3 ms·

But you have three feeds giving you three phases to use, so 3x the power available to you. Out here, even electric stoves (with ovens) have 3 phase connection o

But you have three feeds giving you three phases to use, so 3x the power available to you. Out here, even electric stoves (with ovens) have 3 phase connection options and tankless water heaters almost exclusively come as 3 phase models.

bluGill 3y ago
Power is volts times amps. 3 phase just means you add the power of all three phases, but you can get the same power from one phase with a little algebra. You need different size wires and breakers, but there is nothing there that 3 phases gives you.
- ajsnigrutin 3y ago
  Let's say you have a cable with 2.5mm^2 wires, each of which can carry 20A of current to stay within code. At 230V that's 4600W. Now you want more power, to keep the math simple, let's say 13800W (3x the power above). With a one phase system, for 3x the power, you need 3x the size of wire, so 7.5mm^2, ie. 3x the amount of copper (since all wires, neutral and PE have to be that size too). With a three phase system, you can get the same power with 3x2.5mm^2 live wires (+1 neutral + 1 PE), so instead of 3x the amount of copper, you only need 5/3's of copper to get 3x the power.
  - BenjiWiebe 3y ago
    Not sure what PE is in this example, but you don't need a neutral in 3 phase.
    - ajsnigrutin 3y ago
      You don't need it in a "triangle"/"delta" wiring, but you need it in a "star"/"Y" - https://www.electronicshub.org/comparison-star-delta-connections/ https://www.electronicshub.org/comparison-star-delta-connect... PE is protective earth, grounding wire. Usually you need PE and neutral lines separate for FID (GFCI) protection.
- stephen_g 3y ago
  You’re again talking in hypotheticals and ignoring the practical factors. Around here, it’s usual for the utilities to limit residential services to 80A per phase (commercial properties can get a lot more). So for a residential property you can literally get three times as much power by upgrading from single phase (which is common for small houses) to three phase (less common around here but available) due to this limit. In theory I could just get a single phase service of three times the current, but in the real world the utility won’t give me that and makes me upgrade to three-phase. This is by policy, since it helps balance the phases in the grid back to the local transformer, which the utility wants, so they also limit, for example, how much solar export you can do per phase for residential property - theoretically I should be able to export 15 kW on a single phase, but they don’t let me, so in the real world I am limited to 5 kW per phase, meaning I can only export 5 kW on single phase or 15 kW on three phase. So in terms of pure electrical theory you are correct, but when thinking about real world policies of electrical utilities due to how power grids are designed, you do get a lot of benefit from three-phase.
- applied_heat 3y ago
  P=sqrt(3) IV cos Theta not just three times IV

bluGill 3y ago

Power is volts times amps. 3 phase just means you add the power of all three phases, but you can get the same power from one phase with a little algebra. You need different size wires and breakers, but there is nothing there that 3 phases gives you.

ajsnigrutin 3y ago
Let's say you have a cable with 2.5mm^2 wires, each of which can carry 20A of current to stay within code. At 230V that's 4600W. Now you want more power, to keep the math simple, let's say 13800W (3x the power above). With a one phase system, for 3x the power, you need 3x the size of wire, so 7.5mm^2, ie. 3x the amount of copper (since all wires, neutral and PE have to be that size too). With a three phase system, you can get the same power with 3x2.5mm^2 live wires (+1 neutral + 1 PE), so instead of 3x the amount of copper, you only need 5/3's of copper to get 3x the power.
- BenjiWiebe 3y ago
  Not sure what PE is in this example, but you don't need a neutral in 3 phase.
  - ajsnigrutin 3y ago
    You don't need it in a "triangle"/"delta" wiring, but you need it in a "star"/"Y" - https://www.electronicshub.org/comparison-star-delta-connections/ https://www.electronicshub.org/comparison-star-delta-connect... PE is protective earth, grounding wire. Usually you need PE and neutral lines separate for FID (GFCI) protection.
stephen_g 3y ago
You’re again talking in hypotheticals and ignoring the practical factors. Around here, it’s usual for the utilities to limit residential services to 80A per phase (commercial properties can get a lot more). So for a residential property you can literally get three times as much power by upgrading from single phase (which is common for small houses) to three phase (less common around here but available) due to this limit. In theory I could just get a single phase service of three times the current, but in the real world the utility won’t give me that and makes me upgrade to three-phase. This is by policy, since it helps balance the phases in the grid back to the local transformer, which the utility wants, so they also limit, for example, how much solar export you can do per phase for residential property - theoretically I should be able to export 15 kW on a single phase, but they don’t let me, so in the real world I am limited to 5 kW per phase, meaning I can only export 5 kW on single phase or 15 kW on three phase. So in terms of pure electrical theory you are correct, but when thinking about real world policies of electrical utilities due to how power grids are designed, you do get a lot of benefit from three-phase.
applied_heat 3y ago
P=sqrt(3) IV cos Theta not just three times IV