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Ohms Watts

E with I and R

E with I and P

E with P and R

I with E and R

I with P and E

I with P and R

R with E and I

R with E and P

R with P and I

P with I and E

P with I and R

P with E and R

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Ohms Watts relationships are the foundation calculations for all electrical installations. From sizing of conductors to determining overcurrent protection, Ohms/Watts is important.

Learn each of these formulas. There is no need to memorize them. But be able to apply them with accuracy and speed to be successful on examinations and successful on the job.

You may want to memorize the values for a 100 watt light bulb:

Voltage 120  Amps .83 Ohms 144 watts 100. Not too hard to remember.

This could help you if you are asked to verify a formula on an examination. Just substitute these values into the formula. If you find that one side equals the other after the calculation, then the formula is correct. If the formula substitution produces an inequality, one side does not equal the other, then the formula is incorrect.

These formulas are appropriate for all Direct Current circuits and all Alternating Current resistive circuits. If the circuit or component contains inductance or capacitance in an AC circuit, then these formulas need to be augmented to include power factor. See the AC Formulas on this website.

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