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Standby Generators

What are standby generators?

A standby generator, often called a backup generator, waits for a power outage and restores power to a house or business within seconds after the power shuts off.

A standby generator is an automatic, permanently connected appliance like a water heater, central air conditioner, or furnace. The manufacturer designed it specifically to meet National Electrical Codes for use during a power outage. Connection to the home requires an Automatic Transfer Switch or ATS.

Although manufacturers often advertise small portables as a means of backup power in case of an outage, they only work if you are home to hook them up and fill with fuel several times a day.

A standby generator system detects an outage instantly. Within seconds, the generator starts and reaches operating speed. The automatic transfer switch disconnects the electricity utility and connects the generator to the home’s electrical system. When the utility restores power, the system disconnects the generator and reconnects the utility. Everything is automatic.

Members may connect a generator using only a CVEC-approved open transition transfer switch. An open-transition transfer switch breaks the circuit connection to CVEC’s service wires before making the circuit connection with the member’s standby generator and, conversely, breaks the circuit connection to the member’s standby generator prior to making a reconnection to CVEC’s service wires. The transfer switch must be a double pole, double throw, not fusible, mechanically interlocked transfer switch.

Read the CVEC Standby Generator Requirements prior to installing a standby generator.

What size generator do I need?

The first step to buy a generator determines the capacity required. Standby generators are sized in kilowatts and there are three general categories to consider: whole house generator, managed power backup generator, and standby generator for essential power.

Whole House Generator—All the Power You Can Use

The Best Standby Generator for Large Homes

Whole house generators produce enough power to handle everything in your house at the same time. Buy a unit large enough and you can power all the air conditioners, your large electric appliances, and still have plenty of power left over to run other household appliances.

These standby generators supply from 20 kilowatts all way to 100 kilowatts or more and can provide backup power to midsize houses or the largest luxury homes.

Consider a whole house generator if you run multiple (more than two) central air conditioners and have large power requirements that must be met.

Backup Generator with Managed Power Automatic Transfer Switch

The best standby generator option for most mid-sized homes.

Most homes do not use all the power their electrical panels suggest. Even if every appliance ran at the same time, it is rare for the total power consumption to equal the main panel capacity. Most homeowners will find that a smaller standby generator with the right automatic transfer switch is all they need.

These generators offer 12 to 22 kilowatts of power.

An automatic transfer switch with power management capability can prevent overloading the generator by limiting when certain appliances receive power. A home with two central air conditioners is a good example. The automatic transfer switch can prevent both air conditioners from starting at the same time. When one starts, the second waits for the first to stop before it will run. In many cases, the two units will alternate as necessary to keep the house just as cool.

Home Standby Generator for Essential Power

Many homeowners opt for less power and less expense. Small standby generators with capacities of 12 kilowatts or less can provide varying levels of essential power. They may supply the entire house or only those circuits chosen during installation depending on the automatic transfer switch.

These generators are just as reliable as their larger counterparts, but they cost less to purchase and run. They can run a smaller air conditioner, keep the food in your refrigerator or freezer cold or frozen while you can have some lights and the television.

Terms To Know

Kilowatts (kW) vs kilowatt-hours (kWh)

Watts (W) and Kilowatts (kW) are units of power. They measure how much work electricity is doing or the capacity to do work. Small portable generators are often rated in watts. Standby generators and larger portable generators are rated in Kilowatts.

1 Kilowatt = 1000 Watts. Watts X 1000 = Kilowatts.

Running Watts or Kilowatts refers to the amount of power the generator can produce continuously. Starting Watts or Kilowatts refers to a surge capacity for a few seconds to start motors, which require much higher power to start from fully stopped.

Kilowatt-Hours or kWh is a measure of energy used. 1 kilowatt used for 1 hour is 1 kWh or 1 kilowatt-hour. The number shown on an electric bill or given as the storage capacity of a battery is energy as kWh or watt-hours Wh.

Amperes (Amps)

If you fill a one-gallon bottle of water, you have one gallon. Amperes are a similar measure for how much electricity is flowing at any given moment. Electricity is the movement of electrical charges. One Ampere = 6.2415090744×1018 elementary charges moving past a point in one second. We can say that elementary charges are electrons.

Small quantities do little work. Large quantities can do much more. Motors are a familiar part of everyday life and they do work. Large motors use many amps and do a lot of work like cooling your home when it’s hot. Small motors use only a few amps and do small amounts of work like turn an exhaust fan in your kitchen.

Voltage

What are Volts?

How fast will the faucet fill that one-gallon bottle mentioned in the previous section? It depends on how much pressure there is behind the water in the faucet. High pressure fills the bottle faster than low pressure because it pushes the water harder and faster.

Voltage is very much like water pressure. It pushes electricity through a wire. The harder it pushes, the more work it can do. However, unlike the faucet, electricity always moves at the same speed in a wire no matter how high the voltage.

As we mentioned above, Watts and Kilowatts measure work done or the potential to do work. Volts X Amps = Watts.

120 Volts X 10 Amperes = 1200 Watts or 1.2 Kilowatts.

12 Volts X 10 Amperes = 120 Watts or 0.12 Kilowatts.

240 Volts X 5 Amperes = 1200 Watts or 1.2 Kilowatts.

In the first two examples we have 10 Amperes, but the volts in the first case is 10 times higher than the second case, and the result is 10 times the work. In the third case, we only have 5 Amps, but the Volts is twice that of the first case, so the work done is still 1200 watts.

In North America, the electric utilities supply 240 volts to homes over two wires, each one at 120 Volts (120/240 Volts.) Larger buildings and businesses may use 120/208, 120/240, or 277/480 Volts.

Air-Cooled Generator

Internal combustion engines burn fuel to create rapidly expanding hot gases that push pistons down and turn a shaft. Some heat escapes through the exhaust. The engine absorbs the remaining heat. High engine temperatures can cause catastrophic damage.

Small engines like a lawn mower can cool themselves using the air surrounding the engine. The Larger engines found in a standby generator usually use a fan to move cooler air through the generator enclosure, over the engine and other parts to remove heat.

Air Cooling has limitations. As engines grow larger, some parts of the engine may not transfer heat to the air fast enough to cool it. In hot climates with temperatures frequently above 100 degrees, the hot air doesn’t provide enough cooling.

Liquid Cooled Engine

A liquid-cooled engine has built-in channels for coolant. The coolant pump circulates liquid through the engine to a radiator. An electric or belt-driven fan blows air through the radiator to remove heat from the coolant.

Cars and trucks use this method to keep the engine cool. It works well for larger engines with more than two cylinders. The largest engines in the world use the same basic strategy to remove heat as modern cars and larger generators.

Liquid-cooled engines experience fewer problems in desert climates. They efficiently remove heat in temperatures up to 120 degrees Fahrenheit and beyond. Air Cooled Generators may shut down because they can’t cool themselves faster than they create heat.

Automatic Transfer Switch

Transfer Switches supply power directly to a home or business electrical system. A manual switch requires someone to move the switch from utility power to generator power. An Automatic Transfer Switch (ATS) does it without human intervention.

The ATS is an essential part of the Standby Generator System. Without it, the generator can’t supply power to the building without human intervention.

An ATS makes the generator system fully automatic and starts the generator in any weather, even a hurricane, to restore power a few seconds after it goes out.

Single Phase vs 3 Phase

Throughout most of the world, electric utilities generate 3-phase current. In the section above titled “Voltage—What Are Volts?” we stated that most homes have two lines at 120-Volts each. The two 120-volt lines come a single phase of the local utility’s distribution grid. A standby generator for a home only generates one phase at 120/240-Volts.

Businesses, manufacturing, and industry may use three phases of current from the distribution grid in one of three configurations: 120/208-Volts, 120/240-Volts, or 120/480-Volts 3-phase.

Electrical systems designed to run on 120/240 single phase can’t run on anything else without special equipment. Likewise, 3-phase systems can’t run on single phase without a special converter.

When choosing a generator, it’s important to choose one that supplies the correct voltage and phase.

Portable Generators

Learn more about a Double Throw Switch.
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