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Case1:

If I have three single phase connections with each having its own single phase energy meters And I connect 1kw load on each of these phase continuosly 24/7 for a month.

Case2:

Now next month instead of three single phase connections I opt for a single three phase connection with a 3 phase energy meter and I connect the same single phase loads (1kw) on each of the 3 phases 24/7 for a month.

At the end of the month will by electricity bill in Case 2 be lower than that of Case 1 and why?

P.S. This is not a homework question, I'm trying to understand 3 phase power vs 1 phase power.

Edit:

So single phase loads don't seem to have an advantage in a 3 phase power supply system.

Now how about a single phase 2kW motor running 24/7 on a single phase supply for a month and then the next month i use a 2kw 3phase motor and run it 24/7 on a three phase supply. In this case surely the 3phase system will have an advantage of lower consumption (lower electricity bill). Isn't it?

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    \$\begingroup\$ That will depend on the rates charged for the electricity : companies decide the rates based on their customer base and many other factors... \$\endgroup\$
    – Solar Mike
    May 5, 2018 at 10:06

4 Answers 4

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The bills will normally be the same - unless the 3 phase connection is charged on an industrial tariff while the single phase is a domestic tariff. That's a matter for negotiation with the supplier.

But consider the cost of installing the supplies.

Each single phase supply requires two wires from the substation to your house. That's potentially a total of 6 wires, whereas the 3 phase supply only requires 3 (in Delta).

So in practice those three single phase supplies will be the three phases of a 3-phase supply to save copper. (Normally, with a fourth Neutral to handle any imbalance between them)

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  • \$\begingroup\$ Thanks for the answer ,please see my edited question. \$\endgroup\$ May 5, 2018 at 14:53
  • \$\begingroup\$ What makes you think the edit changes anything? \$\endgroup\$ May 5, 2018 at 14:55
  • \$\begingroup\$ I thought a 3 phase load draws less current from each wire (phase) than a single phase load would. \$\endgroup\$ May 5, 2018 at 15:07
  • \$\begingroup\$ But it draws current from more wires, so ...? \$\endgroup\$ May 5, 2018 at 15:10
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The daily energy usage measured would be the same

But, most consecutive months are not the same length :) and suppliers may charge different tarriffs etc.

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Your electricity bill will be the same. You still need the same amount of power from your provider. Altough if you connect 1 kW to 1 phase it could be that a fuse goes off or you get a unbalanced phase if you have other power-eating devices on that phase (like dish washer, electric cooker). I would take case2. Here is a good explaination to this topic

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  • \$\begingroup\$ So when does a 3 phase system really perform better vs a single phase system? \$\endgroup\$ May 5, 2018 at 14:54
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    \$\begingroup\$ If you need high power you should take the 3 phase system, like you said 2kW Motor, for low power devices you should take the single phase because you have lower costs for converting it into dc for example. Your power supplier looks on all 3 phases and the current (Power) you need on them. So you will have three times more current on one phase than on a 3 phase system on one phase, but you still have the same amount of power drawn \$\endgroup\$
    – Ribisl
    May 5, 2018 at 15:33
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All of the above are incorrect. Must calculate amp requirement by hp of equipment and assess against your providers fee for single vs three.

hp for hp, three phase requires less amps.

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    \$\begingroup\$ Welcome to EE.SE. Note that answers float up and down by votes and user sorting preferences so "All of the above" doesn't work (unless you hope that your post will stay at the bottom which it might as it stands). You may have missed that the motor was an add-on to the question which originally asked about 1 kW loads. "Must calculate amp requirement" generally doesn't help calculate billing charges which are typically kWh only for domestic but include reactive power charges on commercial metered systems. You can edit your answer at any time to improve it. \$\endgroup\$
    – Transistor
    Mar 17, 2021 at 11:33

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