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Building Principles: That's The Night The Lights Went Out
As a child, there was some mystique associated with a power outage. It seldom happened on warm, clear days, but most often during or after a violent weather event. This only made things much more exciting. But when you are charged with keeping things in order and programs on track, power outages can quickly become a logistical nightmare. Meals and evening "lights out" routines can be disrupted and cause program wrinkles. But when the freezers, walk-ins, and water and sewer systems fail, there can be serious financial and health consequences.
More and more, we're hearing from camps considering back-up power supplies for emergencies, and we are occasionally called after fires or other events which involve generators. Camps need to make informed choices. Let's look at some of the issues associated with emergency power supplies to help you make educated decisions.
What size of a generator do I need?
As with almost everything, the answer is: "It depends." The answer depends on what, exactly, you intend to power with the generator. If you want to run a radio, that's obviously a much smaller demand than trying to power camp. Our normal recommendation is that a camp first identifies the critical power needs. If power outages typically only last a couple of hours, then powering the walk-in cooler and freezer will probably not be necessary. Look closely at what the issues have been when the power went out and make an assessment from there.
I only need a generator for the well.
Are you sure? Remember that if you have water, camp is likely generating sewage as well. This is great for camps that use gravity septic systems exclusively. It's as often as not, though, that there is at least one pump from the toilet to the disposal area. Be extremely careful that you're not solving one problem and creating a second somewhere else.
There are still questions to be answered. How deep is your well pump? How much horsepower? How often does it turn on and off? These are important questions since each of these parameters plays a role in how much electricity is required not just to run the well pump, but to start the pump as well.
How do I figure out how much electricity I need?
We've all seen generators rated as "so many" kilowatts. Remember that a "kilo" watt is 1,000 watts (kW). You can calculate the number of watts required by any given device by multiplying the usual voltage (in the US, 120) times the number of amperes (or "amps") the appliance draws. You can find this information in the owner's manual or on the compressor, motor, or appliance data plate. For example, a typical household refrigerator/freezer runs on about 12 amps. The math, then, is: 12 amps x 120 volts = 1,440 watts, or 1.4 kW of power. This is the amount of power it takes to keep these running. But these appliances turn on and off by themselves, and the amount of power required to start the compressors is significantly higher. Depending on the appliance and its age and energy efficiency, it may take three times as much power to start the compressor. Our 1.4 kW has suddenly jumped to 4.3 kW. To help you determine the minimum size for a generator, add all of the peak demands together for all items you want to power.
Three times the normal power requirement? That's absurd!
Actually, it's not absurd at all. Recall from high school physics that things at rest want to stay at rest. The windings for a motor or components for a compressor are very heavy by design (for a host of reasons), and it takes a lot of energy to get them moving. Ever notice the lights dim and then brighten when the well pump or microwave oven comes on? Ever wonder why? Now you know that it's because those appliances are exerting a brief, but heavy, draw on the house network — "cheating" the lights of voltage they need to operate normally.
With the "running size" generator, things will just run slower, right?
Probably not. You'll likely experience a catastrophic domino effect. The biggest electrical demand will fail to come up to speed and will therefore continue to draw more than its share of "running" watts. Another appliance will then try to start with low power, and it too will attempt to run slow — also drawing more than its share. Eventually, the appliances which are running slowly will generate enormous amounts of heat and burn up. Most likely, when the power company gets things back up, the well pump and walk-ins will be dead — and you'll have extended the crisis. This is one of those, "penny-wise and pound-foolish" sort of issues.
How do we get the electricity from the generator to the appliance — just plug it in?
No. Not yet. In many ways, the flow of electricity is similar to the flow of water. Water moves from high pressure areas to lower pressure areas. Electricity moves from high potential to low potential. This means that when you electrify wires in camp while the feed lines into camp are dead, you're also electrifying the power lines out of camp. You could injure or kill the technician off site who is trying to get the power back onto the grid.
Wow. I didn't know that. How do we handle that?
The way to avoid this condition is with a transfer switch. It's a simple device that looks much like the one that Wyle E. Coyote uses to charge up the Acme Super Magnet. Also called a "knife switch," it breaks your connection from the power grid and allows you to be self-contained safely. This isn't just a good idea. It is in the National Electric Code (NEC) and part of your service agreement with the power company. Failure to properly install the transfer switch (and have it inspected) could open you to significant liability and criminal lawsuits.
We bought several smaller generators. Do we need to know anything special about this?
In this configuration, each location that will be powered should (not must) have its own generator. In this case, the transfer switch more than separates the generator from the outside grid; it separates itself from the other generators. Having multiple generators operating on the same grid is a fast way to serious power problems including fires.
The hardware store gave a perfect recommendation.
Maybe so, but sizing a generator is not a simple matter. It's best left to a licensed design professional who can help your camp select and have installed the right equipment for your emergency power needs. In the long run, you will save money by not damaging equipment, wasting food, cleaning up sewage spills — and, most important, you'll keep your campers coming back.
Rick Stryker is a professional engineer with Camp Facilities Consulting providing study, design, permitting, and construction consultation services to the camp and conference center community. Camp personnel may contact him at 570-296-2765 or by e-mail at email@example.com.
Originally published in the 2004 July/August issue of Camping Magazine.