In a plant I work at we have a 5000hp/4160 volt motor that moves feedwater. We have 480 volt switchgear that feeds several motor control centers of which have numerous 3/4 to 11/2 hp motors attached. My question is, why can we use 480 to supply numerous switchgear and we need 4160 for one motor?
Power question concerning feed voltages
- Thread starter Bamaman
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zog
Senior Member
- Location
- Charlotte, NC
The motor was an afterthought?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If you did the calculation you would see that a 5000hp motor at 480 volts would take an enormous size wire and a service very very large. The larger the voltage serving the motor the less amps the motor will draw..
Look at Table 430.250-- it shows a 500 hp motor at 460 volts that draws 590 amps. That in itself is a big deal. Now put a 5000 hp motor and you would not be able to wire it at 480 volts without a tremendous hassle.
Look at Table 430.250-- it shows a 500 hp motor at 460 volts that draws 590 amps. That in itself is a big deal. Now put a 5000 hp motor and you would not be able to wire it at 480 volts without a tremendous hassle.
If I understand your question correctly it basically falls back to a HP = watts equation. The more the HP, the more electrical power (watts) are needed. Watts are a derivative of voltage and current, the higher the watts the more of one (or both) you need.
The amount of current determines the wire size so for a give n wire you can get far more watts the higher the voltage.
The wire size for a 5000 hp motor at 480 (to get enough Watts) would be phenomenal.
For smaller HP the smaller wire sizes at 480 are adequate and higher voltages for the smaller motors pose more design cost and safety factors.
Hopefully this helps.
(Dennis, sorry, I;m a slow typer)
The amount of current determines the wire size so for a give n wire you can get far more watts the higher the voltage.
The wire size for a 5000 hp motor at 480 (to get enough Watts) would be phenomenal.
For smaller HP the smaller wire sizes at 480 are adequate and higher voltages for the smaller motors pose more design cost and safety factors.
Hopefully this helps.
(Dennis, sorry, I;m a slow typer)
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Bama, it's really an extension of the same reason larger loads in your home are 240v instead of 120v.
Think of it this way: Insulation is cheaper than conductor.
Think of it this way: Insulation is cheaper than conductor.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
1000HP is about the practical limit for 480V systems, and even that is rare. A lot of plants now switch to Medium Voltage as soon as you go above standard NEMA frame sizes, essentially 250HP (although 600HP is more common as a cut off point).
- Location
- Massachusetts
Could I even get a 5000 HP 480 volt motor starter?
Yep, we will buy 200HP 480V motors, anything above 200HP is 4160V. From what the motor distributors tell me this is a fairly common standard because up to 200 HP, 3600 RPM and 1800 RPM motors are in stock and available next day, anything larger is hit or miss.
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