# 3-Phase Back-of-the-envelope Calculation Check

Status
Not open for further replies.

#### dksoba

##### Member level 2
Hi All,

My small consulting company is moving into an industrial location since we are getting a used CNC milling machine. The machine takes 208V 3-Phase power, and the required current rating is 40 amps. I know that actual current usage depends on the load, but I'm trying to estimate the worst case scenario for the power usage of the machine.

My calculation is as follows:

P = IV
P = (40A worst case)*(3 since it's 3-phase)*(208V RMS) = 24.96 kilowatt's

The power company charges $0.15 for each killowatt hour, so for each hour the maximum power cost of the machine is estimated as: Cost = (24.96 killowatt)*($0.15/(kw*hour)) = $3.744/hour (About a cup of Starbucks coffee, I'm told) So if I run the machine for 40 hours a week, for a month (which I won't), it would cost: (40 hours/week)*(4 week/month)*($3.744/hour) = $600/month. I can live with that. I just don't want to end up with a$10,000 electric bill as a surprise one month. In reality, I'll run the machine 2 hours a day, at 10% load, so it's probably more like (10 hours/week)*(4 week/month)*($0.3744/hour due to 10% load) =$14.976/month.

Thanks everyone for double checking my 3-phase back-of-the-envelope calculations.

Matt

Status
Not open for further replies.