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# What is Amp, Watt, Volt and Ohm

## What is Amp, Watt, Volt and Ohm

The three most basic units in electricity are:- voltage (V), current (I, uppercase “i”) and resistance (r). Voltage is measured involts, current is measured in amps and resistance is measured in ohms. Electrical power is measured in watts. In an electrical system power(P) is equal to the voltage multiplied by the current. P = VI

It is important to measure how much lighting is added to an electric circuit. How to measure electricity is the tip that we hope will help you to maintain a safe and nicely lighted environment.
Watts = Amps * Volts

The fuse on the circuit will tell you how many amps that circuit will carry, usually 15 or 20 amps. Examples:
1. 110 volts times 15 amps equals 1650 watts
2. 110 volts times 20 amps equals 2200 watts
When lights are going to be left on for more than an hour, a safety factor should be used to offset heat build-up. Eighty percent of the total line wattage should be used as the maximum safe line wattage in these situations (for 153amp circuit: 1650 watts x .80 safety factor = 1320 watts, for 203 amp circuit: 2200 watts x .80 safety factor = 1760 watts).
Amps = Watts / Volts

Examples: How many amps does 1500 watts equal?
It all depends on the supply voltage.
1. If supply voltage is 240V, amps would be 1500w/240v = 6.25A.
2. If supply voltage is 110v, amps would be 1500w/110v = 13.64A.
Example: 15 AMP equal to how many watts?
1. Most fuses or thermal circuit breakers are designed to hold (not trip or melt open) 80% of their rated load.
2. 80% or 15 amps is 12 amps. You should try and not exceed this current on any circuit for the value of breaker or fuse protecting it.
3. The number of outlet plugs is immaterial as each plug may have different loads. Look at the devices you plan to connect to any particular outlet. It should give you a volt amp, watt, or at least current rating for the device. Lamps depend on what wattage bulb you have in them.
4. A 15 amp circuit can reliably hold 12 amps of current. 12 times 120V is 1,440 watts.
5. Your 15 amp breaker could only hold about 14 lamps if they had 100 watt bulbs in them. If you exceed the 80% rating, the breaker may occasionally trip for no apparent reason. The more you exceed the 80% rating the more often it will trip. When your exceed the full 100% of it’s rating it should trip reliably.
6. If you want the full capacity of a circuit breaker, get a magnetic or hydraulic breaker. The will hold reliably until their rating has been reached.