3 Phase Electrical Power Calculations

[chris m]

Good Morning

 

I am getting extremely frustrated searching the internet for help with this topic so I figured I'd throw it out here although it has absolutely nothing to do with Mastercam.

 

Following a recent shop floor reorganization we have developed some issues with our 208V electrical service [excessive voltage drop at the machines, DNC problems, etc] and I have shouldered the task of trying to get it squared away. What I am looking for right now are the calculations for things like: transformer sizing, circuit breaker sizing and conductor sizing based on machine full-load current requirements and distance from the distribution panel. I know that I can get these from the National Electric Code but I'd rather not spend the money to buy a copy if I don't need the whole damned thing.

 

Any spark heads out here?

 

Thanks

 

C

[specv]

You know you can get the NEC books from a public library?

[Müřlıń®]

If your power company is having voltage drops you have to get a special transformer that will hold constant voltage.

 

I think it has some extra capacitors built in.

They are kinda pricy....

 

next fix: I would just go up a tap on your transformer. You might have to change your overloads if you do this...

 

 

Overvoltage protection will shut you off should you surge too high, but low voltage is the circut killer.

[Allan]

I have a wallet card I got from the local electrical supply shop. Motor HP rating to KVA for sizing transformers, does that help?

 

Allan

[Müřlıń®]

Chris there is also some in line boosters you and add to the specific line you are having trouble with.

 

Call your electric company and let them run a voltage test on your service.

 

Sometimes they can make a few adjustments and you wont have to do anything.

 

I have done this several times in the past, I wired all the 3-phase to all my machines including my CNC's.

[chris m]

Pete

 

I thought of that but didn't actually act on it; tough to say 'OK, boss; I'm off to the library...'

 

That being said, I may need to do just that since I am really getting nowhere

 

Allan

 

Thanks for the offer but I did run across one of those and one that charts motor HP to wire size. I am looking for some real formulae to deal with additive loads, etc, on top of the 'simple' stuff

 

Murlin

 

While I appreciate the info, it isn't really what I'm looking for. The power company is involved on their end [outside the building] but I need to do some math to figure out how f__ked up we are on our end. If I have a wire run that should use single-ought wire and we have #3, I want to know about it

 

 

C

[Müřlıń®]

Equation 1: Calculating the actual Voltage Drop in volts Volts Dropped = (2 x 0.866) x L x R x Amps/1000

 

Equation 2: Calculating the Wire Size in circular mils CM = 2 x K x L x Amps/Acceptable Voltage Drop Alternatively, you can algebraically manipulate Equation 1 to: R410002Acceptable Voltage Drop/1.732 x L x Amps and then look up the wire size according to its AC resistance.

 

Equation 3: Calculating the Length in ft Length = 1000 x Acceptable Voltage Drop/ (2 x 0.866) x R x Amps

 

Equation 4: Calculating the Load in amps Amps = 1000 x Acceptable Voltage Drop/ (2 x 0.866) x R x L

 

 

linky