Generator Interlock switch

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mez

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I have a question but cannot find an answer to. I understand the concept of a Generator Interlock switch but don't understand how the circuit breaker (30A) for the Generator Interlock switch is wired to allow all breakers in the panel to run off the Generator. It must be in parallel with the main breaker in my case 200A? The instructions tell you to use the first two slots in the panel for the interlock breaker, wired the generator wires to the interlock breaker but doesn't mention how all the other breakers gets the feed from the Generator interlock breaker. By the way, I already purchase a 6 circuit transfer switch but my son mention to look at the Generator Interlock switch method. Now i am curious how it works. Thanks
 
It's a backfeed. If you look inside your breaker box there are two zigzags that power every other breaker. The single 110v breakers touch one of the bus bars and the 220 volt breakers touch both, getting +110 and -110 which adds up to 220.

There's a mechanical interlock keeping the main breaker off when you've engaged the generator. Normally the power comes in the "top" through the main breaker and flows down the bus bars. You'll be doing this from the side.

The 30 amps will be enough because you'll turn some of the heavy loads off before you plug the generator in.

The capacity of the 200 amp breaker, you'd only come close to hitting if you have electric heat or central air or a welding shop or something.

The six circuit "sidecar" transfer switch stands more of a change of being UL listed and accepted by the manufacturer of your main panel-- something of potential interest to your insurance company
 
I understand what you are saying but i still don't understand how it back feeds all circuits. To me its like any other 2 slot breaker. How does it feed all the other breakers in the panel?
 
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The interlock prevents the main breaker from being switched on when the generator is being ran, this is a safety for line workers not being hit with juice and your house not becoming energized when power is restored from the grid with the possibility of the generator still connected. 30A is ok for temporary hookup, it will give you heat and a few lights and the refrigerator doesn't run often if it is kept closed.

Electric heat and ac compressors are the big amperage suckers you have to watch for.
 
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OK , take a 2 pole 30 amp CB . You have 2 screw terminals on the CB . With household loadcenters using plug in CB's , there are 2 contacts at the opposite end of the CB . These plug into / onto the buss bars .

The 2 hots from your generator cable terminate to the 2 screw terminals . The earth ground terminates in the ground bar and the neutral to the neutral bar .

During normal operation / commercial power this 2P 30 CB is off & the 200 amp main is on .

When you loose commercial power , turn off the 200 amp main , move the interlock to block the handel of this CB to off .

Turn the CB's feeding large loads , off . Start the generator and let it stabilize . Turn the 2P 30 CB on . Power will enter the CB at the 2 terminals , pass through the CB and enter the 2 buss bars where the CB is plugged in to the buss bars . Back feeding the loadcenter .

When commercial power comes back on , reverse the process .
 
Originally Posted by eljefino
It's a backfeed. If you look inside your breaker box there are two zigzags that power every other breaker. The single 110v breakers touch one of the bus bars and the 220 volt breakers touch both, getting +110 and -110 which adds up to 220.

There's a mechanical interlock keeping the main breaker off when you've engaged the generator. Normally the power comes in the "top" through the main breaker and flows down the bus bars. You'll be doing this from the side.

The 30 amps will be enough because you'll turn some of the heavy loads off before you plug the generator in.

The capacity of the 200 amp breaker, you'd only come close to hitting if you have electric heat or central air or a welding shop or something.

The six circuit "sidecar" transfer switch stands more of a change of being UL listed and accepted by the manufacturer of your main panel-- something of potential interest to your insurance company


If you buy the interlock made by the manufacturer of your loadcenter , for your specific loadcenter , I would bet it is UL listed .

But , be ware , you can mess up badly ! So , yes , if you do not know what you are doing , hire a qualified electrician .

https://www.youtube.com/watch?v=c2arBeeU3mY
 
Originally Posted by sloinker
Hire an electrician.

You might think about this option.


Originally Posted by mez
I understand what you are saying but i still don't understand how it back feeds all circuits. To me its like any other 2 slot breaker. How does it feed all the other breakers in the panel?


When you back feed thru a breaker, you are energizing the complete breaker strip that the main input wires are energizing, the wires that the disconnect switch are wired thru. All breakers attach to these breaker power strips. Your just kinda doing it backwards, why its refered to as back feeding.
 
Originally Posted by mez
I understand what you are saying but i still don't understand how it back feeds all circuits. To me its like any other 2 slot breaker. How does it feed all the other breakers in the panel?


They're all connected. You shut off the main so there's no power going into the panel and the generator feeds in 30 amps into the panel so that's feeding all the circuits in the panel instead of the 200 from the power company. The problem you would run into is if the circuits demanded more than 30 amps, then the generator might bog down or shut off or get damaged which is why you'd want to shut off other breakers that might draw a large load like an ac, stove or dryer.

If you have a hard time understanding that, as others said, you should consult an electrician.
 
Originally Posted by madRiver
Most flexible solution and simplie. You can overload your generator though if you too much.


If your generator is not sized to the load of the house , yes , it is easy to overload the generator . Just start turning off high load circuit breakers until the generator is happy .

If your generator is undersized and you do not know what is going on , either purchase a generator large enough to carry the house , or do without .
 
Originally Posted by rubberchicken
My understanding is that only a transfer switch will protect the house, lines and generator. Anything else is cutting corners.



The interlock kit is essentially a transfer switch .
 
Normally, power comes from the utility and the power comes into the panel through the main breaker. The main breaker energizes the two bus bars in the panel. All of the branch circuit breakers are connected to the bus bars (120V breakers are connected to only one of the bus bars, 240V breakers are connected to both). Since the bus bars are energized, and the all of the branch breakers are connected to the bus bars, all of the branch breakers have power.

When the power goes out and you switch to generator power, you shut off the main breaker and turn on the generator breaker. The generator breaker is a 240V breaker, therefore it is connected to both bus bars. The power now comes from the generator, through the generator breaker, and energizes both bus bars. Once again, since both bus bars are now energized, and all of the other branch breakers are connected to the bus bars, all of the branch breakers are energized and can be powered from the generator.

Basically, the goal is to get the bus bars energized, whether it's from the utility or a generator. Energized bus bars = all branch breakers energized.

I think what the OP is failing to realize is that power can flow through a breaker both ways. Normally, the bus bars are energized via the main breaker, THEN the power goes through the branch breaker(s), THEN the power goes through the wire(s) connected to the branch breaker. But breakers also work when power flows "backwards." You install a generator breaker (which is simply a normal 240V branch breaker) and connect wires to it. The wires connect to the generator inlet on the side of your house. Now when you use a generator, power comes from the generator and into the generator inlet. THEN it goes through the wiring to the breaker panel, THEN it goes through the generator/branch breaker, THEN it energizes the bus bars.
 
Interlock is most flexible and cheapest solution for powering your home in emergency.

I have an 8500watt peak gen the important thing for me is not using the electric oven(s) during an outage. I just flip off certain breakers that I know have high loads and the generator is fine.

Those manual transfer switches are not as flexible as you and way more pricey to install since you choose vital outlets in home everything else is dead.

You think you don't need them but day two of power outage you learn you really do.
 
Thanks exranger06. Your explanation got me thinking more about it. What i was not thinking about, is the both bus bars has the 120v/240v and the generator circuit breaker is just back feeding the bus bars.

I have already purchase the transfer switch months ago with the 10/3 wire to put the outlet outside for the generator.
 
Originally Posted by mez
Thanks exranger06. Your explanation got me thinking more about it. What i was not thinking about, is the both bus bars has the 120v/240v and the generator circuit breaker is just back feeding the bus bars.

I have already purchase the transfer switch months ago with the 10/3 wire to put the outlet outside for the generator.


You're most of the way there, bub! Get it done before the next ice storm!

An outlet outside is super classy-- no extension cords sticking through windows etc.
 
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