flengineer
Member
- Location
- Miami, FL
I am redoing a single apartment with a 150A panel with a 120/208V service. The owner wants to change out the tank-type water heater with an insta-hot. Using the Optional Feeder Calculations for dwelling units, I get 151A.
My range, dryer and cooktop are rated 8KVA, 8KVA and 5KVA respectively at 240V. Is it acceptable to calculate the load they will draw at 208V and use those values instead?
I'm using this for my calcs:
V=IR --> I=V/R
P=VI --> P=V*(V/R) --> P=V^2/R
This puts the resistance, R, at:
R=V^2/P --> R=(240^2)/P (where P=rated power at 240V)
Therefore,
P (at 208V) = (208)^2/[(240^2)/P (at 240V)]
P(at 208V)=0.75 * P(at 240V)
Hope I haven't thoroughly confused anyone.
My range, dryer and cooktop are rated 8KVA, 8KVA and 5KVA respectively at 240V. Is it acceptable to calculate the load they will draw at 208V and use those values instead?
I'm using this for my calcs:
V=IR --> I=V/R
P=VI --> P=V*(V/R) --> P=V^2/R
This puts the resistance, R, at:
R=V^2/P --> R=(240^2)/P (where P=rated power at 240V)
Therefore,
P (at 208V) = (208)^2/[(240^2)/P (at 240V)]
P(at 208V)=0.75 * P(at 240V)
Hope I haven't thoroughly confused anyone.