Interlock vs. throwing the main circuit breaker for generator powering a house

[JFoy]

Is there a difference in safety if I just turn off the main 200amp circuit breaker versus having a generator interlock installed? My understanding is the danger of backfeeding power to the outside power pole and transformer.

Thanks,
JFoy

 

[Oldoak]

They both will accomplish the same thing. However, an interlock is your safest bet. An interlock eliminates the chance of human error by forgetting to turn off the main breaker.

 

[RNeumann]

Yes major difference- “just throwing the breaker” requires a manual sequence of events to prevent damage or injury. While the interlock is designed to be in either/or position with one move.

IMHO it’s short sided to setup something that your spouse, neighbor or child couldn’t easily do.

 

[aczlan]

Is there a difference in safety if I just turn off the main 200amp circuit breaker versus having a generator interlock installed? My understanding is the danger of backfeeding power to the outside power pole and transformer.

Thanks,
JFoy

If you don't want to buy an interlock switch, there are companies who make an interlock plate that goes on your existing breaker panel and makes it so that one of the top Breakers cannot be turned on at the same time as the main breaker is on.

Aaron Z

 

[marchanna]

I don’t have an interlock, I wish I did. But because of my particular electrical layout, it was not practical. My wife knows that she should not even attempt to switch it over, and it would be very difficult for someone to figure out if he power we’re to go out, layered safe guards , which I have done intentionally.

 

[RickB]

A legitamate transfer switch interrupts the neutral bond to the electrical grid. Opening a circuit breaker does not. That is a huge safety concern for utility personnel and a major reason that most codes require a transfer switch.

 

[aczlan]

I don稚 have an interlock, I wish I did. But because of my particular electrical layout, it was not practical. My wife knows that she should not even attempt to switch it over, and it would be very difficult for someone to figure out if he power we?*e to go out, layered safe guards , which I have done intentionally.

Look at a trapped key interlock. Something like this: KIRK KEY INTERLOCK QTY 2 (228) "NEW" | eBay

One goes on the main breaker, the other goes on your generator breaker. One key gets locked up as a spare, the other is locked into one lock (that is installed so that it keeps the main breaker off when the key is removed). The other lock is installed so that it keeps the generator breaker off when the key is removed.
To turn on the generator, you turn off the main breaker, lock the interlock to keep it off, remove the key, unlock the generator interlock with that key and turn on the generator breaker.

Aaron Z

 

[marchanna]

That’s a brilliant idea.

 

[dieselcrawler]

My power system is also layed out such that in interlock won't fit the bill. Main breaker is at the house, generator feed is at the barn, which is fed from the house. Things are clearly marked, wife and oldest son understand the process and order of events clearly. We likely have a better understanding of the safety risks than most, as I have 20+ years of electrical background, and have installed many very nice back-up generator systems with auto-transfer switches, and hope to have my own someday.

The point I state clearly, every time we have a power issue, is turn off the main breaker FIRST, and save the life of the guy out in the cold/rain/snow trying to fix the power outage, then go to the barn and hook up the generator, start it, and very last turn on the breaker for generator feed to the barn panel.

 

[Jstpssng]

If you don't want to buy an interlock switch, there are companies who make an interlock plate that goes on your existing breaker panel and makes it so that one of the top Breakers cannot be turned on at the same time as the main breaker is on.

Aaron Z

It looks like this...
Mine was installed when I bought the building, but I have never used it. If my power ever does go out for a long period of time I will have to build a cord before using it.
Until reading RickB's comment below I never really thought about how mine worked; but I have heard that this can still allow power to feed back into the utility line.

 

[dieselcrawler]

It looks like this...
Mine was installed when I bought the building, but I have never used it. If my power ever does go out for a long period of time I will have to build a cord before using it.
Until reading RickB's comment below I never really thought about how mine worked; but I have heard that this can still allow power to feed back into the utility line.

This is true, as the interlock is mounted to the panel cover, and if the cover is removed, both breakers could be in the 'ON' positions at the same time, allowing back-feed to the power lines.

 

[Jstpssng]

^^^^
That's simply a case of user oversight. In the instance which RickB cited you can still get some feed even if my interlock is used properly.
I also have been told though that the power company will ground the lines before working on them to prevent the risk of injury. I don't know if that is true though.

 

[fried1765]

^^^^
That's simply a case of user oversight. In the instance which RickB cited you can still get some feed even if my interlock is used properly.
I also have been told though that the power company will ground the lines before working on them to prevent the risk of injury. I don't know if that is true though.

I have NEVER understood how, when BOTH hot lines are interrupted by tripping the main breaker, any power can flow through the neutral.

 

[marchanna]

A ground fault.

 

[Jstpssng]

^^^
Will physically pulling the main breaker prevent that? I'll admit that I have gotten complacent. Our Coop is very proactive so that in the 25+ years I've lived up here the longest that my power has been out was 12 hours- and that was a one time thing. The only thing I really need my generator for is to run my fridge and freezers, and I can run an extension cord for that.

 

[Lawnranger]

My power system is also layed out such that in interlock won't fit the bill. Main breaker is at the house, generator feed is at the barn, which is fed from the house. Things are clearly marked, wife and oldest son understand the process and order of events clearly.

I agree. I used to have the same set up, had to feed from a sub-panel in my remote garage. I was going to place an interlock on the main panel incorporating the sub panel breaker but never got around to it. I placed laminated magnetic instruction sheets on the panel door, the sub-panel door, and the generator, just in case I wasn't around and my wife had to start it. She understood it well and the instruction sheets just served as a reminder, but gave me a little peace of mind.

In our house now, I feed directly from the main panel, so I opted for the interlock. It is much better than the transfer switch because we didn't have to choose what circuits to power. We can run the whole house but we opt to stagger certain items. Like no need to run the dishwasher or washer and other appliances at the same time. Or don't use the toaster, and the coffee maker when the fridge is powered up. The basics all work fine together. We use a 10000 surge, 8500, and haven't heard it idle up much.

 

[turnkey4099]

They both will accomplish the same thing. However, an interlock is your safest bet. An interlock eliminates the chance of human error by forgetting to turn off the main breaker.

Exactly and that is why, in most places, an interlock is required by code.

 

[ultrarunner]

I have a 400 amp service all electric home.

No main interlock but I have a subpanel with 3 position breakers so I can select which critical circuits to power... not as convenient but then I only have a Honda 5000 Watt Genset.

Don't see these as often but were very common 25 years ago... gives me well pump, refrigerator, lights/convenience

http://img2.wfrcdn.com/lf/50/hash/1...r-Generator-with-6-Circuit-Breaker-51406C.jpg

 

[RickB]

An interlock is an acceptable alternative to a transfer switch in some areas. Stating an interlock is the safest device is not valid. A transfer switch is a complete, positive disconnect from the power grid.

Why a Generator Needs a Transfer Switch

 

[MossRoad]

Is there a difference in safety if I just turn off the main 200amp circuit breaker versus having a generator interlock installed? My understanding is the danger of backfeeding power to the outside power pole and transformer.

Thanks,
JFoy

Yes, there's a difference in safety, because human error is involved and you could accidentally back-feed the lines.

A simple and inexpensive solution is a lockout like this. They are under $75. You can't turn on the generator breaker unless you turn off the main breaker in the panel first. Perfectly legal, elegant, and simple.