Blog Compiled by Daryl Humble, Autumn Faust, Tracey Rector, and Cody Bell
For foodservice operators and facility designers, having a basic knowledge of electricity can go a long way when it comes to making the correct equipment purchasing decisions. Electrical energy accounts for most of the total energy used by the average foodservice facility.
Knowing the basic principles of electricity can help make your life easier and your kitchen safer. Kitchens are outfitted to handle a specific voltage, so selecting a piece of equipment that isn’t compatible can shorten the life of the equipment and even pose safety hazards for you and your staff.
While this introduction to electricity in the kitchen will provide helpful information to understand basic concepts, by no means is it a comprehensive overview. If you are even slightly unsure of what to do, always contact an electrician before making any decisions.
Quick Lesson: Ohm’s Law
Ohm’s law is the most basic law of electricity. It defines the relationship between the three fundamental electrical quantities: current, voltage, and resistance.
Merriam-Webster Dictionary says, “the strength of a direct current is directionally proportional to the potential difference and inversely proportional to the resistance of the circuit.”
Ohm’s Law is as follows:
I = V/R
- I: Current through the conductor (Amperes)
- V: Potential difference measured across the conductor (Voltage)
- R: Resistance of the conductor (Ohms)
This may seem like a foreign language, so an easier way to approach this is to think of Ohm’s Law and electricity as similar to water flowing through a hose:
- Current (I) = flow of water
- Voltage (V) = water pressure
- Resistance (R) = size of hose
If you have a hose (constant size) and increase the water pressure, the flow of water will increase. Too much pressure or water flow and the hose can burst.
If you have a hose (constant size) and decrease the water pressure, the flow of water will decrease. Too little pressure and the hose will underperform.
Increasing the size of the hose allows more water to flow. This is why higher amperages require larger cords. Decreasing the size of the hose (resistance) restricts the flow of water (current).
Watts = Voltage x Amps
How much work can it do?
Although watts did not appear in the original Ohm’s Law equation, in recent years the equation has grown to encompass this factor. Today, electrical power is measured in watts (known as P in equations). Out of current (I), voltage (V), resistance (R) from Ohm’s Law, and power (P) from Watt’s Law, you only need two of the four quantities in order to calculate the other two. We can use the hose analogy again to explain how watts work.
Pointing a hose at a waterwheel, similar to the ones used in grinding stones in watermills, can increase the power generated by the waterwheel in one of two ways:
- When the water pressure is increased as it comes out of the hose, it will hit the waterwheel with more force, making the wheel turn faster and generating more power.
- If the flow rate is increased (more water coming out) the waterwheel will turn faster due to the added weight of the extra water hitting it.
It is important to know the amount of power available in your kitchen before ordering equipment. Larger pieces of equipment may require an upgrade to your electrical system.
Voltage = Watts ÷ Amps
The push behind the current — “How much pressure is there?”
In electricity, a volt is a measure of electrical pressure that pushes the current through the circuit. For a commercial setting, 120V (115V), 208V, and 240V (220V) are the most common voltage types. You may run across 230V, but this is generally an international voltage.
120V is the standard voltage you will see in the majority of households. It is a two-wire system consisting of one hot and one neutral wire. It can be used to power most small appliances and lighting.
What is 240V?
240V is the most common voltage used to power large equipment. It is available in both single and three phase power.
In single phase, it is a two-wire system consisting of two hot wires. The voltage between the two hot wires is 250V, maximum.
In three phase, it is a three-wire Delta connection system consisting of three hot wires. The voltage between any two hot wires is 250V, maximum.
What is 208V?
208V is another option for powering large equipment that requires a lot of power. 208V is typically three phase, and consists of a four-wire system of three hot wires and one neutral.
The voltage between any single hot wire and neutral wirre is 125 volts, maximum.
The voltage between any two hot wires is 208 volt, single phase.
The voltage between three hot wires is 208 volt, three phase.
Single and Three Phase
The term ‘phase’ refers to the number of alternating voltages available from the electric power utility, the source of the power. There are two phase types:
- Single Phase – A single phase circuit is a circuit that is energized by a single alternating voltage.
- Three Phase – A three phase circuit features three sources of alternating current arranged so that the peaks of voltage follow each other in a regular, repeating pattern.
Any piece of equipment rated at 120V is always single phase. When rated at 208V or above, you’ll find many are available in single or three phase.
“Three phase has three hot/live lines and generally a ground line, single phase has just one hot line and a ground line,” said Reed Harrig, Central product consultant.
“Since a customer can’t change the type of power supply they have, I usually concentrate on having them find out what their building is supplied with rather than how the two work. I also stress the importance of consulting an electrician to confirm their voltage and phase available.”
Harrig added three phase power is generally believed to be more economical than single phase because in three phase, the power supplied remains constant.
Amperage = Watts ÷ Voltage
How much is flowing?
The higher the service voltage (denominator), the lower the amps will be. 120V draws more amps than 240V. Even though these two change, the power required remains the same. For example:
- 700 watts at 120V has 5.8 amps (700 watts/120V)
- 700 watts at 208V has 3.36 amps (700 watts/208V)
- 700 watts at 240V has 2.9 amps (700 watts/240V)
A rule of thumb regarding circuit capacity is only 80 percent of the circuit’s capacity can be used.
Twenty percent must be left free for safety reasons.
If you have to fill a circuit over 80 percent, then you must use a larger circuit.
It is worth noting that supplying a piece of equipment at a voltage other than what it’s rated for in an effort to manipulate amps will not work.
For example, if a 240V device is connected to a 120V circuit, it will produce about 25% of its rated output and may cause damage to the equipment and pose a safety risk.
Likewise, a piece of equipment rated for 208V connected to a 240V line will boost the wattage reaching the device by 25%, overloading it and severely reducing the life of the heating elements.
Always check that the voltage supplied to a piece of equipment matches the rating of the equipment.
Consult, Consult, Consult
This has been a brief introduction to help you understand the basics of electricity, but it’s always important to consult an electrician or talk to your product consultant when it comes to electrical questions.
Cody Bell is a content specialist with Central Restaurant Products. With over 7 years of experience in the foodservice industry, Cody has developed knowledge on topics from all aspects of commercial foodservice, from the front of the house to back of the house. He is a NAFEM Certified Foodservice Professional. In his free time, Cody likes to spend time with his wife and puppy.