Capacitors are like electrical batteries that charge and release power super fast. They help with power factor correction, voltage stabilization, and reducing load strain.
When we size them (and their wires, breakers, and disconnects), we need to be very specific — or risk a very cranky capacitor
And cranky capacitors can explode- literally
Use the capacitive reactance formula to figure out how much current the capacitor pulls:
That’s the Rated Current.
To stay safe, your wires must be 135% of the rated current:
You must add an O/C device (breaker or fuse) rated no more than 250% of the capacitor’s rated current:
A disconnect must be rated NOT MORE THAN 135% of the rated current:
If you’ve got 3 capacitors pulling 48A each:
Total = 48 + 48 + 48 = 144A
Step 1
Step 2
Step 3
If one large branch circuit feeds individual capacitor taps, then: -
Each tap conductor must:
Example:
Capacitor draw = 48A (RPC) × 1.35 = 64.8A
Table 2: So each capacitor could be a #6awg
BUT:
**Always go with the LARGER size**
Step 1: Use Xc = 1/2πfC and I = E/Xc
Step 2: Multiply by 1.35 to get conductor ampacity
Step 3: Multiply by 2.5 for max overcurrent device size
Step 4: Multiply by 1.35 for disconnect rating
BONUS: If using tap conductors use 7.5m max & ≥1/3 feeder size
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