Amps, Watts and Volts: Preparing Your Home’s Circuitry for a Growroom

By Eric Hopper
Published: December 1, 2016 | Last updated: May 25, 2021 09:46:37
Key Takeaways

Horticultural lighting equipment requires a reliable source of electricity. Whether you’re using HID fixtures, LED fixtures or any other lighting technology, understanding electricity as it relates to indoor gardening is crucial.

Caption: Electrical panel in hydroponic farm Source: chalermphon tiam/Shutterstock

Mistakes made with a growroom’s electrical wiring can be costly and, more importantly, dangerous. Lighting systems consume a good amount of power and the more power that is required, the more heat that is produced.


When any appliance or lighting system draws a significant amount of power, the wiring needs to be properly sized and done correctly so that the excess heat does not become a safety concern. Although rare, electrical fires can happen and are much more likely to occur in a haphazard electrical system than in one that has been properly planned and executed.

Fire is not the only lurking danger for growers who try to cut corners on the wiring. Expensive equipment such as ballasts, fans, lamps and anything else that plugs into an outlet can be damaged or destroyed if wired incorrectly. The good news is that you do not need to be an electrician or have a vast knowledge of how electricity works to be a successful indoor horticulturist.


A basic understanding of some commonly used electrical terms as they relate to indoor gardening is all you really need to set up a properly wired garden. In many cases, this basic knowledge is enough for you to set up the garden’s entire electrical system on your own. In other cases, a professional electrician should be hired and you can use your basic knowledge to accurately communicate what the garden’s electrical needs will be.

More often than not, growers make electrical mistakes because they misunderstand basic electrical terminology. The three most common electrical terms used by indoor growers are amps, watts and volts. Amps, watts and volts all affect each other in an electrical equation: watts/volts=amps. Put another way, the amount of wattage required, divided by the operating voltage, will determine the required current or amps.

subpanel circuit breakerA subpanel circuit breaker is a smaller service panel that distributes power to a specific area. Source: Nipol Plobmuang/Shutterstock



The best way to think of amps (a.k.a. amperes) is to think of current flow. A good analogy is a water plumbing system. The amps would be comparable to the flow rate within the water pipes. The flow rate of amps will determine the available amount of electricity to the electrical system.

For indoor horticulturists, the number of available amps will determine the amount of lights that can be operated. In some cases, if the house or building’s electrical service does not have enough available amperage for the garden, an electrician may have to be hired to increase the available amperage.


(Read also: Find the Right LED Lights With the Watts Per Square Foot Principle)

For example, a home with a 100-amp service that already has multiple electrical appliances (hot water heater, electric dryer, stove, refrigerator, etc.) operating may not have enough available amperage to provide safe, dedicated power to a garden. In other words, the flow rate of electricity isn’t great enough to provide for all the appliances and the needs of the indoor garden. The grower would need to contact an electrician to upgrade the electrical service to higher available amperage.

So how does a grower determine the amps needed for his or her garden? In most cases, the required amperage will be determined by how many watts are needed to provide light to the garden space.


When speaking of watts in terms of horticulture, what is being discussed is the power needed or used. The wattage of a garden usually is relative to the garden’s size. As an example, a 10,000-watt garden would have a green space roughly 10 times the size of a 1,000-watt garden. Most growers use an equation to figure out the amount of wattage for their given spaces. For example, say you wish to provide horticultural lighting to a 10×10 garden space. In order to provide 50 watts per square foot of garden space, you will need 5,000 watts of horticultural lighting.

Indoor horticulturists also use watts as a way to gauge their gardens’ overall efficiency. It is common for indoor horticulturists to express yields in terms of weight per watt. The higher the weight per watt of energy consumed, the more efficient the garden and the higher the return on investment for the grower. Wattage is used to define the amount of power needed, but it can also be used as a way to express efficiency in the spectral output of different lighting technologies.

(Read also: How to Set Up Your LED Grow Light)

Plants do not use all spectrums of light for photosynthesis and some lighting technologies are better at emitting useable light energy than others. A common way to express horticultural lighting efficiency is in terms of PAR (photosynthetically active radiation) per watt. The higher amount of usable light energy (PAR) per watt of energy consumed, the higher the efficiency of the lighting system. It is important for new growers to understand the PAR per watt of energy ratio. This is currently the best way to compare the efficiency of various light technologies.

Checking voltage indoors with digital multimeterChecking indoor voltage with digital multimeter. Source: New Africa/Shutterstock


The voltage of the lighting system will be another consideration when determining how many amps are required. The higher the voltage, the less amps that are needed to operate the device. There is a lot of confusion about how a grower’s power bill will be affected when operating a ballast on 120 volts versus 240 volts. Many growers mistakenly believe that operating a growroom on 240 volts will cut the power usage in half and, therefore, reduce the power bill by 50 per cent. Unfortunately, this is not the case.

When the operating voltage is increased, the number of amps (current) required will decrease, but the amount to power (watts) required will remain the same. For example, if a grower wants to operate a 1,000-watt lighting system on 120 volts, they will need 8.3 available amps in order to do so. If that same 1,000-watt lighting system is operated on 240 volts, the grower will only need 4.16 available amps to do so.

(Read also: Light It Up: Using More Lights Efficiently and Safely)

What is the advantage of operating an indoor garden on 240 volts instead of 120 volts? The biggest advantage of operating a growroom on 240 volts is that you can operate twice as many lighting systems on the available amperage than if operating on 120 volts. With either voltage, the lighting system will still require 1,000 watts (power). Power companies charge consumers for the amount of power they use, so the bottom line is that operating a growroom on 240 volts versus 120 volts does nothing to reduce the overall amount of power being used in the garden.

Specialized Systems

There are many electrical devices specifically manufactured for making an indoor horticulturist’s job a lot easier. There are electrical boxes that do not require a licensed electrician and are designed to plug into an existing dryer or range outlet. These convenient devices allow growers to use the 240 voltage (commonly used for dryers and ranges) in order to operate more ballasts safely. Many other pre-made devices exist that fulfill the needs of indoor growers. Browsing online or a quick walk-through of the local hydroponic store can give a grower some insight into all the possibilities.

As with planning any part of an indoor growroom, the better you understand exactly what is needed, the easier it will be to find the specific products to meet those needs. Most manufacturers of horticultural electrical equipment are more than happy to answer questions and to help find the products that will best suit a gardener’s needs. As a consumer, never be afraid to ask questions, especially if it will affect the operation of your growroom.

(Read also: How to Choose the Right Grow Lights)

Do I Need a Dedicated Circuit for Horticultural Lighting?

Ideally, growers should have the garden’s horticultural lighting system(s) operating on a dedicated circuit, which is a circuit that is used only by the indoor growroom and has no other appliances or electrical devices connected to it. This is a simple and easy way to avoid blown fuses and potential dangers. It also makes it easier to diagnose electrical problems if they happen to occur.

Extra Amps Are Better

It is a good idea to have extra amps available on the lighting circuit, instead of pushing it to maximum capacity. For example, a 1,000-watt light system operating on 120 volts should be allowed 10 amps, even though it requires only 8.3. Growers who install extra amps are essentially increasing the longevity of the electrical system and providing additional safety.

With a little forethought, providing addition amps for an indoor garden is not difficult. When I helped design growrooms for my store’s customers, I would always plan on extra amps. My rule of thumb was to provide 10 amps per 1,000-watt light operating on 120 volts or five amps per 1,000-watt light operating on 240 volts. Having extra amps is safer and also allows for easier expansion in the future.

Electricity is the sole energy source for an indoor garden. Aside from the potential dangers associated with careless wiring, a grower will never be successful if their electrical system is not operating properly.

Growers who take the time to learn the basics of amps, watts and volts as they relate to indoor horticulture will have the knowledge to safely plan and execute an indoor garden’s electrical system. Whether you use a pre-made horticultural electrical system or hire an electrician, a properly wired indoor garden is the key to safety, efficiency and success.

(Read next: Powering Your Growroom With Solar Technology)


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Written by Eric Hopper | Writer, Consultant, Product Tester

Profile Picture of Eric Hopper

Eric Hopper’s past experiences within the indoor gardening industry include being a hydroponic retail store manager and owner. Currently, he works as a writer, consultant and product tester for various indoor horticulture companies. His inquisitive nature keeps him busy seeking new technologies and methods that could help maximize a garden’s performance.

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