Wiring a Generator

walhondingnashua

Burning Hunk
Jul 23, 2016
217
ohio
I am figuring on wiring a generator with one of the outdoor boxes and a switch in my garage breaker box. I want this to run back into my house to my main box to power the house in power outages. It will be extremely convenient for my to just role the generator out of the garage, plug it in and I'm good in minutes. It will be much more of a struggle to have to move the generator around my house near the house breaker box and run it there.

Here is what I have already...
6/3 wire running from the garage into the house box (220; 50amp)
7800 watt generator
Outdoor 30amp 10/4 4 prong generator cord

I am looking for verification that I have to correct set up, what else I need (breaker box switch, plug, etc) and to see what other people have done to hook a generator up to their house.

Thanks in advance...
 

Highbeam

Minister of Fire
Dec 28, 2006
16,845
Mt. Rainier Foothills, WA
I have a similar legal, permitted setup in my home. I used all 30 amp gear for the generator inlet circuit.

You need to install an interlock on your main panel between the main inlet breaker and the generator 50 amp breaker.

You do have a problem at the generator inlet. As you note, the 30 amp connection is undersized. You need to use one of the higher amperage connections to match your generator inlet circuit. 50 amp stuff. You'll melt the 30 amp plug when you or someone else tries to put 50 amps through it.
 
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Medic21

Minister of Fire
Feb 26, 2017
675
Northern Indiana
I have a similar legal, permitted setup in my home. I used all 30 amp gear for the generator inlet circuit.

You need to install an interlock on your main panel between the main inlet breaker and the generator 50 amp breaker.

You do have a problem at the generator inlet. As you note, the 30 amp connection is undersized. You need to use one of the higher amperage connections to match your generator inlet circuit. 50 amp stuff. You'll melt the 30 amp plug when you or someone else tries to put 50 amps through it.
the generator breaker will open up, 7800 watt generator isn’t capable of 50amp.

Sounds like it’s a decent easy set up. Don’t forget to shut off the main breaker so you don’t backfeed the transformer.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,845
Mt. Rainier Foothills, WA
the generator breaker will open up, 7800 watt generator isn’t capable of 50amp.

Sounds like it’s a decent easy set up. Don’t forget to shut off the main breaker so you don’t backfeed the transformer.
see the mistake? You’ll burn up the 30 amp plug at 31 amps and start your house on fire before the 50 amp breaker pops.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,845
Mt. Rainier Foothills, WA
One more fun trick. Not sure if you can use an interlock to backfeed a sub panel. If you shut the main breaker off at the sub then you won’t get power back to the house main panel.

you’re into high end electrical theory here. Lots of ways to do it wrong and I’m sure you want this to be legal and code compliant.
 

Medic21

Minister of Fire
Feb 26, 2017
675
Northern Indiana
see the mistake? You’ll burn up the 30 amp plug at 31 amps and start your house on fire before the 50 amp breaker pops.
my 8000w has a 30amp breaker man. Your looking at a 15k to get to the 50amp range. 30amp generator plug is enough for a 7800watt generator.
 

Medic21

Minister of Fire
Feb 26, 2017
675
Northern Indiana
As far as my hook up. I 220 outlet for the air compressor in the garage. I just made a double male end chord with the generator plug on one end. All I do is shut off main breaker and plug it in and fire it up.
To disconnect it is very important to shut the breaker off and shut the generator off when it’s disconnected. Mine is wired for a 30amp outlet for the air compressor and the small mig welder.

8k will run the fridge, a few lights, the furnace fan, and the boiler and pumps no problem. I have the well on so we have water but, it the well is running and the microwave is started it will trip the breaker. 8k is about the smallest to do the necessities.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,845
Mt. Rainier Foothills, WA
my 8000w has a 30amp breaker man. Your looking at a 15k to get to the 50amp range. 30amp generator plug is enough for a 7800watt generator.
Sorry man but do the math. 30 amps at 240 volts is just ... 7200 watts. That 7800 watt input exceeds the rating. Regardless, someone else may hook up a larger generator to the unsafe and non compliant generator circuit and burn the house down as well.

The 50 amp breaker is irrelevant when the weak link is the undersized 30 amp plug.
 

Medic21

Minister of Fire
Feb 26, 2017
675
Northern Indiana
Sorry man but do the math. 30 amps at 240 volts is just ... 7200 watts. That 7800 watt input exceeds the rating. Regardless, someone else may hook up a larger generator to the unsafe and non compliant generator circuit and burn the house down as well.

The 50 amp breaker is irrelevant when the weak link is the undersized 30 amp plug.
When the generator has a 30amp breaker on it it doesn’t need anything larger in the circuit than 10/3 wire, if your worried about those 2.5 amps run 10ga thhn it’s rated for 35amps.

That generator will have a 30amp breaker on it. If you want to plan for bigger later that’s fine. But, what he has is 30amp. 7800/240=32.5. That’s a 30amp generator.
 

Medic21

Minister of Fire
Feb 26, 2017
675
Northern Indiana
You can run service wire rated for 200amp and put a 20amp breaker on it and it’s a very expensive 20amp circuit. When the power source that feeds it is only capable of 30amps anything larger in the wiring is just wasting money.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,845
Mt. Rainier Foothills, WA
When the generator has a 30amp breaker on it it doesn’t need anything larger in the circuit than 10/3 wire, if your worried about those 2.5 amps run 10ga thhn it’s rated for 35amps.

That generator will have a 30amp breaker on it. If you want to plan for bigger later that’s fine. But, what he has is 30amp. 7800/240=32.5. That’s a 30amp generator.
I understand what you’re saying. You’re right about the generator. The problem is the illegal and unsafe use of 30 amp components (the plug and section of 10/3 )on a circuit protected by a 50 amp breaker. One way to make it less illegal is to use a 30 amp breaker at the panel for this generator inlet circuit.
 

Medic21

Minister of Fire
Feb 26, 2017
675
Northern Indiana
I understand what you’re saying. You’re right about the generator. The problem is the illegal and unsafe use of 30 amp components (the plug and section of 10/3 )on a circuit protected by a 50 amp breaker. One way to make it less illegal is to use a 30 amp breaker at the panel for this generator inlet circuit.
It’s not protected by a 50amp breaker. It’s a sub panel that has a 50amp circuit feeding it. It’s protected by the 30 amp breaker on the generator.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,845
Mt. Rainier Foothills, WA
It’s not protected by a 50amp breaker. It’s a sub panel that has a 50amp circuit feeding it. It’s protected by the 30 amp breaker on the generator.
nope. Breaker in the panel protects the circuit. The next guy could use a 10k watt generator so codes are written this way.
 
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Medic21

Minister of Fire
Feb 26, 2017
675
Northern Indiana
nope. Breaker in the panel protects the circuit. The next guy could use a 10k watt generator so codes are written this way.
Whatever, I’m done, you don’t understand and you surely aren’t an electrician. I’ve installed and serviced Whole home generators and transfer switches

He is asking about everything outside the walls. The chord going from the generator to the hookup.


Here is what I have already...
6/3 wire running from the garage into the house box (220; 50amp)
7800 watt generator
Outdoor 30amp 10/4 4 prong generator cord
this setup is safe and will do fine. A 50amp generator chord will not plug into this type of plug So there is the safety. The generator output is protected With a breaker on every part able generator. Try to pull more than it’s rated and it pops at the generator and power goes out. That is the protection on the whole damn system when using a portable generator. A whole home generator is hard wired into the main breaker and more times than not it’s 1/2 or less than the rated amps of the main. It’s wired at the output of the generator not the rating of the main breaker. There is a breaker in the generator that becomes the main when it’s running.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,845
Mt. Rainier Foothills, WA
Whatever, I’m done, you don’t understand and you surely aren’t an electrician. I’ve installed and serviced Whole home generators and transfer switches

He is asking about everything outside the walls. The chord going from the generator to the hookup.




this setup is safe and will do fine. A 50amp generator chord will not plug into this type of plug So there is the safety. The generator output is protected With a breaker on every part able generator. Try to pull more than it’s rated and it pops at the generator and power goes out. That is the protection on the whole damn system when using a portable generator. A whole home generator is hard wired into the main breaker and more times than not it’s 1/2 or less than the rated amps of the main. It’s wired at the output of the generator not the rating of the main breaker. There is a breaker in the generator that becomes the main when it’s running.
I do understand that depending on a cheap breaker on the actual portable generator is not appropriate and is a red flag on all of your advice.

I think you’re right about one thing, I didn’t see that only the cord was 10 gauge. That’s better. reading carefully, we don’t know exactly how this thing is wired.I think maybe neither of us actually understand this guy’s setup.

you’re obviously not an electrician either! You don’t have 220 you have 240! I bet your air compressor circuit is undersized too if it’s a typical 5 hp motor. Some people get by with illegal work but recommending it to others is risky. A suicide cord!
 
Last edited:

Medic21

Minister of Fire
Feb 26, 2017
675
Northern Indiana
A 5hp 240v motor is 25 amps. It’s on a 30amp circuit. Try again. I will depend on the breaker everyday. They are used stand alone all the time.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,845
Mt. Rainier Foothills, WA
A 5hp 240v motor is 25 amps. It’s on a 30amp circuit. Try again. I will depend on the breaker everyday. They are used stand alone all the time.
Another mistake. You size a motor circuit for the HP rating of the motor. There’s a whole section in the code that you’ve never seen.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,845
Mt. Rainier Foothills, WA
I suppose a lot depends on whether you want to follow code or you want to do something that is may be good enough. We have some electricians on this forum that are very good and helpful at giving actual code compliant advice.

I would welcome one of them pointing out my mistakes and getting the op asafe and legal generator hookup.

My generator inlet, that was permitted, also uses a 10 gauge 30 amp circuit with a 30 amp inlet plugon the house. Fed by a 30 amp cord. All the numbers match.
 

Medic21

Minister of Fire
Feb 26, 2017
675
Northern Indiana
I suppose a lot depends on whether you want to follow code or you want to do something that is may be good enough. We have some electricians on this forum that are very good and helpful at giving actual code compliant advice.

I would welcome one of them pointing out my mistakes and getting the op asafe and legal generator hookup.

My generator inlet, that was permitted, also uses a 10 gauge 30 amp circuit with a 30 amp inlet plugon the house. Fed by a 30 amp cord. All the numbers match.
thats exactly what he has Dumbass

Unless the electrician works in your area their code advise is mute.
 
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walhondingnashua

Burning Hunk
Jul 23, 2016
217
ohio
I actually don't have the entire set up yet. I don't have the plug to accept the 10/4 from the generator yet or the switch over in the breaker box that allows the generator feed into the system.
I just want to make sure I get as much advice as I can get. Seems like I'm on the right track and I appreciate the advice. I will make sure that I switch the main feed from the power company off when I run the generator. (I'll probably make a reminder on the garage breaker box since the main feed is in the house)
 

zrock

Minister of Fire
Dec 2, 2017
806
bc
I will agree on the 30/50 amp plug debate up their.. Go with a 50 amp rated plug running just a few amps close to 30 plus or minus if you have to use for a extended time will melt the plug and short.. The last several years i have worked at a RV park every single 30 amp plug has been replaced several times over the years as customers were running close to the 30 amp but not enough to pop the beaker. 30 amp may be fine for a day or so but if you ever have a situation where you need to run for more days you may find yourself down as the plug overheated... And you will be running close to the limit of that plug
 

Sodbuster

Minister of Fire
Sep 22, 2012
1,256
Michigan
I backfeed often, because the power in our area is sketchy. My first step is to throw the main. Then I hook up my generator to a welder outlet. with the neutrals and the and the grounds all attached to the same bar how can this push current back into the line?