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Anonymous Poster #1

# Three-Phase Problems

01/22/2017 6:16 AM

Hi, Say in a three phase system, in R phase we have a line current 0f 5 Amps, in Y phase of 6 amps, and in B phase a line current of 4 Amps. But it is visible that the load is not balanced in three phases. How to go for load balancing? Regards,

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Location: Torquay England
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#1

### Re: three phase problems.

01/22/2017 7:25 AM

what are The loads on each of the phases..list them out and look to see what if any can be moved .. ideal the 6 needs to have part sent to the 4 to get as close to 5 as possible.

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Anonymous Poster #1
#25

### Re: three phase problems.

01/23/2017 9:20 AM

load moving is okay......but the loads are (2.A + 2.A=4A; 2.5A+2.5A=5 A; 3A+3A=6A), so, how can we move 1A to R phase to make it 5 A? because the loads are 2*3A in B phase ie it can only be moved in 3 Amps.

My further concern is using RCCB/RCBO here (or in similar cases of current imbalance in three phases), if there is a current difference of more than 30 mA (sensitivity), because there is more current difference already than sensitivity.

Regards,

Guru

Join Date: Feb 2013
Posts: 1318
#26

### Re: three phase problems.

01/23/2017 9:57 AM

Option A: switch something off.

Option B: change earth leakage unit (RCD) to standard 60ma.

Option C: Call 0044 2722 3124 and tell someone who cares.

Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 8399
#27

### Re: three phase problems.

01/23/2017 10:22 AM

That description sound like you are using three single phase Ground Fault Interrupters on a three phase power application rather than a correctly designed three phase GFI device.

Use the correct devices for the job and the balancing issue won't be a problem being you will never ever get a three phase load to stay balanced to within +- 30 mA no matter how hard you try. Basic system voltage variation over time will guarantee it to be impossible.

Guru

Join Date: Dec 2010
Posts: 1263
#28

### Re: three phase problems.

01/23/2017 2:52 PM

3 + 2 = 5

3 + 2 = 5

2.5 + 2.5 = 5

What is the problem?

RCBO takes all 4 wires, 3 phases + neutral through its 30 mA operating detector, it operates on the residual current. Normally, any current going out through one wire of four is balanced by current coming back in another wire(s) - look up "Kirchoff's Law" - there is only a residual if current goes back to source via ground or another circuit.

It does not matter if the 3 line currents are not balanced - any unbalance is cancelled by the neutral current coming back in the opposite direction.

https://en.wikipedia.org/wiki/Residual-current_device

There is some residual in a healthy AC circuit if there is unbalanced capacitance to ground but most circuits are OK - could be problem with circuit with equipment with lots of Electro-Magnetic Interference [EMI] filter capacitors to ground.

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#31

### Re: three phase problems.

01/24/2017 3:01 AM

<...using RCCB/RCBO here (or in similar cases of current imbalance in three phases), if there is a current difference of more than 30 mA (sensitivity), because there is more current difference already than sensitivity...>

Nonsense. That is not what a <...RCCB/RCBO...> is for. The device is not there to deal with imbalance, as imbalance is normal; what it does is establish that the vector sum of all currents passing through it does not exceed its trip setting. So the neutral conductor must pass through the device as well. The vector sum is inferred as the current passing to the earth conductor, possibly via a human being. If that current exceeds its trip setting, in this case <...30mA...>, it operates to disconnect the fault.

Imbalance is normal, regular, and expected; it does not constitute a fault nor anything worth tripping over, and certainly not at <...30mA...>.

If in doubt, consult a qualified local Electrician.

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#32

### Re: three phase problems.

01/24/2017 3:07 AM

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Guru

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#2

### Re: three phase problems.

01/22/2017 8:03 AM

Why do you feel such a small load needs to be precisely balanced to begin with?

Are you saurevbabu from the other thread regarding trying ballace a tiny three phase load for no as yet justified reason figuring that if you ask again but anonymously this time you will get a answer you want and not what you got last time?

Anonymous Poster #1
#3

### Re: three phase problems.

01/22/2017 8:09 AM

as a matter of fact, in my earlier workplace, there used to be a problem of melting of cables. They say - it is because of three phase current imbalance. Thats why I wanted to analyze from the beginning.

Regards,

Off Topic (Score 5)
Anonymous Poster #2
#5

### Re: three phase problems.

01/22/2017 11:12 AM

Well, if your 'cables' here were single strands of #32 wire, you might have a problem...

Off Topic (Score 4)
Guru

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#13

### Re: three phase problems.

01/22/2017 2:39 PM

Sounds more like an undersized Neutral cable melting due to current imbalance or excessive harmonic current in the Neutral cable.

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#14

### Re: three phase problems.

01/22/2017 5:07 PM

Or it could be it was from using Cat 5 ethernet cable as a primary power feeder like the OP must doing to have concern over a 1 - 2 amp phase to phase current imbalance.

Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
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#18

### Re: three phase problems.

01/23/2017 5:08 AM

That's nonsense. The only reason a cable melts is because the overcurrent protection arrangements are inadequate.

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Guru

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#19

### Re: three phase problems.

01/23/2017 5:26 AM

Earthed Neutrals do not have fuses. BS7671 clause 132.14.2

Maybe their problem is reduced CSA neutral conductors in 3Ø, without reduced current.

Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
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#21

### Re: three phase problems.

01/23/2017 7:30 AM

Good guess. Whatever is causing a cable burn at 5-8A remains a curiosity, though.

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#23

### Re: three phase problems.

01/23/2017 8:05 AM

Curiosity solved. Wet string burns when dry.

Label instructions: Keep string wet to conduct. Do not over load as any drips may cause electrical leakage. In case of over-soaking use warm water to reduce shock from coldness. Do not touch energised wet string unless it is dry.

Caution: when dry, the string is a line isolator. To check balanced load use calibrated spirit level. Do not tilt head. Do not puncture bubble. Get an adult to help you.

Transmission line: see rope instruction.

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#29

### Re: three phase problems.

01/23/2017 7:54 PM

OP never said this low current application has a problem, only an application at a previous job had a problem.

as a matter of fact, in my earlier workplace, there used to be a problem of melting of cables. They say - it is because of three phase current imbalance. Thats why I wanted to analyze from the beginning.

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Guru

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#33

### Re: Three Phase Problems

01/24/2017 3:09 AM

<...They say...>

Clearly, <...They...> are wrong.

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#24

### Re: three phase problems.

01/23/2017 8:27 AM

I worked for 3 years at a consulting group in the electrical department. We were quite involved at that time with renovating nursing homes and hospitals. I saw melting cables (wires) in one facility I had to survey before deciding what to change to get then up to code regulations. This was a Mennonite nursing home. Now the Mennonites will not use electricity in their residences on their farms, but had to for a state approved nursing home. They also would hire only their own folks for jobs in the nursing home. So they had a maintenance man / electrician who never had worked with electricity. He had AWG 14 wire (2 mm²) on any thing up to a 50A breaker. He took a breaker and kept putting receptacle and lighting loads on it until it would open, then backed some load out. I suggest this may be what you were seeing if you had wires melting - too much load on too little wire size.

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Off Topic (Score 5)
Anonymous Poster #2
#6

### Re: three phase problems.

01/22/2017 11:48 AM

Because the OP cannot distinguish the subtle nuances between the reasonably-well-balanced three-phase load he has here and somebody else's outrageously ridiculously unbalanced load connected with undersized cables not spec'd for worst-case conditions?

Guru

Join Date: Sep 2016
Posts: 797
#7

### Re: three phase problems.

01/22/2017 12:46 PM

Nah, just be sure your neutral line was properly grounded. Increase of current on one line above tolerance is a sign of defect of perhaps winding coil loosing resistance or shorted along the line loop or, maybe the motor rewinding guy miscounted how many loops he has to make.

Off Topic (Score 4)
6
Anonymous Poster #2
#9

### Re: three phase problems.

01/22/2017 1:01 PM

When you are dead, you don't know that you are dead. It's a pain only felt by others.

Same thing when you are stupid.

Anonymous Poster #4
#16

### Re: three phase problems.

01/22/2017 7:10 PM

Some people though they sèem to live but are actually dead. They walk amongst us.

Oh, they've been tricked alright. Scared of death so they've died.

Guru

Join Date: Dec 2007
Location: Mumbai, India
Posts: 1995
#30

### Re: three phase problems.

01/24/2017 2:14 AM

but the ghost is still alive

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#17

### Re: three phase problems.

01/22/2017 8:44 PM

Harris, you have been outed! Your secrets exposed.

Score 1 for Off Topic
Guru

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#10

### Re: three phase problems.

01/22/2017 1:31 PM

sauravbabu and coolyaar in one week!

What have we done to deserve such torture?

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Guru

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Posts: 40598
#11

### Re: three phase problems.

01/22/2017 2:21 PM

Both posters you mention have been members here long enough to have gotten advanced technical degrees, and yet, seem to have learned nothing, except how to come here for answers.

The latter even suggested that his superior condoned these unethical acts.

If you keep feeding a stray cat, they keep coming back for more.

Tip of the hat to AP 2 for that astute observation.

Guru

Join Date: Feb 2013
Posts: 1318
#20

### Re: three phase problems.

01/23/2017 7:21 AM

Masters of the Con. Worked with many and they learn to hussle at a very early age.

Off Topic (Score 5)
Power-User

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#36

### Re: three phase problems.

01/25/2017 12:52 PM

well i am here to keep the flow going

Guru

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Posts: 797
#4

### Re: three phase problems.

01/22/2017 9:19 AM

http://www.tek.com/dl/55W_28943_0_HR_Letter.pdf

http://stevenengineering.com/Tech_Support/PDFs/45RPHS.pdf

Guru

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#8

### Re: Three Phase Problems

01/22/2017 1:00 PM

You should know the amperage draw of each piece of equipment you have...you should also know which breakers control what machines or other loads...sometimes the circuits are dedicated, one breaker for one machine....sometimes you can just switch the breaker positions in the box to balance a load....loads are rarely balanced all the time, because not everything is being used all the time....Some circuits require momentary starting current, that can be much higher than the running current, this should be taken into account, not only in phase balancing but also wire sizing and breaker type and sizing....

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Guru

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Posts: 1263
#12

### Re: Three Phase Problems

01/22/2017 2:28 PM

2
Anonymous Poster #3
#15

### Re: Three Phase Problems

01/22/2017 6:43 PM

What coolyaar (aka Haris Mahmood, electrical engineer from Lahore, PK) doesn't realize is that all of his postings are visible on Google. Hopefully his boss and clients will come across them someday.

Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 27180
#22

### Re: Three Phase Problems

01/23/2017 7:34 AM

Simple. Take any 1A single-phase load off the Y phase, and connect it to the B instead.

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Associate

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#34

### Re: Three-Phase Problems

01/24/2017 7:11 PM

When designed, the designer tries to allocate balancing 3 phase. But when used not always get the 3 phase balance.

Can replace four poles RCBO by four poles MCCB combination with 3 ELCB 2 poles.

If the neutral wire is out of RBCO, you'll get an error

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Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
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#35

### Re: Three-Phase Problems

01/25/2017 3:50 AM

Quite.

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