Welcome to the first in a series of articles focusing on electrical calculation basics. This month, we'll discuss the most fundamental of calculations — those for current (I) and kilowatts (kW). We'll also show you how you can do these calculations “in your head,” with very reasonable accuracy, through the use of constants.

#### Discuss this Article 32

I have a boiler with no data, but I measured the phase current for each phase. The reading is 19A at 380V? How do I calculate the power?

P = 1.73 x V x I x PF =1.73 x 380 x 19 x 0.80 = 9.9kW

or

P = 1.73 x 380 x (3 x 19) x 0.80 = 29.9kW

Which is correct calculation?

how will I know the ideal load on each circuit (single phase electricity?)

at 1 hp how much current will take 1 phase motor and 3 phase motor approximately please tell me.

hi,

i am having one doubt

if we had not divided 3 phase equally and powered on the current supply what will happen?

I have a 3 motor pump,1hp each single phase.what amperes of breaker that i use for the 3 motor pump?

Sir,

I have single phase lighting load,single phase AC load,single phase geyser load,single phase heater load.How to convert from 1 phase to 3 phase load

Hi ,

I would like know about the calculation of 3-phase line to line, line to neutral and line to ground current. I want to know what the difference between these three is. I design canteen and the supply is line to neutral, 3-phase. My calculation is like this:

I got the initial current ab, bc and ac.

How calculate the total current line to line? line to neutral? line to ground?

Thank you,

JDC

if using single phase 250 volts 200 amps going into transformer / converter running 50 hp motor out power generation of 40 kph what would consumption be per hour or day. would there be surplus or not.

I have one problem. How can I select cable size for 0.75 kW single phase motor? Please give the formula and also define the derating current formula.

Please tell me how to calulate the UPS required for a machine that is using 2.5hp, 3-phase AC motor with 230V 60 Hz AC input.

And please tell me how many Watts it will consume and current.

Please help.

I have the following motor:

1) 40hp, eff=94%, PF=0.83, SF=1.15, Amp=58.4, 3-phase, ambient Temp=55degC.

2) the ampere reading was 44.5 and V=385, but the air flow is low. so the contractor change the pulley.

3) new reading are Amp=68.5/69/68.6 for the 3 wire.

Are the new readings safe for motor or not? And i need to know the FLA for this motor because is not mentioned in the name plate.

I am having trouble nailing down a load calculation.

If,

I = 539

E= 460

PF = 91.0

kW= 39,033.1942

For a 3-Phase electrical motor, what would be my my total draw?

Dear sir,

I have 3-phase, low speed suguna motor. I have single-phase power at 240V. Please suggest a single-phase power to 3-phase converter box.

Dear sir,

I have five power sockets in a circuit. The socket mentions 16A/250V. What will be the VA or kVA of this circuit and which breaker should I use in panelboard?

Thanks

How many amps would 415V / 3-phase / 144A convert to in single phase / 240V?

I have a water pump (5.5kW) and a lift (7.5kW), 3-phase, 380V. I want to operate them using a generator. What capacity of generator is needed, taking in consideration the starting amps?

Hi everybody,

I'm a technician working in Dubai. I have some machinery. One of them is 75kW, 415V, 122A. What size circuit breaker should I use to keep it safe running? And wire size? It's a new setup.

Thanks for your help.

Can anyone help me please?

I need to find out what is the formula to calculate the 'Overload Setting' on a 3-phase motor, based on or assuming (for example) that the 3-phase voltage is 415V, and the rating of the motor is Example A - 800W or Example B - 1,000W.

I am looking to gain a clear understanding of how to be able to do this type of calculation, and any help with this would be greatly appreciated!

Can anyone help me? I have a 3.6kVA motor in an elevator. How much Full Load Amps is required in installation of servo?

I have four motors. Three motor are connected to a three-phase supply and total current is 35A. One motor is connected to a single-phase supply and total current is 7A. What is the total power and formula used to derive the answer? Please help me.

I'm frequently questioning myself about calculations for 480V to 120VAC transformers. I wish I would have did better in my power systems course in college.

Often, two legs of a 480VAC system are connected to the primary of a transformer. The secondary produces a single phase of 120VAC. What is the proper way to calculate the full load current of the primary?

I use the simple, single-phase calculation. However, although there are only two wires, the phase angle between the two legs on the primary is 120 degrees, not 180 degrees. Shouldn't this affect the calculation?

If it's a 3-phase boiler the correct answer is:

V=LINE TO LINE & PF=0.8

P = 1.73 x V x I x PF

P = 1.73 x 380 x 19 x 0.80

P = 9.9925kW, or 10kW

Please answer this question. If I have a 3-phase system, 400VAC and a total load of 140kVA, how do I find the current? I want to find the current but the thing is I have a single-phase load connected. So what voltage should I put to get current (i.e., 400 or 230).

Just wondering if someone can shed some light on this situation.

I am working on an extruder heater requirement. The original extruder is a single-phase barrel heating design. Each Zone is 4.2 Ohm. There are two heating blocks = 10,000W at 208VAC. On three-phase heating (balanced) you would say: 10kW / (208 x 1.732) = 27.28A / Phase.

Simple enough.

What happens if I connect the heater across two phases and the loading is not balanced? I told my boss that you would not have the benefit of the Root3. He told me I was full of it. I told him that 10kW = 460 x I(phase) and that I(phase) = 10kW / 208VAC = 48A.

Who is right?