Distribution of three phase to a home

guest; what country, state do you live in? perry

Hello Guest,

In practice it is difficult to exactly balance the differing loads across three phases at the same time - that is why a neutral conductor is used, in addition to the 3 phases.

However, it is possible to obtain a reasonable balance.

Total up all loads individually.

Divide by 3, and connect each load to the 3 incoming phases accordingly.

It is just a matter of simple mathematics.

If the load is not truly balanced across the 3 phases, it just means there will be a small neutral current, which carries the imbalance current at any time.

Trust that assists you.

Kind Regards....

Thanks for the replies. This is in Bangalore, India.

One of the reasons, I am paranoid about this is By keeping high noise equipments like Borewell Motors in separate phase, I can protect sensitive systems away from noises/spikes in the line. Is my understanding, right?

Vas

Hi!

I'm no electrician BUT, my recommendation is DONT DO IT!

a) It is illegal in most country's to have a single phase wall socket (for example) within 2 meters of another single phase socket working off a different phase. The reasoning behind that is that you could stick your finger in each socket and get a potential of .........lots of elephants creating lots of smoke!

b) and long after your carefully worked out plan is forgotten, someone will come along (to extend a ring main) and caramba! I hope I don't have to explain that one in more detail!

Hi Beej50,

How is ya!

Now .........lots of elephants........is this wot you had in mind???????

Oops!!.....sorry.........these are 'Frican elephants............not Indian elephants

.......would you have red, white or blue currants???????..............may be black as well...........and........ green!!!!!!

and

......someone will come along (to extend a ring main) and caramba!

.....did you have something in mind lie this????

............three things one needs to be afraid of........ac........dc .........and........ JC

Hey Mobi

You've got it EXACTLY! But whats JC? I need to know so that I too can be afraid of it!!!

I can't tell you too much about him, he was a bit before my time............but............they wrote a best seller about him.

The world.........well the "christian" part of it, any how, go mad this time of year..........spending all their money, that they haven't got, on things people don't really want.

I can't suppose one can complain too much.........after all it is only a pagan celebration.........coutesy of Constantine The (not so) Great......I think......me thinks.

This is supposed to be Constantine with his wife Helena (I think)............after becoming a "christian" he had his wife murdered...........he was also responsible for bringing the pagans and their festivals and mixing them up with "christian" practices.

Oh! Sorry............didn't mean to bore you to death.

Hello Spakstation,

Interesting--Guest, Do you have any three phase household items(using all three phases)?

I haven't researched this yet--But I asked a journeyman, during my apprenticeship, about sharing a neutral with out of phase legs and was told that it was permissible(They are common at the panel). I don't like it--If the neutral wire opens then you would have opposed phases shorted through their loads. The other thing is that the neutral may be undersized for two or more differing phase circuits.

Maybe I worry too much.

If the neutral wire opens then you would have opposed phases shorted through their loads.

Just for clarification, the words 'shorted through their loads' would be misleading in that the loads would voltage divide due to being in series between the opposing phases.

If the loads were essentially equal you would not even know the neutral was broken. If a couple of light bulbs from Line A to N go into voltage divide (series) with a refrigerator from Line B to N, then you would really notice the difference, but not a 'short'.

The fact is, it's quite normal and expected that current will run from Line A to Line B through the 120v loads connected in common to neutral from both phases. The neutral is usually downsized for that very reason, since it is only going to carry the difference between the currents in Line A and Line B.

Example, Line A to N loads draw 10 amps. Loads from Line B to N draw 9 amps. The neutral will only be carrying 1 amp. This is the reason it is desirable to balance the loads of the circuits.

What I see as a more important detail is the type of circuit. If 4 wire Delta, or if wye connected, then the responses to the question asked change. It is difficult to balance load on a delta 4 wire since all single phase load will be carried by 2 of the phase lines, and only 3 phase loads can be on the other Line. This is why Wye circuits are preferred in mainly single phase load dominant situations - easier to balance loads.

As for the noise interference issue, keep in mind that the Line currents share the phase currents and therefore any such 'noise' would be shared across the system. Sensitive equipment is usually equipped to handle common disturbance, and if disturbance is higher than common design, then there are devices such as special power supplies and Uninterruptable Power Supply units that can be installed that isolate much of the 'noise'.

I'm thinking the electronic and communications forum might be a good place to share this particular question.

Hi,

Thanks for the post.

Can you someone please explain why neutral should not be carrying current or what are the drawbacks?

Vas

No drawbacks, quite normal for neutral to carry current.

That is it's purpose, however where Line A and Line B both have single phase loads that connect to the same neutral, the majority of the current flows between Line A through the loads, across the neutral connection point, through the line B loads to Line B. Then it reverses and flows back by the same path to complete one cycle of AC.

If the collective values of loads on both sides of the neutral point happened to be exactly equal, then no current would be available to flow on the neutral. As loads are switched on and off, resulting in differences in current draw between the two sides, the neutral Line provides the source or the return path for the current difference. This way the loads on either side of the neutral are not forced to carry current beyond what they would normally draw, which is what becomes the case if the shared neutral gets broken somewhere on the way back to the source.

Excellent--I will have some questions for you sometime, CJ.

Mine is a three-phase design (and subscription - in Israel quite cheap relative to single-phase with the same range of consumption), and the distribution was calculated on the assumption of maximal load at each typical outlet, as the case may be.

Over the years, minor modifications were made, to accommodate for changing gear at those given outlets, and the main concern is not to blow a fuse here and there, but instead to provide ample of available current in cases of emergency

Hi,

I do not have any three phase equipments.

Thank you

Vas

Dear Friend,

The lighting and power load is to be distributed evenly on all the three phase.

hasan Javed.

You may also allocate each phase to a different cascade of applications

Looks like the solution to the problem is being taken to the extreme level.

for one the input supply is coming from the Distribution company (in this case KPTCL) and is bound to have the effect of noise that already exists on the grid on the load connected to it.

as regards distribution suggestion is:-

Connect one phase (say A or R) to lighting load. If you are using an Home Inverter connect the same to this phase and keep only the Lighting load (Lights + Fan + Audio + Video systems ) to this phase

Connect the second phase (Say B or Y) to Heating Load. (Heater, Geyser, Pump, Washing Machine, etc)

Connect the Third Phase (Say C or B) to AC & Ventilation System ( you can connect all your Air Conditioners to this Phase)

Your next door neighbour may have a single phase input (which incidently you will not know to which phase he is tapping into) and he/she may have all the loads connect to that phase which may inject noise to the system.

For Domestic consumption I think this should suffice & unless you want to control the power factor of your loads. If you want to control the Power factor that is another topic of discussion.

Incidently this is how I have connected the loads in my house in Bangalore.

I am a Master Electrician in Wisconsin. I have wired many homes and know work in the industrial sector. I see no reason to need a three phase system in a home. Your usage is never going to be the same because it is rare that all the outlets will have the same things plugged into them and turn on. Same goes with with the lighting. Light will not be on all at the same time and that load is usually small. As far as motor loads there are not generally that many in residential setting. Also the neutral concern is true, that if you are sharing a neutral the breaker handle have to be connected together so if one breaker is turned off they all turn off so if someone is working on a circuit and they would open the neutral there wouldn't be the potential for the other phase ( if loads are being used on them ) to be trying to find a ground and cause a spike in voltage on them blowing electronic items. Stick with the single phase, its safer

Hello,

Since there is so much importance was mentioned in the above threads, what kind of earthing (chemical versus non-chemical ...etc...)you did at Bangalore? Do you have any recommendations/suggestions for vendors?

Thank you

Hi, I am an American E.E. living and working in Thailand.

Voltage here is 220/380-400>< .

The standard practice here on a home with over 300 M2 is using 3 phase power.

It is difficult to balance the load, but planing can make the task fairly easy.

The biggest problem is having no control over who or what is connected to the supply transformer along the road. Phase loss is common here, as are very low voltages below 180 V is not uncommon which presents a whole other problem. Most of the transformers are overloaded and no where near balanced. We routinely use low voltage protectors w/ times delays on both single phase and 3 phase loads, mostly to protect motors like pool and water pumps. Failures here are mainly that the contactor coils melts or the start Cap blows or melts.

We must make our own distribution plans on most all projects so we keep phases as seperated physicaly and by load type as much as possible.

Educating the my staff to the dangers of electricity has been the most difficult. They are very careful and I insist on rubber sole shoes when doing any electrical, difficult in a country where shoes are not worn in the house.

In retrospect I have never had a problem with 3 phase installations here, when properly installed, protected and proper grounding is installed.

Harve a great day

Farang ( an American in Thailand )

Sorry Mr. Farang, for mistaking you with the other guest. Thanks for pointing out and giving additional information.

Now I feel that, what you have at present is the best - better will come if your local distribution system is rectified or else you are ready to spend a huge sum.

Dominic- Bangalore