View Full Version : Another Handyman Club tip

08-25-2003, 02:58 PM
With the recent power blackouts I thought I would post this article from the Handyman site.

DIY Power

Tim Sullivan

Out in the country, some folks go to great lengths - and tremendous risk - to tap emergency power when the lights go out. One of the oldest and most unsafe tricks is to plug a gasoline - powered generator into a 240 - volt electric clothes dryer receptacle by means of a homemade cord with two male ends. A generator transfer switch eliminates the danger while adding convenience.

With the main circuit breaker off and only selected branch - circuit breakers on, the jury - rigged dryer method backfeeds power through the dryer circuit and into both 120 - volt phases at the load center. It also can expose unsuspecting utility workers to electrocution. If the main breaker is flipped on while the generator is running, the homemade power will travel out through the dead incoming service cable and zap anyone who is working on a nearby line. Backfeeding power through a

240 - volt receptacle also can kill appliances. If you try to power too many circuits at the same time, the combined loads will reduce voltage to everything on the lines. This won't bother things like light bulbs, but it can burn out refrigerators, well pumps and washers. An induction motor accumulates a short, heavy surge of power in the capacitor to start the appliance, then discharges. If the capacitor receives insufficient voltage, it will remain in that highly charged state and burn out.

The National Electrical Code (NEC) is very specific about how people can use portable generators in conjunction with residential load centers. The only legal and safe way to wire a secondary power source to your home is via a special three - position transfer switch. The switch should have "line," "generator" and "off" positions, so it is impossible to feed generator power out the incoming service cable.

Keep in mind that the key advantage of installing a generator switch is to power critical appliances and fixtures without running long extension cords. If a storm or Year 2000 (Y2K) date - error glitch leaves you in the dark, the transfer switch can safely distribute emergency power where you need it most.

Alpharetta, Georgia - based Gen/Tran makes five models of generator switches that can distribute power to 4 to 10 circuits. We installed a model 20216 ($270), sized to work with a 5,000 - watt generator. It can support six 120 - volt circuits, or four 120 - volt circuits and one 240 - volt circuit. This model can handle a combined load of 40 amps and features its own 15 - amp breaker for each circuit. Effective February 1999, the handle - tied (single - pull) two - pole circuits are protected by 20 - amp breakers rather than the standard 15 - amp breakers.

Since most portable generators typically provide only 2,500 to 7,500 watts of power, it's important to keep the total draw within the generator's capacity. Fortunately, the Gen/Tran switch has two wattmeters. The left meter tells you how much power circuits A, B and C are drawing and the right meter tells you how much circuits D, E and F are drawing. This enables you to balance your generator load between the two phases to avoid burning out the generator. If you have a 240 - volt circuit straddling the C and D tied breakers, the load will split evenly between the two meters.

It's easy enough to know how much power a light fixture draws: just look at the wattage printed on the bulb (add the wattage for multiple - bulb fixtures). Certain large appliances with motors, such as refrigerators with compressors, require a burst of power when they start up and less when operating.

The Gen/Tran installation manual warns that the transfer switch should be installed by a professional electrician familiar with electrical wiring and codes and experienced in working with portable generators. However, Gen/Tran President Paul Schnacken - berg says warranty cards returned to his company indicate that homeowners install 40 to 50 percent of the units themselves.

Generally, a permit and an inspection are required whenever one alters an electrical circuit. Be sure to contact your local building department beforehand to obtain the necessary permit, schedule an inspection and verify that you are allowed and qualified to do this alteration yourself.

Remember, even with the main breaker off, potentially fatal high voltage will continue to flow to the main breaker if your load center is installed as service equipment (the first power shutoff from the street). While you can kill power to the hot slots that hold the individual circuit breakers, you can't shut off power to the main breaker unless your load center is wired as a subpanel and you have a separate disconnect switch between the load center and the meter. In Texas and some other parts of the country, disconnect switches are required even if the distance between the meter and the load center is short.

Installing a generator transfer switch usually requires three steps. First, wire the switch to the load center. Mount a power inlet box in a sheltered area on the exterior of your house. It should be near the portable generator. Third, wire the power inlet box to a junction box near the load center and hardwire a cord to the box to plug into the transfer switch.

Installing the switch

Begin by turning off the main circuit breaker in the load center. Even better, if you have a main - service disconnect switch at your meter, kill the power there so you will have no live wires inside the load center. Never even remove the cover of the load center without first turning off the main breaker.

Remove a knockout in the bottom of the load center. Slip all of the wires from the Gen/Tran switch through the hole and secure the threaded cable connector with the toothed locknut. Next, mount the transfer switch on the wall beside the load center, avoiding sharp bends in the cable.

Select the circuits in the load center that you want the portable generator to serve. Each transfer switch circuit is lettered, in our case A through F. The manufacturer recommends you designate your most critical circuit (such as your furnace) "A." If you have a critical 240 - volt circuit (such as for a well pump), you must connect it to the C - D wires that extend from the handle - tied breakers on the switch.

Find the red wire and the black wire labeled "A." Loosen the screw terminal and remove the black wire from the first circuit you want to supply. Trim the black "A" wire from the transfer switch and strip 5/8 in. of insulation from the end. Then join the black "A" wire and the black circuit wire with a yellow twist connector (reds are too large). Next, trim the red "A" wire from the transfer switch to length, strip the end and secure it to the vacant screw terminal on the circuit breaker in the load center.

Continue this process in the same manner, wiring the pairs of B, E and F wires to three other critical circuits.

To wire a two - pole, single - pull (tied) 240 - volt circuit, locate the black wires from the Gen/Tran switch labeled C and D. Secure them with twist connectors to the two wires that had been connected to the two - poles on the circuit breaker. Then connect the transfer switch's red C and D wires to the respective terminal screws on the dual breaker.

When all black and red wires are connected, one white wire and one green wire will remain. The white is the neutral wire and the green is the ground. If your load center is wired as a main panel like this one, the white and green wires should be screwed to the same grounded/neutral bus.

However, if your home has a main - service disconnect switch near the meter, the load center will be wired as a subpanel, with the white neutral and bare ground wires kept separate. In this case, it is critical to connect the transfer switch's white neutral wire to the neutral bus where the other white wires terminate. Then connect the transfer switch's green ground wire to the separate bus where the other bare ground wires terminate.

With the transfer switch itself wired, you can replace the load center's cover and restore the power at the main - service disconnect or the load center's main breaker.

Wiring the generator

You can plug your generator directly into the transfer switch via an appropriately sized cord with 240 - volt male and female plugs on the ends. How - ever, it usually makes more sense to install a power inlet box in a sheltered area outdoors and wire it to a box near the Gen/Tran switch.

The inlet box has a self - closing cover that will keep it dry when not in use. Since both the generator and the connection need to stay dry during use, we installed the inlet box on an open porch where the equipment would share shelter and ventilation.

A short length of 3/4 - in. plastic conduit protects the cable from the bottom of the surface - mounted box to where it passes through the rim joist. Check with your local code authority to determine whether the conduit must extend to the junction box near the transfer switch.

Follow the color - coded instructions when wiring the cable to the power inlet box and match colors at the junction box above the transfer switch when installing the short cord. Ground the metal boxes with short pigtails from the green connections. Use a strain relief collar - not just a cable clamp - at the overhead junction box. It secures and cushions the cord from stress.

Once you know how close your generator will be to the power inlet box, you can order an appropriately long cord from Gen/Tran or make your own with components from your local home center. Expect to spend about $40 to assemble even a short cord. Don't plug the generator into the power inlet box or the cord into the transfer switch until the wiring is completed and all the boxes are closed. Chad