Cable for generator

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  #1  
Old 01-26-07, 04:16 PM
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Cable for generator

Hopefully a simple question. In the process of building a garage, we are putting in a generator receptacle and running the cable into a transfer panel. The generator is 5KW (30A) 220V. I would like to have the ability to get a larger generator (say 10KW) if needed. What gauge cable do I need for either application? (is 10 gauge sufficient for the 5KW? Do I need 8 for the 10KW? More?)

The run of cable will be about 25 feet from the garage to the panel in the house.

Thanks
 
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  #2  
Old 01-26-07, 04:22 PM
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A 5KW generator is usually rated for 20 amps and has an integral 20 amp circuit breaker. This means 12 gage wire.

A 10KW generator is usually rated for 40 amps and has an integral 40 amp breaker. This means 8 gage wire.

Run 8-3 with ground cable and you should be fine.
 
  #3  
Old 01-29-07, 11:00 AM
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Dave,

#8-3Cu is definietly OK for your 5kW setup (it's rated at 40A) but for a 10 kW unit, you will peak out at 41.6A, just over the #8's rating. Since #6-3 has a capacity of 55A, you would be OK with the #6 all the way up to 13.2kW. I'm sure that #8-3 will be ok, and won't burn up, especially for a rather short run, but for a little safety margin, use the #6, Copper, of course.
 
  #4  
Old 01-29-07, 11:03 AM
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However, the 10 KW generator probably has a 40 amp circuit breaker protecting the output, so 8 gage wire is fine (and up to code).
 
  #5  
Old 01-30-07, 08:47 AM
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It's better to do it safe (#6) rather than save a few pennies (#8). The difference in cost is far outweighed by the safety margin. Just my $0.02 worth.

Of course, I would hate to explain to the insurance company why I skimped on wiring after a house fire. Again, just my $0.02 worth.
 
  #6  
Old 01-30-07, 09:59 AM
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Circuit Breaker,

Is your house all wired with over-sized wire just for the heck of it? You've advocated conductor upsizing for several different posters on this forum, but have failed to justify the extra expense in my opinion.

While there are many posters here who have legitimate fire hazards, this is clearly not one of those cases. There is no reason or justification in scaring the poster into thinking he'll have a house fire if he doesn't spend an extra $10 on a cable that is larger than what code requires. There may be good reason to install larger cable for the purpose of future expansion, but a 40A circuit is legally and _safely_ served by #8 copper wire.
 
  #7  
Old 01-30-07, 10:52 AM
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I am not disagreeing that #8 does not carry 40A, nor do I claim that it is not rated for 40A. Please go back and read my posts on this and the other threads you have called out.

I said, well, here's my quote:

Dave,

"#8-3Cu is definietly OK for your 5kW setup (it's rated at 40A) but for a 10 kW unit, you will peak out at 41.6A, just over the #8's rating. Since #6-3 has a capacity of 55A, you would be OK with the #6 all the way up to 13.2kW. I'm sure that #8-3 will be ok, and won't burn up, especially for a rather short run, but for a little safety margin, use the #6, Copper, of course."

If you read it carefully, I state that his 10kW set will peak out at 41.6A. Last time I checked, 41.6 was larger than 40.0, though I could be wrong. I'll have to go back and check it......

OK, I've checked it, and 41.6 is indeed larger than 40. Based on that, since his calculated peak current is larger than 40A (10,000W / 240V = 41.66A), and since we all agree that #8 is rated for 40A, and since his calculated peak current will EXCEED 40A, it is safe practice to upsize it the next available size, which is #6AWG, good for 55A.

And, no, I have neither the time nor inclination to justify, or cite chapter and verse, every number posted. These numbers come from a variety of sources, not just one. While we're at it, so what if the big box stores (codetalk for Lowe's & Home Depot) have charts that corroborate these numbers? Would it be better if they recommended stretching things just to save a few pennies? I, for one, would feel uncomfortable if someone recommended a wire size too small, even if it was only a few percentage points too small (40/41.6). If they shave safety margin off this, who knows what else they would shave safety margin off: gas pipe, joist size, etc.?

No one is being scared here into believing that undersizing wire by the numbers in this thread will cause a house fire. This is advice given here, and I'm sure the OP didn't ask for only certain opinions and not others.

Since you asked, my house is #14-2G for all my 15A ckts., and #12-2G for all 20A ckts., and #10-3G for both 30A ckts. I also use #6-3G for my 50A Generator inlet. Any questions?

Dave,

Please don't let the acrimonious tone of my reply to ipbooks discourage you from completing this DIY project. You can, of course, use any wire you want, however, I recommend being safe, and not cheap, however, it is your call, not any of ours. Best of luck with this, and please post results.

Regards,

Steve
 
  #8  
Old 01-30-07, 11:14 AM
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The point is, assuming that the generator does indeed have a 40 amp breaker on the output, that 40 amp is the appropriate size for the cable.

Certainly you can upsize the cable, and it would be prudent to do so if the length of the run were large. But assuming a normal run and a 40 amp breaker on the generator, buying larger cable is only spending more money, and there is no need to do so.
 
  #9  
Old 01-30-07, 01:17 PM
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Thanks a bunch for all the input. Just a note, I wanted to have the ability to go higher (and not restrict myself to the 5KW I have now). What I am hearing is provided I have 40A protection (no matter what the 10KW has the potential of putting out), I will be covered with 8-3. I would assume that would also mean if I installed a 12KW (I am NOT going to do that, this is an example), as long as the feed was limited to 40A, 8-3 would be sufficient.

I also just want to verify, when you talk about 15A (for the 5KW generator), you are referring to the rating for each 110V phase.
 
  #10  
Old 01-30-07, 01:36 PM
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> provided I have 40A protection...I will be covered with 8-3.

Correct. You will be able to increase your generator up to 10kW w/ 40A breaker.

> I also just want to verify, when you talk about 15A (for the 5KW generator),
> you are referring to the rating for each 110V phase.

Most 5kW generators are actually 20A, but some are 15A. Those units have the capability of 20A on both 120V legs; which is equivalent to 20A @ 240V.
 
  #11  
Old 01-30-07, 07:05 PM
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Go by the breaker size on the generator.
 
  #12  
Old 01-30-07, 09:02 PM
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Generator Type/Model

Dave,

Just out of curiosity, what model 10kW generator are you pondering?
 
  #13  
Old 01-31-07, 03:16 AM
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pondering

Actually, I am not pondering any 10KW generator, I just used it as an example because I did not intend to wire the place without the ability to upgrade in the future. I chose 10KW as the example because I could pretty much run the whole house (not at the same time) with a 10 KW, while with the 5KW I have now, I really have to selectively run loads. I have tested it and it will run all but the heat pump (I never tried the heat pump, I know better), including the well pump, but if I want water, I have to turn everything else off. I can run one element of the water heater, but have to watch other loads, etc.

Just wanted to make sure I limited myself to a reasonable upgrage.

Thanks,

Dave
 
  #14  
Old 01-31-07, 12:03 PM
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I was just curious, 'cuz I've been looking for a while, now at the 10000XL from Generac (Briggs). After the big outage of Aug 2003, I wanted to be able to run everything, including the A/C. Lookin' for it at HD/Lowe's and, of course, eBay.
 
  #15  
Old 01-31-07, 07:04 PM
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Originally Posted by Circuit Breaker View Post
I was just curious, 'cuz I've been looking for a while, now at the 10000XL from Generac (Briggs). After the big outage of Aug 2003, I wanted to be able to run everything, including the A/C. Lookin' for it at HD/Lowe's and, of course, eBay.

CB, Try craigs list. Ive found tons and better deals.
 
  #16  
Old 02-01-07, 10:40 AM
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Pardon my naiivtee, but what's "craigs list"? Sounds interesting. Is this a clearance website, or maybe a liquidation website? You see, I really wouldn't mind a 10000XL falling into my lap for pennies on the dollar. Well, maybe not my lap, but you get the picture.....
 
  #17  
Old 02-01-07, 11:23 AM
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www.craigslist.com is a website that people sell things on.. It's grouped by state, city/area, and catagories..
 
  #18  
Old 02-01-07, 11:48 AM
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Watch out for scams on craigslist.
 
  #19  
Old 02-01-07, 02:12 PM
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It's basically unregulated classified ads with no oversight. Buyer beware.
 
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