PER Notebook

Here's a possible scenario: You've recently took advantage of a generator sale at one of the local merchants and bought a generator and manual transfer switch for it. Your neighbor is an electrician and will help you hook it up to your house circuits. You've told him what you want to run during an outage. You bought the big 8500 watt unit and so it should run the whole house according to the salesman (I will say no more). You've got it all hooked up and running, just waiting for that first big outage. Everything's perfect.

Your sitting at home one hot August afternoon, with the temperature above 100 degrees, but the air conditioner is working its little heart out. You just got a new HDTV and had the satellite people sell you a new HD receiver, so you could watch the game on ESPN HD. It cost you $3000 big ones, but it's worth it. The wife is shopping on Ebay with your new computer. Life is good. The Cowboys are on the 10 yard line and about to score when everything goes black. A car hit a power pole down the block. As you jump up, you tell the wife to start the TV as soon as you get the generator running. You don't want to miss the Cowboy touchdown. Sound familiar yet?

You run out and start your pride and joy and hammer the breaker to emergency power on the transfer switch and as soon as the wife sees the lights flicker she hits the remotes. She runs back to her computer and fires it up. As you run back into the house you notice the lights are kind of dim. You sit down to a dim picture just as the play starts. You suddenly hear the generator over speed, the lights get very bright and the TV goes off like a flashbulb. A couple seconds later the lights return to normal and the generator runs fine. The TV and receiver are smoke, the air conditioner is not running and the computer has a blue screen that says fatal error - What happened?

Maybe this will never happen to you, but it could. Lets take a look at what happened. The emergency panel was connected to the freezer, refrigerator and air conditioner. It was a hot day and all three compressors were running at maximum pressure when the power failed. Under these circumstances, without time for the pressure to go down, it might take 10 times or more then normal power to start them again and with all three units, it would take at least a 20 kw generator to have enough power to start them all at once. The point I am trying to make is if you have refrigeration equipment, allow about 15 minutes for the pressure to go back down before putting them on-line again. Commercial power has enough reserve to start them, but a generator does not. What happens is it blows the circuit breaker after few seconds and the generator is at maximum throttle and in the instant that it takes to correct itself, you get a high voltage spike taking out the electronics instantly. All is not lost, you still have the 13 inch TV in the bedroom that wasn't on. So what if it's black and white. Also, Tony Romo bobbled the snap for the cowboys and they lost.

It isn't so much sizing the generator to the load as it is sizing the load to the generator. When you are figuring what you will run on your generator, make a list of just the essentials, probably the air conditioner will not be one of them, nor will 240 volt stuff like the range, hot water heater and dryer. Most appliances have their running watts on a tag. If you have electric heat, you should plan on having some smaller portable heaters you can plug in. You should be able to run a refrigerator and freezer, but may not want to start these for about 15 minutes after the power outage. Keep in mind the 8500 watt generator, like the one in the picture is only rated 5500 watts running. The 8500 watts is for starting. Do not exceed the run rating except for short periods. Consider putting expensive electronics on a UPS or at least have a good surge protector on them. Test the system out before you have an outage, so you know what to expect.

Generator sizing is not all that difficult if you do your homework first and make a list of just the essentials to get by. If you have a 5500/8500 generator like in the picture, try to keep it under 5000 watts. That way you have a little reserve. Keep appliances with motor starting requirements to a minimum. If you must have units with motors, like a domestic well or freezers etc, plan for it and do some research as to what it will take to start them. If possible find out the locked rotor amps of the motor, that is what it will take to start it. If in doubt, hire an electrician to take amperage reading on them both running and starting. One more point, not all recepticles on the generator will give you full generator output, so it may be best to invest in a 4 wire cord. You can then use the 120/240 volt recepticle on the generator for full output. Hopefully, this article will help you avoid having to watch the old black and white again. Here are a couple of links for further reading that may be helpful - Bruce Perrault