Three Phase to Single Phase

Current will only flow through loads in a normal system. There is no spare current. You may worry about the balance of the loads on the phases, but the current will only flow where you have something in use.

If you have the floors separated by phase this could cause a small problem if one of the floors doesn't use any power. Blowing fuses by shorting phases is only going to happen from damage or failure in insulation or improper wiring. But that's what the fuses and breakers in your panel are for.

Is there a problem with your electrical system there?

Hi Kurt

Thanks a lot for your feedback and thoughts.

Yes, floors are separated by phase. But the likelihood that one floor will use zero current is not going to happen. Someone will use something!

Hopefully, my electrical system will have no problems.

Chris, London

Dear Friend

I presume that each floor is fed from individual phase, e.g. Ground Floor by "R", first floor by "Y" & second floor by "B". When your electricity company has given you a total connection for APARTMENT USE, then they are very well aware that UNBALANCE LOADING ON ALL THREE PHASES WILL HAPPEN. Donot worry about it. Electricity company would have already taken care of this or it not, then they will have to take care of this. This is NOT AN UNUSUAL SITUATION FOR THE ELECTRICITY SUPPLY COMPANY. "Sparks" will DEFINITELY not "Fly"!!!!

With good wishes for a happy, prosperous and peaceful new year.

Thanks and regards

Ashok Toshniwal, Bangalore, India

Dear Ashok

Thank you for your (and all the other guys comments - there are some very clever people out there) comments and your advice which I have read with great interest. Yes we have a 3 phase consumer unit/board and each floor will have one phase only. All apartments will be metered eventually as it avoids the problem of complaints later on.

My electrician has assured me that I should have no problems as diversity would kick in.

Chris, London

PS Thanks I feel assured that sparks will not fly (haha)

Dear Chris

Good to know, that now you are satisfied and have peace of mind ( or so I think!!! ). Your electrician got us into this discussion. Had he not told you about this, you wouldnt have started the discussion. Thanks to the internet, we now live in a global village where people can share their views and knowledge.

Now that your electrician is also convinced, then should I send him my bill for the technical info!!!! ( hahahahahaha )

Thanks and regards

Ashok Toshniwal, Bangalore, India

Dear Ashok Toshniwal,

sir ye aadmi (udti hui chingaari) koi hila hua insan lagta hai... aap kyo apna wakt barbaad karte ho...

good day flyingsparks,

interesting handle, do the sparks usually fly?

just a question before more consideration on this. (I have had a similar situation)

how is the metering to these six appartments set up?

Has to be individually metered, why would apartment 1 pay for the consumption of apartment 2 and so on. What if one family is on holiday with practically no consumption? The common area consumption ( security, lighting, lifts etc. ) is separately metered and bill is divided.

Apologies for this "intrusion" since question was directed to "flyingsparks" but my inner urge forced me to answer.

Thanks and regards

Ashok Toshniwal, Bangalore, India

Not allways individually metered, some properties only have a common bill due to each meter connection requiring a monthly basic connection fee wich some property owners feel is an unnessesary cost. Or so it is here in my part africa.

Dear Leonf

Could be true in Africa, & elsewere too where consumption is very low, but then 100 A is a large connection and therefore the incremental cost of individual metering is low. Generally this is taken care by the builder.

Thanks and regards

Ashok Toshniwal, Bangalore, India

hi

it is true that if you have meters installed by the supplier then they would impose what they call infrastructure cost. not so if you introduce your own metering.

hi

yeah i thought the handle would have been taken up a long time ago and surprised that it wasn't!

the meters will be set up after the 3-phase board. if you can what i have written below in your mind.

from left to right - 3phase100A service head to a 3phase meter to 3phase board. the service head and 3phase meter installed and belongs to the supplier (contractor).

the 3phase board has to be purchased by you (consumer). from the 3phase board you will have 6 MCBs, say, of 63A each connected to 6 separate meters and from there to the 6 consumer units. this is the setup i am going to have in the future. i am setting all this up for say in 2 years time when i make the move.

let me know if this helps. take care.

Not really sure why you are worried, I would think 100A for a pair of units is ample. And even though people are not in their apartment, I would be amazed if there is no or low power consumption. The refrigerator and/or freezer would still be on, possibly the PVR is recording, TV is on standby and the computer may be running. Sure more is consumed when people are home.

Trevor.

I agree,

I have a large property and run it off a 40A single Ph main breaker. It's hot here and I run aircons, fridges, pool pumps etc. from this supply constantly.

Hi Trevor

Yes you are right. I am a born worrier. I will find something to worry about when there is nothing to worry about.

Chris, London

Hi Flyingsparks,

What you have is the Max that can be supplied to your apartments. If they use nothing then it costs nothing except the monthly fixed service charge. 12kW is more than enough for an apartment, even with everything electric. You have no need to worry about "wasted" electricity as it is not happening.

regards

Chas

Two comments a) My house has a three phase current supply (due to some electricity norms all the hoses in the coloney has it- I am not sure what and is not logical) It is obvious that the consumption will be inherently unbalanced as higher loads will be most of the time on one phase only. b) In my factory, except the machine loads other ones are on single phase - lighting, welding generators etc. No sparks fly or are likely to fly unless you do a wrong connection and bring in two phases in place of a phase and neutral. However in the distribution transformer(if you have a specific for your apartment complex) you may have a problem and that was what the electrician meant. If neutral is isolated from main (as it will be generally), in case of huge un-balance in the secondary loads, you may land up in a) floating neutral and a significantly high voltage b) negative sequence currents c) High transformer losses.Since your consumption is not too high (only about 71KVA) i dont see much of a problem since your unbalanced load are usually matched up by other unbalances, and definitely it will not blow a fuse at substation (unless they have a small fuse) Ensure that the neutral voltage do not go to a dangerous level. PS:415V between phases are only about 240V LN -

What you have is quite normal for the UK, there is no way round it.

In Germany, each house/apartment gets 3 phase into its own fusebox, so the loading is intrinsically better balanced from house/apartment.....

Over the great mass of houses connected to one transformer, the loads probably equal out on the phases to a great degree.....even in the UK.

Anyway, its not your problem...

Dear Andy

Wow in Germany your homes are supplied via three phase. Intrinisically better and makes more sense. Transmitting over single phase is more wasteful. Wish we were that forward thinking here.

Chris, London

Hi Chris,

You have the power transmitted on three phase. you only have local distribution on single. This is better than a three phase supply of the same power as, in the case of your apartments with 12kW each, if they were supplied with three phase they would have only 4kW/ phase. The result of this is that you would have to distribute the loads around the house evenly across the phases. Since many loads are pluggable devices it would only take an ocupier to connect a hairdryer (1500W) into a phase already occupied by the washing machine, dishwasher or water heater (3000W) and that phase would be overloaded and trip the breaker.

As almost all domestic equipment is only available in single phase it is generally better to supply only single phase to accomodation.

regards

Chas

Hello Capblanc:

I quite agree with you, single phase is much better to individual houses with the power company doing the balancing act. Here we are supplied 240 volts, center tapped, i.e. 120-0-120 which works fine with the mix of 120 volt and 240 volt loads.

Heavier loads, such as electric stoves, clothes dryers, irrigation pumps and water heaters are on 240 volts and the rest of the house is split between the 120 volt lines. This minimizes, about as much as possible, the 3-phase supply line imbalance. One power transformer usually supplies about three to five houses depending on the total loads. 100 amp is common but 150 amp and 200 amp are also available if needed.

You wrote:-"As almost all domestic equipment is only available in single phase it is generally better to supply only single phase to accommodation."

You mix two things up completely and end up on the side of the electrical supply companies (or whoever decides that in certain countries, only single phase power will be delivered for domestic customers!)....I fully agree that most usage is with single phase units, but (as I believe I mentioned before) you will not understand how great it is to have small three phase water heaters under a remote sink or for a remote shower, or for a summer shower when the heating is off, where a PROPER stream of hot water is supplied, not awful small amount, that for example UK household suffer with!!! I hate UK showers!!!

I suppose it is a bit of "what you have never had, you don't miss!"

Also, occasionally we need to use larger AC motors with 3 phase connections to cut wood or mix plaster for spraying on the outside of the house. I had to uprate to 50 amp fuses in the company box for that last summer!! 3 x 50 amp at 415 volts phase to phase!!! That gets a bit of work done!!!!

Andy,

I agree with you on the fact that is better to have a 3 phase system provided to residential customers (just in case you have to connect something that needs higher power). Unfortunately in the US most residential areas are supplied only 2 phases (actually they are not 2 phases, but 240V (120V + 120V) with the (grounded) neutral as middle point, spaced at 180 deg apart). A normal Y 3-phase system is 208/120V, in industrial applications, which leads to equipment rated for 240V and equipment rated for 208V "single phase". In reality the 208V is is a phase-phase connection, so correctly it should be called "two-phase".

But about the difference between "3 small 3-phase water heaters" and (I assume) " 1 bigger 1-phase water heater", if they have the same total rating (assume 4.5 kW = 1.5+1.5+1.5 kW), why should the stream of hot water supplied be different ?

It is true that in the first case you would need (2) 20A wires, while in the second you would need (3) 10A wires, but the effect would be the same.

In europe, you are limited to either 13 amps per phase (UK) or 16 amps per phase in the rest.

A 16 amp water heater is slow, painfully slow (a 13 amp even slower!!), but a water heater with 3 x 16 amps, with 3 heating elements, not only keeps the phases balanced, but supplies 3 TIMES the amount of heating energy into the water!!!! So what takes 30 seconds on a single phase, takes only 10 seconds on three phase!!!

That is why 3 phase water heaters are much, much better. No they do not have the same total rating!!! They have 3 times the single phase rating!!!

Instant water heaters always (in my limited UK and German experience) use the maximum current allowed. There is no point in using less as it just makes the heating even slower.......and you have wash/shower in even less water......

Interesting Andy I didn't know that in Germany they brought 3-phase to every apartment and house.

However I must correct you in the permissable loads available in the UK. 13amps is the maximum on a UK plugtop. I have never heard of a limit of 16amps on single phase anywhere in Europe. 100amp single phase service is normal to a UK house, as it is here in NZ, dropping to 63-80 amps for small apartments. Single phase showers are available up to 12kW or so; a 10kW or 45amp shower is very satisfactory and certainly enough to turn my wife into a lobster!

If 3-phase is supplied to every house, I totally disagree that this is either necessary or appropriate. This increases the efficiency for the minority, but simply increases the cost, complexity and to a certain extent the risk for less benefit to the vast majority. Balancing 3-phase only becomes necessary at sub-station and street-feeder level.

A 3-phase supply to a house will never be balanced. Balancing requires an "aggregate of loads" and there are too few in an average house. So for example as soon as you boil a kettle there are no corresponding single-phase devices used elsewhere in the home (and there must be 2) to compensate. You will get an aggregate of loads across a street or apartment block, as everyone tends to use the same devices at the same time, but only if these devices are on different phases. If you can control which house gets which phase, this is possible and the sub-station is happy, but only if the supply authority delivers 1-phase to each dwelling. The authority accepts the (irrelevant) fact that a house is "imbalanced", on the proviso the entire street is in balance, and apportions phases to each dwelling in rotation.

However if you supply each house with 3-phase, the Authority loses this control. We ignore 3-phase loads as these are balanced already. However there is no way to ensure that a kitchen is on phase A in one house, but phase B the next and so on. It is perfectly possible that every kitchen in a street is on Phase A for example. So when the advert arrives in the middle of Das Boot and everyone runs to the kettle, the whole street is imbalanced and no-one finds out if Jürgen Prochnow lives :-)

So I support the system that everyone gets 1-phase and the associated lower cost, simplicity and greater safety this option provides. 3-phase is available then to those who need it and are willing to pay. Above 100amps, 3-phase is provided in the UK anyway.

Interested to hear yours and other comments on this subject. Perhaps this should be another forum topic.

Folks,

This is how I think that it works.

It is a 415 volt 3 phase service. In the UK, household standard is 240 volts.

Each apartment gets 2 hot legs, of the 3. This is 415 volts leg to leg. Now we have a ground and a neutral. The ground and the neutral are bonded and each leg to neutral gives 415/1.732=240 volts.

Dear Guest,

That is not the way it works. Each apartment gets one phase wire and neutral and gets 240V. The resultant currents in the phases is the sum of the two connected apartments on each phase and the neutral wire will carry the current equal to the vector sum (or imbalance) of the three phases

Chas

Flyingsparks,

Based on what you describe, the 3-phase system (phases A,B and C) feeds a total of 6 apartments (2 on each floor). In this case the total available power for each set of 2 apartments would be 100A * 240V = 24000 W. How that maximum load is split between the 2 apartments depends on what is connected in each apartment, but it is on the same phase (ground floor (2 apartments) on phase A, floor 1 (2 aparatments) on phase B and floor 2 (2 apartments) on phase C). Apartment loads are connected between one phase and neutral.

The neutral, which is probably used for all 3 phases (all 6 apartments share it), can carry a maximum of 100A (when either one or two of the phases is at zero load). If all 3 phases are equally loaded, the current through the neutral is zero (balanced system). Every other load combination leads to a current in the neutral between 0 (zero) and max (100A).

It's the same situation as having, say, this building on R, next-door on Y and the building down the road on B.

So, there's nothing to worry about.

Fuses are there to take out a fault downstream of them and to protect the downstream cables.

Firstly i would like to tell you that our bill do not come on the basis of current. But it come on the basis of energy consumed by you i.e kwh. Another thing is that current is depend on the load. SO, if u have problem of overload or u want more energy than u should go to power supplier and demand for more energy. It is your right to get proper supply. So go and talk to them. I think surely they will solve your problem

Regards:

Ashish Kumar Rai

From India

Arish,

You are right about the fact that customers pay for the consumed energy (kWh). but it is dependent on the average power (kW), which, in turn, is depenedent on the drawn current (A) at a predetermined voltage (V).

So, you use more energy in a longer time period, but you cannot exceed the maximum power for which the system is designed ( indirectly the drawn current -> wire sizes, overcurrent protection devices, etc).