Do-it-Yourself Electrical Wiring Articles | Electrical Wiring Diagrams | Electrical Questions and Answers | Electrical Questions Blog
<< Home Electrical Service Calculation Glossary of Electrical Wiring Terms >>

Ohms Law Formula


ohms-law-electrical Summary: Ohms Law Formula and how it is used for determining electrical loads as it pertains to Watts, Volts and Amps. Ohms Law is very helpful to help us understand sizing electrical circuits for the home electrical system.


Basic Ohms Law Formula for Electrical Wiring Calculations

The Ohm's Law Calculations for Electrical

Using the Ohm's Law is a way to determine information needed to understand how to design electrical circuits.

This formula works with three main variables and depending on what is known can produce a missing factor which is needed to determine the circuit size.

The Ohm's Law is also used when designing appliances and building electrical equipment and devices.



Microwave Oven Circuit Example:
A Microwave Oven circuit 
Circuit Planning:

Device ________________

Volts __________________

Amps _________________

Quantity _______________

Circuit Size Amps ________

Wire Size _______________
[ see wire size chart ]
Ohms Law Formula to Convert Watts:
(calculating watts to amps)

Watts / Volts x Quantity = *Total Amps.

* Note: This does not include Power Factor or Voltage Drop (wire distance).

Knowing the specified circuit size as amps will not require the Ohms Law Calculation.


Help with understanding Electrical Appliance LabelsMicrowave Oven

Electrical Appliance Label 



This Microwave Oven requires a 1500 Watt Circuit of 120 Volts.

1500 /120 Volts = 12.5 Amps.

A good rule is to never load a circuit past 80% of the circuit capacity. An 80% load on a 15 Amp circuit would be 1000 Watts so this would require a circuit one size larger.

Installing a circuit for this microwave oven would require a 20 Amp / 120 Volt Circuit.

In kitchens it is common practice that if a microwave oven will be installed at a given location, such as Hood-Fan Microwave Ovens, that a Dedicated 20 Amp Circuit is always installed.

Electrical Calculations and Formulas

Electrical Calculations and Formulas
Electrical Projects Guidelines


<<- Home Electrical Service Calculation Glossary of Electrical Wiring Terms->>
-
Basic Ohms Law Formula Example: A Microwave Oven Circuit Top of Page -
electrical-books

ask-an-electrician

installing-a-ceiling-fan
NEC® and National Electrical Code® are registered trade marks of the National Fire Protection Association (NFPA).
CE® and Canadian Electrical Code® CSA C22.1 are registered trade marks of the Canadian Standards Association (CSA).
Part P® - Electrical Safety© is registered Crown Copyright of the UK Government Planning Department for Communities
©Copyright 2007 - 2010 Ask-The-Electrician