jtb
Senior Member
- Location
- Pennsylvania
If one has a 3PH 4W 208Y/120V panel rated 225A,
what is the max KVA that can be supplied from it?
Thanx!
what is the max KVA that can be supplied from it?
Thanx!
panel kva rating??
- Thread starter jtb
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ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: panel kva rating??
kVA=three phase Volts x Amps * 1.73 / 1000
208 x 225 * 1.73 / 1000
= 81 kVA of noncontinuous load
[ July 14, 2003, 08:27 PM: Message edited by: ron ]
kVA=three phase Volts x Amps * 1.73 / 1000
208 x 225 * 1.73 / 1000
= 81 kVA of noncontinuous load
[ July 14, 2003, 08:27 PM: Message edited by: ron ]
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: panel kva rating??
That would work for a single phase panel. For three phase, you use the line-to-line voltage, and insert the square root of 3 into the formula.
208 * 228 * 1.732 / 1000 = 81 kva.
That would work for a single phase panel. For three phase, you use the line-to-line voltage, and insert the square root of 3 into the formula.
208 * 228 * 1.732 / 1000 = 81 kva.
charlie
Senior Member
- Location
- Indianapolis
Re: panel kva rating??
Ron, you calculated the transformer coil kVA. Just multiply your answer by three to get 81 kVA, the same as Charlie B.
jtb
Senior Member
- Location
- Pennsylvania
Re: panel kva rating??
Thanks Guys. I had 81 KVA, just wanted to check.
Thanks Guys. I had 81 KVA, just wanted to check.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: panel kva rating??
Whoops!
Whoops!
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: panel kva rating??
I?ve never dealt with 2-phase systems, not even in college. But I have a suspicion that the power formula for a 2-phase system is not as simple as V * I. My reasoning comes from understanding why and how the square root of three comes into the 3-phase system power formula. The 1.732 results from adding (trigonometrically) Va * Ia + Vb * Ib + Vc * Ic, under circumstances that place the three voltages 120 degrees apart from each other, and the three currents 120 degrees apart from each other. When you do a similar calculation with two phase voltages 90 degrees apart from each other and two phase currents 90 degrees apart from each other, the math should not work out as simple as V*I. It would not surprise me if a factor of the square root of 2 found its way into the picture. Does anyone have a reference that tells how to calculate 2-phase power?
I?ve never dealt with 2-phase systems, not even in college. But I have a suspicion that the power formula for a 2-phase system is not as simple as V * I. My reasoning comes from understanding why and how the square root of three comes into the 3-phase system power formula. The 1.732 results from adding (trigonometrically) Va * Ia + Vb * Ib + Vc * Ic, under circumstances that place the three voltages 120 degrees apart from each other, and the three currents 120 degrees apart from each other. When you do a similar calculation with two phase voltages 90 degrees apart from each other and two phase currents 90 degrees apart from each other, the math should not work out as simple as V*I. It would not surprise me if a factor of the square root of 2 found its way into the picture. Does anyone have a reference that tells how to calculate 2-phase power?
Re: panel kva rating??
Charlie, you are correct, the square root of two is the number for calculating two phase.
The neutral of a two phase system will carry 1.41 times the highest current on one active line.
An 80 amp load will produce 112 amps on the neutral. Two phase systems had fused neutrals when used for services to lighting panels.
Two phase systems were originally intended only for motor starting purposes.
[ July 22, 2003, 12:29 PM: Message edited by: bennie ]
Charlie, you are correct, the square root of two is the number for calculating two phase.
The neutral of a two phase system will carry 1.41 times the highest current on one active line.
An 80 amp load will produce 112 amps on the neutral. Two phase systems had fused neutrals when used for services to lighting panels.
Two phase systems were originally intended only for motor starting purposes.
[ July 22, 2003, 12:29 PM: Message edited by: bennie ]
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