If your first grow is a small closet grow, power ratings may not have even crossed your radar but once you start upgrading to multiple lights, pieces of equipment, high-energy consumers like dehumidifiers and air conditioning, and ancillary items like fans, you will slowly creep towards the limits of most standard residential setups. If things like Voltage, Wattage, and Amperage have you questioning your power situation, here’s a brief rundown of what it all means as well as a few tips for knowing when it’s time to pull out the big guns.
I was lucky enough that, after I had been growing a few years, I had an electrician that explained the different power setups to me when I moved out to Colorado. There are points in your life where you learn certain things and you don’t know how valuable they truly are until later on; that was one of those conversations.
Volts, Watts & Amps
Starting with the basics, these terms are used to refer to various aspects of the power consumed, needed, and generated by your electrical equipment.
Volts: Volts, or voltage, measure the energy potential of a given circuit or device. So, a system with 120v has a maximum energy potential of providing 120v.
Watts: As you may recall from our lighting piece, a Watt is a unit of power that measures the rate of energy transferred. For “equivalency” ratings of systems like LEDs, it is important to pay attention to the actual wattage pulled rather than the equivalent amount being marketed. A 1000w HPS bulb draws 1000W from the system, whereas a 1000W equivalency light may draw 600W or less (depending on the unit).
Amps: Amps, or Amperes, are units of measurement used to measure the electromagnetic force between two electrical conductors carrying an electric current. Amperage is the strength of that current expressed in Amps. Amperage can be thought of as the speed at which current is flowing through your system.
Most commonly, power ratings relate to each other with the following equation: Watts = Amps x Volts.
So, if you are running 1000 watts on a 120v setup, your amperage would be 8.3 amps. This formula can be rearranged depending on what you’re solving for.
What you want to be careful of is drawing more power from a particular circuit or fuse than it has available to provide safely, which can cause you to burst a fuse. It’s important to determine what outlets pull from what fuses, and to understand how many amps you can pull per fuse.
Most Common Power Ratings (Voltage) in the U.S.
The most common voltages for outlets in non-commercial buildings are 110-120v and 220-240v. These systems have a maximum potential of providing their respective voltage. There exists a weird misnomer that running 240v is somehow using half the power of 120v–it's not; the electrical capacity of a 240v line itself and the amperage it can handle is higher than a 120v, and running lower wattage devices on a higher voltage system will put less of a strain on the system, but they are not directly correlated. Because 240v draws from two lines instead of one, the numbers can be deceiving if you don’t understand how they are drawing power.
• 110-120V (Single Phase): Your average, common residential power outlet. These can be found on most walls.
• 220-240V (2-Phase): A heavy-duty power line. Residential buildings typically have at least two of these outlets; one for the kitchen and one for the dryer. The fuse is typically at 40 amps or higher.
When to Upgrade Your Grow's Electricity
A note before you begin: it’s important to remember that electrical work can be dangerous. Hire a professional whenever possible.
I was introduced to someone who learned how to master power in the grow, and he would take a drop panel that runs autonomously from the main board (your home/apartment/building circuit breaker panel) and bring it into the grow room so we knew exactly what we were working with (and I highly recommend doing this if you have the option). He would run 120v and 240v off of the drop panel with outlets and he was able to tell us exactly how many amps we had available and how much we could pull without blowing a fuse.
At the time, I’d only been growing a few years and had not grown with more than 2000W. Typically, we were growing with 400-800W, and then I made the jump to growing with 2000W, and electricity quickly became a variable that it had never been.
When to upgrade: If you are running a system with anything over 1000W in light, you should be running a 240v circuit to that room. You don’t want to be pressing your luck with the amount and capacity that your breakers can take, and it is much better to run a much lighter load on something that can carry a lot more.
Colin’s Power Preferences
I like to have the ability to have both 120v and 240v running in the grow. We run autonomous panels (from the main) in each grow room; this is an individual panel that runs off the power of your main panel but is controlled separately, allowing you to have more versatility in each grow room.
In our first grows, back in the 90s, we would run extension cords to the grow room from different outlets all over the house, making sure that each outlet was on a different fuse to avoid too much draw on a 110V outlet (I don’t recommend this). You can comfortably go up to about 1200W (of lights) on a single 110v outlet fuse, and that’s probably a safe threshold, but you’re cutting it very close if you plan to run additional equipment on the same fuse.
I run fans and other ancillary energy consumers in my room and don’t want to have to worry about pushing the limits on a 120v, which is why I recommend upgrading to a 220-240v. I typically run all of my lights off of 240v outlets and use 120v for all other items (fans, water pumps, miscellaneous items). Commercial facilities are running almost everything on 240v or a 3-phase (3-phase is anything bigger than 240v, designed for intensive commercial applications).
As mentioned, almost all panels these days have at least two 240v outlets; one for kitchen and one for dryer, and I’m not joking when I say that I have opted not to run a dryer in previous residences in an effort to power the grow safely and without worry.
The bottom line when it comes to power is that you want to have enough available that you aren’t pulling too hard on your system. If you’re pushing more than 1200W (actual draw, not equivalency) in lights, you’ll want to switch your lights to 240v; especially if you plan to run ancillary items.