminals (as seen in the image), and of course will make 380v potential difference with the red phase, so my question is what happens if we connected a motor or a 3 phase tool to the 380 V plug? Feel free to share your opinion upon anything about the post.


enter image description here

  • \$\begingroup\$ Was it a temporary repair for lighting only? \$\endgroup\$
    – Solar Mike
    Apr 18, 2021 at 18:05
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    \$\begingroup\$ Cross posted: engineering.stackexchange.com/q/42665/10902 \$\endgroup\$
    – Solar Mike
    Apr 18, 2021 at 18:07
  • \$\begingroup\$ @Solar Mike I was told to post it here, and no not only for lighting if you look closely you will see that the three wires enters the input of a 380v RCD circuit-breaker and it connects to two 380v receptacles so someone could power a three phase motor or tool to this wiring when two phases has a potential difference of zero and they make 380v potential difference with the first phase, what would happen because I know if 1 phase is disconnected it could burn out the motor! \$\endgroup\$ Apr 18, 2021 at 18:21
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    \$\begingroup\$ No, you were told it had a better chance of it being answered here... but adding the info that you did post in both places would prevent people from wasting their time by duplicating answers. \$\endgroup\$
    – Solar Mike
    Apr 18, 2021 at 18:25
  • \$\begingroup\$ Three phases creates a rotating magnetic field that pulls the rotor along. But two phases won't get through 360 degrees of rotation. If you could then three phases are not required. And why be brief? You paying by the character. \$\endgroup\$ Apr 19, 2021 at 6:14

1 Answer 1


what happens if we connected a motor or a 3 phase tool to the 380v plug? (the output with only 2 phases connected.)

It would never be wired to a 3 phase output from 2 phases, but if it were , the motor would not run and would overheat.

It is very common to create single-phase higher voltage from two Line-to-Line phases to meet equipment requirements. The 1st 3 breakers on the left share 2 sequential phases e.g. AB BC CA with double pole breakers. This is the proper way to distribute 3 single phases at the higher line to line voltage. If all 3 breakers were loaded roughly the same , then the power source would see balanced loads. It is up to the electrician to ensure these loads are fairly well balanced.

The next breaker has all 3 lines + neutral ganged through breakers.

If you have a logic diagram to show what you think is wrong use the schematic tool or draw it.

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    \$\begingroup\$ For the wrong part: it looks like there is a blue jumper across two phases on the incoming side at the (bottom) main breaker. \$\endgroup\$
    – KristoferA
    Apr 19, 2021 at 2:37
  • \$\begingroup\$ @KristoferA TY This must be a silly skill testing photo with how many code violations can you count. or the electrician was smoking too much stuff. \$\endgroup\$ Apr 19, 2021 at 12:07
  • \$\begingroup\$ Good one .That's a violation. \$\endgroup\$ Apr 19, 2021 at 12:13
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    \$\begingroup\$ "Code violations" is not a concept in some parts of the world. Around where I live, an "electrician" is a guy with a screwdriver and some electrical tape. Some of them live a long and happy life, others don't. Needless to say, I will not let an "electrician" past the front gate. :) \$\endgroup\$
    – KristoferA
    Apr 19, 2021 at 12:14
  • \$\begingroup\$ @KristoferA I dismissed that panel completely, my question was what would happen to a 3 phase motor or a tool if connected as such, I imagine that one pole has a 380v potential difference than the others so it would start to rotate when the others have 380v potential difference & 120° with the first and they have 0° difference will begin to rotate together dismissing the synchrony of three phases, so what could happen to the motor if connected as such, I wanna know for myself, so I can have a better understanding, lastly can anyone suggest a good schematic circuit drawing software, Thanks \$\endgroup\$ Apr 19, 2021 at 15:59

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