# Three phase to Single phase current calculation

I have a three phase 380V system using 16A MCCB. Phase to Neutral is 220V. I want to install a single phase elevator that has the following specs: Voltage = 220V. Power = 3700Watt. If I calculate the current requirement with the following formula: I = P/V I get 16.81A (3700W/220V). I called the sales to reconfirm and they told me that the required current to operate the elevator is 25A. Now, since I am taking the power from a three phase system, will it provide enough power for the elevator? Can someone please teach me how to calculate the current conversion from 3P to 1P?

UPDATE #1: Thank you for the responses so far. However, if we put in the variables in rapidtables, it gives me just 7A (W=3700, V Type = Line to neutral, V=220, pf=0.8). Please note that my three phase source is 380V and I am using one of the three line to neutral to get 220V for the elevator.

• The only real answer is replace the single-phase motor with a three-phase motor. – StainlessSteelRat Dec 14 '17 at 15:19
• I see three options. Increase to 3x25 A service (monthly cost), get a big 400->230 V transformer and connect across two phases and get in just under 10 A or get a three phase elevator. – winny Dec 14 '17 at 19:46

You have 16A MCCB. Safety regulations require that you can only use 80% of that, which is 12.8A. So no matter the single-phase math, you have to do something different.

If I put your single-phase numbers into rapidtables I get 21A. 7A is the three-phase calculation. Hence my comment:

The only real answer is replace the single-phase motor with a three-phase motor.

Apparent Power $$pf = \frac {P} {S}$$ $$S = \frac {P} {pf} = \frac {3,700W} {0.8} = 4,625VA$$

Means a single-phase current of: $$I_{Phase} = \frac {S} {V_{Phase}} = \frac {4,625VA} {220V} = 21.0A$$

So maximum CB is 16A, safety is 12.8A. You cannot supply power to your elevator using a single-phase motor.

Three-phase power:

$$P_T = \sqrt {3}\ V_{Line}\ I_{Line}\ cos\ \theta$$ $$I_{Line} = \frac {P_T} {\sqrt {3}\ V_{Line}\ cos\ \theta} = \frac {3,700W} {\sqrt {3}\ \times \ 380V\ \times\ 0.8} = 7.03A$$

Under 12.8A.

At this point, the best advice we could give you is consult an electrician. If you have three-phase power available, it is always best to use it.

You have 3x16A. It this is mains, you can load only 1 phase without much problems.
This will get your three times 1x16A. But you want 1x25A, so you're 9A short.

The only way to use this elevator is to upgrade your connection to 3x25A or more.

I suggest you get an elevator with three phase motors or variable frequency drives instead.

There is a difference between true power (P) and apparent power (S), extra you may add also the efficiency of the electrical to mechanical conversion. Some machines do specify the mechanical power, so:

$$P_{el}=\dfrac{P_{mech}}{\eta}$$ $$S^2=P^2+Q^2$$ $$P=S\cos\varphi$$ $$S=\dfrac{P_{el}}{\cos\varphi}=\dfrac{P_{mech}}{\eta\cdot\cos\varphi}=U\cdot I$$

Buy a three phase motor, it's much better if you already own a three phase installation.