ELECTRICITY BASICS & LOAD CALCULATION

by Joey Ereñeta

Electrical Service Equipment

All work should be done by a licensed, bonded electrician. No one should attempt to do any electrical work without one. It is important, however, for indoor cultivators to understand the makeup of their electrical system and to recognize potential hazards. Whether assessing and upgrading an existing operation, or vetting the scope and cost of establishing a new one, it is essential for cultivators to be able to roughly calculate their needs, coordinate with electricians and electrical engineers on proper design, and troubleshoot potential issues if and when they arise.

Electrical power travels along a network of high voltage wires and is broken into grids based on geography and commercial or residential demand. The amount and type of power allocated to each customer is based on the service contract, equipment, and infrastructure tied to their property.

Along the grid, the power company installs transformers which convert high voltage electricity to the lower voltage service supplying each location. This transformer feeds the electrical wires that carry power to each property, typically referred to as the “service drop.” Each cultivator and their electrical contractor will need to know the capacity of their existing electrical service, as well as any unused capacity from nearby transformers, in order to determine the potential size and scope of the operation they can design and implement.

The service drop passes through a meter and terminates at the main service panel. The utility meter measures the kilowatts of electricity consumed in order for the power company to bill for usage. After the meter, there is a service disconnect that can cut all the power to the facility. The main service disconnect may be a special breaker switch housed in an exterior box enclosure, or it may simply be the main circuit breaker inside the main service panel. The electricity coming through the main panel can be distributed to sub panels throughout the property. Each panel or sub panel then distributes electricity via circuits that power outlets in different locations throughout the facility.

In the past, some growers in the unregulated market would bypass the meter and service disconnect in order to steal unmetered electricity from the grid. Not only is

this a serious crime, but it puts workers in the facility and first responders during an emergency in serious danger. In the case of a fire, the service disconnect is typically switched off before the fire is doused with water. If the stolen power bypasses this essential safety mechanism, it can lead to electrocution and death of a first responder. Never bypass the main service disconnect.

Circuit Breakers

Circuit breakers are safety devices installed in each panel which control the flow of electricity to, and limit the overloading of, each circuit. Breakers have an on, off, and tripped position. “On” and “Off” positions are typically labeled, while the tripped position falls in between the two.

A circuit can be overloaded from plugging in equipment that pulls too much power or by plugging in too many devices into its connected outlets. When 100% or more of the rated capacity of the circuit is used, the breaker will flip to the tripped position, stopping the flow of electricity to that circuit. The breaker should never trip when using the 80% Rule. The number located on the end of each breaker is the electrical capacity of the circuit, rated in amperage. (The number “20” signifies that the rated capacity of that circuit is 20 amps.) The bigger the number, the greater the circuit’s capacity.

The panel should have a schedule or map that lists which rooms/locations each breaker (and its circuit) powers. If any panel in a facility has not already been mapped, it should be before use. This is done by plugging an electrical device into each outlet and flipping circuit breakers off at the panel, one at a time. Since the panel may be located far from some of the outlets being mapped, this should be done with a partner. If solo, plugging a loud radio into each outlet can help determine when a breaker turns power on and off, as the sound will go on and off with the breaker. The process can be repeated until each outlet and the entire panel of circuit breakers is mapped. This map is typically kept inside the cover of the electrical panel.

Amperage, Voltage, Wattage & Load Calculations

The amperage, voltage, and wattage of a circuit are electrical concepts that may be easier to understand by using the analogy of water in a pipe. Amperage would be the volume of water flowing through the pipe. Voltage is the water pressure. Wattage is the amount of power that water would generate if it were powering a watermill. Too much water being pushed too quickly through too small of a pipe will increase pressure and resistance and eventually cause the pipe to burst. Similar effects can occur when overloading a circuit, such as overheating, melting, shorts, and fires.

Power service voltages come in a variety of sizes. Most home and commercial cultivators make use of low and medium voltage systems and equipment.

Low voltage is typically under 50 volts, often available in 12v, 24v, or 48v. Examples of low voltage applications in commercial and residential buildings are network data, telephone, Wi-Fi, HD video, audio, and computer networking systems such as phone, internet, security cameras, and alarms. All of these components require a low voltage wiring network that is separate from standard electrical wiring. Low voltage wiring does not require an electrician but does require a certified technician who specializes in installing low voltage networks throughout a building.

Medium voltage options vary depending on the location and application. Residential voltages range between 110v to 240v. Commercial/industrial voltage options range from 110v to 480v. Lower voltages in this range are typically used for powering low wattage devices, such as fans, small pumps, low intensity lighting, and small dehumidifiers. Higher voltages in this range are reserved for powering high wattage devices, such as large air conditioners and dehumidification systems, high-intensity lighting, plant waste shredders, soil sterilizers, and large water-system pumps. Each device will be rated to run at certain voltages.

Certain higher wattage devices in the garden may be rated to run at multiple voltage options. To maximize the efficiency, longevity, and integrity of electrical systems and grow equipment, the rule of thumb is to run high wattage devices at the highest available voltage for which they are rated. Using lower voltages with higher wattage devices creates inefficiencies that affect the quality and yield of plants.

Cultivators must familiarize themselves with the voltage options available from their power service. Electricians can create different voltage circuits using the available electrical “legs” or wires running from the power grid to the main service panel.

Load Calculation (Ohm’s Law)

There is a basic equation in electrical engineering that explains the relationship between amperage, voltage, and wattage. It is called “Ohm’s Law.” It states that amperage is equal to wattage divided by voltage. Alternately, it also states that wattage is equal to amperage multiplied by voltage. The third part of the equation can be calculated with the other two;

Ohm’s Law:

Amps = Watts ÷ Volts

Watts = Amps x Volts

Volts = Watts ÷ Amps

Ohm’s Law can be used to perform a “load calculation.” This is a way to determine what can safely be plugged into the outlets on any circuit without overloading it. The circuit’s amperage capacity (the number found on the circuit breaker) is converted to its wattage capacity, and then the maximum number of total watts that can be safely plugged into the circuit can be determined using the 80% rule.

Example: What can safely be plugged into all the combined outlets of a 20 amp 120 volt circuit?

20 amps x 120 volts = 2,400 watts (100% of the circuit’s rated capacity)

2,400 watts x 80% = 1,920 watts (using the 80% Rule)

Therefore, according to the 80% Rule, the total combined wattage of all devices plugged into the outlets of that 20amp/120v circuit should never exceed 1,920 watts.