# Generator wire size



## livefreeordie (Dec 29, 2010)

I have a troy built 5500w gen. I'm going to wire the house this weekend and would like to know what size wire would be best. 8-3 or 10-3 thanks


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## Former Farmer (Dec 30, 2010)

10-3 romex is rated for 30 amps.  8-3 romex is rated for 40 amps.  5500 watts / 240 volts = 23 amps.  You can get by with 10-3 wire.  If the length of wire is going to be over 75 feet, use 8-3 wire for voltage drop.


What type of wire are you referring to?  Romex, SO cord?

Remember to have a means of disconnecting from the local electrical provider so the power does not back feed onto the power grid.


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## livefreeordie (Dec 30, 2010)

Former Farmer said:
			
		

> 10-3 romex is rated for 30 amps.  8-3 romex is rated for 40 amps.  5500 watts / 240 volts = 23 amps.  You can get by with 10-3 wire.  If the length of wire is going to be over 75 feet, use 8-3 wire for voltage drop.
> 
> 
> What type of wire are you referring to?  Romex, SO cord?
> ...



Romex is what i had in mind. I will be wireing a transfer box to my main box so i don't cook the guy on the pole. The length won't be any more than 30 feet max. Thanks for the help.


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## seige101 (Dec 30, 2010)

Also do not forget the constant use de-rating factor, 80%. Making that #10 line good for 24 amps.


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## livefreeordie (Dec 30, 2010)

seige101 said:
			
		

> Also do not forget the constant use de-rating factor, 80%. Making that #10 line good for 24 amps.



Way over my head, please explain more.


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## wingman1776 (Dec 30, 2010)

If you are going to run a load on the line for long peroids on time you should de-rate the line by 20 % due to heat in the line. It is a standard code thing for saftey. 30 amps - 20 % = 24 amps


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## livefreeordie (Dec 30, 2010)

Got it, thanks for the help


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## btuser (Dec 31, 2010)

But a generator @5500 watts is not going to be delivering 100% all the time, so it comes down to load and more math.  Most of the time its closer to 50%.


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## livefreeordie (Dec 31, 2010)

I should get more than half if i don't run a bunch of stuff all at once right? This is all new to me. All i want to do is run the fridge,some lights if i need them, the furance blower fan if needed and the pellet stove, maybe a TV. So i'm looking at one 30amp breaker and four 15 amp breakers thats it.


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## velvetfoot (Dec 31, 2010)

You may be interested in putting in an interlock kit so that you can run anything, not pay that much,  and still be safe.  I have a SquareD panel so I got this one:  
http://static.schneider-electric.us/docs/Electrical Distribution/Load Centers/Accessories-Homeline-HOM-LK-PK-QOM/40273-809-02.pdf

I would've used a 5kw generator I already had if it wouldn't have been for that darn deep well pump.


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## btuser (Dec 31, 2010)

livefreeordie said:
			
		

> I should get more than P if i don't run a bunch of stuff all at once right? This is all new to me. All i want to do is run the fridge,some lights if i need them, the furance blower fan if needed and the pellet stove, maybe a TV. So i'm looking at one 30amp breaker and four 15 amp breakers thats it.



If you don't have the well pump then you're all set.  A simple transfer switch like Reliance with 6 breakers/switches will work.  You're going to want the bathroom lights, some outlets, the fridge and the furnace.  If you've got sub panels to run it gets more complicated.  30 amps (aka 10/3 ) is good enough.


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## livefreeordie (Dec 31, 2010)

btuser said:
			
		

> livefreeordie said:
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One sub panel that runs the den with the pellet stove and a TV, thats a 30 amp breaker. The other four breakers will cover the rest that i need. No sump pump.


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## livefreeordie (Dec 31, 2010)

velvetfoot said:
			
		

> You may be interested in putting in an interlock kit so that you can run anything, not pay that much,  and still be safe.  I have a SquareD panel so I got this one:
> http://static.schneider-electric.us/docs/Electrical Distribution/Load Centers/Accessories-Homeline-HOM-LK-PK-QOM/40273-809-02.pdf
> 
> I would've used a 5kw generator I already had if it wouldn't have been for that darn deep well pump.



The link is bad can you repost it please.


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## velvetfoot (Dec 31, 2010)

Cut and paste.  Link good.


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## livefreeordie (Dec 31, 2010)

Ok, thanks i'll try it


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## oldspark (Jan 1, 2011)

wingman1776 said:
			
		

> If you are going to run a load on the line for long peroids on time you should de-rate the line by 20 % due to heat in the line. It is a standard code thing for saftey. 30 amps - 20 % = 24 amps


 I do not understand that as I can run 30 amps through #10 wire for 24/7 and the wire will not even be warm to the touch as long as the voltage drop is with in the guide lines.


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## btuser (Jan 1, 2011)

oldspark said:
			
		

> wingman1776 said:
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I've argued this on both sides of the fence in code classes.  One side convinced that you have to degrade for corrosion/aging (like wine I guess) and the ever present "round up in case we f*ck up" therory, and others who will run a single circuit to one end of the house and back again, confident that the breaker is going to do the math for them.   Its also about the conductor rating at the ambient temp.  Is the conductor going to be spray-foamed, or in a pipe?   I've got 13 amps running through my 16 gauge vacuum cord and it get's hot, but I haven't burned my house down yet.


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## thinkxingu (Jan 1, 2011)

Hi All,
     I recently wired in my generator to my main panel using an interlock kit from here (http://www.interlockkit.com).  It's a bit expensive for a couple pieces of metal ($140), but now I can access any of the circuits in my house instead of only chosen ones--this works well because I have a split and if I'd only had a few circuits, I'd lose a lot of light/outlets.  Of course, I have electric heat so I'll only be running my fridge, microwave, some lights, water heater, etc.  Just got completed and inspected a month ago; of course, now that it's ready to go I'll probably never need it.

Godspeed, and Happy New Year!

S


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## livefreeordie (Jan 2, 2011)

I like the interlock system, thanks for the link.


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## thinkxingu (Jan 2, 2011)

Yeah, it's cool--in my situation, I'll need to shut off all my electric heat circuits, but it will be nice to have the garage openers available and all the lights around the house.  Thought we might need it this last storm, but nope!

Good luck,

S


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## btuser (Jan 2, 2011)

I'm probably going to go with the interlock kit, but I'm having a hard time paying $150 for a two metal plates.  My other choice is a 10 circuit transfer switch + a lot of rewiring from a sub panel which is going to come to about $500 all said and done.


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## velvetfoot (Jan 2, 2011)

I found it cheaper to get it from SquareD, since I have a SquareD panel.  It's cheaper to get it from the maker, if possible, instead of going with the web site above.


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## livefreeordie (Jan 2, 2011)

thinkxingu said:
			
		

> Yeah, it's cool--in my situation, I'll need to shut off all my electric heat circuits, but it will be nice to have the garage openers available and all the lights around the house.  Thought we might need it this last storm, but nope!
> 
> Good luck,
> 
> S



Yeah, we thought the same thing about the last storm, glad we didn't lose the power because i'm still in the process of wiring the basement.


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## thinkxingu (Jan 2, 2011)

Yeah, the Square D version is less expensive, but it only works on some of their panels.  Most other companies don't make one, which is why Interlock is able to stay in business!

btuser: I hear ya on the 10-circuit transfer, but at that point you might as well save the $ and have access to all!

S


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## Highbeam (Jan 2, 2011)

I used an interlock "panel" that came from the factory with the sliding mechanism. I think it is a great idea and the BEST way to do power your house with a generator.

Use 10/3 for up to 30 amps and forget you ever heard about this continuous derating jive, it does not apply to this situation. It is much easier to work with 10/3 than 8/3 as well. I feed the 30 amp generator circuit with a 3500 watt genset, the smallest 220 volter I could find. That 5000 watter will suck some major fuel, expect more than .5 gallon per hour nomatter how it is loaded.


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## seige101 (Jan 3, 2011)

Highbeam said:
			
		

> Use 10/3 for up to 30 amps and forget you ever heard about this continuous derating jive, it does not apply to this situation. It is much easier to work with 10/3 than 8/3 as well.



And how does that not apply in this situation?


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## Highbeam (Jan 3, 2011)

seige101 said:
			
		

> Highbeam said:
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First of all and most importantly, 5000 watts from the chosen genset is not 30 amps. Second, it is not a continuous load. This is not a load but a supply for an intermittent load, by nature not applicable to a continuous loading rule. 

The derating rule, I always used 75% but 80% is fine too, applies perfectly to things like baseboard heaters where you actually in practice only put a 16 amp heater on a dedicated 20 amp circuit. Since the 16 amp heater will always be 16 amps when on and is designed for continuous operation at 100%.

So how many 20 amp outlets do you install and only allow 16 amp appliances to be used? How do you prevent someone from plugging in a 20 amp device? Do you use 15 amp breakers on 12 guage wire circuits just to make you feel better about the continuous loading rule? Do your inspectors require this? Mine sure don't.


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## oldspark (Jan 3, 2011)

Thats the thing I could never figure out, the wire has a saftey margin but they want you to derate it. I would not be afraid to put a continuous 30 amps on #10 wire.


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## livefreeordie (Jan 3, 2011)

Lots of great info here and i thanks you for that.


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## Highbeam (Jan 3, 2011)

I just discovered that Seige is an electrician. That's good. I'm not, and am willing to be told I am wrong. 

Here's the thing about derating. You still build the ciruit properly meaning a 10 gauge wire on a 30 amp circuit. The derating applies to the load so you would only hardwire a 24 amp load to it. You don't oversize the wire and still put the same 30 amp breaker on it. In other words, if you have a continuous 30 amp load you would bump up to a 40 amp circuit with corresponding wire size.


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## oldspark (Jan 3, 2011)

Highbeam said:
			
		

> I just discovered that Seige is an electrician. That's good. I'm not, and am willing to be told I am wrong.
> 
> Here's the thing about derating. You still build the ciruit properly meaning a 10 gauge wire on a 30 amp circuit. The derating applies to the load so you would only hardwire a 24 amp load to it. You don't oversize the wire and still put the same 30 amp breaker on it. In other words, if you have a continuous 30 amp load you would bump up to a 40 amp circuit with corresponding wire size.


 I am too (electrician is past life) and if the load is a solid 30 amps all the time yea good to bump up, still 30 amps on #10 wire is not going to make it hot, I how ever was an electrician in a plant so the house codes and stuff I did not have to deal with.


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## seige101 (Jan 4, 2011)

Highbeam said:
			
		

> I just discovered that Seige is an electrician. That's good. I'm not, and am willing to be told I am wrong.
> 
> Here's the thing about derating. You still build the ciruit properly meaning a 10 gauge wire on a 30 amp circuit. The derating applies to the load so you would only hardwire a 24 amp load to it. You don't oversize the wire and still put the same 30 amp breaker on it. In other words, if you have a continuous 30 amp load you would bump up to a 40 amp circuit with corresponding wire size.



Yep electrician is my day job to pay the bills. No offence taken. When i do give advice here i give it according to minimum code requirements. I do see lets of shody work on a daily basis and see lots of stuff on a daily basis that shows me that minimum code is not always adequate. I am always a big fan on going over kill no matter that the task on hand is. For a small bit extra the peace of mind and longevity is well worth it in the long run for me.

Just a little something learned from my father and 10+ years in the trade.


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## oldspark (Jan 4, 2011)

In all the wiring I ever did in our plant we just went by the rating of the wire, motor starters and breakers, never had to over size any thing and no problems to be found.


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