Power In A Pinch

During a residential electric outage, motorhome owners need not remain in the dark.  

By Bill Hendrix, F761S
November 2014

Whether from winter ice storms, summer brownouts, or high winds, the electric grid can go down any time of year and leave your home without power. In the worst cases, severe weather causes widespread power-line damage and long-term outages. I don’t consider wind generators and solar electric, or photovoltaic (PV), cells to be suitable backups in such situations, because the wind may stop blowing, and PV cells won’t work at night or when covered with snow. Virtually all motorhomes, though, have an auxiliary power plant that can supply electricity for your stationary residence during an outage, and it’s especially useful if the disruption lasts several days. Also, fuel tanks in motorhomes are huge compared to those in portable generators; that’s just one reason to keep the tank full.

The following preparation will cost a few dollars, but frozen pipes and spoiled food would be much more expensive. Just consider it a smart investment.

First, decide where to locate the RV; this may be beside the house or in the street or driveway. Local ordinances may restrict long-term parking of RVs, but many also allow for a grace period of a few days. If you do have a touchy situation, your best defense is declaring that the motorhome is no longer an RV but a portable emergency power plant; offer to apply for a permit, if necessary. I believe most reasonable people will accept this, under the circumstances.

A word of caution at the outset: Never connect the output of your RV generator to a wall socket or other house wiring without first installing a disconnect/transfer switch. The transfer switch ensures that the household wiring can’t be connected to the utility grid and to your generator at the same time. Without the transfer switch, you risk “back feed,” which sends the generator’s electricity back into the power grid. That could seriously injure a utility worker repairing the lines. We’ll discuss more about transfer switches shortly.

A transfer switch is not necessary, however, if you use extension cords from your motorhome to plug in to individual appliances. This requires some planning. First, make a list of the critical appliances you would like to connect to the RV, rank them by priority, and note the amperage for each. All electrical appliances have the wattage and/or amperage rating affixed to them somewhere. Often it is molded into or stamped onto an out-of-the-way place. Wattage may be converted to amperes by dividing by the voltage. For example, 600 watts divided by 120 volts equals 5 amps.

When using extension cords, you will have to forgo powering the central air conditioning and high-wattage items such as an electric water heater and electric range, but a gas or oil furnace is a necessity, because the most severe outages happen in the winter. If you have an all-electric home with a heat pump or an electric furnace, you should purchase a couple of electric space heaters, because it is imperative that the house temperature be kept above freezing. The milk-house-type of electric heater is safe and can be operated on half (750) or full (1,500) wattage. Of course, you would need to manage the wattage on each line selectively.

Most RV generators can supply two 15-amp circuits, so you will need two appropriately long 12-gauge extension cords to get service from the RV into the dwelling. You also will need a few shorter ones for inside, depending on the number of items you want to service and their locations. Extension cords can present a trip hazard, so route them carefully. Some generators have convenience outlets on the electrical box, but many do not. An electrician can add a duplex outlet, or you may find two outlets on the RV somewhere. Just be sure these two outlets are on different breakers.

There are several ways to bring the extension cords into the house. The front door is not practical, because you can’t seal the large air gap, and you probably will be using that door. A window is better; remove the screen and close the air gap with duct tape. Another option: Run the cords through a vent to the crawl space and then into the living area or a permanent passage through a wall. You may need to be a little creative with the last option.

If your furnace is hardwired to the electrical box, as most furnaces are, this will have to be changed to a convenience outlet, and the furnace will have to be plugged in to the outlet.  This allows you to unplug the furnace from the house and plug it in to the generator power.  Unless you are skilled with electrical wiring, an electrician should be hired for this task; it is a simple job, though, and the cost should be minimal.

Other household items likely to be serviced include the refrigerator, the freezer, the TV, the microwave oven, and probably a couple of lamps. Be aware of the power consumption of all these items so you do not exceed the available 15 amps per line. (The sidebar shows typical amperages for various appliances.) If you have a shallow water well, it probably has a 120-volt pump that also can be powered by the RV generator. Pumps for deep wells are usually 240 volts, which might require an electrician for additional preparation, and it might be too involved to utilize a pair of extension cords.

Keep in mind that the well pump, the furnace, the fridge, and the freezer do not run 100 percent of the time, so you can unplug them selectively when you want to connect other appliances, such as a hot plate or a microwave oven. During an extended outage, if you have an electric water heater, you will need a little hot water from time to time. Use the gas burners on the house or RV range, an outdoor propane grill, or a hot plate.  Never use an open-flame appliance for indoor heat!

I’ve just described a fairly low-cost way to get emergency power, but there is another option that is more professional and more costly. It calls for the motorhome to be positioned near the side of the residence that has the house breaker panel, or load center. This method requires a transfer switch, available at home-improvement stores. A six-circuit configuration costs about $300. Larger transfer switches cost up to $600, but you are limited to the total amperage output of the generator. In most cases, the six-circuit type will suffice.

A transfer switch eliminates the need to run extension cords throughout the house and allows you to operate devices that are not connected by cords, such as ceiling light fixtures. Another big advantage of the transfer switch: You can have two 30-amp legs if your RV has a generator of 7,000 watts or greater. This offers the ability to selectively power up to a dozen circuits, except for high-wattage items such as the electric range, the electric water heater, the electric furnace, and the air conditioner. With a transfer switch, the power supply to a gas or oil furnace would not need to be changed. And, you have the option of supplying 240 volts for a well pump. Providing power to an electric furnace would require a very large generator, heavy-gauge wiring, and a high-capacity transfer switch — a serious investment. A friend tells me that his electrical co-op will install an unmetered, whole-house transfer switch for a fee. That would allow use of a large generator, either from the RV or an auxiliary power plant.

To connect the generator to the transfer switch, a four-pole twist lock connector (L-1430) is needed. A power line must run from the RV and terminate at the twist lock junction box mounted on the house, which requires the motorhome to be positioned near the side of the house with the breaker panel.  (A portable generator could be an alternative if you choose this route.)

From the twist lock box mounted on the house, install a four-conductor power line to the transfer switch, which is mounted adjacent to the home breaker panel. The transfer switch then is wired to the appropriate circuits within the breaker panel. One brand (Reliance) comes with an instructional DVD; reading the product reviews indicates many of the buyers did the installation themselves in about two hours. No doubt this group possessed good electrical skills. Unless you are very comfortable working with electricity, the job should be handled by a licensed electrician.

When a power outage occurs, you can manually select the circuits of the transfer switch to activate, observing the allowed amperage. This disconnects those selected circuits from the breaker panel and connects them to the auxiliary power source. When grid power returns, it is necessary to reverse the selection to return the panel to normal power.

It is not necessary to run the generator all the time. You can vary the “time on/time off” as circumstances and temperature allow. Two hours on and two hours off might be appropriate to conserve fuel in a longer outage. Be sure to use a gasoline additive such as STA-BIL, and while you are in emergency preparation mode, have on hand flashlights, spare batteries, extra food, and water. If you are using a portable generator, have some backup fuel. If your electricity is out, it will probably be out at the service station also.

Typical gasoline consumption is about 0.5 gallons per hour for 4-kilowatt generators and about 0.7 gallons per hour for 7-kilowatt generators. Mid-range diesels (7-kilowatt to 12-kilowatt) consume about 0.5 gallons per hour. These numbers are at average 50 percent load factor. Full load will consume about 50 percent more fuel.

Make your preparations when the weather is decent so you will be ready for what you hope will never happen. The adage “an ounce of prevention is worth a pound of cure” certainly applies here.