# 3 phase 4 wire system

#### ajitnayak

Joined Feb 22, 2013
49
Dear all.

I have most common question here. I have system 3 phase 4 wire system. Assume i have connected Rphase/Yphase /B phase neutral wire connected separated with 230VAC supply.
VL = √3 VPH for Line to line calculation
and if i measure line to neutral it should show 230VAC

Suppose i have connected in this setup. RPhase/Bphase/Y phase are shorted and single Rphase voltage is given. In this case what should be line to neutral voltage should be read and line to line neutral voltage should be read.

SInce phase shift no more 120 degree

#### Ramussons

Joined May 3, 2013
1,059
Dear all.

I have most common question here. I have system 3 phase 4 wire system. Assume i have connected Rphase/Yphase /B phase neutral wire connected separated with 230VAC supply.
VL = √3 VPH for Line to line calculation
and if i measure line to neutral it should show 230VAC

Suppose i have connected in this setup. RPhase/Bphase/Y phase are shorted and single Rphase voltage is given. In this case what should be line to neutral voltage should be read and line to line neutral voltage should be read.

SInce phase shift no more 120 degree
You got it mixed up.
V (p-p)= √3 V(p-n)
So, your voltage from any Phase to Neutral will be 230 volts. It is only when you measure the Voltage across Phases the 120 degree phase factor comes in.

#### crutschow

Joined Mar 14, 2008
27,696
Is that 4th wire neutral or safety ground?

#### DNA Robotics

Joined Jun 13, 2014
608
RPhase/Bphase/Y phase are shorted
0 volts. You blew the circuit breaker.

Joined Jul 18, 2013
23,595
Show schematic.
Is this a supply or load? 3ph star transformer? Device?
Max.

#### MisterBill2

Joined Jan 23, 2018
9,233
Is that 4th wire neutral or safety ground?
IT IS A NEUTRAL!!!! We are not discussing safety wiring here, this discussion is about line-to-line and line-to-neutral voltages.
The green wire is a totally separate discussion, not happening here.
Dear all.

I have most common question here. I have system 3 phase 4 wire system. Assume i have connected Rphase/Yphase /B phase neutral wire connected separated with 230VAC supply.
VL = √3 VPH for Line to line calculation
and if i measure line to neutral it should show 230VAC

Suppose i have connected in this setup. RPhase/Bphase/Y phase are shorted and single Rphase voltage is given. In this case what should be line to neutral voltage should be read and line to line neutral voltage should be read.

SInce phase shift no more 120 degree
Since the TS is describing a 3-phase Y connection with 230 volts to neutral at the ends of the "Y", the voltage between ends is a bout 1.73 times the 230 volts, = to SQRT3 x 230 volts.
The theoretical condition of legs being short circuited to some unknown point makes no sense and hence no answer is offered.

#### ajitnayak

Joined Feb 22, 2013
49
I haven't connected anything. I wanted to test in one of 3 phase voltmeter. neutral is separately only.
Before connecting connection i would like to know what should be expected answer.

As per me Line to neutral it should show value of 230V but where line to line it should be zero.
i wanna test in this model https://www.lntebg.com/ems/pdf/1. WL1XXX Single Function meter.pdf I am not giving any load.

ok suppose . i wont give neutral wire . i have connected in delta form what should it give me answer

#### MisterBill2

Joined Jan 23, 2018
9,233
If there is 230 volts from each line to neutral then the voltage between phases should be around 400 volts, probably close to 390 volts. That is because of the way 3-phase voltages add. For the 3 phase 480 volt systems I worked with the typical phase to neutral was 277 volts, which was often used for powering lighting.

Joined Jan 15, 2015
6,058
The meter is designed to work with 3 phase WYE or Delta distribution.

As per me Line to neutral it should show value of 230V but where line to line it should be zero.
No, You should present exactly what you have as a WYE or Delta configuration. I suggest you read a little on each till you have an understanding of them.

Ron

#### MisterBill2

Joined Jan 23, 2018
9,233
If the TS is really an electrical engineer, with a BE EEE degree, or some similar education, this question should not even exist. Or possibly the whole degree was towards integrated circuit design.
It may be that the circuit in discussion is not three phase at all, but rather single phase with a separate neutral and safety ground. Or, it might possibly be a 230 volt isolated source with a separate conductor intended to be a neutral, plus a safety ground connection, or maybe a tapped 230 volts intended to be two 115 volt legs, with the neutral somehow disconnected.
Going back to post #1, the whole concept of shorting all three phases together and having any voltage at all is not valid, nor even close to valid.

Joined Jan 15, 2015
6,058
Beats the heck out of me. When people can't clearly state or identify what they have it makes it hard to give an answer. Last 25 years in my facility we used 3 phase Delta but while only 3 wires were required there was also a Ground so a total of 4 wires. That did not make it a 3 phase 4 wire system. My typical phase to ground voltage was about 470 volts give or take.

This forum is an English speaking forum and while I can appreciate many of our visitors use English as a second language it is really important to state a problem or question clearly in detail. Less detail we have no clue?

Ron

#### MisterBill2

Joined Jan 23, 2018
9,233
Beats the heck out of me. When people can't clearly state or identify what they have it makes it hard to give an answer. Last 25 years in my facility we used 3 phase Delta but while only 3 wires were required there was also a Ground so a total of 4 wires. That did not make it a 3 phase 4 wire system. My typical phase to ground voltage was about 470 volts give or take.

This forum is an English speaking forum and while I can appreciate many of our visitors use English as a second language it is really important to state a problem or question clearly in detail. Less detail we have no clue?

Ron
I am aware of there being 460 3-phase with one point of the delta grounded , which is interesting, but around here it seems to be like a Y source with the center common as neutral, which reduces the shock hazard a bit, because oof 277 to ground instead of 480.

Now, this has been a comment of mine for quite some time. Making it more interesting, many of the questions, including this one, come from people claiming to be electrical or electronic engineers. So where did they go to school???

I did have one person, with an MSEE from Oakland University here in Michigan, not really able to read a electrical circuit diagram. But he did relate to me that he could design a custom IC for our standard product that used four ICs, CD4000 series, total cost less that \$5. Given that we did not anticipate selling more than 50 of the product a year THAT made no sense at all.