What is the proper way to set up and use a generator?

14 years ago

I would like to have a backup generator for when the power is out after a hurricane. As I understand it, the method a generator is generally used is to simply turn the generator on and plug into an outlet, which will then feed the home (although it would seem that it would not be able to exceed the current rating for that circuit). But this method seems to have adverse effects such as producing a line load to the utility, among others. Is this accurate? What are all the implications using this method?

However, there seems to be a better method, in which there would be a dedicated line (perhaps at a higher current rating?) that would go directly into the panel (perhaps connected differently there?). This method would not have the adverse effects as the preceding method. How exactly is this method implemented?

The main design load for the generator is to keep the 3.5 ton A/C running (~ 3 kW), as well as enough for the lights, TV or computer, and a tank hot water heater. (I can leave my powerful audio system off until the power would come back on.)

And of course, I would welcome any comments about using a generator in general.

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Comments (5)

Ron Natalie
14 years ago
Back feeding an outlet *IS NOT* the way to do it. Not only for quite a number of reasons, one it energizes the utility connection as you mention. Second, back feeding one outlet is only going to pass what that is rated for (15A or so). Lastly, it will almost certainly involve a suicide cord (plugs on both ends) which endanger your and your families safety.

There are essentially two ways to do this:

1. Run independent wiring (extension cords, etc..) from the generator to the essential loads and manually unplug from the house wiring and onto the generator.

2. Connect to the panel through a mechanical interlock and back fed breaker. In this case you'll have to manually turn off the non-essential circuits, turn off the main breaker, move the interlock, and turn on the generator feed.

3. Get an automatic transfer switch. Essentially you'll move your essential circuits to a panel which will automatically move them to the generator when the mains are out and the generator is producing power. Fancier systems will also start the generator automatically.

It's all a matter of how much convenience versus how much money you want to spend.
wayne440
14 years ago
Here is a recent thread about standby power. "stinkytiger" posted a pretty good summary of various generator configurations.

Here is a link that might be useful: previous discussion
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stinkytiger
14 years ago
Hi,

Wow thanks for the recomendation Wayne. Hope my advice is correct! :)

Some of the things are covered on the other thread. But I would like to add two comments.

1) Transfer switches and lock outs. In general you should never connect your generator and the utility power lines together. Bad things happen like electricuted utility workers and fires. What a transfer switch (and lock outs) ensure is that when your generator is connected, the utility mains power is discounnected. It is designed to be "goof proof" and hence ensure safety. Alternatively, a safe way is not to use the houses' electical system, and run an extension cord from your light to the generator. Note this does not help you to run heating, sump pumps or anything that does not have a plug and is hardwired into your house.

2) Your power requirements. I think you are looking at quite a bit of power there. A 3.5 ton A/C unit I think is one of those central A/C outside whole house units. I am not an HVAC person so bear with me a bit. The compressor bit, the cooling tower that sits outside, has a motor in it. This is the most power consuming thing. I think you may be correct saying that it is about 3kw power to run, but the key thing is the starting current. At start up you may be seeing a power spike of maybe 8 times that. It only lasts maybe 1/2 a second hence your breakers do not trip. However that spike will mean that your genset has to handle it. In general if you want to run your whole house HVAC I would recommend a 15kw and up genset, but you need someone to check out what exactly you have installed there. Your generator needs to supply enough initial power to start that compressor up.

One solution that people do is to avoid running whole house A/C on generators. They buy a smaller in the window A/C unit (get them from Sams Club, Costco, Sears) with a plug. That AC will only cool one room, but the familly camps out there until the utility power is back online. That way you can get by with smaller genset installation.

Hope this is useful.

Warmest regards, Mike.
wayne440
14 years ago
It is safe to say that with your water heater going, a 3.5 ton A/C will be an attention getter for most 15kw sets on start up. I have a 2.5 ton A/C and a 15kw diesel set, made back when generator makers didn't let the sales department influence ratings. It would probably start a 3.5 with my house load and WH on, but I wouldn't bet any money on it.

If your loads must include A/C and a water heater, you will need a transfer switch and should get someone familiar with standby power to do a load survey. Any reputable vendor should do that either "free" or for a charge which they credit back to you on the purchase of a generator.
brickeyee
14 years ago
Either a correct transfer switch or a pile of extension cords.

There are lockout devices made for some panels that allow a breaker to be back-fed from a generator, and those are also safe when installed correctly.
They mechanically require the panel main to be off before the generator feed can be turned on.

For large installations a transfer switch is still the best bet.

What is the proper way to set up and use a generator?

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Ron Natalie

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