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NGuy 03-24-2008 09:43 PM

Generator as sole power source
 
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!!!!

goose134 03-24-2008 11:31 PM

How big is your cabin? Off the cuff it seems like you need a bigger generator.

elkangorito 03-25-2008 06:09 AM

My comments in blue.

Quote:

Originally Posted by NGuy (Post 110536)
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!!!!

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.

frenchelectrican 03-25-2008 10:49 AM

3 Kw is little smallish but with the portable units most useally don't last more than 500 ~ 1000 hours running life espcally that is true with cheap and light duty generators

if you want something last pretty long time get a hevey duty unit the engine will be much larger than the small portables are and they last heckva longer as well if you are running on LPG [ propane ] or Diesel both last pretty long life as long you do the proper manatince on them.

oh by the way i can give you a rough head up with the fuel useage something like 3KW will use about 1/2~3/4 gallon per hour at full load

and most honda generators reqired change lube oil every 25~50 running hours.

so you have to add up the manatince factor pretty fast with it.

but however #10 is the smallest size wire it allow to use i rather run with #8 anyway [ ya never know if you going to bump up with bigger generator ] and if run hardwired from breaker box to the inlet box just run with 8-3 with ground [ you only can use the black white and ground for now but save the red later when you get 120/240 volt verison later date so you dont have to redo the wire twice ]

to run underground you have to use eitehr UF [ Underground Feeder ] or run in the PVC conduct with #8 THHN/THWN wires

Merci,Marc

jrclen 03-25-2008 11:17 AM

I'd like to add to what Marc said. He covered the generator and wire size.

You asked about the ground rod. Ground rods serve no purpose except in cases of lightning strikes and high voltage surges on the grid. They have nothing at all to do with the electricity from your generator. Install the ground rod outside your cabin distribution panel. Connect it to the ground buss only, not to the neutrals. There is no reason to move it to the shed later. If you drive a well, bond the ground to the well casing or pipe as well.

In the cabin panel, keep the neutrals and grounds separated. Do not bond them together as would be done in a normal service panel. The reason I point that out, is most new generators supply power through a GFCI protected circuit. Bonding the neutral to the ground downstream from the generator will trip the generator GFCI.

I live in farm and tourist country. There are many weekenders here who use small generators for their cabins as you wish to do.

NGuy 03-25-2008 04:02 PM

Thanks a lot for all of your help folks. I really appreciate it.

Jrclen, thanks for the tip on the grounding, as well as seperating the ground and neutrals. My generator is on a GFI.

As far as the generator size goes, I agree that it would be small for any significant use. Truth be told, I want to plan for the ability to use a bigger generator in the future, simply because I started from the ground up on the building, but I really hate the idea of sneaking away for a weekend and having to listen to a generator (or anything that it powers!) As of right now it's pretty much used to charge drill and saw batteries. The only real use it will see is about 2-3 hours of game time on the occasional fall weekend to power a small TV. My lights are LP and if I can't keep it in a cooler or cook it on a grill I will do without it at the cabin.

In all seriousness though, it does bring me to another question that some of you may be able to shed some light on. I have built a water supply system for hot and cold water based on a 12v pump, much like a motor home or camper. I am heating the water with a small LP tankless water heater installed inside a utility closet. I have also run some dedicated 12v circuits (completely seperate from the 120v) in case I someday decide to install a 12v ceiling fan, window fan or who knows what else. If i did this, I would likely eventually add a solar panel to maintain the battery(s).

How concerned should I be about having the battery(s) that will power the 12v system in the same utility closet as the standing pilot water heater? When I say closet, I'm talking about an enclosure that is completely open at the top and will have 48" wide screened doors for planty of air movement needed for the high deman of the tankless water heater.

Thanks again for the help!!

LawnGuyLandSparky 03-25-2008 05:40 PM

Any relation?
http://www.colesgazette.com/unibomber.jpg

elkangorito 03-26-2008 09:47 AM

Quote:

Originally Posted by NGuy (Post 110803)
In all seriousness though, it does bring me to another question that some of you may be able to shed some light on. I have built a water supply system for hot and cold water based on a 12v pump, much like a motor home or camper. I am heating the water with a small LP tankless water heater installed inside a utility closet. I have also run some dedicated 12v circuits (completely seperate from the 120v) in case I someday decide to install a 12v ceiling fan, window fan or who knows what else. If i did this, I would likely eventually add a solar panel to maintain the battery(s).

How concerned should I be about having the battery(s) that will power the 12v system in the same utility closet as the standing pilot water heater? When I say closet, I'm talking about an enclosure that is completely open at the top and will have 48" wide screened doors for planty of air movement needed for the high deman of the tankless water heater.

Thanks again for the help!!

If I was in your shoes, I wouldn't store lead-acid batteries in a closet with any other equipment. There are 2 reasons for this;

1. Explosive Hydrogen gas is produced during the charging process.
2. Gases produced from a charging battery (Oxygen & Hydrogen) are known as "wet" gases. These gases are therefore very acidic & can/will corrode any nearby surfaces.

I would store them in a separate plastic enclosure that is well ventilated to outside air.

jrclen 03-26-2008 10:55 AM

Quote:

Originally Posted by LawnGuyLandSparky (Post 110834)

OK, I'll bite. Who is that?

NGuy 03-26-2008 04:28 PM

Thanks elkangorito. I am worried about the hydrogen gas but I hadn't even thought about the corrosive aspect.

As far as the picture goes, It has my curiosity as well. Not only who but why the question?

220/221 03-26-2008 05:16 PM

Come on folks. Anyone who has a cabin know that is Ted Kosinsky....the Unibomber

You might want to consider a separate solar charged battery powered system for lighting and a few items like radio,TV. That generator could really get on your nerves after a while. That's what happened to Ted :)

RV supply houses would have all kinds of fixtures and accessories.


I built one in Rocky Point Mexico years ago and hooked it up to a car battery I brought along for thr weekend.


Don't forget FUSES!

jrclen 03-26-2008 05:56 PM

Quote:

Originally Posted by 220/221 (Post 111112)
Come on folks. Anyone who has a cabin know that is Ted Kosinsky....the Unibomber

Oh. I remember hearing something about him, but never knew what he looked like. Just another wacko. Why would owning a cabin make someone interested in a wacko? I think this might have went over my head. I'm just an old country boy. :eek:

220/221 03-26-2008 06:37 PM

He lived for several years in a 10x10 cabin in Montana.

jrclen 03-27-2008 10:22 AM

Quote:

Originally Posted by 220/221 (Post 111132)
He lived for several years in a 10x10 cabin in Montana.

So the cabin is to blame for him being wacky? Cabins don't bomb people, people bomb people. :laughing:

Silk 03-27-2008 11:07 AM

I have a hunting shack out in the bush. I bring a Honda 3000EU generator to run 4 bulbs and a toaster, and nobody has ever accused me of being crazy. Strike that, except my wife. Little does she know I go out there to keep her from driving me crazy!


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