Conductor Calculation

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mstrlucky74

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What is the 1.732 for? Thanks



Branch Circuit Continuous Load Example: What size branch-circuit overcurrent protection device and conductor (THHN) is required for a 19 kVA of nonlinear loads (75?C terminals). The branch-circuit is supplied by a 208/120 volt, 4-wire, 3-phase, Wye connected system.
Step 1 - Size the overcurrent protection device in accordance with Sections 210-20(a) and 384-16(d). The first thing that we must do convert the nonlinear load from kVA to amperes:
Amperes = VA/(Volts x 1.732), Amperes = 19,000/(208 volts x 1.732), Amperes = 52.74 amperes, rounded to 53 amperes
The branch-circuit overcurrent protection device must be sized not less than 125% of 53 amperes, 53 amperes x 125% = 66 amperes. According to Section 240-6(a) we must select a minimum 70 ampere overcurrent protection device.
 
mstrlucky74 said:
What is the 1.732 for?...
Click to expand...
The solution assumes the 19kVA load is supplied via all three phases. When load is balanced on all three phases...

I = (kVA ? 1,000) ? (E ? ?3)

...where:
I = line current
E = line-to-line voltage
?3 = 1.732 rounded

Edit: the ? represents the square root symbol... which isn't supported on the forum any more.
 
Smart $ said:
The solution assumes the 19kVA load is supplied via all three phases. When load is balanced on all three phases...

I = (kVA ? 1,000) ? (E ? ?3)

...where:
I = line current
E = line-to-line voltage
?3 = 1.732 rounded

Edit: the ? represents the square root symbol... which isn't supported on the forum any more.
Click to expand...


???really????

Edit, I guess it doesn't. It showed up as square root symbol when I was composing and changed it to question marks after posting.
 
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