Electrical Considerations in Your Microgreen Farm
Written by Garrett Corwin
Introduction
Electricity is a scary thing. It’s invisible, flowing through the walls and outlets, with the power to kill you in an instant. Modern safety features make it hard to electrocute yourself, but I’m not willing to take that risk. Yet, every indoor farmer should understand electricity. A baseline understanding will help you make smart choices about lighting, equipment, and safety. In this blog, I’ll walk you through everything you need to know about electricity, outlets, circuits, and circuit breakers. We’ll explain how to calculate your electrical load. This helps you avoid overloading an outlet, damaging your equipment, and tripping the breaker. This blog is a must-read before diving into future posts about various lighting options.
Note: I am not a licensed electrician. Hire a licensed and insured electrician for any electrical work on your farm.
Watts, Volts, & Amps
Volts (V) | Watts (W) | Amps (A)
W = V*A | A = W/V | V = W/A
V, W, and A are the three electrical variables to focus on. The three equations listed above show how to determine one variable, given the other two. I’m writing this blog from North America, so we’ll use American standards for this discussion. The standard American outlet provides 115-120V. If an appliance doesn’t explicitly list the voltage, you can assume it’s 115-120V. Therefore, the appliance will either list V and W or A, or only W or A, and you can calculate the rest.
If we look at the details for a cheap Amazon light below, we’ll see it uses 22W and requires a 120V outlet. We can use the above equation A = W/V to determine the amperage. This specific light also allows you to connect up to six lights in sequence. So, if you connect six lights in sequence and plug that single plug into a wall outlet, you'll be using 1.1 amps.
A = 22W/120V
A = 0.1833
Usage = 0.1833A*6
Usage = 1.10A
Why focus on A instead of W or V? I always focus on A because your circuit breaker will list the circuit’s capacity in amps. My main concern when making electrical decisions is not overloading my circuit.
Below are images of the circuit breaker at my commercial space. The one for your home should look nearly identical. There will be a “Main Breaker” or “Main Circuit Breaker” switch at the top or bottom, which controls power to the entire panel. The number listed on the switch is the amperage rating. Most will be rated for 200A. Turning OFF the main breaker will cut power to all individual circuit breakers. Each individual circuit breaker will have its respective capacity listed on the switch. Most circuit breakers are rated for 10-20A. A few of the circuits dedicated to large systems, like HVAC, will be greater than 20A. As you can see in the photo, there’s a 60A current for each of our two heating systems. The larger of our two HVAC units also gets a dedicated 30A circuit for cooling. You can see that all 13 of our circuits for lights, fridges, and other equipment are rated for 20A.
The 80% Rule
If the current is rated for 20A, we can plug in appliances that add up to 20A, right? Not quite. The 80% Rule is a safety guideline. It recommends loading a circuit to only 80% of its rated capacity when the load is continuous. A continuous load is a load that lasts longer than three hours. For example, HVAC systems cooling the farm, grow lights, and fridges. To be extra cautious, I’d assume every appliance is running a continuous load. The rule exists for two reasons. First, breakers can overheat and trip if run continuously at capacity. Second, appliances can have a “startup surge.” This means they use more electricity when starting up than during regular use. The 80% Rule means a 20A circuit should only be loaded to 16A at most.
Lighting Example
Let’s look at a clear example using grow lights and the limits of your circuits when you expand. As we have just shown, all of our standard circuits, which feed our grow racks, fridges, and equipment, are 20A. We know we shouldn’t load them with more than 16A of draw. The lights we discussed draw 0.1833A per light. That means we can put (16A/0.1833A) 87 of these lights on a circuit. That seems like a lot, but let me show you why it’s not. Our “rack systems” consist of two rows of wire racks placed back to back. Our systems are either three or four racks deep, or six to eight racks total. Each rack has five shelves, and each shelf has two grow lights.
6 Rack System = 30 Shelves = 60 Lights * 0.1833A/Light = 11.0A
8 Racks System = 40 Shelves = 80 Lights * 0.1833A/Light = 14.67A
If we instead use these popular 42W Barrina grow lights, the story changes. At 42W they pull 0.35A each.
6 Rack System = 30 Shelves = 60 Lights * 0.35A/Light = 21A
8 Rack System = 40 Shelves = 80 Lights *0.35A/Light = 28A
We could also run the calculations in reverse. If we have 16A of power to supply, what is the highest wattage light we could use for a six and eight rack system?
16A/60 Lights = 0.2667A/Light * 120V = 32W
16A/80 Lights = 0.2A/Light * 120V = 24W
I linked a few other popular grow light options. As you can see, many 'specialized' grow light options are much higher wattage. Our calculations show that 24W is the max allowable per light wattage for an eight rack system. The point is to pay close attention to your appliance's wattage and your circuit capacity. Grow lights are just the easiest way to make this point clear.
As you can see, the capacity of your circuits limits the number of lights you can use. Of course, you can design your electrical systems and grow systems differently. You can add more circuits, load fewer lights per circuit, or buy different lights. All of these things are true for any appliance; I just want you to understand there are trade-offs. When we renovated our commercial space, we had the electrician add dozens of outlets and circuits. We planned for each rack system to have a dedicated 20A circuit. We could've doubled the number of circuits, but electrical work isn't cheap. We spent $15,000 on electrical work. If we had doubled the outlets and circuits for our grow racks, the cost would have jumped to $25,000.
Final Thoughts
Electricity is critical to running your indoor microgreen farm. You don’t need to be an expert, but you should know the basics of electricity, both to keep yourself safe and to make smart buying decisions. Always remember the following rules.
- W = V * A
- V is usually 115-120V in North America
- Assuming V = 120, you can solve for W or A, given the other variable
- Don’t load your circuits past 80% of their rated capacity
- Always hire a licensed and insured electrician for all electrical work
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