Don’t Let Your Greenhouse Electrical System Come Up Short – Part 1
Installing an electrical system in a greenhouse isn’t for amateurs. There are many factors to consider, including size of operation, load demands, wire location and environmental considerations, to name a few. Growers must keep in mind immediate and future needs and prepare for emergencies when they arise. The first step is finding a qualified electrician who can be relied upon to get the job done right.
Choosing An Electrician
Depending on the type of greenhouse project, Tom Manning, a project engineer at Rutgers University’s New Jersey Agricultural Experiment Station in New Brunswick, N.J., says if a grower has worked with an electrician he is comfortable with that would be the first choice to consider.
“If the grower doesn’t know an electrician suitable for the project, there are two levels of competence a grower might look for,” he says. “Consider an electrician who has some experience or can provide recommendations for working on a greenhouse project. If an electrician hasn’t worked on greenhouse projects, the grower can ask if he has worked on other agricultural facilities. These structures usually have some of the same types of needs and applications. This should provide some insight as to whether an electrician is going to be the right one for the project.”
Meeting Immediate, Future Needs
The size of a greenhouse operation is one of the biggest factors when determining the type of electrical system to install.
“For small-size operations of an acre or less, a grower is not going to have the same electrical loads for the big motors running the equipment that large operations would have,” Manning says. “The first decision a grower may face when determining the type of electrical system to install is whether it is worth putting in single-phase or three-phase electrical power.”
Manning says not all locations have three-phase power available. Where three-phase power is available, it offers the possibility of using more efficient motors and lower installation costs.
“Another consideration, which is a factor of scale, is where to locate the primary service entrance for the electricity and any additional subpanels,” he says. “In a larger operation, the greenhouse operator needs to be thinking about where the power is going to come into the facility, where the big electrical loads are and where the electricity is going to be distributed.”
An electric service entrance consists of the wires that go to the electrical pole and come into a metering device, which is typically owned by the utility company.
“The utility’s electrical wires are connected to wires that are owned by the greenhouse operator, and they go into the main electric panel. The panel can be either a single disconnect switch that can turn off the power, or it can be a main panel box that has a main disconnect breaker and circuit breakers for subcircuits,” Manning says. “The wires that come from the pole to the meter may or may not be owned by the utility. Everything on the pole belongs to the utility. That becomes an issue with installing a new service and who has to pay for the installation.”
Another consideration is expansion to make sure that the main panels and subpanels that are installed have enough room for additional circuits, as it is not uncommon for growers to install panels that are not large enough.
“The number of subpanels depends a lot on electricity usage. In most cases, it’s probably best to have one subpanel for every 2 acres and no more than four to five greenhouse zones on a single panel,” Mannning says. “If the zones are not geographically close together, a grower may want to consider more than one subpanel for every five zones. This will eliminate having to walk a long distance to get to an electric panel.”
Manning says the electrician and utility company a grower works with should be able to assist in determining the electrical capacity that will be needed for expansion.
“A grower should have sufficient amps to meet an operation’s projected needs for five to 10 years,” he says. “The minimum should be a 200 amp service. To have anything larger really depends on the size of the greenhouse and anticipated future needs.”
Preparing For Backup Power
Part of determining future needs is preparing for emergencies. When a grower is planning the electrical system installation, he should determine if he wants to add a backup generator.
“He should consider what is the critical equipment that should be backed up,” Manning says. “A grower may even want to set up an emergency panel at the time of the initial installation with a manual or automatic transfer switch to switch between the electric utility and a backup generator, even if the generator is installed at a later date.”
Manning says the electrician can recommend the size of the generator needed based on the equipment a grower wants to keep operating during a power outage.
“It’s good to have a discussion with the electrician in regards to what the emergency needs really are,” he says. “The costs are considerably higher as the size of the generator increases. A generator that is larger than necessary usually operates less efficiently.”
For more: Tom Manning, Rutgers University, New Jersey Agricultural Experiment Station, New Brunswick, NJ 08901; (908) 310-0244; [email protected]