Generator cord wire sizing

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  #1  
Old 08-23-11, 11:10 AM
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Generator cord wire sizing

Looking at some of the generator power cords offered to connect my generator to a transfer switch. My gen is a B&S 7500w surge 1000c running at 30 A output. The cords offered for 30A at 100 feet are only 10 ga. Is that the right size? I would think it would be 8?
BTW; the largest draw I will have is 15A @ 120 for one fridge and 11A at 115 for the other. In addition I have a boiler and sump pump figured in to run as well as some lights in the house on Reliance Q310A transfer switch. The largest breaker on here will be 20A. Is this cord sufficent to handle the load? Just curious before I spend the dough.
 
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Old 08-23-11, 11:29 AM
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I'm sure if thats a UL listed cord...it's fine. Prob due to different types of insulation and such.

Also...if it's a 240V cord...are you sure you aren't confusing 120V ratings...though I'm not sure that matters.
 
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Old 08-23-11, 11:43 AM
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What is the continuous rating on your generator and is it a 120 volt only or 120/240 volt model?
 
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Old 08-23-11, 12:33 PM
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Furd

Sorry I forgot that in the post. It is a 120/240 volt model, but I will have nothing on it to draw the 240. I got this to run basics. I have a barbecue for cooking!
Just wondering because it is the one touted for this machine (B&S 30471) and it just seemed undersized. If so I was pondering making up my own, but #8 SO power connect cord may get a bit unwieldy, maybe that is why they all only go to 10 gauge.
 
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Old 08-23-11, 01:14 PM
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If the running watts is less than 7200 10AWG is large enough.
 
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Old 08-23-11, 01:25 PM
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Justin

Thanks;
I believe I will be well below that but just was thrown by the size when doing some reading on it. Internet info is great for really confusing the issue! Considering the price, weight and ship I just might make my own out of #10 SO with the NEMA L14-30 (p&c) ends. I can get that at the local electrical supply much cheaper.
 
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Old 08-23-11, 01:54 PM
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Originally Posted by Bob M View Post
Thanks;
I believe I will be well below that but just was thrown by the size when doing some reading on it. Internet info is great for really confusing the issue! Considering the price, weight and ship I just might make my own out of #10 SO with the NEMA L14-30 (p&c) ends. I can get that at the local electrical supply much cheaper.
The Pass and seymour connectors seem to be of better quality than moulded connectors, anyway. The SO is more flexible and won't get eaten away if you spill oil or something on it.
 
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Old 08-23-11, 09:56 PM
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Flexible cords have a lower Ampacity than the same wire size used in premises wiring. For a #10 conductor the Ampacity is 25 amperes.

As long as the continuous load on the generator is 25 amperes or less the #10 conductors are acceptable. If you wanted to utilize the full 8000 watts continuously you really should upgrade both the connectors (plugs/receptacles/inlets) to ones with a 50 ampere rating and use a connecting cable with #8 conductors at a minimum. I don't think that is necessary because it is doubtful that you would have that kind of load AND I don't think that engine-generator combination would last very long at a continuous load of 8 kW.

One thing to be careful of...you state that you have only 120 volt loads, that means that you MUST balance these loads between both "hot" leads and the neutral lead. You also need to use a four-conductor interconnect cable between the generator and the transfer panel.
 
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Old 08-24-11, 07:33 PM
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Furd;

Thanks for your response.
I figured in the low ampacity when sizing the cord. Drove me a bit crazy but I figured since the highest draw curcuit was rated at 20 amps I would be okay. I worked awhile to ensure that the balancing of the legs would be right.
I had the electrician in today and he hooked up the panel. After he was done, we ran the gen and switched to that for power. The needles on the indicators indicated that I was well within bounds even when the when the old refridge cycled. You could see the tempoary draw and then it would go back down.
The electrician was really impressed on the panel and the gen and the way I had set everything up beforehand.
Where the draw was not listed on a piece of equipment I either went to the literature or called the manufacturer for the information then charted the info. as well as the circuits. Anal I know but I have it all listed by the panels now for reference.
 
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Old 08-24-11, 09:59 PM
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Good job and thank you for telling us the outcome. Now let's hope you never need to use it.
 
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Old 08-31-11, 12:12 PM
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Update

Just thought I would post a update on the switch. I had the electrician install it on Weds , as I had posted, and on Saturday night Irene came calling. Well it is now Thursday and I am still waiting for the power company . As I type my gennie is giving the power to my house and some to my neighbor for his refridges. It turns out I balanced the panel really good! I am off by 300 watts for complete balance on all major appliances. So far so good!!!!

BTW at that load and a little more I burned 6 gallons in 10 hours.
 
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Old 08-31-11, 04:18 PM
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I'm sorry that you have needed the generator so soon but I am also glad that it is working well for you and your neighbor. Thank you for also being a good neighbor and helping him/her.

After enduring two separate three-day outages in the dead of winter I bought a generator. That was about five years ago and since then I have had ONE outage of about four hours and none since converting to natural gas operation. I figure it's Murphy's Law at its best. Even though I have about $2800 invested if I never need to use it I'll be happy.
 
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Old 08-31-11, 08:07 PM
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Congrats on the install! Glad it works! Good helping the neighbor!
 
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