Portable Generators. Do it Right!

We just came off of 9 days without power after CT was hit with a freakish, pre-Halloween snowstorm that brought 12″ of snow to our area.  Trees, many still full of leaves, couldn’t handle the weight of a foot of wet heavy snow.   Downed trees and snapped branches ended up also bringing down power lines on a huge scale.

While almost all of our neighbors fled to hotels and friends’ houses, we survived the ordeal (rather easily) because of our portable generator system.  The generator, a 12 years-old Makita (Model G6100R, 4.8 kW) performed admirably for all 9 days.  We enjoyed power for heat (oil-fired furnace), water (240 volt well water pump), hot water (oil-fired), refrigerator, basement chest freezer, kitchen stove (propane), kitchen counter outlets, kitchen lights and other minimal lights.   The generator (which we ran for about 9 hours over 3 intervals between 7am and 11pm daily) not only kept us warm, but let us prepare typical meals in our lighted kitchen and enjoy them in our lighted dining room.

Needless to say, there has been a real buzz about generators since the storm hit.  Many have been sold as fast as retailers could get them and you couldn’t find an extension cord or gas container anywhere.  Unfortunately, many folks don’t understand the limitations of portable generators and the right way to plan and install them.

Here are some basics for planning a “portable” generator system.  In this discussion, I’m talking about a generator that is intended to be used for “emergency” conditions.  That means it must have the capacity to provide MINIMAL  power for survive.  This approach will be most cost effective because it will reduce the size of the system and reduce gas consumption  (availability is often a concern).   Obviously, you can buy as big a system as you want – even a whole house generator!

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Bottom line, here’s what I think you minimally need to remain in your home when you’re faced with  several days without grid power:  heat, potable water, hot water, refrigerator, kitchen counter outlets, cooking device (not necessarily a stove) and lights.  The power “load” for each of these items will determine the size of the generator system you need.  Remember, the more load, the bigger the generator, the more capital cost and the more operating cost (gas, maintenance).

There are 3 components to the “system”:  the generator, the cord and the transfer switch.  Here’s what we have.  Perhaps it can give you an idea of what a simple system looks like.  Here is a photo of our Makita generator, the heart of the system. (I really wanted a similarly sized Honda back in 1999, but chose not to spend the   30% extra.  The Makita has not disappointed us).   At 4.8 kW (4800 watts) it is not a very large capacity machine- but it does offer both 120 and 240 volts.  We house it in a shed behind our house.  With the wheel kit,  it easily pushes out on a small deck that is level with the shed floor.  Manual start, 5 gallon gas tank (lasts about 9 hours which is what we run it per day)  Gas Costs: $20/day.

The cord runs from the generator (you can see it in the pic), through a basement window to the transfer switch that is located next to the main electrical panel.  The cord is sized based on the power it will carry and its length (voltage drops as length increases).  The cord’s plug and outlet need to mate with the profiles at the generator and the transfer switch.  Ours are the 4-pronged heavy duty type.  Instead of having to run through the basement window, it is possible to buy a 4th component for your system: a weather-proof exterior power inlet box into which you can plug the cord from the generator.  This is convenient, but adds additional material cost, as well as labor cost for your electrician to run a wire from the transfer switch to the outlet box.  We opted not to do this.


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Here’s a picture of our Gentran transfer switch (Model 20216).  This was installed by our electrician when we built the house in 1995.  This is a device that allows the circuits that you plan to power by the generator to be “switched” between the main panel (where they are on the public grid power, labeled “LINE”) and the generator (where they are isolated from the main panel and only powered by the generator, labeled “GEN”).  There is also a center OFF position to each switch.  Using a transfer switch is the right way to do it!  This transfer switch is manual, which means I have to actually flip each circuit’s switch to “transfer” that circuit to the generator.  There are automatic transfer switches that are available for bigger systems, but they can be costly.  Many folks try to skip the transfer switch and instead choose to “back-feed” into the main panel from the generator through an existing house outlet.  This approach is not only non code compliant, it can be extremely dangerous for the house occupants and utility workers out on the street.  I can’t tell you how many people I’ve heard this past week talking about how they had planned to use this “back-feed” method to utilize their new generator.   I do not recommend that approach!

You can see the power cord from the generator coming into the bottom right of the transfer switch.  This switch has 6 (A-F)  15 amp, 120 volt circuits. Actually, the two center circuits are ganged to provide 240 volts for our well pump.  Above the switches you’ll notice 6 pop-out circuit breakers that protect each circuit.  At the bottom left you can see 2 wattage meters to monitor load and between them,what I really like, an extra “courtesy” outlet  just like the one that is often next to the main panel.  Our circuits are as follows: A: Stove/Kitchen Outlets, B: Refrig, C/D: Water Pump, E: Kitchen/Dining Lights, F: Furnace/Hot Water Heater.

This simple portable generator system has performed well for us.  We’ve never had a problem.  It’s been tested lately with Hurricane Irene, where we were without power for 3 days and now the Halloween Storm.  Except for wattage spikes at motor start-ups (which the generator has some excess capacity to absorb),  I never see the wattage meters “maxed” out.  Here’s a summary to planning:  First, determine what circuits you want (actually need) to power.  Those selected circuits will then determine  the  size transfer switch you need, which will dictate the size generator required.

You can do some of the planning.  Perhaps even buy all the equipment.  But do it right! Size the system correctly.  Use a transfer switch that is installed by a licensed electrician—and sleep well at night in your warm house powered by your generator, while your neighbors are down at the Holiday Inn.    Good Luck!  DN

I hope this is helpful. Comments are always welcome!
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