About Generator as sole power source

[Carlos]

This is a three part question really, and I apologize if it has already been answered but I am really drawing a blank on this one.

I have built a cabin that will be powered only by a generator. There is no, and will be no grid power, unless of course I hit the lottery. I have five 20a circuits and plan to wire them to a panel directly. I have a Honda 3000w generator with a max output of 30a at 120v. (I overwired the circuits just to plan for that lottery jackpot) Here are my questions.

1. I will hardwire the breaker panel to an outlet on the outside of the cabin. The total length of that feed wire, by the time I string it through the walls, will be approximately 40 ft. What size wire will that feeder wire need to be? #8?

2. In time I intend to build a small storage shed near the cabin and eventually locate the generator next to the shed. When I do this I will bury the wire from the cabin ( at the point that the outlet will be located) to the shed. I anticipate the total length of that wire to be approximately 40 feet, for a total feed wire length of about 80 feet from generator to the panel. Am I still OK with a #8 wire, using approved wire for direct bury, for a length of 80 ft total? Do I need to go to a #6 because of the distance?

3. How do I ground this system? Do I ground the system at the outlet on the outside of the cabin with a driven ground rod, and then later disconnect that rod and drive another one at the location of the generator in the shed?

Any help would be greatly appreciated!!!!

[Valdi]

I actually am unable to definitively answer questions 1. & 2 because I'm only familiar with Australian electrical regulations. With regard to your third question, in Australia it is illegal to ground (earth) a generator unless it is done so in a dedicated generator switchboard & only if the generator has a provision for being earthed. Something tells me that the rules for this are different in the USA.

I also think you may like to check the sizing of your generator. I have prepared an example of sizing (for single phase 120 volts) as follows;

Continuous Load calculation.
4 x 60 Watt incandescent lights - - - - - - - - - - 240 divided by 120 = 2 Amps.
1 x 300 Watt fridge - - - - - - - - - - - - - - - - - - - 300 divided by (120 x 0.8) = 3.125 Amps.
1 x 300 Watt freezer - - - - - - - - - - - - - - - - - - 300 divided by (120 x 0.8) = 3.125 Amps.
1 x 300 Watt TV - - - - - - - - - - - - - - - - - - - - - 300 divided by 120 = 2.5 Amps.
1 x 100W "printer" fax/phone - - - - - - - - - - - - 100 divided by 120 = 0.8 Amps.

Total continuous Watts as listed - 1240 Watts.
Total continuous current as calculated - approx 11.55 Amps.

Surge Load calculation.
The only items that will have a surge current are the fridge, freezer & TV.

1 x 300 Watt fridge - - - - - - - - - 3.125 Amps x 4 = 12.5 Amps.
Fridge surge - - - - - - - - - - - - - - 12.5 Amps - 3.12.5 Amps = 9.375 Amps.

1 x 300 Watt freezer - - - - - - - - 3.125 Amps x 4 = 12.5 Amps.
Freezer surge - - - - - - - - - - - - - 12.5 Amps - 3.125 Amps = 9.375 Amps.

1 x 300 Watt TV - - - - - - - - - - - TV surge is approx 1 Amps.

Total surge current - 19.75 Amps.

Your generator will need to supply a continuous current of 11.55 Amps (12 Amps).
Your generator will need to supply a total surge current of 11.55 Amps + 19.75 Amps = 31.3 Amps.
Converting these figures to "Apparent Power" (VA);
31.3 Amps x 120v = 3 756 VA surge.
11.55 Amps x 120v = 1 386 VA continuous.

Since you will not find a generator with these exact "continuous" & "surge" ratings, you must buy a generator that can accommodate the surge rating. ie you will need a generator with a surge rating of no less than 3 760 VA for the above situation.

Also, most "portable" generators have a duty cycle, whereby it can only operate at full load for a maximum period of time. If this operation time is exceeded, the life of the generator can be dramatically reduced. Generally, reduced loads mean a longer operating time.

Unless your "portable" generator has inverter technology, it may produce a waveform that can be detrimental to certain equipment.

In your situation, "standby" generators are used because they are designed to operate continuously & they also provide a "clean" output waveform.